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Aguirre NM, Ochoa ME, Holmlund HI, Palmeri GN, Lancaster ER, Gilderman GS, Taylor SR, Sauer KE, Borges AJ, Lamb AND, Jacques SB, Ewers FW, Davis SD. How megadrought causes extensive mortality in a deep-rooted shrub species normally resistant to drought-induced dieback: The role of a biotic mortality agent. PLANT, CELL & ENVIRONMENT 2024; 47:1053-1069. [PMID: 38017668 DOI: 10.1111/pce.14768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 10/21/2023] [Accepted: 11/03/2023] [Indexed: 11/30/2023]
Abstract
Southern California experienced unprecedented megadrought between 2012 and 2018. During this time, Malosma laurina, a chaparral species normally resilient to single-year intense drought, developed extensive mortality exceeding 60% throughout low-elevation coastal populations of the Santa Monica Mountains. We assessed the physiological mechanisms by which the advent of megadrought predisposed M. laurina to extensive shoot dieback and whole-plant death. We found that hydraulic conductance of stem xylem (Ks, native ) was reduced seven to 11-fold in dieback adult and resprout branches, respectively. Staining of stem xylem vessels revealed that dieback plants experienced 68% solid-blockage, explaining the reduction in water transport. Following Koch's postulates, persistent isolation of a microorganism in stem xylem of dieback plants but not healthy controls indicated that the causative agent of xylem blockage was an opportunistic endophytic fungus, Botryosphaeria dothidea. We inoculated healthy M. laurina saplings with fungal isolates and compared hyphal elongation rates under well-watered, water-deficit, and carbon-deficit treatments. Relative to controls, we found that both water deficit and carbon-deficit increased hyphal extension rates and the incidence of shoot dieback.
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Affiliation(s)
- Natalie M Aguirre
- Ecology and Evolutionary Biology Program, Texas A&M University, College Station, Texas, USA
- Natural Science Division, Pepperdine University, Malibu, California, USA
| | - Marissa E Ochoa
- Natural Science Division, Pepperdine University, Malibu, California, USA
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California, USA
| | - Helen I Holmlund
- Natural Science Division, Pepperdine University, Malibu, California, USA
| | | | - Emily R Lancaster
- Natural Science Division, Pepperdine University, Malibu, California, USA
- School of Marine Sciences, University of Maine, Orono, Maine, USA
| | - Gina S Gilderman
- Natural Science Division, Pepperdine University, Malibu, California, USA
| | - Shaquetta R Taylor
- Natural Science Division, Pepperdine University, Malibu, California, USA
| | - Kaitlyn E Sauer
- Natural Science Division, Pepperdine University, Malibu, California, USA
| | - Adriana J Borges
- Natural Science Division, Pepperdine University, Malibu, California, USA
| | - Avery N D Lamb
- Natural Science Division, Pepperdine University, Malibu, California, USA
- Nicholas School of the Environment, The Divinity School, Duke University, Durham, North Carolina, USA
| | - Sarah B Jacques
- Natural Science Division, Pepperdine University, Malibu, California, USA
- Department of Surgery, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA
| | - Frank W Ewers
- Department of Biological Sciences, California State Polytechnic University, Pomona, California, USA
| | - Stephen D Davis
- Natural Science Division, Pepperdine University, Malibu, California, USA
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2
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Ehleringer JR, Driscoll AW. Intrinsic water-use efficiency influences establishment in Encelia farinosa. Oecologia 2022; 199:563-578. [PMID: 35819533 DOI: 10.1007/s00442-022-05217-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Accepted: 06/21/2022] [Indexed: 11/25/2022]
Abstract
We describe establishment of Encelia farinosa, a drought-deciduous shrub common to the Mojave and Sonoran Deserts, based on annual observations of two populations between 1980 and 2020. Only 11 establishment events of 50 + yearlings (0.02-0.03 individuals m-2) occurred during this monitoring period; in 68% of the years fewer than 10 yearlings were established. Yearling survival to adulthood (age 4) ranged from 88 to 5% and was significantly related to cumulative precipitation. Juvenile survival rates were lowest during the current megadrought period. We calculated intrinsic water-use efficiency (iWUE) and observed the widest variations in iWUE values among the youngest plants. Among juveniles, surviving yearlings with the lowest iWUE values exhibited upward ontogenetic shifts in iWUE values, whereas those yearlings with the highest initial iWUE values exhibited little if any change. Juvenile size, higher iWUE values, and greater likelihood of surviving were all positively related with each other over the past several decades. Furthermore, iWUE and photosynthetic capacity were positively related to each other, providing a mechanistic explanation for why increased iWUE values among juveniles could lead to greater survival rates and to larger plants under water-deficit conditions. We posit that there is bi-directional selection for genotypic variations in iWUE values among E. farinosa and that this variation is selected for because of interannual environmental heterogeneity in precipitation and VPD associated with both high- and low-frequency climate cycles. Extreme drought cycles may favor plants with higher iWUE values, whereas more mesic periods may allow for greater persistence of lower iWUE genotypes.
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Affiliation(s)
- James R Ehleringer
- School of Biological Sciences, University of Utah, 257 South 1400 East, Salt Lake City, UT, 84112, USA.
| | - Avery W Driscoll
- School of Biological Sciences, University of Utah, 257 South 1400 East, Salt Lake City, UT, 84112, USA
- Present Address: Department of Soil and Crop Sciences, Colorado State University, 301 University Avenue, Fort Collins, CO, 80523, USA
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3
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Rapid increases in shrubland and forest intrinsic water-use efficiency during an ongoing megadrought. Proc Natl Acad Sci U S A 2021; 118:2118052118. [PMID: 34930849 DOI: 10.1073/pnas.2118052118] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/11/2021] [Indexed: 11/18/2022] Open
Abstract
Globally, intrinsic water-use efficiency (iWUE) has risen dramatically over the past century in concert with increases in atmospheric CO2 concentration. This increase could be further accelerated by long-term drought events, such as the ongoing multidecadal "megadrought" in the American Southwest. However, direct measurements of iWUE in this region are rare and largely constrained to trees, which may bias estimates of iWUE trends toward more mesic, high elevation areas and neglect the responses of other key plant functional types such as shrubs that are dominant across much of the region. Here, we found evidence that iWUE is increasing in the Southwest at one of the fastest rates documented due to the recent drying trend. These increases were particularly large across three common shrub species, which had a greater iWUE sensitivity to aridity than Pinus ponderosa, a common tree species in the western United States. The sensitivity of both shrub and tree iWUE to variability in atmospheric aridity exceeded their sensitivity to increasing atmospheric [CO2]. The shift to more water-efficient vegetation would be, all else being equal, a net positive for plant health. However, ongoing trends toward lower plant density, diminished growth, and increasing vegetation mortality across the Southwest indicate that this increase in iWUE is unlikely to offset the negative impacts of aridification.
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Driscoll AW, Kannenberg SA, Ehleringer JR. Long-term nitrogen isotope dynamics in Encelia farinosa reflect plant demographics and climate. THE NEW PHYTOLOGIST 2021; 232:1226-1237. [PMID: 34352127 DOI: 10.1111/nph.17668] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 08/02/2021] [Indexed: 06/13/2023]
Abstract
While plant δ15 N values have been applied to understand nitrogen (N) dynamics, uncertainties regarding intraspecific and temporal variability currently limit their application. We used a 28 yr record of δ15 N values from two Mojave Desert populations of Encelia farinosa to clarify sources of population-level variability. We leveraged > 3500 foliar δ15 N observations collected alongside structural, physiological, and climatic data to identify plant and environmental contributors to δ15 N values. Additional sampling of soils, roots, stems, and leaves enabled assessment of the distribution of soil N content and δ15 N, intra-plant fractionations, and relationships between soil and plant δ15 N values. We observed extensive within-population variability in foliar δ15 N values and found plant age and foliar %N to be the strongest predictors of individual δ15 N values. There were consistent differences between root, stem, and leaf δ15 N values (spanning c. 3‰), but plant and bulk soil δ15 N values were unrelated. Plant-level variables played a strong role in influencing foliar δ15 N values, and interannual relationships between climate and δ15 N values were counter to previously recognized spatial patterns. This long-term record provides insights regarding the interpretation of δ15 N values that were not available from previous large-scale syntheses, broadly enabling more effective application of foliar δ15 N values.
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Affiliation(s)
- Avery W Driscoll
- School of Biological Sciences, University of Utah, 257 S 1400 E, Salt Lake City, UT, 84112, USA
| | - Steven A Kannenberg
- School of Biological Sciences, University of Utah, 257 S 1400 E, Salt Lake City, UT, 84112, USA
| | - James R Ehleringer
- School of Biological Sciences, University of Utah, 257 S 1400 E, Salt Lake City, UT, 84112, USA
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5
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Rader AJ, Chiquoine LP, Weigand JF, Perkins JL, Munson SM, Abella SR. Biotic and abiotic treatments as a bet‐hedging approach to restoring plant communities and soil functions. Restor Ecol 2021. [DOI: 10.1111/rec.13527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Audrey J. Rader
- University of Nevada Las Vegas School of Life Sciences Las Vegas NV 89154‐4004 U.S.A
| | - Lindsay P. Chiquoine
- University of Nevada Las Vegas School of Life Sciences Las Vegas NV 89154‐4004 U.S.A
| | - James F. Weigand
- U.S. Bureau of Land Management California State Office 2800 Cottage Way Sacramento CA 95825 U.S.A
| | - Judy L. Perkins
- U.S. Bureau of Land Management California State Office 2800 Cottage Way Sacramento CA 95825 U.S.A
| | - Seth M. Munson
- U.S. Geological Survey Southwest Biological Science Center 2255 North Gemini Drive Flagstaff AZ 86001 U.S.A
| | - Scott R. Abella
- University of Nevada Las Vegas School of Life Sciences Las Vegas NV 89154‐4004 U.S.A
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6
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Bitter NQ, Ehleringer JR. Machine learning prediction of mortality in the common desert shrub Encelia farinosa. ECOL INFORM 2021. [DOI: 10.1016/j.ecoinf.2021.101376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Mackin HC, Shek KL, Thornton TE, Evens KC, Hallett LM, McGuire KL, DeMarche ML, Roy BA. The 'black box' of plant demography: how do seed type, climate and seed fungal communities affect grass seed germination? THE NEW PHYTOLOGIST 2021; 231:2319-2332. [PMID: 34091913 DOI: 10.1111/nph.17532] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 05/23/2021] [Indexed: 06/12/2023]
Abstract
Demographic studies measure drivers of plant fecundity including seed production and survival, but few address both abiotic and biotic drivers of germination such as variation in climate among sites, population density, maternal plants, seed type and fungal pathogen abundance. We examined germination and microbial communities of seeds of Danthonia californica, which are either chasmogamous (external, wind-pollinated) or cleistogamous (internal, self-fertilized) and Festuca roemeri, which are solely chasmogamous. Seed populations were sourced across environmental gradients. We tested germination and used high-throughput sequencing to characterize seed fungal community structure. For F. roemeri, maternal plants significantly influenced germination as did climate and pathogens; germination increased from wetter, cooler sites. For D. californica, the main drivers of germination were maternal plant, seed type and pathogens; on average, more chasmogamous seeds germinated. Fungal communities depended largely on seed type, with fewer fungi associated with cleistogamous seeds, but the communities also depended on site factors such as vapor pressure deficit, plant density and whether the seeds had germinated. Putative pathogens that were negatively correlated with germination were more abundant for both D. californica and F. roemeri chasmogamous seeds than D. californica cleistogamous seeds. In D. californica, cleistogamous and chasmogamous seeds contain vastly different fungal communities.
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Affiliation(s)
- Hunter C Mackin
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
| | - Katherine L Shek
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
| | - Tiffany E Thornton
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
| | - Kayla C Evens
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
| | - Lauren M Hallett
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
| | - Krista L McGuire
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
- Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Panama
- Environmental Studies Program, University of Oregon, Eugene, OR, 97403, USA
| | - Megan L DeMarche
- Department of Plant Biology, University of Georgia, Athens, GA, 30602, USA
| | - Bitty A Roy
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
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8
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Félix-Burruel RE, Larios E, González EJ, Búrquez A. Episodic recruitment in the saguaro cactus is driven by multidecadal periodicities. Ecology 2021; 102:e03458. [PMID: 34171124 DOI: 10.1002/ecy.3458] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 04/06/2021] [Indexed: 11/12/2022]
Abstract
Each year, an individual mature large saguaro cactus produces about one million seeds in attractive juicy fruits that lure seed predators and seed dispersers to a 3-month feast. From the million seeds produced, however, only a few will persist into mature saguaros. A century of research on saguaro population dynamics has led to the conclusion that saguaro recruitment is an episodic event that depends on the convergence of suitable conditions for survival during the critical early stages. Because most data have been collected in Arizona, particularly in the surroundings of Tucson, most research has relied on a limited amount of environmental variation. In this study, we upscaled this knowledge on saguaro recruitment to a regional scale with a new method that used the inverse-growth modeling of 1,487 saguaros belonging to 13 populations in a latitudinal gradient ranging from arid desert to tropical thornscrub forest in Sonora, Mexico. Using generalized linear and additive mixed models, we created two 110-yr-long saguaro recruitment curves: one driven only by previous size, and the second driven by size, drought, and soil structure. We found evidence that saguaro recruitment is indeed episodic, with periodicities of 20-30 yr, possibly related to strong El Niño Southern Oscillation events. Our results suggest that saguaros rely on multidecadal periodic pulses of good beneficial years to incorporate new individuals into their populations. Inverse-growth modeling can be used in a wide variety of plant species to study their recruitment dynamics.
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Affiliation(s)
- Ricardo E Félix-Burruel
- Posgrado en Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de Mexico, Mexico City, 04510, Mexico.,Ecología para la Conservación del Gran Desierto, A.C., Hermosillo, Sonora, 83174, Mexico
| | - Eugenio Larios
- Ecología para la Conservación del Gran Desierto, A.C., Hermosillo, Sonora, 83174, Mexico.,Instituto de Ecología, Universidad Nacional Autónoma de México, Hermosillo, Sonora, 83000, Mexico
| | - Edgar J González
- Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico
| | - Alberto Búrquez
- Instituto de Ecología, Universidad Nacional Autónoma de México, Hermosillo, Sonora, 83000, Mexico
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9
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Singhal S, Roddy AB, DiVittorio C, Sanchez-Amaya A, Henriquez CL, Brodersen CR, Fehlberg S, Zapata F. Diversification, disparification and hybridization in the desert shrubs Encelia. THE NEW PHYTOLOGIST 2021; 230:1228-1241. [PMID: 33460447 DOI: 10.1111/nph.17212] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Accepted: 01/10/2021] [Indexed: 05/28/2023]
Abstract
There are multiple hypotheses for the spectacular plant diversity found in deserts. We explore how different factors, including the roles of ecological opportunity and selection, promote diversification and disparification in Encelia, a lineage of woody plants in the deserts of the Americas. Using a nearly complete species-level phylogeny based on double-digest restriction-aided sequencing along with a broad set of phenotypic traits, we estimate divergence times and diversification rates, identify instances of hybridization, quantify trait disparity and assess phenotypic divergence across environmental gradients. We show that Encelia originated and diversified recently (mid-Pleistocene) and rapidly, with rates comparable to notable adaptive radiations in plants. Encelia probably originated in the hot deserts of North America, with subsequent diversification across steep environmental gradients. We uncover multiple instances of gene flow between species. The radiation of Encelia is characterized by fast rates of phenotypic evolution, trait lability and extreme disparity across environments and between species pairs with overlapping geographic ranges. Encelia exemplifies how interspecific gene flow in combination with high trait lability can enable exceptionally fast diversification and disparification across steep environmental gradients.
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Affiliation(s)
- Sonal Singhal
- Department of Biology, CSU Dominguez Hills, 1000 E Victoria Street, Carson, CA, 90747, USA
| | - Adam B Roddy
- Institute of Environment, Department of Biological Sciences, Florida International University, Miami, FL, 33133, USA
| | - Christopher DiVittorio
- University of California Institute for México and the United States, University of California, 3324 Olmsted Hall, Riverside, CA, 92521, USA
- Pinecrest Research Corporation, 5627 Telegraph Avenue, Suite 420, Oakland, CA, 94609, USA
| | - Ary Sanchez-Amaya
- Department of Ecology and Evolutionary Biology, University of California, 612 Charles E. Young Dr. South, Los Angeles, CA, 90095, USA
| | - Claudia L Henriquez
- Department of Ecology and Evolutionary Biology, University of California, 612 Charles E. Young Dr. South, Los Angeles, CA, 90095, USA
| | - Craig R Brodersen
- School of the Environment, Yale University, New Haven, CT, 06511, USA
| | - Shannon Fehlberg
- Research, Conservation, and Collections, Desert Botanical Garden, 1201 N Galvin Parkway, Phoenix, AZ, 85008, USA
| | - Felipe Zapata
- Department of Ecology and Evolutionary Biology, University of California, 612 Charles E. Young Dr. South, Los Angeles, CA, 90095, USA
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10
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Driscoll AW, Bitter NQ, Ehleringer JR. Interactions among intrinsic water-use efficiency and climate influence growth and flowering in a common desert shrub. Oecologia 2021; 197:1027-1038. [PMID: 33387007 DOI: 10.1007/s00442-020-04825-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 12/05/2020] [Indexed: 12/16/2022]
Abstract
Plants make leaf-level trade-offs between photosynthetic carbon assimilation and water loss, and the optimal balance between the two is dependent, in part, on water availability. "Conservative" water-use strategies, in which minimizing water loss is prioritized over assimilating carbon, tend to be favored in arid environments, while "aggressive" water-use strategies, in which carbon assimilation is prioritized over water conservation, are often favored in mesic environments. When derived from foliar carbon isotope ratios, intrinsic water-use efficiency (iWUE) serves as a seasonally integrated indicator of the balance of carbon assimilation to water loss at the leaf level. Here, we used a multi-decadal record of annual iWUE, growth, and flowering from a single population of Encelia farinosa in the Mojave Desert to evaluate the effect of iWUE on plant performance across interannual fluctuations in water availability. We identified substantial variability in iWUE among individuals and found that iWUE interacted with water availability to significantly influence growth and flowering. However, the relationships between iWUE, water availability, and plant performance did not universally suggest that "conservative" water-use strategies were advantageous in dry years or that "aggressive" strategies were advantageous in wet years. iWUE was positively related to the odds of growth regardless of water availability and to the odds of flowering in dry years, but negatively related to growth rates in dry years. In addition, we found that leaf nitrogen content affected interannual plant performance and that an individual's iWUE plasticity in response to fluctuations in aridity was negatively related to early life drought survival and growth.
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Affiliation(s)
- Avery W Driscoll
- School of Biological Sciences, University of Utah, 257 S 1400 E, Salt Lake City, UT, 84112, USA.
| | - Nicholas Q Bitter
- School of Biological Sciences, University of Utah, 257 S 1400 E, Salt Lake City, UT, 84112, USA
| | - James R Ehleringer
- School of Biological Sciences, University of Utah, 257 S 1400 E, Salt Lake City, UT, 84112, USA
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11
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Johnson RA. Desiccation limits recruitment in the pleometrotic desert seed-harvester ant Veromessor pergandei. Ecol Evol 2021; 11:294-308. [PMID: 33437430 PMCID: PMC7790620 DOI: 10.1002/ece3.7039] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 10/07/2020] [Accepted: 10/21/2020] [Indexed: 11/14/2022] Open
Abstract
The desert harvester ant Veromessor pergandei displays geographic variation in colony founding with queens initiating nests singly (haplometrosis) or in groups (pleometrosis). The transition from haplo- to pleometrotic founding is associated with lower rainfall. Numerous hypotheses have been proposed to explain the evolution of cooperative founding in this species, but the ultimate explanation remains unanswered. In laboratory experiments, water level was positively associated with survival, condition, and brood production by single queens. Queen survival also was positively influenced by water level and queen number in a two-factor experiment. Water level also was a significant effect for three measures of queen condition, but queen number was not significant for any measure. Foundress queens excavated after two weeks of desiccating conditions were dehydrated compared to alate queens captured from their natal colony, indicating that desiccation can be a source of queen mortality. Long-term monitoring in central Arizona, USA, documented that recruitment only occurred in four of 20 years. A discriminant analysis using rainfall as a predictor of recruitment correctly predicted recruitment in 17 of 20 years for total rainfall from January to June (the period for mating flights and establishment) and in 19 of 20 years for early plus late rainfall (January-March and April-June, respectively), often with a posterior probability > 0.90. Moreover, recruitment occurred only in years in which both early and late rainfall exceeded the long-term mean. This result also was supported by the discriminant analysis predicting no recruitment when long-term mean early and late rainfall were included as ungrouped periods. These data suggest that pleometrosis in V. pergandei evolved to enhance colony survival in areas with harsh abiotic (desiccating) conditions, facilitating colonization of habitats in which solitary queens could not establish even in wet years. This favorable-year hypothesis supports enhanced worker production as the primary advantage of pleometrosis.
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12
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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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13
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Driscoll AW, Bitter NQ, Sandquist DR, Ehleringer JR. Multidecadal records of intrinsic water-use efficiency in the desert shrub Encelia farinosa reveal strong responses to climate change. Proc Natl Acad Sci U S A 2020; 117:18161-18168. [PMID: 32719142 PMCID: PMC7414048 DOI: 10.1073/pnas.2008345117] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
While tree rings have enabled interannual examination of the influence of climate on trees, this is not possible for most shrubs. Here, we leverage a multidecadal record of annual foliar carbon isotope ratio collections coupled with 39 y of survey data from two populations of the drought-deciduous desert shrub Encelia farinosa to provide insight into water-use dynamics and climate. This carbon isotope record provides a unique opportunity to examine the response of desert shrubs to increasing temperature and water stress in a region where climate is changing rapidly. Population mean carbon isotope ratios fluctuated predictably in response to interannual variations in temperature, vapor pressure deficit, and precipitation, and responses were similar among individuals. We leveraged the well-established relationships between leaf carbon isotope ratios and the ratio of intracellular to ambient CO2 concentrations to calculate intrinsic water-use efficiency (iWUE) of the plants and to quantify plant responses to long-term environmental change. The population mean iWUE value increased by 53 to 58% over the study period, much more than the 20 to 30% increase that has been measured in forests [J. Peñuelas, J. G. Canadell, R. Ogaya, Glob. Ecol. Biogeogr. 20, 597-608 (2011)]. Changes were associated with both increased CO2 concentration and increased water stress. Individuals whose lifetimes spanned the entire study period exhibited increases in iWUE that were very similar to the population mean, suggesting that there was significant plasticity within individuals rather than selection at the population scale.
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Affiliation(s)
- Avery W Driscoll
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112
| | - Nicholas Q Bitter
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112
| | - Darren R Sandquist
- Department of Biological Science, California State University, Fullerton, CA 92834
| | - James R Ehleringer
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112;
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14
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Winkler DE, Belnap J, Hoover D, Reed SC, Duniway MC. Shrub persistence and increased grass mortality in response to drought in dryland systems. GLOBAL CHANGE BIOLOGY 2019; 25:3121-3135. [PMID: 31025434 DOI: 10.1111/gcb.14667] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 04/15/2019] [Indexed: 05/13/2023]
Abstract
Droughts in the southwest United States have led to major forest and grassland die-off events in recent decades, suggesting plant community and ecosystem shifts are imminent as native perennial grass populations are replaced by shrub- and invasive plant-dominated systems. These patterns are similar to those observed in arid and semiarid systems around the globe, but our ability to predict which species will experience increased drought-induced mortality in response to climate change remains limited. We investigated meteorological drought-induced mortality of nine dominant plant species in the Colorado Plateau Desert by experimentally imposing a year-round 35% precipitation reduction for eight continuous years. We distributed experimental plots across numerous plant, soil, and parent material types, resulting in 40 distinct sites across a 4,500 km2 region of the Colorado Plateau Desert. For all 8 years, we tracked c. 400 individual plants and evaluated mortality responses to treatments within and across species, and through time. We also examined the influence of abiotic and biotic site factors in driving mortality responses. Overall, high mortality trends were driven by dominant grass species, including Achnatherum hymenoides, Pleuraphis jamesii, and Sporobolus cryptandrus. Responses varied widely from year to year and dominant shrub species were generally resistant to meteorological drought, likely due to their ability to access deeper soil water. Importantly, mortality increased in the presence of invasive species regardless of treatment, and native plant die-off occurred even under ambient conditions, suggesting that recent climate changes are already negatively impacting dominant species in these systems. Results from this long-term drought experiment suggest major shifts in community composition and, as a result, ecosystem function. Patterns also show that, across multiple soil and plant community types, native perennial grass species may be replaced by shrubs and invasive annuals in the Colorado Plateau Desert.
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Affiliation(s)
- Daniel E Winkler
- U.S. Geological Survey, Southwest Biological Science Center, Moab, Utah
| | - Jayne Belnap
- U.S. Geological Survey, Southwest Biological Science Center, Moab, Utah
| | - David Hoover
- Rangeland Resources & Systems Research Unit, U.S. Department of Agriculture, Agricultural Research Service, Fort Collins, Colorado
| | - Sasha C Reed
- U.S. Geological Survey, Southwest Biological Science Center, Moab, Utah
| | - Michael C Duniway
- U.S. Geological Survey, Southwest Biological Science Center, Moab, Utah
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15
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Treonis AM, Sutton KA, Unangst SK, Wren JE, Dragan ES, McQueen JP. Soil organic matter determines the distribution and abundance of nematodes on alluvial fans in Death Valley, California. Ecosphere 2019. [DOI: 10.1002/ecs2.2659] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- Amy M. Treonis
- Department of Biology University of Richmond Richmond Virginia 23173 USA
| | - Kelsey A. Sutton
- Department of Biology University of Richmond Richmond Virginia 23173 USA
| | | | - Julia E. Wren
- Department of Biology University of Richmond Richmond Virginia 23173 USA
| | - Emma S. Dragan
- Department of Biology University of Richmond Richmond Virginia 23173 USA
| | - J. Parr McQueen
- Department of Biology University of Richmond Richmond Virginia 23173 USA
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