Publications (29)153.8 Total impact
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Article: Hybrid speciation and independent evolution in lineages of alpine butterflies.
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ABSTRACT: The power of hybridization between species to generate variation and fuel adaptation is poorly understood despite long-standing interest. There is, however, increasing evidence that hybridization often generates biodiversity, including via hybrid speciation. We tested the hypothesis of hybrid speciation in butterflies occupying extreme, high-altitude habitats in four mountain ranges in western North America with an explicit, probabilistic model, and genome-wide DNA sequence data. Using this approach, in concert with ecological experiments and observations and morphological data, we document three lineages of hybrid origin. These lineages have different genome admixture proportions and distinctive trait combinations that suggest unique and independent evolutionary histories.Evolution 04/2013; 67(4):1055-68. · 5.15 Impact Factor -
Article: Geographically multifarious phenotypic divergence during speciation.
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ABSTRACT: Speciation is an important evolutionary process that occurs when barriers to gene flow evolve between previously panmictic populations. Although individual barriers to gene flow have been studied extensively, we know relatively little regarding the number of barriers that isolate species or whether these barriers are polymorphic within species. Herein, we use a series of field and lab experiments to quantify phenotypic divergence and identify possible barriers to gene flow between the butterfly species Lycaeides idas and Lycaeides melissa. We found evidence that L. idas and L. melissa have diverged along multiple phenotypic axes. Specifically, we identified major phenotypic differences in female oviposition preference and diapause initiation, and more moderate divergence in mate preference. Multiple phenotypic differences might operate as barriers to gene flow, as shown by correlations between genetic distance and phenotypic divergence and patterns of phenotypic variation in admixed Lycaeides populations. Although some of these traits differed primarily between species (e.g., diapause initiation), several traits also varied among conspecific populations (e.g., male mate preference and oviposition preference).Ecology and evolution. 03/2013; 3(3):595-613. -
Article: Ecological and Evolutionary Processes Drive the Origin and Maintenance of Imperfect Mimicry.
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ABSTRACT: Although the forces behind the evolution of imperfect mimicry remain poorly studied, recent hypotheses suggest that relaxed selection on small-bodied individuals leads to imperfect mimicry. While evolutionary history undoubtedly affects the development of imperfect mimicry, ecological community context has largely been ignored and may be an important driver of imperfect mimicry. Here we investigate how evolutionary and ecological contexts might influence mimetic fidelity in Müllerian and Batesian mimicry systems. In Batesian hoverfly systems we find that body size is not a strong predictor of mimetic fidelity. However, in Müllerian velvet ants we find a weak positive relationship between body size and mimetic fidelity when evolutionary context is controlled for and a much stronger relationship between community diversity and mimetic fidelity. These results suggest that reduced selection on small-bodied individuals may not be a major driver of the evolution of imperfect mimicry and that other factors, such as ecological community context, should be considered when studying the evolution of imperfect mimicry.PLoS ONE 01/2013; 8(4):e61610. · 4.09 Impact Factor -
Article: Repeated evolution in overlapping mimicry rings among North American velvet ants.
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ABSTRACT: Müllerian mimicry, in which two or more harmful species share a similar appearance for mutual benefit, is a widely appreciated, yet relatively uncommon natural phenomenon. Although Müllerian mimicry occurs in vertebrates, most studies are focused on tropical, herbivorous invertebrates. Here we identify a large Müllerian mimicry complex in North American velvet ants (Hymenoptera: Mutillidae). These are conspicuous, diurnal parasitoids of bees and wasps that defend themselves with a powerful sting. We investigate morphological and genetic variation and ask whether morphological similarities are the result of convergent evolution or shared ancestry. We find that 65 species in the velvet ant genus Dasymutilla can be placed into one of six morphologically distinct and geographically delimited mimicry rings. Müllerian colour patterns are primarily the result of independent evolution rather than shared, phylogenetic history. These convergent colour syndromes represent one of the largest known Müllerian mimicry complexes yet identified, particularly in the Northern Hemisphere.Nature Communications 12/2012; 3:1272. · 7.40 Impact Factor -
Article: Genomic regions with a history of divergent selection affect fitness of hybrids between two butterfly species.
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ABSTRACT: Speciation is the process by which reproductively isolated lineages arise, and is one of the fundamental means by which the diversity of life increases. Whereas numerous studies have documented an association between ecological divergence and reproductive isolation, relatively little is known about the role of natural selection in genome divergence during the process of speciation. Here, we use genome-wide DNA sequences and Bayesian models to test the hypothesis that loci under divergent selection between two butterfly species (Lycaeides idas and L. melissa) also affect fitness in an admixed population. Locus-specific measures of genetic differentiation between L. idas and L. melissa and genomic introgression in hybrids varied across the genome. The most differentiated genetic regions were characterized by elevated L. idas ancestry in the admixed population, which occurs in L. idas-like habitat, consistent with the hypothesis that local adaptation contributes to speciation. Moreover, locus-specific measures of genetic differentiation (a metric of divergent selection) were positively associated with extreme genomic introgression (a metric of hybrid fitness). Interestingly, concordance of differentiation and introgression was only partial. We discuss multiple, complementary explanations for this partial concordance.Evolution 07/2012; 66(7):2167-81. · 5.15 Impact Factor -
Article: Considering evolutionary processes in the use of single-locus genetic data for conservation, with examples from the Lepidoptera
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ABSTRACT: The increasing popularity of molecular taxonomy will undoubtedly have a major impact on the practice of conservation biology. The appeal of such approaches is undeniable since they will clearly be an asset in rapid biological assessments of poorly known taxa or unexplored areas, and for discovery of cryptic biodiversity. However, as an approach for diagnosing units for conservation, some caution is warranted. The essential issue is that mitochondrial DNA variation is unlikely to be causally related to, and thus correlated with, ecologically important components of fitness. This is true for DNA barcoding, molecular taxonomy in general, or any technique that relies on variation at a single, presumed neutral locus. Given that natural selection operates on a time scale that is often much more rapid than the rates of mutation and allele frequency changes due to genetic drift, neutral genetic variation at a single locus can be a poor predictor of adaptive variation within or among species. Furthermore, reticulate processes, such as introgressive hybridization, may also constrain the utility of molecular taxonomy to accurately detect significant units for conservation. A survey of published genetic data from the Lepidoptera indicates that these problems may be more prevalent than previously suspected. Molecular approaches must be used with caution for conservation genetics which is best accomplished using large sample sizes over extensive geography in addition to data from multiple loci.Journal of Insect Conservation 04/2012; 12(1):37-51. · 1.69 Impact Factor -
Article: Drivers of hybridization in a 66-generation record of Colias butterflies.
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ABSTRACT: Hybridization significantly affects the ecology and evolution of numerous plant and animal lineages. Most studies have focused on endogenous drivers of hybridization and neglected variation in exogenous factors, such as seasonal weather patterns. In this study, we take advantage of a unique dataset consisting of records of hybridization between the butterflies Colias eurytheme and C. eriphyle (Pieridae) for 66 generations (22 years) to investigate the importance of seasonal weather on the production and survival of hybrid offspring. Important seasonal weather variables for each parental species and hybrid offspring were determined using model averaging, and these weather variables, along with butterfly abundances, were analyzed using path analysis. The most important drivers of hybridization were the abundance of C. eriphyle, summer minimum temperature, and spring maximum temperature. In contrast, the abundance of C. eurytheme and weather variables prior to the current flight season were relatively unimportant for variation in hybrid abundance. Parental abundances were mostly driven by weather variables prior to the flight season possibly because these variables affect host plant quality. Our results suggest that exogenous, climatic factors can influence hybridization in natural systems, and that these factors can act both directly on hybrid abundance and indirectly through the population dynamics of parental species.Evolution 03/2012; 66(3):818-30. · 5.15 Impact Factor -
Article: The race is not to the swift: long-term data reveal pervasive declines in California's low-elevation butterfly fauna.
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ABSTRACT: Understanding the ecology of extinction is one of the primary challenges facing ecologists in the 21st century. Much of our current understanding of extinction, particularly for invertebrates, comes from studies with large geographic coverage but less temporal resolution, such as comparisons between historical collection records and contemporary surveys for geographic regions or political entities. We present a complementary approach involving a data set that is geographically restricted but temporally intensive: we focus on three sites in the Central Valley of California, and utilize 35 years of biweekly (every two weeks) surveys at our most long-sampled site. Previous analyses of these data revealed declines in richness over recent decades. Here, we take a more detailed approach to investigate the mode of decline for this fauna. We ask if all species are in decline, or only a subset. We also investigate traits commonly found to be predictors of extinction risk in other studies, such as body size, diet breadth, habitat association, and geographic range. We find that population declines are ubiquitous: the majority of species at our three focal sites (but not at a nearby site at higher elevation) are characterized by reductions in the fraction of days that they are observed per year. These declines are not readily predicted by ecological traits, with the possible exception of ruderal/non-ruderal status. Ruderal species, in slightly less precipitous decline than non-ruderal taxa, are more dispersive and more likely to be associated with disturbed habitats and exotic hosts. We conclude that population declines and extirpation, particularly in regions severely and recently impacted by anthropogenic alteration, might not be as predictable as has been suggested by other studies on the ecology of extinction.Ecology 12/2011; 92(12):2222-35. · 4.85 Impact Factor -
Article: Use of exotic hosts by Lepidoptera: widespread species colonize more novel hosts.
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ABSTRACT: The study of host shifts by herbivorous insects has played an important role in evolutionary biology, contributing to research in coevolution, ecological speciation, and adaptive radiation. As invasive plants become more abundant in many ecosystems, the potential for exotic host use by native insects increases. Graves and Shapiro (2003) have documented exotic host use by 34% of Californian butterflies, suggesting that the plants and butterflies of California might be an important model system for the colonization and utilization of novel resources. In this study, we analyze relationships among geographic range, native diet breadth, and the use of exotic hosts by Californian butterflies and skippers (Lepidoptera). Geographic range and, to a lesser extent, native diet breadth are significant predictors of exotic host use, with positive relationships found both before and after phylogenetic correction. These results give insight into the process of insect host range evolution, as geographically widespread generalists have an apparently greater tendency to use novel, exotic hosts than geographically constrained specialists. Increasing occurrences of exotic host use are expected and those species not capable of shifting to nonnative hosts are likely to have higher vulnerability to extirpation and extinction in the future.Evolution 09/2011; 65(9):2719-24. · 5.15 Impact Factor -
Article: A hierarchical bayesian approach to ecological count data: a flexible tool for ecologists.
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ABSTRACT: Many ecological studies use the analysis of count data to arrive at biologically meaningful inferences. Here, we introduce a hierarchical bayesian approach to count data. This approach has the advantage over traditional approaches in that it directly estimates the parameters of interest at both the individual-level and population-level, appropriately models uncertainty, and allows for comparisons among models, including those that exceed the complexity of many traditional approaches, such as ANOVA or non-parametric analogs. As an example, we apply this method to oviposition preference data for butterflies in the genus Lycaeides. Using this method, we estimate the parameters that describe preference for each population, compare the preference hierarchies among populations, and explore various models that group populations that share the same preference hierarchy.PLoS ONE 01/2011; 6(11):e26785. · 4.09 Impact Factor -
Article: A complete record from colonization to extinction reveals density dependence and the importance of winter conditions for a population of the silvery blue, Glaucopsyche lygdamus.
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ABSTRACT: Butterflies in the family Lycaenidac are often the focus of conservation efforts. However, our understanding of lycaenid population dynamics has been limited to relatively few examples of long-term monitoring data that have been reported. Here, factors associated with population regulation are investigated using a complete record of a single population of the silvery blue, Glaucopsyche lygdamus Doubleday (Lepidoptera: Lycaenidae). Adults of G. lygdamus were first observed in an annual grassland near Davis, California, in 1982 and were last seen in 2003. Relationships between inter-annual variation in abundance and climatic variables were examined, accounting for density dependent effects. Significant effects of both negative density dependence and climatic variation were detected, particularly precipitation and temperature during winter months. Variation in precipitation, the strongest predictor of abundance, was associated directly and positively with butterfly abundance in the same year. Winter temperatures had a negative effect in the same year, but had a lagged, positive effect on abundance in the subsequent year. Mechanistic hypotheses are posed that include climatic effects mediated through both larval and adult plant resources.Journal of Insect Science 01/2011; 11:130. · 0.95 Impact Factor -
Article: After 60 years, an answer to the question: what is the Karner blue butterfly?
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ABSTRACT: The Karner blue butterfly (KBB), Lycaeides melissa samuelis, is a federally protected taxon whose relationship to the Melissa blue, Lycaeides melissa, has been a point of contention during the 66 years since the KBB was first described. Using a large population-genomic dataset and a model of population divergence with migration, we investigated the relationship between the KBB and L. melissa, as well as the relationship between L. melissa and a third taxon, Lycaeides idas. We report that gene flow between the KBB and L. melissa is low, and comparable to gene flow between L. melissa and L. idas. Considering this population-genetic evidence, we conclude that the KBB is a unique evolutionary lineage that should be recognized as Lycaeides samuelis.Biology letters 12/2010; 7(3):399-402. · 3.76 Impact Factor -
Article: Ant association facilitates the evolution of diet breadth in a lycaenid butterfly.
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ABSTRACT: The role of mutualistic interactions in adaptive diversification has not been thoroughly examined. Lycaenid butterflies provide excellent systems for exploring mutualistic interactions, as more than half of this family is known to use ants as a resource in interactions that range from parasitism to mutualism. We investigate the hypothesis that protection from predators offered to caterpillars by ants might facilitate host-range evolution. Specifically, experiments with the butterfly Lycaeides melissa investigated the role of ant association in the use of a novel host, alfalfa, Medicago sativa, which is a sub-optimal host for larval development. Survival on alfalfa is increased by the presence of ants, thus supporting the hypothesis that interaction with ants might be important for host-range evolution. Using a demographic model to explore ecological conditions associated with host-range expansion in L. melissa, we conclude that the presence of ants might be an essential component for populations persisting on the novel, sub-optimal host.Proceedings of the Royal Society B: Biological Sciences 11/2010; 278(1711):1539-47. · 5.41 Impact Factor -
Article: Secondary contact between Lycaeides idas and L. melissa in the Rocky Mountains: extensive admixture and a patchy hybrid zone.
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ABSTRACT: Studies of hybridization have increased our understanding of the nature of species boundaries, the process of speciation, and the effects of hybridization on the evolution of populations and species. In the present study we use genetic and morphological data to determine the outcome and consequences of secondary contact and hybridization between the butterfly species Lycaeides idas and L. melissa in the Rocky Mountains. Admixture proportions estimated from structure and geographical cline analysis indicate L. idas and L. melissa have hybridized extensively in the Rocky Mountains and that reproductive isolation was insufficient to prevent introgression for much of the genome. Geographical patterns of admixture suggest that hybridization between L. idas and L. melissa has led to the formation of a hybrid zone. The hybrid zone is relatively wide, given estimates of dispersal for Lycaeides butterflies, and does not show strong evidence of cline concordance among characters. We believe the structure of the Lycaeides hybrid zone might be best explained by the patchy distribution of Lycaeides, local extinction and colonization of habitat patches, environmental variation and weak overall selection against hybrids. We found no evidence that hybridization in the Rocky Mountains has resulted in the formation of independent hybrid species, in contrast to the outcome of hybridization between L. idas and L. melissa in the Sierra Nevada. Finally, our results suggest that differences in male morphology between L. idas and L. melissa might contribute to isolation, or perhaps even that selection has favoured the spread of L. melissa male genitalia alleles.Molecular Ecology 08/2010; 19(15):3171-92. · 5.52 Impact Factor -
Article: Bayesian analysis of molecular variance in pyrosequences quantifies population genetic structure across the genome of Lycaeides butterflies.
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ABSTRACT: The distribution of genetic variation within and among populations is commonly used to infer their demographic and evolutionary histories. This endeavour has the potential to benefit substantially from high-throughput next-generation sequencing technologies through a rapid increase in the amount of data available and a corresponding increase in the precision of parameter estimation. Here we report the results of a phylogeographic study of the North American butterfly genus Lycaeides using 454 sequence data. This study serves the dual purpose of demonstrating novel molecular and analytical methods for population genetic analyses with 454 sequence data and expanding our knowledge of the phylogeographic history of Lycaeides. We obtained 341,045 sequence reads from 12 populations that we were able to assemble into 15,262 contigs (most of which were variable), representing one of the largest population genetic data sets for a non-model organism to date. We examined patterns of genetic variation using a hierarchical Bayesian analysis of molecular variance model, which provides precise estimates of genome-level phi(ST) while appropriately modelling uncertainty in locus-specific phi(ST). We found that approximately 36% of sequence variation was partitioned among populations, suggesting historical or current isolation among the sampled populations. Estimates of pairwise genome-level phi(ST) were largely consistent with a previous phylogeographic model for Lycaeides, suggesting fragmentation into two to three refugia during Pleistocene glacial cycles followed by post-Pleistocene range expansion and secondary contact leading to introgressive hybridization. This study demonstrates the potential of using genome-level data to better understand the phylogeographic history of populations.Molecular Ecology 05/2010; 19(12):2455-73. · 5.52 Impact Factor -
Article: Compounded effects of climate change and habitat alteration shift patterns of butterfly diversity.
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ABSTRACT: Climate change and habitat destruction have been linked to global declines in vertebrate biodiversity, including mammals, amphibians, birds, and fishes. However, invertebrates make up the vast majority of global species richness, and the combined effects of climate change and land use on invertebrates remain poorly understood. Here we present 35 years of data on 159 species of butterflies from 10 sites along an elevational gradient spanning 0-2,775 m in a biodiversity hotspot, the Sierra Nevada Mountains of Northern California. Species richness has declined at half of the sites, with the most severe reductions at the lowest elevations, where habitat destruction is greatest. At higher elevations, we observed clear upward shifts in the elevational ranges of species, consistent with the influence of global warming. Taken together, these long-term data reveal the interacting negative effects of human-induced changes on both the climate and habitat available to butterfly species in California. Furthermore, the decline of ruderal, disturbance-associated species indicates that the traditional focus of conservation efforts on more specialized and less dispersive species should be broadened to include entire faunas when estimating and predicting the effects of pervasive stressors.Proceedings of the National Academy of Sciences 02/2010; 107(5):2088-92. · 9.68 Impact Factor -
Article: Compounded effects of climate change and habitat alteration shift patterns of butterfly diversity
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ABSTRACT: Climate change and habitat destruction have been linked to global declines in vertebrate biodiversity, including mammals, amphibians, birds, and fishes. However, invertebrates make up the vast majority of global species richness, and the combined effects of climate change and land use on invertebrates remain poorly understood. Here we present 35 years of data on 159 species of butterflies from 10 sites along an elevational gradient spanning 0–2,775 m in a biodiversity hotspot, the Sierra Nevada Mountains of Northern California. Species richness has declined at half of the sites, with the most severe reductions at the lowest elevations, where habitat destruction is greatest. At higher elevations, we observed clear upward shifts in the elevational ranges of species, consistent with the influence of global warming. Taken together, these long-term data reveal the interacting negative effects of human-induced changes on both the climate and habitat available to butterfly species in California. Furthermore, the decline of ruderal, disturbance-associated species indicates that the traditional focus of conservation efforts on more specialized and less dispersive species should be broadened to include entire faunas when estimating and predicting the effects of pervasive stressors.Proceedings of the National Academy of Sciences 02/2010; 107(5):2088-2092. · 9.68 Impact Factor -
Article: Anthropogenic islands in the arid West: comparing the richness and diversity of insect communities in cultivated fields and neighboring wildlands.
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ABSTRACT: The interface between cultivated fields and wildlands has become a central focus for conservation biology, particularly as previously uncultivated lands worldwide are converted to agriculture at an escalating pace. Although research in some parts of the world has highlighted the potential value of agricultural lands for managing and preserving native animals, we know comparatively little about native animals spanning the cultivated/wildlands interface in North America. The study reported here investigated insect communities at three sets of paired sites (cultivated alfalfa fields and native, sagebrush areas) on the western edge of the Great Basin. Two hundred ninety-nine morphospecies were sorted from a collection of >9,000 insects: 221 morphospecies were found in cultivated fields, and 143 were found in the native areas. Insect communities in alfalfa fields were higher in species richness and abundance than communities in adjacent, native fields. However, communities in the cultivated habitat were relatively more homogenous: species composition was more similar among cultivated fields than among native fields. Considering the number of individual insects and morphospecies found in the cultivated habitat, and the relatively small number of species that overlap the two habitat types, the potential ecological consequences of the widespread, anthropogenic habitat are discussed.Environmental Entomology 08/2009; 38(4):1028-37. · 1.56 Impact Factor -
Article: Egg Morphology Varies Among Populations and Habitats Along a Suture Zone in the Lycaeides idas-melissa Species Complex (Lepidoptera: Lycaenidae)
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ABSTRACT: Insect eggs are often characterized by an intricately sculptured external surface, which has been used to a limited extent as a taxonomic character, but not at all in comparisons among populations within a species or among populations of closely related species. We describe egg morphology by using scanning electron microscopy from 12 populations within a species complex of host-specific butterflies in the family Lycaenidae. Variation is found among populations and habitats. Adaptive hypotheses are discussed, and the observed variation is placed within the biogeographical context of the Sierra Nevada Mountains and adjacent regions.Annals of the Entomological Society of America 01/2009; · 1.32 Impact Factor -
Article: Widespread mito-nuclear discordance with evidence for introgressive hybridization and selective sweeps in Lycaeides.
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ABSTRACT: We investigated the extent and potential cause(s) of mitochondrial introgression within the polytypic North American Lycaeides species complex (Lepidoptera). By comparing population genetic structure based on mitochondrial DNA (COI and COII) and nuclear DNA (251 polymorphic amplified fragment length polymorphism markers), we detected substantial mito-nuclear discordance, primarily involving a single mitochondrial haplotype (h01), which is likely due to mitochondrial introgression between differentiated Lycaeides populations and/or species. We detected reduced mitochondrial genetic diversity relative to nuclear genetic diversity in populations where mitochondrial haplotype h01 occurs, suggesting that the spread of this haplotype was facilitated by selection. We found no evidence that haplotype h01 is associated with increased fitness (in terms of survival to eclosion, fresh adult weight, and adult longevity) in a polymorphic Lycaeides melissa population. However, we did find a positive association between mitochondrial haplotype h01 and infection by the endoparasitic bacterium Wolbachia in one out of three lineages tested. Linkage disequilibrium between mitochondrial haplotype h01 and Wolbachia infection status may have resulted in indirect selection favouring the spread of haplotype h01 in at least one lineage of North American Lycaeides. These results illustrate the potential for introgressive hybridization to produce substantial mito-nuclear discordance and demonstrate that an individual's mitochondrial and nuclear genome may have strikingly different evolutionary histories resulting from non-neutral processes and intrinsic differences in the inheritance and biology of these genomes.Molecular Ecology 01/2009; 17(24):5231-44. · 5.52 Impact Factor
Top co-authors
Top Journals
Institutions
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2010–2013
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University of Wyoming
- Botany
Laramie, WY, USA
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2007–2012
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University of Nevada, Reno
- • Department of Biology
- • Department of Natural Resources and Environmental Science
Reno, NV, USA
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2011
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University of Tennessee
- Department of Ecology and Evolutionary Biology
Knoxville, TN, USA
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2009
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Stony Brook University
- Department of Ecology and Evolution
Stony Brook, NY, USA
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2006–2009
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Texas State University
- Department of Biology
San Marcos, TX, USA
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2003–2006
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University of California, Davis
- • Department of Environmental Science and Policy
- • Center for Population Biology
- • Department of Evolution & Ecology
Davis, CA, USA
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