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Campbell DR, Powers JM, Crowell M. Pollinator and habitat-mediated selection as potential contributors to ecological speciation in two closely related species. Evol Lett 2024; 8:311-321. [PMID: 38525033 PMCID: PMC10959478 DOI: 10.1093/evlett/qrad060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Revised: 10/27/2023] [Accepted: 11/09/2023] [Indexed: 03/26/2024] Open
Abstract
In ecological speciation, incipient species diverge due to natural selection that is ecologically based. In flowering plants, different pollinators could mediate that selection (pollinator-mediated divergent selection) or other features of the environment that differ between habitats of 2 species could do so (environment-mediated divergent selection). Although these mechanisms are well understood, they have received little rigorous testing, as few studies of divergent selection across sites of closely related species include both floral traits that influence pollination and vegetative traits that influence survival. This study employed common gardens in sites of the 2 parental species and a hybrid site, each containing advanced generation hybrids along with the parental species, to test these forms of ecological speciation in plants of the genus Ipomopsis. A total of 3 vegetative traits (specific leaf area, leaf trichomes, and photosynthetic water-use efficiency) and 5 floral traits (corolla length and width, anther insertion, petal color, and nectar production) were analyzed for impacts on fitness components (survival to flowering and seeds per flower, respectively). These traits exhibited strong clines across the elevational gradient in the hybrid zone, with narrower clines in theory reflecting stronger selection or higher genetic variance. Plants with long corollas and inserted anthers had higher seeds per flower at the Ipomopsis tenuituba site, whereas selection favored the reverse condition at the Ipomopsis aggregata site, a signature of divergent selection. In contrast, no divergent selection due to variation in survival was detected on any vegetative trait. Selection within the hybrid zone most closely resembled selection within the I. aggregata site. Across traits, the strength of divergent selection was not significantly correlated with width of the cline, which was better predicted by evolvability (standardized genetic variance). These results support the role of pollinator-mediated divergent selection in ecological speciation and illustrate the importance of genetic variance in determining divergence across hybrid zones.
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Affiliation(s)
- Diane R Campbell
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, United States
- Rocky Mountain Biological Laboratory, Crested Butte, CO, United States
| | - John M Powers
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, United States
- Rocky Mountain Biological Laboratory, Crested Butte, CO, United States
| | - Madison Crowell
- Rocky Mountain Biological Laboratory, Crested Butte, CO, United States
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2
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Campbell DR, Raguso RA, Midzik M, Bischoff M, Broadhead GT. Genetic and spatial variation in vegetative and floral traits across a hybrid zone. AMERICAN JOURNAL OF BOTANY 2022; 109:1780-1793. [PMID: 36193908 PMCID: PMC9828138 DOI: 10.1002/ajb2.16067] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 06/14/2022] [Accepted: 06/15/2022] [Indexed: 06/16/2023]
Abstract
PREMISE Genetic variation influences the potential for evolution to rescue populations from impacts of environmental change. Most studies of genetic variation in fitness-related traits focus on either vegetative or floral traits, with few on floral scent. How vegetative and floral traits compare in potential for adaptive evolution is poorly understood. METHODS We measured variation across source populations, planting sites, and genetic families for vegetative and floral traits in a hybrid zone. Seeds from families of Ipomopsis aggregata, I. tenuituba, and F1 and F2 hybrids of the two species were planted into three common gardens. Measured traits included specific leaf area (SLA), trichomes, water-use efficiency (WUE), floral morphology, petal color, nectar, and floral volatiles. RESULTS Vegetative traits SLA and WUE varied greatly among planting sites, while showing weak or no genetic variation among source populations. Specific leaf area and trichomes responded plastically to snowmelt date, and SLA exhibited within-population genetic variation. All aspects of floral morphology varied genetically among source populations, and corolla length, corolla width, and sepal width varied genetically within populations. Heritability was not detected for volatiles due to high environmental variation, although one terpene had high evolvability, and high emission of two terpenes, a class of compounds emitted more strongly from the calyx than the corolla, correlated genetically with sepal width. Environmental variation across sites was weak for floral morphology and stronger for volatiles and vegetative traits. The inheritance of three of four volatiles departed from additive. CONCLUSIONS Results indicate stronger genetic potential for evolutionary responses to selection in floral morphology compared with scent and vegetative traits and suggest potentially adaptive plasticity in some vegetative traits.
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Affiliation(s)
- Diane R. Campbell
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaIrvineCA92697USA
- Rocky Mountain Biological LaboratoryCrested ButteCO81224USA
| | - Robert A. Raguso
- Department of Neurobiology and BehaviorCornell UniversityIthacaNY14853USA
| | - Maya Midzik
- Rocky Mountain Biological LaboratoryCrested ButteCO81224USA
| | - Mascha Bischoff
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaIrvineCA92697USA
- Rocky Mountain Biological LaboratoryCrested ButteCO81224USA
- Department of Neurobiology and BehaviorCornell UniversityIthacaNY14853USA
- Environmental Research Institute, North Highland CollegeCastle StreetThursoKW14 7JDUK
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Heredia-Pech M, Chávez-Pesqueira M, Ortiz-García MM, Andueza-Noh RH, Chacón-Sánchez MI, Martínez-Castillo J. Consequences of introgression and gene flow on the genetic structure and diversity of Lima bean ( Phaseolus lunatus L.) in its Mesoamerican diversity area. PeerJ 2022; 10:e13690. [PMID: 35811827 PMCID: PMC9266586 DOI: 10.7717/peerj.13690] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 06/16/2022] [Indexed: 01/17/2023] Open
Abstract
We evaluated the role of gene flow and wild-crop introgression on the structure and genetic diversity of Lima bean (Phaseolus lunatus) in the Yucatan Peninsula, an important Mesoamerican diversity area for this crop, using a genotyping-by-sequencing approach (15,168 SNP markers) and two scales. At the local scale, STRUCTURE and NGSEP analyses showed predominantly crop-to-wild introgression, but also evidence of a bidirectional gene flow in the two wild-weedy-crop complexes studied (Itzinté and Dzitnup). The ABBA-BABA tests showed a higher introgression in Itzinté (the older complex) than in Dzitnup (the younger one); at the allelic level, the wild-crop introgression in Itzinté was similar in both directions, in Dzitnup it was higher from crop-to-wild; and at the chromosomal level, introgression in Itzinté was from wild-to-crop, whereas in Dzitnup it occured in the opposite direction. Also, we found H E values slightly higher in the domesticated accessions than in the wild ones, in both complexes (Itzinté: wild = 0.31, domesticated = 0.34; Dzinup: wild = 0.27, domesticated = 0.36), but %P and π estimators were higher in the wild accessions than in the domesticated ones. At a regional scale, STRUCTURE and MIGRATE showed a low gene flow, predominantly from crop-to-wild; and STRUCTURE, Neighbor-Joining and PCoA analyses indicated the existence of two wild groups and one domesticated group, with a marked genetic structure based in the existence of domesticated MI and wild MII gene pools. Also, at the regional scale, we found a higher genetic diversity in the wild accessions than in the domesticated ones, in all estimators used (e.g., H E = 0.27 and H E = 0.17, respectively). Our results indicate that gene flow and introgression are playing an important role at the local scale, but its consequences on the structure and genetic diversity of the Lima bean are not clearly reflected at the regional scale, where diversity patterns between wild and domesticated populations could be reflecting historical events.
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Affiliation(s)
- Mauricio Heredia-Pech
- Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A.C., Mérida, Yucatán, México
| | - Mariana Chávez-Pesqueira
- Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A.C., Mérida, Yucatán, México
| | - Matilde M. Ortiz-García
- Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A.C., Mérida, Yucatán, México
| | - Rubén Humberto Andueza-Noh
- División de Estudios de Posgrado e Investigación, Instituto Tecnológico de Conkal, Conkal, Yucatán, México
| | - María Isabel Chacón-Sánchez
- Departamento de Agronomía, Facultad de Ciencias Agrarias, Universidad Nacional de Colombia, Bogotá, D.C., Colombia
| | - Jaime Martínez-Castillo
- Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A.C., Mérida, Yucatán, México
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Endres KL, Morozumi CN, Loy X, Briggs HM, CaraDonna PJ, Iler AM, Picklum DA, Barr WA, Brosi BJ. Plant-pollinator interaction niche broadens in response to severe drought perturbations. Oecologia 2021; 197:577-588. [PMID: 34546496 DOI: 10.1007/s00442-021-05036-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Accepted: 08/16/2021] [Indexed: 11/30/2022]
Abstract
The composition of plant-pollinator interactions-i.e., who interacts with whom in diverse communities-is highly dynamic, and we have a very limited understanding of how interaction identities change in response to perturbations in nature. One prediction from niche and diet theory is that resource niches will broaden to compensate for resource reductions driven by perturbations, yet this has not been empirically tested in plant-pollinator systems in response to real-world perturbations in the field. Here, we use a long-term dataset of floral visitation to Ipomopsis aggregata, a montane perennial herb, to test whether the breadth of its floral visitation niche (i.e., flower visitor richness) changed in response to naturally occurring drought perturbations. Fewer floral resources are available in drought years, which could drive pollinators to expand their foraging niches, thereby expanding plants' floral visitation niches. We compared two drought years to three non-drought years to analyze changes in niche breadth and community composition of floral visitors to I. aggregata, predicting broadened niche breadth and distinct visitor community composition in drought years compared to non-drought years. We found statistically significant increases in niche breadth in drought years as compared to non-drought conditions, but no statistically distinguishable changes in community composition of flower visitors. Our findings suggest that plants' floral visitation niches may exhibit considerable plasticity in response to disturbance. This may have widespread consequences for community-level stability as well as functional consequences if increased niche overlap affects pollination services.
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Affiliation(s)
- Kelly L Endres
- Department of Environmental Sciences, Emory University, Atlanta, GA, USA
| | - Connor N Morozumi
- Program in Population Biology, Ecology, and Evolution, Emory University, Atlanta, GA, USA.
- Rocky Mountain Biological Laboratory, Crested Butte, CO, USA.
| | - Xingwen Loy
- Program in Population Biology, Ecology, and Evolution, Emory University, Atlanta, GA, USA
- Rocky Mountain Biological Laboratory, Crested Butte, CO, USA
| | | | - Paul J CaraDonna
- Rocky Mountain Biological Laboratory, Crested Butte, CO, USA
- Plant Biology and Conservation, Northwestern University, Evanston, IL, USA
- Chicago Botanic Garden, The Negaunee Institute of Plant Conservation Science and Action, Glencoe, IL, USA
| | - Amy M Iler
- Rocky Mountain Biological Laboratory, Crested Butte, CO, USA
- Plant Biology and Conservation, Northwestern University, Evanston, IL, USA
- Chicago Botanic Garden, The Negaunee Institute of Plant Conservation Science and Action, Glencoe, IL, USA
| | - Devon A Picklum
- Rocky Mountain Biological Laboratory, Crested Butte, CO, USA
- Graduate Program in Ecology, Evolution, and Conservation Biology, University of Nevada, Reno, USA
| | - William A Barr
- Rocky Mountain Biological Laboratory, Crested Butte, CO, USA
| | - Berry J Brosi
- Department of Environmental Sciences, Emory University, Atlanta, GA, USA
- Rocky Mountain Biological Laboratory, Crested Butte, CO, USA
- Department of Ecology and Evolution, University of Washington, Seattle, WA, USA
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Shukla K, Laursen AE, Benavides J, Ejbari N, Campbell LG. Growth and fecundity of colonizing hybrid Raphanus populations are environmentally dependent. AMERICAN JOURNAL OF BOTANY 2021; 108:580-597. [PMID: 33855711 DOI: 10.1002/ajb2.1640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 12/09/2020] [Indexed: 06/12/2023]
Abstract
PREMISE Hybrid gene pools harbor more genetic variation than progenitor populations. Thus, we expect hybrid populations to exhibit more dynamic evolutionary responses to environmental variation. We ask how environmental variation experienced by adapted and transplanted populations influence the success of late-generation hybrid populations during invasion. METHODS For four generations, 20 wild (Raphanus raphanistrum) and 20 hybrid radish (R. sativus × R. raphanistrum) plant populations evolved under experimentally manipulated moisture conditions (dry, wet, control-sheltered, or control-unsheltered plots; i.e., evolutionary environment) in old fields near Toronto, Canada. We planted advanced-generation wild and hybrid radishes in sheltered plots and exposed them to either an evolutionary or a novel watering environment. To determine how soil moisture would influence invasion success, we compared the phenotype and fecundity of plants grown in these various environments. RESULTS Hybridization produced larger plants. In wet environments, hybrid seedlings emerged more frequently and expressed higher photosynthetic activity. Low-moisture, novel conditions delayed and reduced seedling emergence frequency. Hybrid plants and those that evolved under relatively wet environments exhibited higher aboveground biomass. Hybrid plants from control-sheltered plots colonizing novel moisture environments were more fecund than comparable wild plants. CONCLUSIONS Dry environments are less likely than other evolutionary environments to contribute colonists. However, relatively wet locations support the evolution of relatively fecund plants, especially crop-wild hybrid populations. Thus, our results provide a strong mechanistic explanation for variation in the relative success of crop-wild hybrids among study locations and a new standard for studies that assess the risk of crop-wild hybridization events.
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Affiliation(s)
- Kruti Shukla
- Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
| | - Andrew E Laursen
- Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
| | - Jessica Benavides
- Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
| | - Neda Ejbari
- Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
| | - Lesley G Campbell
- Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
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Tominaga A, Matsui M, Matsui M. Structure and movement of the hybrid zone between two divergent lineages of the Japanese newt
Cynops pyrrhogaster
(Amphibia: Urodela) in central Japan. J ZOOL SYST EVOL RES 2021. [DOI: 10.1111/jzs.12467] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
| | - Masafumi Matsui
- Graduate School of Human and Environmental Studies Kyoto University Kyoto Japan
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7
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Thompson KA, Urquhart-Cronish M, Whitney KD, Rieseberg LH, Schluter D. Patterns, Predictors, and Consequences of Dominance in Hybrids. Am Nat 2021; 197:E72-E88. [PMID: 33625966 DOI: 10.1086/712603] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractCompared to those of their parents, are the traits of first-generation (F1) hybrids typically intermediate, biased toward one parent, or mismatched for alternative parental phenotypes? To address this empirical gap, we compiled data from 233 crosses in which traits were measured in a common environment for two parent taxa and their F1 hybrids. We find that individual traits in F1s are halfway between the parental midpoint and one parental value. Considering pairs of traits together, a hybrid's bivariate phenotype tends to resemble one parent (parent bias) about 50% more than the other, while also exhibiting a similar magnitude of mismatch due to different traits having dominance in conflicting directions. Using data from an experimental field planting of recombinant hybrid sunflowers, we illustrate that parent bias improves fitness, whereas mismatch reduces fitness. Our study has three major conclusions. First, hybrids are not phenotypically intermediate but rather exhibit substantial mismatch. Second, dominance is likely determined by the idiosyncratic evolutionary trajectories of individual traits and populations. Finally, selection against hybrids likely results from selection against both intermediate and mismatched phenotypes.
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DiVittorio CT, Singhal S, Roddy AB, Zapata F, Ackerly DD, Baldwin BG, Brodersen CR, Búrquez A, Fine PVA, Padilla Flores M, Solis E, Morales-Villavicencio J, Morales-Arce D, Kyhos DW. Natural selection maintains species despite frequent hybridization in the desert shrub Encelia. Proc Natl Acad Sci U S A 2020; 117:33373-33383. [PMID: 33318178 PMCID: PMC7776959 DOI: 10.1073/pnas.2001337117] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 11/03/2020] [Indexed: 01/01/2023] Open
Abstract
Natural selection is an important driver of genetic and phenotypic differentiation between species. For species in which potential gene flow is high but realized gene flow is low, adaptation via natural selection may be a particularly important force maintaining species. For a recent radiation of New World desert shrubs (Encelia: Asteraceae), we use fine-scale geographic sampling and population genomics to determine patterns of gene flow across two hybrid zones formed between two independent pairs of species with parapatric distributions. After finding evidence for extremely strong selection at both hybrid zones, we use a combination of field experiments, high-resolution imaging, and physiological measurements to determine the ecological basis for selection at one of the hybrid zones. Our results identify multiple ecological mechanisms of selection (drought, salinity, herbivory, and burial) that together are sufficient to maintain species boundaries despite high rates of hybridization. Given that multiple pairs of Encelia species hybridize at ecologically divergent parapatric boundaries, such mechanisms may maintain species boundaries throughout Encelia.
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Affiliation(s)
- Christopher T DiVittorio
- Department of Integrative Biology, University of California, Berkeley, CA 94720;
- TruBreed Technologies, Oakland, CA 94609
| | - Sonal Singhal
- Department of Biology, California State University - Dominguez Hills, Carson, CA 90747;
| | - Adam B Roddy
- School of the Environment, Yale University, New Haven, CT 06511
- Institute of Environment, Department of Biological Sciences, Florida International University, Miami, FL 33199
| | - Felipe Zapata
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095
| | - David D Ackerly
- Department of Integrative Biology, University of California, Berkeley, CA 94720
- Jepson Herbarium, University of California, Berkeley, CA 94720
- Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720
| | - Bruce G Baldwin
- Department of Integrative Biology, University of California, Berkeley, CA 94720
- Jepson Herbarium, University of California, Berkeley, CA 94720
| | | | - Alberto Búrquez
- Instituto de Ecología, Universidad Autónoma de México, Sonora, 83000 Hermosillo, México
| | - Paul V A Fine
- Department of Integrative Biology, University of California, Berkeley, CA 94720
| | - Mayra Padilla Flores
- Department of Biology, California State University - Dominguez Hills, Carson, CA 90747
| | - Elizabeth Solis
- Department of Biology, California State University - Dominguez Hills, Carson, CA 90747
| | | | - David Morales-Arce
- Benito Juárez s/n, Colonia Barrio La Punta, Bahia Asunción, 23960 Baja California Sur, México
| | - Donald W Kyhos
- Department of Plant Biology, University of California, Davis, CA 95616
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Pollinator divergence and pollination isolation between hybrids with different floral color and morphology in two sympatric Penstemon species. Sci Rep 2020; 10:8126. [PMID: 32415216 PMCID: PMC7229217 DOI: 10.1038/s41598-020-64964-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Accepted: 04/27/2020] [Indexed: 11/08/2022] Open
Abstract
Differential visitation of pollinators due to divergent floral traits can lead to reproductive isolation via assortative pollen flow, which may ultimately be a driving force in plant speciation, particularly in areas of overlap. We evaluate the effects of pollinator behavioral responses to variation of intraspecific floral color and nectar rewards, on reproductive isolation between two hybrid flower color morphs (fuchsia and blue) and their parental species Penstemon roseus and P. gentianoides with a mixed-pollination system. We show that pollinators (bumblebees and hummingbirds) exhibit different behavioral responses to fuchsia and blue morphs, which could result from differential attraction or deterrence. In addition to differences in color (spectral reflectance), we found that plants with fuchsia flowers produced more and larger flowers, produced more nectar and were more visited by pollinators than those with blue flowers. These differences influenced the foraging behavior and effectiveness as pollinators of both bumblebees and hummingbirds, which contributed to reproductive isolation between the two hybrid flower color morphs and parental species. This study demonstrates how differentiation of pollination traits promotes the formation of hybrid zones leading to pollinator shifts and reproductive isolation. While phenotypic traits of fuchsia and red flowers might encourage more efficient hummingbird pollination in a mixed-pollination system, the costs of bumblebee pollination on plant reproduction could be the drivers for the repeated shifts from bumblebee- to hummingbird-mediated pollination.
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Moreira-Hernández JI, Muchhala N. Importance of Pollinator-Mediated Interspecific Pollen Transfer for Angiosperm Evolution. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2019. [DOI: 10.1146/annurev-ecolsys-110218-024804] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Understanding how pollen moves between species is critical to understanding speciation, diversification, and evolution of flowering plants. For co-flowering species that share pollinators, competition through interspecific pollen transfer (IPT) can profoundly impact floral evolution, decreasing female fitness via heterospecific pollen deposition on stigmas and male fitness via pollen misplacement during visits to heterospecific flowers. The pollination literature demonstrates that such reproductive interference frequently selects for reproductive character displacement in floral traits linked to pollinator attraction, pollen placement, and mating systems and has also revealed that IPT between given pairs of species is typically asymmetric. More recent work is starting to elucidate its importance to the speciation process, clarifying the link between IPT and current and historical patterns of hybridization, the evolution of phenotypic novelty through adaptive introgression, and the rise of reproductive isolation. Our review aims to stimulate further research on IPT as a ubiquitous mechanism that plays a central role in angiosperm diversification.
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Affiliation(s)
- Juan Isaac Moreira-Hernández
- Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri–St. Louis, St. Louis, Missouri 63121, USA;,
| | - Nathan Muchhala
- Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri–St. Louis, St. Louis, Missouri 63121, USA;,
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11
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Early snowmelt projected to cause population decline in a subalpine plant. Proc Natl Acad Sci U S A 2019; 116:12901-12906. [PMID: 31182600 DOI: 10.1073/pnas.1820096116] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
How climate change influences the dynamics of plant populations is not well understood, as few plant studies have measured responses of vital rates to climatic variables and modeled the impact on population growth. The present study used 25 y of demographic data to analyze how survival, growth, and fecundity respond to date of spring snowmelt for a subalpine plant. Fecundity was estimated by seed production (over 15 y) and also divided into flower number, fruit set, seeds per fruit, and escape from seed predation. Despite no apparent effects on flower number, plants produced more seeds in years with later snowmelt. Survival and probability of flowering were reduced by early snowmelt in the previous year. Based on demographic models, earlier snowmelt with warming is expected to lead to negative population growth, driven especially by changes in seedling establishment and seed production. These results provide a rare example of how climate change is expected to influence the dynamics of a plant population. They furthermore illustrate the potential for strong population impacts even in the absence of more commonly reported visual signs, such as earlier blooming or reduced floral display in early melting years.
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12
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Yan LJ, Burgess KS, Zheng W, Tao ZB, Li DZ, Gao LM. Incomplete reproductive isolation between Rhododendron taxa enables hybrid formation and persistence. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2019; 61:433-448. [PMID: 30192058 DOI: 10.1111/jipb.12718] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2018] [Accepted: 09/06/2018] [Indexed: 06/08/2023]
Abstract
The evolutionary consequences of hybridization ultimately depend on the magnitude of reproductive isolation between hybrids and their parents. We evaluated the relative contributions of pre- and post-zygotic barriers to reproduction for hybrid formation, hybrid persistence and potential for reproductive isolation of hybrids formed between two Rhododendron species, R. spiciferum and R. spinuliferum. Our study established that incomplete reproductive isolation promotes hybrid formation and persistence and delays hybrid speciation. All pre-zygotic barriers to reproduction leading to hybrid formation are incomplete: parental species have overlapping flowering; they share the same pollinators; reciprocal assessments of pollen tube germination and growth do not differ among parents. The absence of post-zygotic barriers between parental taxa indicates that the persistence of hybrids is likely. Reproductive isolation was incomplete between hybrids and parents in all cases studied, although asymmetric differences in reproductive fitness were prevalent and possibly explain the genetic structure of natural hybrid swarms where hybridization is known to be bidirectional but asymmetric. Introgression, rather than speciation, is a probable evolutionary outcome of hybridization between the two Rhododendron taxa. Our study provides insights into understanding the evolutionary implications of natural hybridization in woody plants.
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Affiliation(s)
- Li-Jun Yan
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
- Germplasm Bank of Wild Species, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
- Kunming College of Life Science, University of the Chinese Academy of Sciences, Kunming 650201, China
- College of Vocational and Technical Education, Yunnan Normal University, Kunming 650092, China
| | - Kevin S Burgess
- Department of Biology, College of Letters & Sciences, Columbus State University, University System of Georgia, 31907-5645 Columbus, GA, USA
| | - Wei Zheng
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
- Kunming College of Life Science, University of the Chinese Academy of Sciences, Kunming 650201, China
| | - Zhi-Bin Tao
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
- Kunming College of Life Science, University of the Chinese Academy of Sciences, Kunming 650201, China
| | - De-Zhu Li
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
- Germplasm Bank of Wild Species, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
- Kunming College of Life Science, University of the Chinese Academy of Sciences, Kunming 650201, China
| | - Lian-Ming Gao
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
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13
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Campbell DR, Faidiga A, Trujillo G. Clines in traits compared over two decades in a plant hybrid zone. ANNALS OF BOTANY 2018; 122:315-324. [PMID: 29800076 PMCID: PMC6070099 DOI: 10.1093/aob/mcy072] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 04/17/2018] [Indexed: 05/30/2023]
Abstract
Background and Aims Clines in traits across hybrid zones reflect a balance between natural selection and gene flow. Changes over time in average values for traits, and especially the shapes of their clines, are rarely investigated in plants, but could result from evolution in an unstable hybrid zone. Differences in clines between floral and vegetative traits could indicate different strengths of divergent selection. Methods Five floral and two vegetative traits were measured in 12 populations along an elevational gradient spanning a natural hybrid zone between Ipomopsis aggregata and Ipomopsis tenuituba. We compared clines in the floral traits with those measured 25 years ago. Observed changes in mean trait values were compared with predictions based on prior estimates of natural selection. We also compared the steepness and position of clines between the floral and vegetative traits. Key Results Corolla length has increased over five generations to an extent that matches predictions from measurements of phenotypic selection and heritability. The shape of its cline, and that of other traits, has not changed detectably. Clines varied across traits, but not all floral traits showed steeper clines than did vegetative traits. Both suites of morphological traits had steeper clines than did neutral molecular markers. Conclusions The increase in corolla length provides a rare example of a match between predicted and observed evolution of a plant trait in natural populations. The clinal properties are consistent with the hypothesis that habitat-mediated divergent selection on vegetative traits and pollinator-mediated selection on floral traits both maintain species differences across the hybrid zone.
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Affiliation(s)
- Diane R Campbell
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA
- Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA
| | | | - Gabriel Trujillo
- Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA
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Gramlich S, Hörandl E. Fitness of natural willow hybrids in a pioneer mosaic hybrid zone. Ecol Evol 2016; 6:7645-7655. [PMID: 30128118 PMCID: PMC6093150 DOI: 10.1002/ece3.2470] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 08/10/2016] [Accepted: 08/24/2016] [Indexed: 01/20/2023] Open
Abstract
Hybrid fitness is an important parameter to predict the evolutionary consequences of a hybridization event and to characterize hybrid zones. We studied fitness parameters of F1 and later-generation hybrids between the lowland species Salix purpurea and the alpine S. helvetica that have recently emerged during colonization of an alpine glacier forefield. Fruit production (number of capsules per catkin and fruit set) did not differ between hybrids and parents, but the number of seeds per capsule of F1 hybrids was slightly lower than that of later-generation hybrids and of the parents. Germination rates and seedling growth were tested on three substrates (pH 4.5, 7.0, and 8.0). Germination rates of seeds collected from F1 hybrids were lower on acid and neutral substrates, but equal at pH 8.0 compared to all other groups, while the seeds from later-generation hybrids performed as well as the parents on all three substrates. In seedling growth, the colonizer S. purpurea performed better than all other taxa on all three substrates, while hybrids resembled the subalpine species S. helvetica. Results suggest that endogenous selection acts against F1 hybrids, but favors fitter genotypes in later-generation hybrids. Exogenous selection via soil pH appears to be weak during seedling establishment. The pioneer vegetation on the glacier forefield may offer sufficient niche space for hybrid seedlings. Owing to the relatively high fitness of the hybrids and the scattered distribution of hybrids and parental individuals on the glacier forefield, this hybrid zone can be assigned to a mosaic model, probably facilitating gene flow and introgression between the parental species. As establishment of the hybrid zone appears to be linked to a colonization process, we propose to call it a pioneer mosaic hybrid zone.
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Affiliation(s)
- Susanne Gramlich
- Department of Systematics, Biodiversity and Evolution of Plants (with Herbarium)Georg August University GöttingenGöttingenGermany
| | - Elvira Hörandl
- Department of Systematics, Biodiversity and Evolution of Plants (with Herbarium)Georg August University GöttingenGöttingenGermany
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Wang J, Lamer JT, Gaughan S, Wachholtz M, Wang C, Lu G. Transcriptomic comparison of invasive bigheaded carps ( Hypophthalmichthys nobilis and Hypophthalmichthys molitrix) and their hybrids. Ecol Evol 2016; 6:8452-8459. [PMID: 28031797 PMCID: PMC5167015 DOI: 10.1002/ece3.2574] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 09/30/2016] [Accepted: 10/05/2016] [Indexed: 11/15/2022] Open
Abstract
Bighead carp (Hypophthalmichthys nobilis) and silver carp (Hypophthalmichthys molitrix), collectively called bigheaded carps, are invasive species in the Mississippi River Basin (MRB). Interspecific hybridization between bigheaded carps has been considered rare within their native rivers in China; however, it is prevalent in the MRB. We conducted de novo transcriptome analysis of pure and hybrid bigheaded carps and obtained 40,759 to 51,706 transcripts for pure, F1 hybrid, and backcross bigheaded carps. The search against protein databases resulted in 20,336–28,133 annotated transcripts (over 50% of the transcriptome) with over 13,000 transcripts mapped to 23 Gene Ontology biological processes and 127 KEGG metabolic pathways. More transcripts were detected in silver carp than in bighead carp; however, comparable numbers of transcripts were annotated. Transcriptomic variation detected between two F1 hybrids may indicate a potential loss of fitness in hybrids. The neighbor‐joining distance tree constructed using over 2,500 one‐to‐one orthologous sequences suggests transcriptomes could be used to infer the history of introgression and hybridization. Moreover, we detected 24,792 candidate SNPs that can be used to identify different species. The transcriptomes, orthologous sequences, and candidate SNPs obtained in this study should provide further knowledge of interspecific hybridization and introgression.
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Affiliation(s)
- Jun Wang
- Department of Biology University of Nebraska at Omaha Omaha NE 68182 USA; Key Laboratory of Freshwater Fisheries Germplasm Resources Ministry of Agriculture Shanghai Ocean University Shanghai 201306 China
| | - James T Lamer
- Department of Biological Sciences Western Illinois University Macomb IL 61455 USA
| | - Sarah Gaughan
- Department of Biology University of Nebraska at Omaha Omaha NE 68182 USA
| | - Michael Wachholtz
- Department of Biology University of Nebraska at Omaha Omaha NE 68182 USA
| | - Chenghui Wang
- Key Laboratory of Freshwater Fisheries Germplasm Resources Ministry of Agriculture Shanghai Ocean University Shanghai 201306 China
| | - Guoqing Lu
- Department of Biology University of Nebraska at Omaha Omaha NE 68182 USA; School of Interdisciplinary Informatics University of Nebraska at Omaha Omaha NE 68182 USA
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Patel S, Schell T, Eifert C, Feldmeyer B, Pfenninger M. Characterizing a hybrid zone between a cryptic species pair of freshwater snails. Mol Ecol 2015; 24:643-55. [PMID: 25533031 DOI: 10.1111/mec.13049] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Revised: 12/11/2014] [Accepted: 12/16/2014] [Indexed: 12/25/2022]
Abstract
Characterizing hybrid zones and their dynamics is a central goal in evolutionary biology, but this is particularly challenging for morphologically cryptic species. The lack of conspicuous divergence between parental types means intermediate hybrid forms often go undetected. We aimed to detect and characterize a suspected hybrid zone between a pair of morphologically cryptic lineages of the freshwater snail, Radix. We sampled Radix from across a contact zone between two mitochondrial lineages (Radix balthica and an undescribed lineage termed 'MOTU3') and detected admixture between two nuclear genotype clusters, which were significantly but not categorically associated with the mitochondrial lineages. Using a model selection approach, we show that the admixture cline is best explained by an interaction between precipitation and temperature gradients over the area, rather than geographic distance. We thus hypothesize that the correlation with climatic gradients suggests environmental selection has played a role in maintaining the hybrid zone. In a 2050 climate change scenario, we furthermore predict an expansion of one of the nuclear clusters and a widening of the hybrid zone as the climate warms and dries.
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Affiliation(s)
- Simit Patel
- Biodiversity und Climate Research Centre by Senckenberg Naturforschende Gesellschaft and Goethe-Universität, 60325, Frankfurt, Germany
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Meng J, Mao JF, Zhao W, Xing F, Chen X, Liu H, Xing Z, Wang XR, Li Y. Adaptive differentiation in seedling traits in a hybrid pine species complex, Pinus densata and its parental species, on the Tibetan Plateau. PLoS One 2015; 10:e0118501. [PMID: 25757072 PMCID: PMC4355066 DOI: 10.1371/journal.pone.0118501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Accepted: 01/19/2015] [Indexed: 11/24/2022] Open
Abstract
Evidence from molecular genetics demonstrates that Pinus densata is a natural homoploid hybrid originating from the parent species Pinus tabuliformis and Pinus yunnanensis, and ecological selection may have played a role in the speciation of P. densata. However, data on differentiation in adaptive traits in the species complex are scarce. In this study, we performed a common garden test on 16 seedling traits to examine the differences between P. densata and its parental species in a high altitude environment. We found that among the 16 analyzed traits, 15 were significantly different among the species. Pinus tabuliformis had much earlier bud set and a relatively higher bud set ratio but poorer seedling growth, and P. yunnanensis had opposite responses for the same traits. P. densata had the greatest fitness with higher viability and growth rates than the parents. The relatively high genetic contribution of seedling traits among populations suggested that within each species the evolutionary background is complex. The correlations between the seedling traits of a population within a species and the environmental factors indicated different impacts of the environment on species evolution. The winter temperature is among the most important climate factors that affected the fitness of the three pine species. Our investigation provides empirical evidence on adaptive differentiation among this pine species complex at seedling stages.
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Affiliation(s)
- Jingxiang Meng
- State Engineering Laboratory of Forest Tree Breeding, Key Laboratory of Genetic and Breeding in Forest Trees and Ornamental Plants, Beijing Forestry University, Beijing, China
- College of Biology Sciences and Technology, Beijing Forestry University, Beijing, China
| | - Jian-Feng Mao
- State Engineering Laboratory of Forest Tree Breeding, Key Laboratory of Genetic and Breeding in Forest Trees and Ornamental Plants, Beijing Forestry University, Beijing, China
- College of Biology Sciences and Technology, Beijing Forestry University, Beijing, China
| | - Wei Zhao
- State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Fangqian Xing
- State Engineering Laboratory of Forest Tree Breeding, Key Laboratory of Genetic and Breeding in Forest Trees and Ornamental Plants, Beijing Forestry University, Beijing, China
- College of Biology Sciences and Technology, Beijing Forestry University, Beijing, China
| | - Xinyu Chen
- State Engineering Laboratory of Forest Tree Breeding, Key Laboratory of Genetic and Breeding in Forest Trees and Ornamental Plants, Beijing Forestry University, Beijing, China
- College of Biology Sciences and Technology, Beijing Forestry University, Beijing, China
| | - Hao Liu
- College of Resources and Environment, College of Agriculture and Animal Husbandry of Tibet University, Linzhi, Tibet, China
| | - Zhen Xing
- College of Resources and Environment, College of Agriculture and Animal Husbandry of Tibet University, Linzhi, Tibet, China
| | - Xiao-Ru Wang
- Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden
| | - Yue Li
- State Engineering Laboratory of Forest Tree Breeding, Key Laboratory of Genetic and Breeding in Forest Trees and Ornamental Plants, Beijing Forestry University, Beijing, China
- College of Biology Sciences and Technology, Beijing Forestry University, Beijing, China
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Mercer KL, Emry DJ, Snow AA, Kost MA, Pace BA, Alexander HM. Fitness of crop-wild hybrid sunflower under competitive conditions: implications for crop-to-wild introgression. PLoS One 2014; 9:e109001. [PMID: 25295859 PMCID: PMC4189920 DOI: 10.1371/journal.pone.0109001] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Accepted: 08/18/2014] [Indexed: 11/20/2022] Open
Abstract
Understanding the likelihood and extent of introgression of novel alleles in hybrid zones requires comparison of lifetime fitness of parents and hybrid progeny. However, fitness differences among cross types can vary depending on biotic conditions, thereby influencing introgression patterns. Based on past work, we predicted that increased competition would enhance introgression between cultivated and wild sunflower (Helianthus annuus) by reducing fitness advantages of wild plants. To test this prediction, we established a factorial field experiment in Kansas, USA where we monitored the fitness of four cross types (Wild, F1, F2, and BCw hybrids) under different levels of interspecific and intraspecific competition. Intraspecific manipulations consisted both of density of competitors and of frequency of crop-wild hybrids. We recorded emergence of overwintered seeds, survival to reproduction, and numbers of seeds produced per reproductive plant. We also calculated two compound fitness measures: seeds produced per emerged seedling and seeds produced per planted seed. Cross type and intraspecific competition affected emergence and survival to reproduction, respectively. Further, cross type interacted with competitive treatments to influence all other fitness traits. More intense competition treatments, especially related to density of intraspecific competitors, repeatedly reduced the fitness advantage of wild plants when considering seeds produced per reproductive plant and per emerged seedling, and F2 plants often became indistinguishable from the wilds. Wild fitness remained superior when seedling emergence was also considered as part of fitness, but the fitness of F2 hybrids relative to wild plants more than quadrupled with the addition of interspecific competitors and high densities of intraspecific competitors. Meanwhile, contrary to prediction, lower hybrid frequency reduced wild fitness advantage. These results emphasize the importance of taking a full life cycle perspective. Additionally, due to effects of exogenous selection, a given hybrid generation may be especially well-suited to hastening introgression under particular environmental conditions.
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Affiliation(s)
- Kristin L. Mercer
- Ohio State University, Department of Horticulture and Crop Science, Columbus, Ohio, United States of America
- * E-mail:
| | - D. Jason Emry
- University of Kansas, Department of Ecology and Evolutionary Biology, Lawrence, Kansas, United States of America
- Washburn University, Topeka, Kansas, United States of America
| | - Allison A. Snow
- Ohio State University, Department of Evolution, Ecology, and Organismal Biology, Columbus, Ohio, United States of America
| | - Matthew A. Kost
- Ohio State University, Department of Horticulture and Crop Science, Columbus, Ohio, United States of America
| | - Brian A. Pace
- Ohio State University, Department of Horticulture and Crop Science, Columbus, Ohio, United States of America
| | - Helen M. Alexander
- University of Kansas, Department of Ecology and Evolutionary Biology, Lawrence, Kansas, United States of America
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Roe AD, MacQuarrie CJK, Gros-Louis MC, Simpson JD, Lamarche J, Beardmore T, Thompson SL, Tanguay P, Isabel N. Fitness dynamics within a poplar hybrid zone: II. Impact of exotic sex on native poplars in an urban jungle. Ecol Evol 2014; 4:1876-89. [PMID: 24963382 PMCID: PMC4063481 DOI: 10.1002/ece3.1028] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Revised: 12/20/2013] [Accepted: 12/31/2013] [Indexed: 01/11/2023] Open
Abstract
Trees bearing novel or exotic gene components are poised to contribute to the bioeconomy for a variety of purposes such as bioenergy production, phytoremediation, and carbon sequestration within the forestry sector, but sustainable release of trees with novel traits in large-scale plantations requires the quantification of risks posed to native tree populations. Over the last century, exotic hybrid poplars produced through artificial crosses were planted throughout eastern Canada as ornamentals or windbreaks and these exotics provide a proxy by which to examine the fitness of exotic poplar traits within the natural environment to assess risk of exotic gene escape, establishment, and spread into native gene pools. We assessed postzygotic fitness traits of native and exotic poplars within a naturally regenerated stand in eastern Canada (Quebec City, QC). Pure natives (P. balsamifera and P. deltoides spp. deltoides), native hybrids (P. deltoides × P. balsamifera), and exotic hybrids (trees bearing Populus nigra and P. maximowiczii genetic components) were screened for reproductive biomass, yield, seed germination, and fungal disease susceptibility. Exotic hybrids expressed fitness traits intermediate to pure species and were not significantly different from native hybrids. They formed fully viable seed and backcrossed predominantly with P. balsamifera. These data show that exotic hybrids were not unfit and were capable of establishing and competing within the native stand. Future research will seek to examine the impact of exotic gene regions on associated biotic communities to fully quantify the risk exotic poplars pose to native poplar forests.
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Affiliation(s)
- Amanda D Roe
- Natural Resources Canada, Canadian Forest ServiceQuébec, Québec, Canada
- Natural Resources Canada, Canadian Forest ServiceSault Ste. Marie, Ontario, Canada
| | - Chris JK MacQuarrie
- Natural Resources Canada, Canadian Forest ServiceSault Ste. Marie, Ontario, Canada
| | | | - J Dale Simpson
- Natural Resources Canada, Canadian Forest ServiceFredericton, New-Brunswick, Canada
| | - Josyanne Lamarche
- Natural Resources Canada, Canadian Forest ServiceSault Ste. Marie, Ontario, Canada
| | - Tannis Beardmore
- Natural Resources Canada, Canadian Forest ServiceFredericton, New-Brunswick, Canada
| | - Stacey L Thompson
- Natural Resources Canada, Canadian Forest ServiceQuébec, Québec, Canada
- Umeå University, Department of Ecology and Environmental Science, Umeå Plant Science CentreUmeå, Sweden
| | - Philippe Tanguay
- Natural Resources Canada, Canadian Forest ServiceQuébec, Québec, Canada
| | - Nathalie Isabel
- Natural Resources Canada, Canadian Forest ServiceQuébec, Québec, Canada
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Bischoff M, Jürgens A, Campbell DR. Floral scent in natural hybrids of Ipomopsis (Polemoniaceae) and their parental species. ANNALS OF BOTANY 2014; 113:533-44. [PMID: 24355404 PMCID: PMC3906972 DOI: 10.1093/aob/mct279] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 10/15/2013] [Indexed: 05/27/2023]
Abstract
BACKGROUND AND AIMS Floral traits, such as floral volatiles, can contribute to pre-zygotic reproductive isolation by promoting species-specific pollinator foraging. When hybrid zones form, floral traits could also influence post-zygotic isolation. This study examined floral volatiles in parental species and natural hybrids in order to explore potential scent mediation of pre-zygotic and post-zygotic isolation. METHODS Floral bouquets were analysed for the sister species Ipomopsis aggregata and I. tenuituba and their natural hybrids at two contact sites differing in both hybridization rate and temporal foraging pattern of hawkmoth pollinators. Floral volatiles were quantified in diurnal and nocturnal scent samples using gas chromatography-mass spectrometry. KEY RESULTS The bouquets of parental species and hybrids showed qualitative overlap. All flowers emitted similar sets of monoterpenoid, sesquiterpenoid, aliphatic and benzenoid compounds, but separated into groups defined by multivariate analysis of quantitative emissions. The parental species differed most strikingly in the nitrogenous compound indole, which was found almost exclusively in nocturnal bouquets of I. tenuituba. Natural hybrid bouquets were highly variable, and showed emission rates of several compounds that appeared transgressive. However, indole emission rates were intermediate in the hybrids compared with rates in the parents. Volatile bouquets at the contact site with lower hybridization did not show greater species specificity in overall scent emission, but I. tenuituba presented a stronger indole signal during peak hawkmoth activity at that site. CONCLUSIONS The two species of Ipomopsis differed in patterns of floral bouquets, with indole emitted in nocturnal I. tenuituba, but not in I. aggregata. Natural hybrid bouquets were not consistently intermediate between the parents, although hybrids were intermediate in indole emission. The indole signal could potentially serve as a hawkmoth attractant that mediates reproductive isolation both before and after hybrid formation.
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Affiliation(s)
- Mascha Bischoff
- Department of Neurobiology and Behavior, Cornell University, 215 Tower Road, Ithaca, NY 14853, USA
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA
- Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA
| | - Andreas Jürgens
- University of KwaZulu-Natal, School of Life Sciences, P. Bag X01 Scottsville, Pietermaritzburg 3209, South Africa
| | - Diane R. Campbell
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA
- Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA
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Hargreaves AL, Samis KE, Eckert CG. Are Species’ Range Limits Simply Niche Limits Writ Large? A Review of Transplant Experiments beyond the Range. Am Nat 2014; 183:157-73. [DOI: 10.1086/674525] [Citation(s) in RCA: 269] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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De La Torre AR, Wang T, Jaquish B, Aitken SN. Adaptation and exogenous selection in a Picea glauca × Picea engelmannii hybrid zone: implications for forest management under climate change. THE NEW PHYTOLOGIST 2014; 201:687-699. [PMID: 24200028 PMCID: PMC4285121 DOI: 10.1111/nph.12540] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Accepted: 08/30/2013] [Indexed: 05/04/2023]
Abstract
The nature of selection responsible for the maintenance of the economically and ecologically important Picea glauca × Picea engelmannii hybrid zone was investigated. Genomic, phenotypic and climatic data were used to test assumptions of hybrid zone maintenance and to model future scenarios under climate change. Genome-wide estimates of admixture based on a panel of 86 candidate gene single nucleotide polymorphisms were combined with long-term quantitative data on growth and survival (over 20 yr), as well as one-time assessments of bud burst and bud set phenology, and cold hardiness traits. A total of 15,498 individuals were phenotyped for growth and survival. Our results suggest that the P. glauca × P. engelmannii hybrid zone is maintained by local adaptation to growing season length and snowpack (exogenous selection). Hybrids appeared to be fitter than pure species in intermediate environments, which fits expectations of the bounded hybrid superiority model of hybrid zone maintenance. Adaptive introgression from parental species has probably contributed to increased hybrid fitness in intermediate habitats. While P. engelmannii ancestry is higher than P. glauca ancestry in hybrid populations, on average, selective breeding in managed hybrid populations is shifting genomic composition towards P. glauca, potentially pre-adapting managed populations to warmer climates.
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Affiliation(s)
- Amanda R De La Torre
- Centre for Forest Conservation Genetics, Department of Forest and Conservation Sciences, University of British Columbia3041–2424 Main Mall, Vancouver, BC, V6T1Z4, Canada
- Department of Ecology and Environmental Sciences, Umeå UniversityLinneaus väg 6, SE-901 87, Umeå, Sweden
- Author for correspondence:Amanda R. De La Torre, Tel: +46 090 7865475,
| | - Tongli Wang
- Centre for Forest Conservation Genetics, Department of Forest and Conservation Sciences, University of British Columbia3041–2424 Main Mall, Vancouver, BC, V6T1Z4, Canada
| | - Barry Jaquish
- Kalamalka Forestry Centre, Tree Improvement Branch, BC Ministry of Forests, Lands & Natural Resource Operations3401 Reservoir Rd, Vernon, BC, V1B2C7, Canada
| | - Sally N Aitken
- Centre for Forest Conservation Genetics, Department of Forest and Conservation Sciences, University of British Columbia3041–2424 Main Mall, Vancouver, BC, V6T1Z4, Canada
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Burge DO, Hopkins R, Tsai YHE, Manos PS. Limited hybridization across an edaphic disjunction between the gabbro-endemic shrub Ceanothus roderickii (Rhamnaceae) and the soil-generalist Ceanothus cuneatus. AMERICAN JOURNAL OF BOTANY 2013; 100:1883-1895. [PMID: 24018856 DOI: 10.3732/ajb.1200604] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
PREMISE OF THE STUDY Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. • METHODS AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. • KEY RESULTS Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. • CONCLUSIONS There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants.
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Affiliation(s)
- Dylan O Burge
- Duke University Department of Biology, Box 90338 Durham, North Carolina 27705, USA
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Campbell DR, Wendlandt C. Altered precipitation affects plant hybrids differently than their parental species. AMERICAN JOURNAL OF BOTANY 2013; 100:1322-1331. [PMID: 23748678 DOI: 10.3732/ajb.1200473] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
PREMISE OF THE STUDY Future changes in environmental conditions may alter evolutionary processes, including hybridization in nature. Frequency of hybrids could be altered via range shifts by the parental species or by changes in prezygotic or postzygotic reproductive isolation. We examined the potential for range shifts and change in postzygotic isolation by determining effects of increasing and decreasing precipitation on leaf physiology and fitness components in the subalpine herbs Ipomopsis aggregata (Polemoniaceae), I. tenuituba¸ and their natural hybrids in a common garden in the habitat of I. aggregata. METHODS Summer precipitation was experimentally doubled or halved over 3 yr in comparison with ambient conditions. We measured relative growth rate, specific leaf area, intrinsic water-use efficiency, survival to reproduction, biomass, number of flowers produced, and floral morphology. KEY RESULTS Ipomopsis tenuituba increased relative growth rate with higher precipitation more so than did I. aggregata during the first summer, but this response did not result in changes across treatments in relative survival or final reproductive success of the two species. When precipitation was reduced, the relative success of hybrids was greater than that of the home species, I. aggregata. In dry conditions, hybrids increased water-use efficiency and fitness as indexed by number of flowers more so than the other plant types did. CONCLUSIONS Increased reproduction in hybrids in the reduced precipitation regime indicates that postzygotic reproductive isolation may breakdown under imposition of dry conditions. These results suggest the potential for frequency of hybrids to increase if severe droughts become more common.
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Affiliation(s)
- Diane R Campbell
- Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697, USA.
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Gomulkiewicz R, Shaw RG. Evolutionary rescue beyond the models. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120093. [PMID: 23209173 DOI: 10.1098/rstb.2012.0093] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Laboratory model systems and mathematical models have shed considerable light on the fundamental properties and processes of evolutionary rescue. But it remains to determine the extent to which these model-based findings can help biologists predict when evolution will fail or succeed in rescuing natural populations that are facing novel conditions that threaten their persistence. In this article, we present a prospectus for transferring our basic understanding of evolutionary rescue to wild and other non-laboratory populations. Current experimental and theoretical results emphasize how the interplay between inheritance processes and absolute fitness in changed environments drive population dynamics and determine prospects of extinction. We discuss the challenge of inferring these elements of the evolutionary rescue process in field and natural settings. Addressing this challenge will contribute to a more comprehensive understanding of population persistence that combines processes of evolutionary rescue with developmental and ecological mechanisms.
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Affiliation(s)
- Richard Gomulkiewicz
- School of Biological Sciences, Washington State University, Pullman, WA 99164, USA.
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Greiner S, Bock R. Tuning a ménage à trois: Co-evolution and co-adaptation of nuclear and organellar genomes in plants. Bioessays 2013; 35:354-65. [DOI: 10.1002/bies.201200137] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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McKenzie-Gopsill A, Kirk H, Drunen WV, Freeland JR, Dorken ME. No evidence for niche segregation in a North American Cattail (Typha) species complex. Ecol Evol 2012; 2:952-61. [PMID: 22837840 PMCID: PMC3399161 DOI: 10.1002/ece3.225] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2011] [Revised: 01/16/2012] [Accepted: 01/19/2012] [Indexed: 11/09/2022] Open
Abstract
Interspecific hybridization can lead to a breakdown of species boundaries, and is of particular concern in cases in which one of the parental species is invasive. Cattails (Typha spp.) have increased their abundance in the Great Lakes region of North America over the past 150 years. This increase in the distribution of cattails is associated with hybridization between broad-leaved (Typha latifolia) and narrow-leaved cattails (T. angustifolia). The resulting hybrids occur predominantly as F(1)s, which are known as T. × glauca, although later-generation hybrids have also been documented. It has been proposed that in sympatric populations, the parental species and hybrids are often spatially segregated according to growth in contrasting water depths, and that this should promote the maintenance of parental species. In this study, we tested the hypothesis that the two species and their hybrids segregate along a water-depth gradient at sites where they are sympatric. We identified the two parental species and their hybrids using molecular genetic markers (SSR), and measured shoot elevations (a proxy for water depth) at 18 sites in Southern Ontario, Canada. We found no evidence for niche segregation among species based on elevation. Our data indicate that all three lineages compete for similar habitat where they co-occur suggesting that there is potential for an overall loss of biodiversity in the species complex, particularly if the hybrid lineage is more vigorous compared to the parental species, as has been suggested by other authors.
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Affiliation(s)
- Andrew McKenzie-Gopsill
- Department of Biology, Trent University 1600 West Bank Drive, Peterborough, ON, K9J 7B8, Canada
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Affiliation(s)
- I Keller
- Department of Fish Ecology and Evolution, EAWAG Swiss Federal Institute of Aquatic Science and Technology, Center of Ecology, Evolution and Biochemistry, Seestrasse 79, CH-6047 Kastanienbaum, Switzerland.
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Mitsui Y, Nomura N, Isagi Y, Tobe H, Setoguchi H. Ecological barriers to gene flow between riparian and forest species of Ainsliaea (Asteraceae). Evolution 2010; 65:335-49. [PMID: 20840597 DOI: 10.1111/j.1558-5646.2010.01129.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Understanding the role of habitat-associated adaptation in reducing gene flow resulting in population differentiation and speciation is a major issue in evolutionary biology. We demonstrate a significant role for habitat divergence in species isolation between two naturally hybridizing riparian and nonriparian plants, Ainsliaea faurieana and A. apiculata (Asteraceae), on Yakushima Island, Japan. By analyzing the fine-scale population structure at six sympatric sites, we found that variations in leaf shape, geography, light conditions, and genotype were strongly correlated across riverbank-forest transitions. No evidence of effective gene flow was found between the two species across the majority of the transition zones, although the NewHybrid clustering analysis confirmed interspecific hybridization. However, a relatively high level of gene flow was observed across one zone with a more diffuse ecotone and intermediate flooding and light conditions, possibly generated by human disturbances. These results suggest that the barriers to gene flow between the riparian and forest species are primarily ecological. Additional common garden experiments indicated that the two species are adaptively differentiated to contrasting flooding and light environments. Overall, our study suggests that adaptations to different habitats can lead to the formation of reproductive isolating barriers and the maintenance of distinct species boundaries.
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Affiliation(s)
- Yuki Mitsui
- Graduate School of Human and Environmental Studies, Kyoto University, Yoshida, Nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan.
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Leinonen PH, Remington DL, Savolainen O. LOCAL ADAPTATION, PHENOTYPIC DIFFERENTIATION, AND HYBRID FITNESS IN DIVERGED NATURAL POPULATIONS OF ARABIDOPSIS LYRATA. Evolution 2010; 65:90-107. [DOI: 10.1111/j.1558-5646.2010.01119.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Arnold ML, Martin NH. Hybrid fitness across time and habitats. Trends Ecol Evol 2010; 25:530-6. [PMID: 20598770 DOI: 10.1016/j.tree.2010.06.005] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2010] [Revised: 06/09/2010] [Accepted: 06/10/2010] [Indexed: 12/09/2022]
Abstract
There has been considerable debate about the role of hybrids in the evolutionary process. One question has involved the relative fitness of hybrid versus non-hybrid genotypes. For some, the assumption of lower hybrid fitness continues to be integral to their concept of species and speciation. In contrast, numerous workers have suggested that hybrid genotypes might demonstrate higher relative fitness under various environmental settings. Of particular importance in deciding between these opposing hypotheses are long-term analyses coupling ecological and genetic information. Although currently rare, such analyses have provided a test of the fitness of hybrid genotypes across generations and habitats and their role in adaptation and speciation. Here we discuss examples of these analyses applied to viruses, prokaryotes, plants and Darwin's Finches.
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Affiliation(s)
- Michael L Arnold
- Department of Genetics, University of Georgia, Athens, GA 30602, USA.
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Campbell DR, Wu CA, Travers SE. Photosynthetic and growth responses of reciprocal hybrids to variation in water and nitrogen availability. AMERICAN JOURNAL OF BOTANY 2010; 97:925-33. [PMID: 21622463 DOI: 10.3732/ajb.0900387] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
PREMISE OF THE STUDY Fitness of plant hybrids often depends upon the environment, but physiological mechanisms underlying the differential responses to habitat are poorly understood. We examined physiological responses of Ipomopsis species and hybrids, including reciprocal F(1)s and F(2)s, to variation in soil moisture and nitrogen. • METHODS To examine responses to moisture, we subjected plants to a dry-down experiment. Nitrogen was manipulated in three independent experiments, one in the field and two in common environments. • KEY RESULTS Plants with I. tenuituba cytoplasmic background had lower optimal soil moisture for photosynthesis, appearing better adapted to dry conditions, than plants with I. aggregata cytoplasm. This result supported a prediction from prior studies. The species and hybrids did not differ greatly in physiological responses to nitrogen. An increase in soil nitrogen increased leaf nitrogen, carbon assimilation, integrated water-use efficiency, and growth, but the increases in growth were not mediated primarily by an increase in photosynthesis. In neither the field, nor in common-garden studies, did physiological responses to soil nitrogen differ detectably across plant types, although only I. aggregata and hybrids increased seed production in the field. • CONCLUSIONS These results demonstrate differences in photosynthetic responses between reciprocal hybrids and suggest that water use is more important than nitrogen in explaining the relative photosynthetic performance of these hybrids compared to their parents.
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Affiliation(s)
- Diane R Campbell
- Department of Ecology & Evolutionary Biology, University of California, Irvine, California 92697 USA
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DONOVAN LA, ROSENTHAL DR, SANCHEZ-VELENOSI M, RIESEBERG LH, LUDWIG F. Are hybrid species more fit than ancestral parent species in the current hybrid species habitats? J Evol Biol 2010; 23:805-16. [DOI: 10.1111/j.1420-9101.2010.01950.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Fitzpatrick BM, Johnson JR, Kump DK, Shaffer HB, Smith JJ, Voss SR. Rapid fixation of non-native alleles revealed by genome-wide SNP analysis of hybrid tiger salamanders. BMC Evol Biol 2009; 9:176. [PMID: 19630983 PMCID: PMC2724412 DOI: 10.1186/1471-2148-9-176] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Accepted: 07/24/2009] [Indexed: 01/10/2023] Open
Abstract
Background Hybrid zones represent valuable opportunities to observe evolution in systems that are unusually dynamic and where the potential for the origin of novelty and rapid adaptation co-occur with the potential for dysfunction. Recently initiated hybrid zones are particularly exciting evolutionary experiments because ongoing natural selection on novel genetic combinations can be studied in ecological time. Moreover, when hybrid zones involve native and introduced species, complex genetic patterns present important challenges for conservation policy. To assess variation of admixture dynamics, we scored a large panel of markers in five wild hybrid populations formed when Barred Tiger Salamanders were introduced into the range of California Tiger Salamanders. Results At three of 64 markers, introduced alleles have largely displaced native alleles within the hybrid populations. Another marker (GNAT1) showed consistent heterozygote deficits in the wild, and this marker was associated with embryonic mortality in laboratory F2's. Other deviations from equilibrium expectations were idiosyncratic among breeding ponds, consistent with highly stochastic demographic effects. Conclusion While most markers retain native and introduced alleles in expected proportions, strong selection appears to be eliminating native alleles at a smaller set of loci. Such rapid fixation of alleles is detectable only in recently formed hybrid zones, though it might be representative of dynamics that frequently occur in nature. These results underscore the variable and mosaic nature of hybrid genomes and illustrate the potency of recombination and selection in promoting variable, and often unpredictable genetic outcomes. Introgression of a few, strongly selected introduced alleles should not necessarily affect the conservation status of California Tiger Salamanders, but suggests that genetically pure populations of this endangered species will be difficult to maintain.
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Kimball S, Campbell D. Physiological differences among two Penstemon species and their hybrids in field and common garden environments. THE NEW PHYTOLOGIST 2009; 181:478-488. [PMID: 19121042 DOI: 10.1111/j.1469-8137.2008.02654.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Hybrids can exhibit unique combinations of the physiological traits of their parents. These particular combinations may influence hybrid fitness and the evolutionary trajectory of a hybrid zone. Here, a hybrid zone between Penstemon newberryi and Penstemon davidsonii along an elevational gradient was examined, and physiological traits of parents and hybrids were measured in their native environment and a common garden. Gas exchange rates of nine different crosses were also measured. Alpine P. davidsonii had less negative pre-dawn water potential and lower water use efficiency (WUE) than its montane relative P. newberryi in a common garden and in field measurements. The species difference in WUE was attributable to lower conductance in P. newberryi in the field, but to a higher photosynthetic rate in this species in the common garden. The alpine species took less time to produce mature fruits and reached maximum photosynthetic rate at a lower temperature. Natural hybrids were intermediate for most characters. F(1) hybrids had lower conductance than progeny of natural hybrids. The intermediate WUE of natural hybrids may be one factor that allows them to persist in intermediate environments. Comparisons of different crosses suggest that the genotypic composition of hybrids influences their physiological performance.
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Affiliation(s)
- Sarah Kimball
- Ecology & Evolutionary Biology, 5205 McGaugh Hall, University of California, Irvine, CA 92697, USA;Present address: Ecology & Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
| | - Diane Campbell
- Ecology & Evolutionary Biology, 5205 McGaugh Hall, University of California, Irvine, CA 92697, USA;Present address: Ecology & Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
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Genetic and morphological patterns show variation in frequency of hybrids between Ipomopsis (Polemoniaceae) zones of sympatry. Heredity (Edinb) 2008; 102:257-65. [PMID: 18971956 DOI: 10.1038/hdy.2008.112] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Variation in rates of hybridization among zones of sympatry between a pair of species provides a useful window into the effect of local conditions on the evolution of reproductive isolation. We employed floral morphological traits and neutral genetic markers to quantify the frequency of individuals intermediate to the two parental species in two zones of sympatry between Ipomopsis aggregata and I. tenuituba, using clustering methods that make no a priori assumptions about population structure. The sites differed not only in the frequency of intermediate individuals, but also in climate, pollinator abundance and behavior and spatial structure of plant populations. Both floral traits, which are likely to be under natural selection and molecular markers, which are quasi-neutral, indicated more population structure at one site than the other, the pattern being more pronounced for floral morphology. One likely explanation for this difference between sites is that local ecological conditions, particularly pollinator choice of flowers, have promoted different rates of hybridization between these species. Hence, the evolution of reproductive isolation might depend in part on local conditions, and thus differ among populations of the same pair of species.
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Campbell DR, Waser NM, Aldridge G, Wu CA. LIFETIME FITNESS IN TWO GENERATIONS OFIPOMOPSISHYBRIDS. Evolution 2008; 62:2616-27. [DOI: 10.1111/j.1558-5646.2008.00460.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Johnson LA, Chan LM, Weese TL, Busby LD, McMurry S. Nuclear and cpDNA sequences combined provide strong inference of higher phylogenetic relationships in the phlox family (Polemoniaceae). Mol Phylogenet Evol 2008; 48:997-1012. [DOI: 10.1016/j.ympev.2008.05.036] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Revised: 05/03/2008] [Accepted: 05/28/2008] [Indexed: 11/30/2022]
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Abstract
Adaptive divergence due to habitat differences is thought to play a major role in formation of new species. However it is rarely clear the extent to which individual reproductive isolating barriers related to habitat differentiation contribute to total isolation. Furthermore, it is often difficult to determine the specific environmental variables that drive the evolution of those ecological barriers, and the geographic scale at which habitat-mediated speciation occurs. Here, we address these questions through an analysis of the population structure and reproductive isolation between coastal perennial and inland annual forms of the yellow monkeyflower, Mimulus guttatus. We found substantial morphological and molecular genetic divergence among populations derived from coast and inland habitats. Reciprocal transplant experiments revealed nearly complete reproductive isolation between coast and inland populations mediated by selection against immigrants and flowering time differences, but not postzygotic isolation. Our results suggest that selection against immigrants is a function of adaptations to seasonal drought in inland habitat and to year round soil moisture and salt spray in coastal habitat. We conclude that the coast and inland populations collectively comprise distinct ecological races. Overall, this study suggests that adaptations to widespread habitats can lead to the formation of reproductively isolated species.
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Affiliation(s)
- David B Lowry
- University Program in Genetics and Genomics, Duke University Medical Center, Box 3565, and Department of Biology, Box 90338, Duke University Medical Center, Durham, North Carolina 27710, USA.
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Sambatti JBM, Ortiz-Barrientos D, Baack EJ, Rieseberg LH. Ecological selection maintains cytonuclear incompatibilities in hybridizing sunflowers. Ecol Lett 2008; 11:1082-91. [PMID: 18643842 DOI: 10.1111/j.1461-0248.2008.01224.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Despite the recent renaissance in studies of ecological speciation, the connection between ecological selection and the evolution of reproductive isolation remains tenuous. We tested whether habitat adaptation of cytoplasmic genomes contributes to the maintenance of reproductive barriers in hybridizing sunflower species, Helianthus annuus and Helianthus petiolaris. We transplanted genotypes of the parental species, reciprocal F1 hybrids and all eight possible backcross combinations of nuclear and cytoplasmic genomes into the contrasting xeric and mesic habitats of the parental species. Analysis of survivorship across two growing seasons revealed that the parental species' cytoplasms were strongly locally adapted and that cytonuclear interactions (CNIs) significantly affected the fitness and architecture of hybrid plants. A significant fraction of the CNIs have transgenerational effects, perhaps due to divergence in imprinting patterns. Our results suggest a common means by which ecological selection may contribute to speciation and have significant implications for the persistence of hybridizing species.
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Affiliation(s)
- Julianno B M Sambatti
- Department of Botany, University of British Columbia, 3529-6270 University Blvd., Vancouver, BC, Canada V6T1Z4
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Mercure M, Bruneau A. Hybridization between the escaped Rosa rugosa (Rosaceae) and native R. blanda in eastern North America. AMERICAN JOURNAL OF BOTANY 2008; 95:597-607. [PMID: 21632386 DOI: 10.3732/ajb.2007385] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Rosa rugosa, a vigorous ornamental shrub introduced from Asia in the 19th century, is now naturalized in coastal northeastern North America, where it occasionally grows in sympatry with the native R. blanda. To document hybridization between these species, evaluate its extent across the area of sympatry, and examine the use of morphology as a field monitoring tool, we sampled 179 individuals of parental species and putative hybrids in 13 pure and 11 mixed populations. We developed allele-specific primers to assay single nucleotide polymorphisms (SNPs) markers from one chloroplast region and four low-copy nuclear introns. Our results revealed frequent bidirectional hybridization and infrequent introgression in sympatric populations of these species. The recurrent presence of F(1) hybrids in mixed populations indicated the weakness of early-acting reproductive barriers. Morphological data were concordant with molecular data and provided additional evidence for the presence of a few backcrosses. Morphological analyses yielded diagnostic characters for identifying hybrids and monitoring the hybrid zone. Such hybridization could ultimately lead to the genetic assimilation of R. blanda in mixed populations and to the formation of invasive hybrid genotypes, a phenomenon that is of economic and ecological concern because of the increasing number of exotic species worldwide.
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Affiliation(s)
- Marjorie Mercure
- Institut de recherche en biologie végétale, Université de Montréal, 4101 Sherbrooke Est, Montreal, Quebec, Canada H1X 2B2
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MYERS EM, TUCKER JK, CHANDLER CH. Experimental analysis of body size and shape during critical life-history events of hatchling slider turtles, Trachemys scripta elegans. Funct Ecol 2007. [DOI: 10.1111/j.1365-2435.2007.01337.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Gow JL, Peichel CL, Taylor EB. Ecological selection against hybrids in natural populations of sympatric threespine sticklebacks. J Evol Biol 2007; 20:2173-80. [PMID: 17887972 DOI: 10.1111/j.1420-9101.2007.01427.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Experimental work has provided evidence for extrinsic post-zygotic isolation, a phenomenon unique to ecological speciation. The role that ecological components to reduced hybrid fitness play in promoting speciation and maintaining species integrity in the wild, however, is not as well understood. We addressed this problem by testing for selection against naturally occurring hybrids in two sympatric species pairs of benthic and limnetic threespine sticklebacks (Gasterosteus aculeatus). If post-zygotic isolation is a significant reproductive barrier, the relative frequency of hybrids within a population should decline significantly across the life-cycle. Such a trend in a natural population would give independent support to experimental evidence for extrinsic, rather than intrinsic, post-zygotic isolation in this system. Indeed, tracing mean individual hybridity (genetic intermediateness) across three life-history stages spanning four generations revealed just such a decline. This provides compelling evidence that extrinsic selection plays an important role in maintaining species divergence and supports a role for ecological speciation in sticklebacks.
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Affiliation(s)
- J L Gow
- Department of Zoology, Biodiversity Research Centre and Native Fishes Research Group, University of British Columbia, Vancouver, BC, Canada.
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46
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Brody AK, Price MV, Waser NM. Life-history consequences of vegetative damage in scarlet gilia, a monocarpic plant. OIKOS 2007. [DOI: 10.1111/j.0030-1299.2007.15705.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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47
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K. Brody A, V. Price M, M. Waser N. Life-history consequences of vegetative damage in scarlet gilia, a monocarpic plant. OIKOS 2007. [DOI: 10.1111/j.2007.0030-1299.15705.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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