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Delmore K, Justen H, Kay KM, Kitano J, Moyle LC, Stelkens R, Streisfeld MA, Yamasaki YY, Ross J. Genomic Approaches Are Improving Taxonomic Representation in Genetic Studies of Speciation. Cold Spring Harb Perspect Biol 2024; 16:a041438. [PMID: 37848243 PMCID: PMC10835617 DOI: 10.1101/cshperspect.a041438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2023]
Abstract
Until recently, our understanding of the genetics of speciation was limited to a narrow group of model species with a specific set of characteristics that made genetic analysis feasible. Rapidly advancing genomic technologies are eliminating many of the distinctions between laboratory and natural systems. In light of these genomic developments, we review the history of speciation genetics, advances that have been gleaned from model and non-model organisms, the current state of the field, and prospects for broadening the diversity of taxa included in future studies. Responses to a survey of speciation scientists across the world reveal the ongoing division between the types of questions that are addressed in model and non-model organisms. To bridge this gap, we suggest integrating genetic studies from model systems that can be reared in the laboratory or greenhouse with genomic studies in related non-models where extensive ecological knowledge exists.
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Affiliation(s)
- Kira Delmore
- Department of Biology, Texas A&M University, College Station, Texas 77843, USA
| | - Hannah Justen
- Department of Biology, Texas A&M University, College Station, Texas 77843, USA
| | - Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, California 95060, USA
| | - Jun Kitano
- Ecological Genetics Laboratory, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan
| | - Leonie C Moyle
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA
| | - Rike Stelkens
- Division of Population Genetics, Department of Zoology, Stockholm University, 106 91 Stockholm, Sweden
| | - Matthew A Streisfeld
- Institute of Ecology and Evolution, University of Oregon, Eugene, Oregon 97403, USA
| | - Yo Y Yamasaki
- Ecological Genetics Laboratory, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan
| | - Joseph Ross
- Department of Biology, California State University, Fresno, California 93740, USA
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Merrill RM, Arenas-Castro H, Feller AF, Harenčár J, Rossi M, Streisfeld MA, Kay KM. Genetics and the Evolution of Prezygotic Isolation. Cold Spring Harb Perspect Biol 2024; 16:a041439. [PMID: 37848246 PMCID: PMC10835618 DOI: 10.1101/cshperspect.a041439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2023]
Abstract
The significance of prezygotic isolation for speciation has been recognized at least since the Modern Synthesis. However, fundamental questions remain. For example, how are genetic associations between traits that contribute to prezygotic isolation maintained? What is the source of genetic variation underlying the evolution of these traits? And how do prezygotic barriers affect patterns of gene flow? We address these questions by reviewing genetic features shared across plants and animals that influence prezygotic isolation. Emerging technologies increasingly enable the identification and functional characterization of the genes involved, allowing us to test established theoretical expectations. Embedding these genes in their developmental context will allow further predictions about what constrains the evolution of prezygotic isolation. Ongoing improvements in statistical and computational tools will reveal how pre- and postzygotic isolation may differ in how they influence gene flow across the genome. Finally, we highlight opportunities for progress by combining theory with appropriate data.
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Affiliation(s)
- Richard M Merrill
- Faculty of Biology, Division of Evolutionary Biology, LMU Munich, 82152 Planegg-Martinsried, Germany
| | - Henry Arenas-Castro
- School of Biological Sciences, University of Queensland, St. Lucia, Queensland 4072, Australia
| | - Anna F Feller
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA
- Arnold Arboretum of Harvard University, Boston, Massachusetts 02131, USA
| | - Julia Harenčár
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, California 95060, USA
| | - Matteo Rossi
- Faculty of Biology, Division of Evolutionary Biology, LMU Munich, 82152 Planegg-Martinsried, Germany
| | - Matthew A Streisfeld
- Institute of Ecology and Evolution, University of Oregon, Eugene, Oregon 97403-5289, USA
| | - Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, California 95060, USA
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Diaz-Martin Z, Cisternas-Fuentes A, Kay KM, Raguso RA, Skogen K, Fant J. Reproductive strategies and their consequences for divergence, gene flow, and genetic diversity in three taxa of Clarkia. Heredity (Edinb) 2023; 131:338-349. [PMID: 37700028 PMCID: PMC10673949 DOI: 10.1038/s41437-023-00649-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 08/25/2023] [Accepted: 08/25/2023] [Indexed: 09/14/2023] Open
Abstract
Differences in reproductive strategies can have important implications for macro- and micro-evolutionary processes. We used a comparative approach through a population genetics lens to evaluate how three distinct reproductive strategies shape patterns of divergence among as well as gene flow and genetic diversity within three closely related taxa in the genus Clarkia. One taxon is a predominantly autonomous self-fertilizer and the other two taxa are predominantly outcrossing but vary in the primary pollinator they attract. In genotyping populations using genotyping-by-sequencing and comparing loci shared across taxa, our results suggest that differences in reproductive strategies in part promote evolutionary divergence among these closely related taxa. Contrary to expectations, we found that the selfing taxon had the highest levels of heterozygosity but a low rate of polymorphism. The high levels of fixed heterozygosity for a subset of loci suggests this pattern is driven by the presence of structural rearrangements in chromosomes common in other Clarkia taxa. In evaluating patterns within taxa, we found a complex interplay between reproductive strategy and geographic distribution. Differences in the mobility of primary pollinators did not translate to a difference in rates of genetic diversity and gene flow within taxa - a pattern likely due to one taxon having a patchier distribution and a less temporally and spatially reliable pollinator. Taken together, this work advances our understanding of the factors that shape gene flow and the distribution of genetic diversity within and among closely related taxa.
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Affiliation(s)
- Zoe Diaz-Martin
- Department of Biology, Spelman College, Atlanta, GA, 30314, USA.
- Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL, 60035, USA.
| | - Anita Cisternas-Fuentes
- Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL, 60035, USA
- Plant Biology and Conservation, Northwestern University, 2205 Tech Drive, Evanston, IL, 60208, USA
- Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción, Chile
| | - Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA, 95060, USA
| | - Robert A Raguso
- Department of Neurobiology and Behavior, Cornell University, Ithaca, NY, 14853, USA
| | - Krissa Skogen
- Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL, 60035, USA
- Plant Biology and Conservation, Northwestern University, 2205 Tech Drive, Evanston, IL, 60208, USA
- Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC, 29631, USA
| | - Jeremie Fant
- Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL, 60035, USA
- Plant Biology and Conservation, Northwestern University, 2205 Tech Drive, Evanston, IL, 60208, USA
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Maguiña‐Conde R, Zuñiga‐Rivas D, Kay KM. An elevational gradient in floral traits and pollinator assemblages in the Neotropical species Costus guanaiensis var. tarmicus in Peru. Ecol Evol 2023; 13:e10314. [PMID: 37529588 PMCID: PMC10375365 DOI: 10.1002/ece3.10314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 07/04/2023] [Indexed: 08/03/2023] Open
Abstract
Different populations of plant species can adapt to their local pollinators and diverge in floral traits accordingly. Floral traits are subject to pollinator-driven natural selection to enhance plant reproductive success. Studies on temperate plant systems have shown pollinator-driven selection results in floral trait variation along elevational gradients, but studies in tropical systems are lacking. We analyzed floral traits and pollinator assemblages in the Neotropical bee-pollinated taxon Costus guanaiensis var. tarmicus across four sites along a steep elevational gradient in Peru. We found variations in floral traits of size, color, and reward, and in the pollinator assemblage along the elevational gradient. We examined our results considering two hypotheses, (1) local adaptation to different bee assemblages, and (2) the early stages of an evolutionary shift to a new pollinator functional group (hummingbirds). We found some evidence consistent with the adaptation of C. guanaiensis var. tarmicus to the local bee fauna along the studied elevational gradient. Corolla width across sites was associated with bee thorax width of the local most frequent pollinator. However, we could not rule out the possibility of the beginning of a bee-to-hummingbird pollination shift in the highest-studied site. Our study is one of the few geographic-scale analyses of floral trait and pollinator assemblage variation in tropical plant species. Our results broaden our understanding of plant-pollinator interactions beyond temperate systems by showing substantial intraspecific divergence in both floral traits and pollinator assemblages across geographic space in a tropical plant species.
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Affiliation(s)
- Rossana Maguiña‐Conde
- Ecology and Evolutionary Biology DepartmentUniversity of California Santa CruzSanta CruzCaliforniaUSA
| | - Dorali Zuñiga‐Rivas
- Laboratorio de EntomologíaUniversidad Nacional San Antonio Abad del CuscoCuscoPeru
| | - Kathleen M. Kay
- Ecology and Evolutionary Biology DepartmentUniversity of California Santa CruzSanta CruzCaliforniaUSA
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Harenčár J, Vargas OM, Escalona M, Schemske DW, Kay KM. Genome assemblies and comparison of two Neotropical spiral gingers: Costus pulverulentus and C. lasius. J Hered 2023; 114:286-293. [PMID: 36928286 PMCID: PMC10212132 DOI: 10.1093/jhered/esad018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 03/15/2023] [Indexed: 03/18/2023] Open
Abstract
The spiral gingers (Costus L.) are a pantropical genus of herbaceous perennial monocots; the Neotropical clade of Costus radiated rapidly in the past few million years into over 60 species. The Neotropical spiral gingers have a rich history of evolutionary and ecological research that can motivate and inform modern genetic investigations. Here, we present the first 2 chromosome-level genome assemblies in the genus, for C. pulverulentus and C. lasius, and briefly compare their synteny. We assembled the C. pulverulentus genome from a combination of short-read data, Chicago and Dovetail Hi-C chromatin-proximity sequencing, and alignment with a linkage map. We annotated the genome by mapping a C. pulverulentus transcriptome and querying mapped transcripts against a protein database. We assembled the C. lasius genome with Pacific Biosciences HiFi long reads and alignment to the C. pulverulentus genome. These 2 assemblies are the first published genomes for non-cultivated tropical plants. These genomes solidify the spiral gingers as a model system and will facilitate research on the poorly understood genetic basis of tropical plant diversification.
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Affiliation(s)
- Julia Harenčár
- Ecology and Evolutionary Biology Department, University of California, Santa Cruz, Santa Cruz, CA, United States
| | - Oscar M Vargas
- Department of Biological Sciences, California State Polytechnic University, Humboldt, Arcata, CA, United States
| | - Merly Escalona
- Department of Biomolecular Engineering, University of California, Santa Cruz, Santa Cruz, CA, United States
| | - Douglas W Schemske
- Department of Plant Biology, Michigan State University, East Lansing, MI, United States
| | - Kathleen M Kay
- Ecology and Evolutionary Biology Department, University of California, Santa Cruz, Santa Cruz, CA, United States
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Kay KM, Grossenbacher DL. Evolutionary convergence on hummingbird pollination in Neotropical Costus provides insight into the causes of pollinator shifts. New Phytol 2022; 236:1572-1583. [PMID: 36068995 PMCID: PMC9826479 DOI: 10.1111/nph.18464] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Accepted: 08/10/2022] [Indexed: 06/15/2023]
Abstract
The evolution of hummingbird pollination is common across angiosperms throughout the Americas, presenting an opportunity to examine convergence in both traits and environments to better understand how complex phenotypes arise. Here we examine independent shifts from bee to hummingbird pollination in the Neotropical spiral gingers (Costus) and address common explanations for the prevalence of transitions from bee to hummingbird pollination. We use floral traits of species with observed pollinators to predict pollinators of unobserved species and reconstruct ancestral pollination states on a well-resolved phylogeny. We examine whether independent transitions evolve towards the same phenotypic optimum and whether shifts to hummingbird pollination correlate with elevation or climate. Traits predicting hummingbird pollination include small flower size, brightly colored floral bracts and the absence of nectar guides. We find many shifts to hummingbird pollination and no reversals, a single shared phenotypic optimum across hummingbird flowers, and no association between pollination and elevation or climate. Evolutionary shifts to hummingbird pollination in Costus are highly convergent and directional, involve a surprising set of traits when compared with other plants with analogous transitions and refute the generality of several common explanations for the prevalence of transitions from bee to hummingbird pollination.
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Affiliation(s)
- Kathleen M. Kay
- Department of Ecology and Evolutionary BiologyUniversity of California, Santa CruzSanta CruzCA95060USA
| | - Dena L. Grossenbacher
- Department of BiologyCalifornia Polytechnic State UniversitySan Luis ObispoCA93401USA
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7
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Harenčár JG, Ávila‐Lovera E, Goldsmith GR, Chen GF, Kay KM. Flexible drought deciduousness in a neotropical understory herb. Am J Bot 2022; 109:1262-1272. [PMID: 35862815 PMCID: PMC9545341 DOI: 10.1002/ajb2.16037] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 06/21/2022] [Accepted: 06/24/2022] [Indexed: 06/15/2023]
Abstract
PREMISE Adaptive divergence across environmental gradients is a key driver of speciation. Precipitation seasonality gradients are common in the tropics, yet drought adaptation is nearly unexplored in neotropical understory herbs. Here, we examined two recently diverged neotropical spiral gingers, one adapted to seasonal drought and one reliant on perennial water, to uncover the basis of drought adaptation. METHODS We combined ecophysiological trait measurements in the field and greenhouse with experimental and observational assessments of real-time drought response to determine how Costus villosissimus (Costaceae) differs from C. allenii to achieve drought adaptation. RESULTS We found that drought-adapted C. villosissimus has several characteristics indicating flexible dehydration avoidance via semi-drought-deciduousness and a fast economic strategy. Although the two species do not differ in water-use efficiency, C. villosissimus has a more rapid growth rate, lower leaf mass per area, lower stem density, higher leaf nitrogen, and a strong trend of greater light-saturated photosynthetic rates. These fast economic strategy traits align with both field-based observations and experimental dry-down results. During drought, C. villosissimus displays facultative drought-deciduousness, losing lower leaves during the dry season and rapidly growing new leaves in the wet season. CONCLUSIONS We revealed a drought adaptation strategy that has not, to our knowledge, previously been documented in tropical herbs. This divergent drought adaptation evolved recently and is an important component of reproductive isolation between C. villosissimus and C. allenii, indicating that adaptive shifts to survive seasonal drought may be an underappreciated axis of neotropical understory plant diversification.
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Affiliation(s)
- Julia G. Harenčár
- Ecology and Evolutionary Biology DepartmentUniversity of California, Santa CruzSanta CruzCA95060USA
| | - Eleinis Ávila‐Lovera
- Smithsonian Tropical Research InstituteApartado Postal 0843‐03092Panamá, República de Panamá
- Schmid College of Science and TechnologyChapman UniversityOrangeCA92866USA
| | | | - Grace F. Chen
- Department of BiologyEast Carolina UniversityGreenvilleNC27858USA
| | - Kathleen M. Kay
- Ecology and Evolutionary Biology DepartmentUniversity of California, Santa CruzSanta CruzCA95060USA
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Sianta SA, Kay KM. Phylogenomic analysis does not support a classic but controversial hypothesis of progenitor-derivative origins for the serpentine endemic Clarkia franciscana. Evolution 2022; 76:1246-1259. [PMID: 35403214 PMCID: PMC9322428 DOI: 10.1111/evo.14484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Revised: 02/25/2022] [Accepted: 03/04/2022] [Indexed: 01/21/2023]
Abstract
Budding speciation involves isolation of marginal populations at the periphery of a species range and is thought to be a prominent mode of speciation in organisms with low dispersal and/or strong local adaptation among populations. Budding speciation is typically evidenced by abutting, asymmetric ranges of ecologically divergent sister species and low genetic diversity in putative budded species. Yet these indirect patterns may be unreliable, instead caused by postspeciation processes such as range or demographic shifts. Nested phylogenetic relationships provide the most conclusive evidence of budding speciation. A putative case of budding speciation in the serpentine endemic Clarkia franciscana and two closely related widespread congeners was studied by Harlan Lewis, Peter Raven, Leslie Gottlieb, and others over a 20-year period, yet the origin of C. franciscana remains controversial. Here, we reinvestigate this system with phylogenomic analyses to determine whether C. franciscana is a recently derived budded species, phylogenetically nested within one of the other two putative progenitor species. In contrast to the hypothesized pattern of relatedness among the three Clarkia species, we find no evidence for recent budding speciation. Instead, the data suggest the three species diverged simultaneously. We urge caution in using contemporary range patterns to infer geographic modes of speciation.
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Affiliation(s)
- Shelley A. Sianta
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaSanta CruzCalifornia95060,Current Address: Department of Plant and Microbial BiologyUniversity of MinnesotaSt. PaulMinnesota55108
| | - Kathleen M. Kay
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaSanta CruzCalifornia95060
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Ávila-Lovera E, Goldsmith GR, Kay KM, Funk JL. Above- and below-ground functional trait coordination in the Neotropical understory genus Costus. AoB Plants 2022; 14:plab073. [PMID: 35035869 PMCID: PMC8757582 DOI: 10.1093/aobpla/plab073] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Accepted: 11/30/2021] [Indexed: 06/14/2023]
Abstract
The study of plant functional traits and variation among and within species can help illuminate functional coordination and trade-offs in key processes that allow plants to grow, reproduce and survive. We studied 20 leaf, above-ground stem, below-ground stem and fine-root traits of 17 Costus species from forests in Costa Rica and Panama to answer the following questions: (i) Do congeneric species show above-ground and below-ground trait coordination and trade-offs consistent with theory of resource acquisition and conservation? (ii) Is there correlated evolution among traits? (iii) Given the diversity of habitats over which Costus occurs, what is the relative contribution of site and species to trait variation? We performed a principal components analysis (PCA) to assess for the existence of a spectrum of trait variation and found that the first two PCs accounted for 21.4 % and 17.8 % of the total trait variation, respectively, with the first axis of variation being consistent with a continuum of resource-acquisitive and resource-conservative traits in water acquisition and use, and the second axis of variation being related to the leaf economics spectrum. Stomatal conductance was negatively related to both above-ground stem and rhizome specific density, and these relationships became stronger after accounting for evolutionary relatedness, indicating correlated evolution. Despite elevation and climatic differences among sites, high trait variation was ascribed to individuals rather than to sites. We conclude that Costus species present trait coordination and trade-offs that allow species to be categorized as having a resource-acquisitive or resource-conservative functional strategy, consistent with a whole-plant functional strategy with evident coordination and trade-offs between above-ground and below-ground function. Our results also show that herbaceous species and species with rhizomes tend to agree with trade-offs found in more species-rich comparisons.
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Affiliation(s)
- Eleinis Ávila-Lovera
- Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
| | - Gregory R Goldsmith
- Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
| | - Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060, USA
| | - Jennifer L Funk
- Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
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Goff KA, Martinez Del Rio C, Kay KM. A greenhouse experiment partially supports inferences of ecogeographic isolation from niche models of Clarkia sister species. Am J Bot 2021; 108:2002-2014. [PMID: 34661904 PMCID: PMC9298282 DOI: 10.1002/ajb2.1756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 07/10/2021] [Accepted: 07/12/2021] [Indexed: 06/13/2023]
Abstract
PREMISE Ecogeographic isolation, or geographic isolation caused by ecological divergence, is thought to be of primary importance in speciation, yet is difficult to demonstrate and quantify. To determine whether distributions are limited by divergent adaptation or historical contingency, the gold standard is to reciprocally transplant species between their geographic ranges. Alternatively, ecogeographic isolation is inferred from species distribution models and niche divergence tests using widely available environmental and occurrence data. METHODS We tested for ecogeographic isolation between two sister species of California annual wildflowers, Clarkia concinna and C. breweri, with a hybrid approach. We used niche models to predict water availability as the major axis of ecological divergence and then tested that with a greenhouse experiment. Specifically, we manipulated water availability in field soils for two populations of each species and predicted higher fitness in conditions representing home habitats to those representing the environment of each's sister species. RESULTS Water availability and soil representing C. concinna generally increased both species' fitness. Thus, water and soil may indeed limit C. concinna from colonizing the range of C. breweri, but not vice versa. We suggest that the competitive environment and pollinator availability, which are not directly captured with either approach, may be key biotic factors correlated with climate that contribute to unexplained ecogeographic isolation for C. breweri. CONCLUSIONS Ours is a valuable approach to assessing ecogeographic isolation, in that it balances feasibility with model validation, and our results have implications for species distribution modeling efforts geared toward predicting climate change responses.
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Affiliation(s)
- Kaleb A. Goff
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaSanta CruzCA95060USA
- Present address:
Kaleb A. Goff, Department of Plant and Microbial BiologyNorth Carolina State UniversityRaleighNC 27695USA
| | | | - Kathleen M. Kay
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaSanta CruzCA95060USA
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Kay KM, Surget-Groba Y. The genetic basis of floral mechanical isolation between two hummingbird-pollinated Neotropical understorey herbs. Mol Ecol 2021; 31:4351-4363. [PMID: 34487383 DOI: 10.1111/mec.16165] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 07/29/2021] [Accepted: 08/31/2021] [Indexed: 12/29/2022]
Abstract
Floral divergence can contribute to reproductive isolation among plant lineages, and thus provides an opportunity to study the genetics of speciation, including the number, effect size, mode of action and interactions of quantitative trait loci (QTL). Moreover, flowers represent suites of functionally interrelated traits, but it is unclear to what extent the phenotypic integration of the flower is underlain by a shared genetic architecture, which could facilitate or constrain correlated evolution of floral traits. Here, we examine the genetic architecture of floral morphological traits involved in an evolutionary switch from bill to forehead pollen placement between two species of hummingbird-pollinated Neotropical understorey herbs that are reproductively isolated by these floral differences. For the majority of traits, we find multiple QTL of relatively small effect spread throughout the genome. We also find substantial colocalization and alignment of effects of QTL underlying different floral traits that function together to promote outcrossing and reduce heterospecific pollen transfer. Our results are consistent with adaptive pleiotropy or linkage of many co-adapted genes, either of which could have facilitated a response to correlated selection and helped to stabilize divergent phenotypes in the face of low levels of hybridization. Moreover, our results indicate that floral mechanical isolation can be consistent with an infinitesimal model of adaptation.
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Affiliation(s)
- Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, USA
| | - Yann Surget-Groba
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, USA.,Département de Biologie, Université du Québec en Outaouais, Ripon, QC, Canada
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Abstract
Understanding the relative importance of reproductive isolating mechanisms across the speciation continuum remains an outstanding challenge in evolutionary biology. Here, we examine a common isolating mechanism, reproductive phenology, between plant sister taxa at different stages of adaptive divergence to gain insight into its relative importance during speciation. We study 17 plant taxa that have independently adapted to inhospitable serpentine soils, and contrast each with a nonserpentine sister taxon to form pairs at either ecotypic or species-level divergence. We use greenhouse-based reciprocal transplants in field soils to quantify how often flowering time (FT) shifts accompany serpentine adaptation, when FT shifts evolve during speciation, and the genetic versus plastic basis of these shifts. We find that genetically based shifts in FT in serpentine-adapted taxa are pervasive regardless of the stage of divergence. Although plasticity increases FT shifts in five of the pairs, the degree of plasticity does not differ when comparing ecotypic versus species-level divergence. FT shifts generally led to significant, but incomplete, reproductive isolation that did not vary in strength by stage of divergence. Our work shows that adaptation to a novel habitat may predictably drive phenological isolation early in the speciation process.
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Affiliation(s)
- Shelley A Sianta
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA 95060, USA
| | - Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA 95060, USA
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13
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Kay KM, Jogesh T, Tataru D, Akiba S. Darwin's vexing contrivance: a new hypothesis for why some flowers have two kinds of anther. Proc Biol Sci 2020. [PMID: 33352073 DOI: 10.1098/rspb.2020.2593rspb20202593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/06/2023] Open
Abstract
Heteranthery, the presence of two or more anther types in the same flower, is taxonomically widespread among bee-pollinated angiosperms, yet has puzzled botanists since Darwin. We test two competing hypotheses for its evolution: the long-standing 'division of labour' hypothesis, which posits that some anthers are specialized as food rewards for bees whereas others are specialized for surreptitious pollination, and our new hypothesis that heteranthery is a way to gradually release pollen that maximizes pollen delivery. We examine the evolution of heteranthery and associated traits across the genus Clarkia (Onagraceae) and study plant-pollinator interactions in two heterantherous Clarkia species. Across species, heteranthery is associated with bee pollination, delayed dehiscence and colour crypsis of one anther whorl, and movement of that anther whorl upon dehiscence. Our mechanistic studies in heterantherous species show that bees notice, forage on and export pollen from each anther whorl when it is dehiscing, and that heteranthery promotes pollen export. We find no support for division of labour, but multifarious evidence that heteranthery is a mechanism for gradual pollen presentation that probably evolved through indirect male-male competition for siring success.
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Affiliation(s)
- Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA 95060, USA
| | - Tania Jogesh
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA 95060, USA
| | - Diana Tataru
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA 95060, USA
| | - Sami Akiba
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA 95060, USA
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Kay KM, Jogesh T, Tataru D, Akiba S. Darwin's vexing contrivance: a new hypothesis for why some flowers have two kinds of anther. Proc Biol Sci 2020; 287:20202593. [PMID: 33352073 PMCID: PMC7779490 DOI: 10.1098/rspb.2020.2593] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Accepted: 11/26/2020] [Indexed: 01/26/2023] Open
Abstract
Heteranthery, the presence of two or more anther types in the same flower, is taxonomically widespread among bee-pollinated angiosperms, yet has puzzled botanists since Darwin. We test two competing hypotheses for its evolution: the long-standing 'division of labour' hypothesis, which posits that some anthers are specialized as food rewards for bees whereas others are specialized for surreptitious pollination, and our new hypothesis that heteranthery is a way to gradually release pollen that maximizes pollen delivery. We examine the evolution of heteranthery and associated traits across the genus Clarkia (Onagraceae) and study plant-pollinator interactions in two heterantherous Clarkia species. Across species, heteranthery is associated with bee pollination, delayed dehiscence and colour crypsis of one anther whorl, and movement of that anther whorl upon dehiscence. Our mechanistic studies in heterantherous species show that bees notice, forage on and export pollen from each anther whorl when it is dehiscing, and that heteranthery promotes pollen export. We find no support for division of labour, but multifarious evidence that heteranthery is a mechanism for gradual pollen presentation that probably evolved through indirect male-male competition for siring success.
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Affiliation(s)
- Kathleen M. Kay
- Department of Ecology and Evolutionary Biology, University of California, 130 McAllister Way, Santa Cruz, CA 95060, USA
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Vargas OM, Goldston B, Grossenbacher DL, Kay KM. Patterns of speciation are similar across mountainous and lowland regions for a Neotropical plant radiation (Costaceae: Costus). Evolution 2020; 74:2644-2661. [PMID: 33047821 DOI: 10.1111/evo.14108] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 08/28/2020] [Accepted: 09/21/2020] [Indexed: 01/05/2023]
Abstract
High species richness and endemism in tropical mountains are recognized as major contributors to the latitudinal diversity gradient. The processes underlying mountain speciation, however, are largely untested. The prevalence of steep ecogeographic gradients and the geographic isolation of populations by topographic features are predicted to promote speciation in mountains. We evaluate these processes in a species-rich Neotropical genus of understory herbs that range from the lowlands to montane forests and have higher species richness in topographically complex regions. We ask whether climatic niche divergence, geographic isolation, and pollination shifts differ between mountain-influenced and lowland Amazonian sister pairs inferred from a 756-gene phylogeny. Neotropical Costus ancestors diverged in Central America during a period of mountain formation in the last 3 million years with later colonization of Amazonia. Although climatic divergence, geographic isolation, and pollination shifts are prevalent in general, these factors do not differ between mountain-influenced and Amazonian sister pairs. Despite higher climatic niche and species diversity in the mountains, speciation modes in Costus appear similar across regions. Thus, greater species richness in tropical mountains may reflect differences in colonization history, diversification rates, or the prevalence of rapidly evolving plant life forms, rather than differences in speciation mode.
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Affiliation(s)
- Oscar M Vargas
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, California, 95060.,Department of Biological Sciences, Humboldt State University, Arcata, California, 95521
| | - Brittany Goldston
- Department of Biology, California Polytechnic State University, San Luis Obispo, California, 93401
| | - Dena L Grossenbacher
- Department of Biology, California Polytechnic State University, San Luis Obispo, California, 93401
| | - Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, California, 95060
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Peterson ML, Angert AL, Kay KM. Experimental migration upward in elevation is associated with strong selection on life history traits. Ecol Evol 2020; 10:612-625. [PMID: 32015830 PMCID: PMC6988539 DOI: 10.1002/ece3.5710] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Revised: 08/10/2019] [Accepted: 09/05/2019] [Indexed: 12/26/2022] Open
Abstract
One of the strongest biological impacts of climate change has been the movement of species poleward and upward in elevation. Yet, what is not clear is the extent to which the spatial distribution of locally adapted lineages and ecologically important traits may also shift with continued climate change. Here, we take advantage of a transplant experiment mimicking up-slope seed dispersal for a suite of ecologically diverse populations of yellow monkeyflower (Mimulus guttatus sensu lato) into a high-elevation common garden during an extreme drought period in the Sierra Nevada mountains, California, USA. We use a demographic approach to quantify fitness and test for selection on life history traits in local versus lower-elevation populations and in normal versus drought years to test the potential for up-slope migration and phenotypic selection to alter the distribution of key life history traits in montane environments. We find that lower-elevation populations tend to outperform local populations, confirming the potential for up-slope migration. Although selection generally favored some local montane traits, including larger flowers and larger stem size at flowering, drought conditions tended to select for earlier flowering typical of lower-elevation genotypes. Taken together, this suggests that monkeyflower lineages moving upward in elevation could experience selection for novel trait combinations, particularly under warmer and drier conditions that are predicted to occur with continued climate change.
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Affiliation(s)
- Megan L. Peterson
- Ecology and Evolutionary BiologyUniversity of California Santa CruzSanta CruzCalifornia
| | - Amy L. Angert
- Department of Botany and ZoologyUniversity of British ColumbiaVancouverBCCanada
| | - Kathleen M. Kay
- Ecology and Evolutionary BiologyUniversity of California Santa CruzSanta CruzCalifornia
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Sianta SA, Kay KM. Adaptation and divergence in edaphic specialists and generalists: serpentine soil endemics in the California flora occur in barer serpentine habitats with lower soil calcium levels than serpentine tolerators. Am J Bot 2019; 106:690-703. [PMID: 31070790 DOI: 10.1002/ajb2.1285] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 03/19/2019] [Indexed: 06/09/2023]
Abstract
PREMISE Adaptation to harsh edaphic substrates has repeatedly led to the evolution of edaphic specialists and generalists. Yet, it is unclear what factors promote specialization versus generalization. Here, we search for habitat use patterns associated with serpentine endemics (specialists) and serpentine tolerators (generalists) to indirectly test the hypothesis that trade-offs associated with serpentine adaptation promote specialization. We predict that (1) endemics have adapted to chemically harsher and more bare serpentine habitats than tolerators, and (2) edaphic endemics show more habitat divergence from their sister species than tolerators do among on- and off-serpentine populations. METHODS We selected 8 serpentine endemic and 9 serpentine tolerator species representing independent adaptation to serpentine. We characterized soil chemistry and microhabitat bareness from one serpentine taxon of each species and from a paired nonserpentine sister taxon, resulting in 8 endemic and 9 tolerator sister-taxa pairs. RESULTS We find endemic serpentine taxa occur in serpentine habitats averaging twice as much bare ground as tolerator serpentine taxa and 25% less soil calcium, a limiting macronutrient in serpentine soils. We do not find strong evidence that habitat divergence between sister taxa of endemic pairs is greater than between sister taxa of tolerator pairs. CONCLUSIONS These results suggest serpentine endemism is associated with adaptation to chemically harsher and more bare serpentine habitats. It may be that this adaptation trades off with competitive ability, which would support the longstanding, but rarely tested, competitive trade-off hypothesis.
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Affiliation(s)
- Shelley A Sianta
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California
| | - Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California
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Kay KM, Zepeda AM, Raguso RA. Experimental sympatry reveals geographic variation in floral isolation by hawkmoths. Ann Bot 2019; 123:405-413. [PMID: 30032166 PMCID: PMC6344223 DOI: 10.1093/aob/mcy143] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Accepted: 07/06/2018] [Indexed: 06/08/2023]
Abstract
BACKGROUND AND AIMS Under a widely accepted model of pollinator-driven speciation, geographic variation in pollinator assemblage drives floral divergence and automatically causes reproductive isolation. Yet it is unclear whether divergent floral adaptation initially confers strong reproductive isolation, or whether that comes at later stages of speciation and requires other forms of reproductive isolation. This study uses a pair of recently diverged, interfertile and parapatric species in the genus Clarkia to determine whether adaptation to hawkmoths, a novel pollinator functional group, would automatically confer floral isolation upon sympatric contact. METHODS First, genetically based differences in floral traits between C. breweri and C. concinna that would be maintained upon migration are quantified. Then scenarios of experimental sympatry are constructed in which arrays of flowers are exposed to the novel pollinator, the hawkmoth Hyles lineata, and pollinator preference and heterospecific pollen transfer are assessed. Source populations from across the ranges of each species are used to understand how geographic variation in floral traits within species may affect floral isolation. KEY RESULTS Although H. lineata has never been observed visiting C. concinna in the wild, it regularly moves between species in experimental floral arrays. Hawkmoth preference and heterospecific pollen transfer vary both among moths and among geographic source locations of C. concinna. The strength of floral isolation in this system is related to variation in flower size, especially hypanthium tube width, and nectar reward among C. concinna forms. CONCLUSIONS Although C. breweri has adopted a novel hawkmoth pollination system, both ethological and mechanical floral isolation by hawkmoths are incomplete and vary according to the specific phenotype of the C. concinna source population. The results suggest that strong floral isolation is not automatically conferred by a pollinator shift and may require additional evolution of deterrent floral traits and habitat isolation that reduces the immediate spatial co-occurrence of young species.
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Affiliation(s)
- Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, USA
| | - Aubrey M Zepeda
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, USA
| | - Robert A Raguso
- Department of Neurobiology and Behavior, Cornell University, Ithaca, NY, USA
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Kay KM, Woolhouse S, Smith BA, Pope NS, Rajakaruna N. Sympatric serpentine endemic
Monardella
(Lamiaceae) species maintain habitat differences despite hybridization. Mol Ecol 2018; 27:2302-2316. [DOI: 10.1111/mec.14582] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 02/09/2018] [Accepted: 02/20/2018] [Indexed: 01/09/2023]
Affiliation(s)
- Kathleen M. Kay
- Department of Ecology and Evolutionary Biology University of California Santa Cruz California
| | - Suzie Woolhouse
- Department of Biological Sciences San José State University San José California
| | - Brett A. Smith
- Department of Ecology and Evolutionary Biology University of California Santa Cruz California
| | - Nathaniel S. Pope
- Department of Integrative Biology The University of Texas at Austin Austin Texas
| | - Nishanta Rajakaruna
- Biological Sciences Department California Polytechnic State University San Luis Obispo California
- Unit for Environmental Sciences and Management North‐West University Potchefstroom South Africa
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DeMarche ML, Kay KM, Angert AL. The scale of local adaptation in Mimulus guttatus: comparing life history races, ecotypes, and populations. New Phytol 2016; 211:345-356. [PMID: 27102088 DOI: 10.1111/nph.13971] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 03/16/2016] [Indexed: 06/05/2023]
Abstract
Fitness trade-offs between environments are central to the evolution of biodiversity. Although transplant studies often document fitness trade-offs consistent with local adaptation (LA), many have also found an advantage of foreign genotypes (foreign advantage (FA)). Understanding the mechanisms driving the magnitude and distribution of fitness variation requires comparative approaches that test the ecological scales at which these different patterns emerge. We used a common garden transplant experiment to compare the relative fitnesses of native vs foreign genotypes at three nested ecological scales within Mimulus guttatus: annual vs perennial life history races, perennial ecotypes across an elevational range, and populations within perennial elevational ecotypes. We integrated fitness across the life-cycle and decomposed LA vs FA into contributions from different fitness components. We found LA, measured as home-site advantage, between annual and perennial races and a trend towards LA among populations within montane habitats. Conversely, we found strong FA of low-elevation perennials in a montane environment. LA between life history races reflects the fitness advantages of adult survival and vegetative growth in a mesic environment. Within the perennial race, recent climate conditions or nonselective processes, such as dispersal limitation or mutational load, could explain FA of low-elevation perennials in a montane environment.
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Affiliation(s)
- Megan L DeMarche
- Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA
| | - Kathleen M Kay
- Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA
| | - Amy L Angert
- Departments of Botany and Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
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Peterson ML, Miller TJ, Kay KM. An ultraviolet floral polymorphism associated with life history drives pollinator discrimination in Mimulus guttatus. Am J Bot 2015; 102:396-406. [PMID: 25784473 DOI: 10.3732/ajb.1400415] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
UNLABELLED • PREMISE OF THE STUDY Ultraviolet (UV) floral patterns are common in angiosperms and mediate pollinator attraction, efficiency, and constancy. UV patterns may vary within species, yet are cryptic to human observers. Thus, few studies have explicitly described the distribution or ecological significance of intraspecific variation in UV floral patterning. Here, we describe the geographic distribution and pattern of inheritance of a UV polymorphism in the model plant species Mimulus guttatus (Phrymaceae). We then test whether naturally occurring UV phenotypes influence pollinator interactions within M. guttatus.• METHODS We document UV patterns in 18 annual and 19 perennial populations and test whether UV pattern is associated with life history. To examine the pattern of inheritance, we conducted crosses within and between UV phenotypes. Finally, we tested whether bee pollinators discriminate among naturally occurring UV phenotypes in two settings: wild bee communities and captive Bombus impatiens.• KEY RESULTS Within M. guttatus, perennial populations exhibit a small bulls-eye pattern, whereas a bilaterally symmetric runway pattern occurs mainly in annual populations. Inheritance of UV patterning is consistent with a single-locus Mendelian model in which the runway phenotype is dominant. Bee pollinators discriminate against unfamiliar UV patterns in both natural and controlled settings.• CONCLUSIONS We describe a widespread UV polymorphism associated with life history divergence within Mimulus guttatus. UV pattern influences pollinator visitation and should be considered when estimating reproductive barriers between life history ecotypes. This work develops a new system to investigate the ecology and evolution of UV floral patterning in a species with extensive genomic resources.
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Affiliation(s)
- Megan L Peterson
- Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064 USA
| | - Timothy J Miller
- Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064 USA
| | - Kathleen M Kay
- Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064 USA
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Peterson ML, Kay KM. Mating System Plasticity Promotes Persistence and Adaptation of Colonizing Populations of Hermaphroditic Angiosperms. Am Nat 2015; 185:28-43. [DOI: 10.1086/679107] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Miller TJ, Raguso RA, Kay KM. Novel adaptation to hawkmoth pollinators in Clarkia reduces efficiency, not attraction of diurnal visitors. Ann Bot 2014; 113:317-29. [PMID: 24187032 PMCID: PMC3890391 DOI: 10.1093/aob/mct237] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 08/21/2013] [Indexed: 05/23/2023]
Abstract
BACKGROUND AND AIMS Plant populations experiencing divergent pollination environments may be under selection to modify floral traits in ways that increase both attractiveness to and efficiency of novel pollinators. These changes may come at the cost of reducing overall effectiveness of other pollinators. The goal of this study was to examine differences in attractiveness and efficiency between Clarkia concinna and C. breweri, sister species of annual plants with parapatric distributions. METHODS An assessment was made as to whether observed differences in visitors between natural populations are driven by differences in floral traits or differences in the local pollination environment. Differences in floral attractiveness were quantified by setting out arrays of both species in the geographical range of each species and exposing both species to nocturnal hawkmoths (Hyles lineata) in flight cages. Differences in visitor efficiency were estimated by measuring stigma-visitor contact frequency and pollen loads for diurnal visitors, and pollen deposition on stigmas for hawkmoths. KEY RESULTS The composition of visitors to arrayed plants was similar between plant species at any particular site, but highly divergent among sites, and reflected differences in visitors to natural populations. Diurnal insects visited both species, but were more common at C. concinna populations. Hummingbirds and hawkmoths were only observed visiting within the range of C. breweri. Despite attracting similar species when artificially presented together, C. concinna and C. breweri showed large differences in pollinator efficiency. All visitors except hawkmoths pollinated C. concinna more efficiently. CONCLUSIONS Differences in the available pollinator community may play a larger role than differences in floral traits in determining visitors to natural populations of C. concinna and C. breweri. However, floral traits mediate differences in pollinator efficiency. Increased effectiveness of the novel hawkmoth pollinator on C. breweri comes at relatively little cost in attractiveness to other visitors, but at large cost in their efficiency as pollinators.
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Affiliation(s)
- Timothy J. Miller
- Department of Ecology and Evolution, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
| | - Robert A. Raguso
- Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA
| | - Kathleen M. Kay
- Department of Ecology and Evolution, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
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Frick WF, Shipley JR, Kelly JF, Heady PA, Kay KM. Seasonal reliance on nectar by an insectivorous bat revealed by stable isotopes. Oecologia 2013; 174:55-65. [PMID: 24276770 DOI: 10.1007/s00442-013-2771-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2013] [Accepted: 09/02/2013] [Indexed: 10/26/2022]
Abstract
Many animals have seasonally plastic diets to take advantage of seasonally abundant plant resources, such as fruit or nectar. Switches from insectivorous diets that are protein rich to fruits or nectar that are carbohydrate rich present physiological challenges, but are routinely done by insectivorous songbirds during migration. In contrast, insectivorous bat species are not known to switch diets to consume fruit or nectar. Here, we use carbon stable isotope ratios to establish the first known case of a temperate bat species consuming substantial quantities of nectar during spring. We show that pallid bats (Antrozous pallidus) switch from a diet indistinguishable from that of sympatric insectivorous bat species in winter (when no cactus nectar is present) to a diet intermediate between those of insectivorous bats and nectarivorous bats during the spring bloom of a bat-adapted cactus species. Combined with previous results that established that pallid bats are effective pollinators of the cardon cactus (Pachycereus pringlei), our results suggest that the interaction between pallid bats and cardon cacti represents the first-known plant-pollinator mutualism between a plant and a temperate bat. Diet plasticity in pallid bats raises questions about the degree of physiological adaptations of insectivorous bats for incorporation of carbohydrate-rich foods, such as nectar or fruit, into the diet.
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Affiliation(s)
- Winifred F Frick
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, 95064, USA,
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Surget-Groba Y, Kay KM. Restricted gene flow within and between rapidly diverging Neotropical plant species. Mol Ecol 2013; 22:4931-42. [PMID: 23952304 DOI: 10.1111/mec.12442] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 07/02/2013] [Accepted: 07/04/2013] [Indexed: 11/30/2022]
Abstract
Speciation involves the evolution of traits and genetic differences that contribute to reproductive isolation and the cessation of gene flow, and studying closely related species and divergent populations gives insight into how these phenomena proceed. Here, we document patterns of gene flow within and between two members of a rapid Neotropical species radiation, Costus pulverulentus and Costus scaber (Costaceae). These species co-occur in the tropical rainforest and share pollinators, but are reproductively isolated by a series of prezygotic barriers, some of which show evidence of reinforcement at sympatric sites. Here, we genotype microsatellite markers in plants from eight sites that span the geographical range of both species, including four sympatric sites. We also genotype putative hybrids found at two sympatric sites. We find high levels of genetic isolation among populations within each species and low but detectable levels of introgression between species at sympatric sites. Putative hybrids identified by morphology are consistent with F1 or more advanced hybrids. Our results highlight the effectiveness of prezygotic isolating mechanisms at maintaining species boundaries in young radiations and provide empirical data on levels of gene flow consistent with reinforcement.
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Affiliation(s)
- Yann Surget-Groba
- Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Menglun, Yunnan, 666303, China
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Lancaster LT, Kay KM. ORIGIN AND DIVERSIFICATION OF THE CALIFORNIA FLORA: RE-EXAMINING CLASSIC HYPOTHESES WITH MOLECULAR PHYLOGENIES. Evolution 2013; 67:1041-54. [DOI: 10.1111/evo.12016] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Frick WF, Price RD, Heady PA, Kay KM. Insectivorous Bat Pollinates Columnar Cactus More Effectively per Visit than Specialized Nectar Bat. Am Nat 2013; 181:137-44. [DOI: 10.1086/668595] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Abstract
PREMISE OF THE STUDY Divergent edaphic adaptation can contribute to reproductive isolation and coexistence between closely related species, yet we know little about how small-scale continuous edaphic gradients contribute to this phenomenon. We investigated edaphic adaptation between two cryptic species of California wildflower, Lasthenia californica and L. gracilis (Asteraceae), which grow in close parapatry on serpentine soil. METHODS We reciprocally transplanted both species into the center of each species' habitat and the transition zone between species. We quantified multiple components of fitness and used aster models to predict fitness based on environmental variables. We sampled soil across the ridge throughout the growing season to document edaphic changes through time. We sampled naturally germinating seedlings to determine whether there was dispersal into the adjacent habitat and to help pinpoint the timing of any selection against migrants. KEY RESULTS We documented within-serpentine adaptation contributing to habitat isolation between close relatives. Both species were adapted to the edaphic conditions in their native region and suffered fitness trade-offs when moved outside that region. However, observed fitness values did not perfectly match those predicted by edaphic variables alone, indicating that other factors, such as competition, also contributed to plant fitness. Soil water content and concentrations of calcium, magnesium, sodium, and potassium were likely drivers of differential fitness. Plants either had limited dispersal ability or migrants experienced early-season mortality outside their native region. CONCLUSIONS Demonstrating that continuous habitats can support differently adapted, yet closely related, taxa is important to a broader understanding of how species are generated and maintained in nature.
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Affiliation(s)
- Jenn M Yost
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA.
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Abreu AG, Albaina A, Alpermann TJ, Apkenas VE, Bankhead-Dronnet S, Bergek S, Berumen ML, Cho CH, Clobert J, Coulon A, DE Feraudy D, Estonba A, Hankeln T, Hochkirch A, Hsu TW, Huang TJ, Irigoien X, Iriondo M, Kay KM, Kinitz T, Kothera L, LE Hénanff M, Lieutier F, Lourdais O, Macrini CMT, Manzano C, Martin C, Morris VRF, Nanninga G, Pardo MA, Plieske J, Pointeau S, Prestegaard T, Quack M, Richard M, Savage HM, Schwarcz KD, Shade J, Simms EL, Solferini VN, Stevens VM, Veith M, Wen MJ, Wicker F, Yost JM, Zarraonaindia I. Permanent genetic resources added to Molecular Ecology Resources Database 1 October 2011-30 November 2011. Mol Ecol Resour 2012; 12:374-6. [PMID: 22296658 DOI: 10.1111/j.1755-0998.2011.03109.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This article documents the addition of 139 microsatellite marker loci and 90 pairs of single-nucleotide polymorphism sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Aglaoctenus lagotis, Costus pulverulentus, Costus scaber, Culex pipiens, Dascyllus marginatus, Lupinus nanus Benth, Phloeomyzus passerini, Podarcis muralis, Rhododendron rubropilosum Hayata var. taiwanalpinum and Zoarces viviparus. These loci were cross-tested on the following species: Culex quinquefasciatus, Rhododendron pseudochrysanthum Hay. ssp. morii (Hay.) Yamazaki and R. pseudochrysanthum Hayata. This article also documents the addition of 48 sequencing primer pairs and 90 allele-specific primers for Engraulis encrasicolus.
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Affiliation(s)
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- Molecular Ecology Resources Editorial Office, 6270 University Blvd, Vancouver BC V6T1Z4, Canada.
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Louthan AM, Kay KM. Comparing the adaptive landscape across trait types: larger QTL effect size in traits under biotic selection. BMC Evol Biol 2011; 11:60. [PMID: 21385379 PMCID: PMC3061918 DOI: 10.1186/1471-2148-11-60] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Accepted: 03/07/2011] [Indexed: 11/10/2022] Open
Abstract
Background In a spatially and temporally variable adaptive landscape, mutations operating in opposite directions and mutations of large effect should be commonly fixed due to the shifting locations of phenotypic optima. Similarly, an adaptive landscape with multiple phenotypic optima and deep valleys of low fitness between peaks will favor mutations of large effect. Traits under biotic selection should experience a more spatially and temporally variable adaptive landscape with more phenotypic optima than that experienced by traits under abiotic selection. To test this hypothesis, we assemble information from QTL mapping studies conducted in plants, comparing effect directions and effect sizes of detected QTL controlling traits putatively under abiotic selection to those controlling traits putatively under biotic selection. Results We find no differences in the fraction of antagonistic QTL in traits under abiotic and biotic selection, suggesting similar consistency in selection pressure on these two types of traits. However, we find that QTL controlling traits under biotic selection have a larger effect size than those under abiotic selection, supporting our hypothesis that QTL of large effect are more commonly detected in traits under biotic selection than in traits under abiotic selection. For traits under both abiotic and biotic selection, we find a large number of QTL of large effect, with 10.7% of all QTLs detected controlling more than 20% of the variance in phenotype. Conclusion These results suggest that mutations of large effect are more common in adaptive landscapes strongly determined by biotic forces, but that these types of adaptive landscapes do not result in a higher fraction of mutations acting in opposite directions. The high number of QTL of large effect detected shows that QTL of large effect are more common than predicted by the infinitesimal model of genetic adaptation.
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Affiliation(s)
- Allison M Louthan
- Program in Ecology and Department of Zoology and Physiology, University of Wyoming, Laramie, WY, USA.
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Affiliation(s)
- Kathleen M. Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064;
| | - Risa D. Sargent
- Department of Biology, University of Ottawa, Ontario, K1N6N5, Canada;
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Abstract
The importance of reinforcement, that is, natural selection that strengthens reproductive isolation between incipient species, remains controversial. We used two approaches to test for reinforcement in a species radiation of Neotropical gingers in the genus Costus. First, we conducted an intensive study of Costus pulverulentus and Costus scaber, two recently diverged species that co-occur and share hummingbird pollinators. The hummingbird pollinators transfer pollen between these Costus species, but hybrids are rarely found in nature. By performing pollinations between populations of C. pulverulentus and C. scaber from three sites across the species' geographic ranges, we find that pollen-pistil incompatibilities acting prior to fertilization have evolved only between locally sympatric populations, whereas geographically distant populations within the region of sympatry and allopatric populations remain fully interfertile. Second, we conducted a comparative study of isolating mechanisms across the genus. We find lower seed set due to pollen-pistil incompatibility between species pairs that co-occur and experience pollen transfer in nature compared to species pairs that are otherwise isolated, regardless of genetic distance. Taken together, these studies indicate that crossing barriers prevent potentially maladaptive hybridization and effectively reinforce the speciation process. Our results add to mounting evidence for reinforcement from animal studies and show that plant speciation may also involve complex mate recognition systems. Reinforcement may be particularly important in rapidly diverging lineages where ecological factors play a primary role in reproductive isolation, as may often be the case in tropical communities.
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Affiliation(s)
- Kathleen M Kay
- Department of Plant Biology, 166 Plant Biology Building, Michigan State University, East Lansing, Michigan 48824, USA.
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Kay KM, Whittall JB, Hodges SA. A survey of nuclear ribosomal internal transcribed spacer substitution rates across angiosperms: an approximate molecular clock with life history effects. BMC Evol Biol 2006; 6:36. [PMID: 16638138 PMCID: PMC1484492 DOI: 10.1186/1471-2148-6-36] [Citation(s) in RCA: 259] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 04/25/2006] [Indexed: 11/10/2022] Open
Abstract
Background A full understanding of the patterns and processes of biological diversification requires the dating of evolutionary events, yet the fossil record is inadequate for most lineages under study. Alternatively, a molecular clock approach, in which DNA or amino acid substitution rates are calibrated with fossils or geological/climatic events, can provide indirect estimates of clade ages and diversification rates. The utility of this approach depends on the rate constancy of molecular evolution at a genetic locus across time and across lineages. Although the nuclear ribosomal internal transcribed spacer region (nrITS) is increasingly being used to infer clade ages in plants, little is known about the sources or magnitude of variation in its substitution rate. Here, we systematically review the literature to assess substitution rate variation in nrITS among angiosperms, and we evaluate possible correlates of the variation. Results We summarize 28 independently calibrated nrITS substitution rates ranging from 0.38 × 10-9 to 8.34 × 10-9 substitutions/site/yr. We find that herbaceous lineages have substitution rates almost twice as high as woody plants, on average. We do not find any among-lineage phylogenetic constraint to the rates, or any effect of the type of calibration used. Within life history categories, both the magnitude of the rates and the variance among rates tend to decrease with calibration age. Conclusion Angiosperm nrITS substitution rates vary by approximately an order of magnitude, and some of this variation can be attributed to life history categories. We make cautious recommendations for the use of nrITS as an approximate plant molecular clock, including an outline of more appropriate phylogenetic methodology and caveats against over interpretation of results. We also suggest that for lineages with independent calibrations, much of the variation in nrITS substitution rates may come from uncertainty in calibration date estimates, highlighting the importance of accurate and/or multiple calibration dates.
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Affiliation(s)
- Kathleen M Kay
- Department of Plant Biology, Michigan State University, 166 Plant Biology Building, East Lansing, MI, 48824, USA
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, 93106, USA
| | - Justen B Whittall
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, 93106, USA
- Section of Evolution and Ecology, University of California, One Shields Ave., Davis, CA, 95616, USA
| | - Scott A Hodges
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, 93106, USA
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Kay KM. Reproductive isolation between two closely related hummingbird-pollinated neotropical gingers. Evolution 2006; 60:538-52. [PMID: 16637499] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Empirical estimates of the relative importance of different barriers to gene flow between recently diverged species are important for understanding processes of speciation. I investigated the factors contributing to reproductive isolation between Costus pulverulentus and C. scaber (Costaceae), two closely related hummingbird-pollinated understory Neotropical herbs. I studied broad-scale geographic isolation, microhabitat isolation, flowering phenology, overlap in pollinator assemblages, floral constancy by pollinators, mechanical floral isolation, pollen-pistil interactions, seed set in interspecific crosses, and postzygotic isolation (hybrid seed germination, greenhouse survival to flowering, and pollen fertility). Aside from substantial geographic isolation, I found evidence for several factors contributing to reproductive isolation in the sympatric portion of their geographic ranges, but the identity and relative strength of these factors varied depending on the direction of potential gene flow. For C. pulverulentus as the maternal parent, mechanical floral isolation was the most important factor, acting as a complete block to interspecific pollen deposition. For C. scaber as the maternal parent, microhabitat isolation, pollinator assemblage, mechanical floral isolation, and postpollination pollen-pistil incompatibility were important. Overall, prezygotic barriers were found to be strong, resulting in 100% reproductive isolation for C. pulverulentus as the maternal parent and 99.0% reproductive isolation for C. scaber as the maternal parent. Some postzygotic isolation also was identified in the F1 generation, increasing total isolation for C. scaber to 99.4%. The results suggest that ecological factors, including habitat use and plant-pollinator interactions, contributed to speciation in this system and evolved before extensive intrinsic postzygotic isolation.
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Affiliation(s)
- Kathleen M Kay
- Department of Plant Biology, Michigan State University, East Lansing 48824, USA.
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Affiliation(s)
- Kathleen M. Kay
- Department of Plant Biology, Michigan State University, 166 Plant Biology Building, East Lansing, Michigan 48824
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Kay KM. REPRODUCTIVE ISOLATION BETWEEN TWO CLOSELY RELATED HUMMINGBIRD-POLLINATED NEOTROPICAL GINGERS. Evolution 2006. [DOI: 10.1554/05-339.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Kay KM, Reeves PA, Olmstead RG, Schemske DW. Rapid speciation and the evolution of hummingbird pollination in neotropical Costus subgenus Costus (Costaceae): evidence from nrDNA ITS and ETS sequences. Am J Bot 2005; 92:1899-910. [PMID: 21646107 DOI: 10.3732/ajb.92.11.1899] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We estimate phylogenetic relationships and the biogeographic and pollination history of Costus subgenus Costus (Costaceae) using sequence data from the internal and external transcribed spacer (ITS and ETS) regions of 18S-26S nuclear ribosomal DNA. The African members of the subgenus form a series of lineages basal to a monophyletic neotropical species radiation. The neotropical species have large, showy flowers visited by either euglossine bees or hummingbirds. The hummingbird pollination syndrome is supported as a derived character state from the bee pollination syndrome, and we estimate that it has evolved independently seven or more times in the neotropics. A molecular clock approach suggests that diversification of the neotropical clade has been recent and rapid and that it coincides with dramatic climatic and geologic changes, Andean orogeny, and the closing of the Panama isthmus that occurred in the Pliocene and Pleistocene epochs. We propose a scenario for the diversification of Costus, in which rapid floral adaptation in geographic isolation and range shifts in response to environmental changes contribute to reproductive isolation among close relatives. We suggest that these processes may be common in other recently diversified plant lineages centered in Central America or the Northern Andean phytogeographic region.
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Affiliation(s)
- Kathleen M Kay
- Department of Plant Biology, Michigan State University, 166 Plant Biology Building, East Lansing, Michigan 48824 USA; W. K. Kellogg Biological Station, 3700 East Gull Lake Drive, Hickory Corners, Michigan 49060 USA
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