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ABSTRACT: Adaptive radiation involves ecological shifts coupled with isolation of gene pools. However, we know little about what drives the initial stages of divergence. We study a system in which ecological diversification is found within a chronologically well-defined geological matrix to provide insight into this enigmatic phase of radiation. We tested the hypothesis that a period of geographic isolation precedes ecological specialization in an adaptive radiation of host-specialized Hawaiian planthoppers. We examined population structure and history using mitochondrial and multiple independent microsatellite loci in a species whose geographic distribution on the island of Hawaii enabled us to observe the chronology of divergence in its very earliest stages. We found that genetic divergence is associated with geographic features but not different plant hosts and that divergence times are very recent and on the same timescales as the dynamic geology of the island. Our results suggest an important role for geography in the dynamics of the early stages of divergence.
Evolution 09/2012; 66(9):2798-814. · 5.15 Impact Factor
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ABSTRACT: Spatial and environmental heterogeneity are major factors in structuring species distributions in alpine landscapes. These landscapes have also been affected by glacial advances and retreats, causing alpine taxa to undergo range shifts and demographic changes. These nonequilibrium population dynamics have the potential to obscure the effects of environmental factors on the distribution of genetic variation. Here, we investigate how demographic change and environmental factors influence genetic variation in the alpine butterfly Colias behrii. Data from 14 microsatellite loci provide evidence of bottlenecks in all population samples. We test several alternative models of demography using approximate Bayesian computation (ABC), with the results favouring a model in which a recent bottleneck precedes rapid population growth. Applying independent calibrations to microsatellite loci and a nuclear gene, we estimate that this bottleneck affected both northern and southern populations 531-281 years ago, coinciding with a period of global cooling. Using regression approaches, we attempt to separate the effects of population structure, geographical distance and landscape on patterns of population genetic differentiation. Only 40% of the variation in F(ST) is explained by these models, with geographical distance and least-cost distance among meadow patches selected as the best predictors. Various measures of genetic diversity within populations are also decoupled from estimates of local abundance and habitat patch characteristics. Our results demonstrate that demographic change can have a disproportionate influence on genetic diversity in alpine species, contrasting with other studies that suggest landscape features control contemporary demographic processes in high-elevation environments.
Molecular Ecology 07/2012; 21(17):4242-56. · 5.52 Impact Factor
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Evolutionary Applications 07/2012; 5(5):419-23. · 4.92 Impact Factor
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ABSTRACT: Species formation during adaptive radiation often occurs in the context of a changing environment. The establishment and arrangement of populations, in space and time, sets up ecological and genetic processes that dictate the rate and pattern of differentiation. Here, we focus on how a dynamic habitat can affect genetic structure, and ultimately, differentiation among populations. We make use of the chronology and geographical history provided by the Hawaiian archipelago to examine the initial stages of population establishment and genetic divergence. We use data from a set of 6 spider lineages that differ in habitat affinities, some preferring low elevation habitats with a longer history of connection, others being more specialized for high elevation and/or wet forest, some with more general habitat affinities. We show that habitat preferences associated with lineages are important in ecological and genetic structuring. Lineages that have more restricted habitat preferences are subject to repeated episodes of isolation and fragmentation as a result of lava flows and vegetation succession. The initial dynamic set up by the landscape translates over time into discrete lineages. Further work is needed to understand how genetic changes interact with a changing set of ecological interactions amongst a shifting mosaic of landscapes to achieve species formation.
Evolutionary Biology 06/2012; 39(2):192-206. · 3.61 Impact Factor
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ABSTRACT: Tests of hypotheses about the biogeographical consequences of long-distance dispersal have long eluded biologists, largely because of the rarity and presumed unpredictability of such events. Here, we examine data for terrestrial (including littoral) organisms in the Pacific to show that knowledge of dispersal by wind, birds and oceanic drift or rafting, coupled with information about the natural environment and biology of the organisms, can be used to generate broad biogeographic predictions. We then examine the predictions in the context of the origin, frequency of arrival and location of establishment of dispersed organisms, as well as subsequent patterns of endemism and diversification on remote islands. The predicted patterns are being increasingly supported by phylogenetic data for both terrestrial and littoral organisms.
Trends in Ecology & Evolution 01/2012; 27(1):47-56. · 15.75 Impact Factor
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Journal of Marine Biology. 01/2011;
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ABSTRACT: Alpine environments underwent dramatic transformation during glacial-interglacial cycles, with the consequence that geographical, ecological and demographic changes of alpine populations provided the opportunity for formation of neoendemic species. Several biogeographical models have been proposed to account for the unique history of alpine populations, with different expectations of genetic divergence and speciation. The expanding alpine archipelago model proposes that alpine populations expand spatially and demographically during glacial events, dispersing between mountain ranges. Under this model, alpine populations are unlikely to diverge in isolation due to substantial interpopulation gene flow. In contrast, the alpine archipelago refuge model proposes that gene flow during glacial phases is limited and populations expand demographically during interglacial phases, increasing genetic isolation and the likelihood of speciation. We assess these models by reconstructing the evolutionary history of Colias behrii, a morphologically and ecologically distinct alpine butterfly restricted to the California Sierra Nevada. C. behrii exhibits very low genetic diversity at mitochondrial and nuclear loci, limited population structure and evidence of population expansion. C. behrii and Rocky Mountain C. meadii share identical mitochondrial haplotypes, while in contrast, nuclear data indicate common ancestry between C. behrii and Cascades Range Colias pelidne. The conflict in gene genealogies may be a result of recent expansion in North American Colias, but an isolation with migration analysis indicates that genetic patterns in C. behrii might result from differential introgression following hybridization. Based on the timing of population expansion and gene flow between mountain ranges, the expanding alpine archipelago model is supported in C. behrii.
Molecular Ecology 01/2011; 20(6):1233-47. · 5.52 Impact Factor
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ABSTRACT: Evolutionary biologists have been puzzled by the success of introduced species: despite founder effects that reduce genetic variability, invasive species are still successful at colonizing new environments. It is possible that the evolutionary processes during the post-colonization period may increase the genetic diversity and gene flow among invasive populations over time, facilitating their long-term success. Therefore, genetic diversity and population structure would be expected to show greater temporal variation for successful introduced populations than for native populations. We studied the population genetics of the walnut husk fly, Rhagoletis completa, which was introduced into California from the Midwestern US in the early 1900s. We used microsatellites and allozymes to genotype current and historic fly populations, providing a rare perspective on temporal variability in population genetic parameters. We found that introduced populations showed greater temporal fluctuations in allele frequencies than native populations. Some introduced populations also showed an increase in genetic diversity over time, indicating multiple introductions had occurred. Population genetic structure decreased in both native and introduced populations over time. Our study demonstrates that introduced species are not at equilibrium and post-colonization processes may be important in ameliorating the loss of genetic diversity associated with biological invasions.
Genetica 10/2010; 138(9-10):1059-75. · 2.15 Impact Factor
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Junghwa An,
Arnaud Bechet,
Asa Berggren,
Sarah K Brown,
Michael W Bruford,
Qingui Cai,
Anna Cassel-Lundhagen,
Frank Cezilly,
Song-Lin Chen,
Wei Cheng, [......],
Stefan Woltmann,
Yong-Jin Won,
Jing Wu,
M L Xie,
Genbo Xu,
Xiao-Jun Xu,
Hai-Hui Ye,
Xiangjiang Zhan,
F Zhang,
J Zhong
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ABSTRACT: This article documents the addition of 411 microsatellite marker loci and 15 pairs of Single Nucleotide Polymorphism (SNP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Acanthopagrus schlegeli, Anopheles lesteri, Aspergillus clavatus, Aspergillus flavus, Aspergillus fumigatus, Aspergillus oryzae, Aspergillus terreus, Branchiostoma japonicum, Branchiostoma belcheri, Colias behrii, Coryphopterus personatus, Cynogolssus semilaevis, Cynoglossus semilaevis, Dendrobium officinale, Dendrobium officinale, Dysoxylum malabaricum, Metrioptera roeselii, Myrmeciza exsul, Ochotona thibetana, Neosartorya fischeri, Nothofagus pumilio, Onychodactylus fischeri, Phoenicopterus roseus, Salvia officinalis L., Scylla paramamosain, Silene latifo, Sula sula, and Vulpes vulpes. These loci were cross-tested on the following species: Aspergillus giganteus, Colias pelidne, Colias interior, Colias meadii, Colias eurytheme, Coryphopterus lipernes, Coryphopterus glaucofrenum, Coryphopterus eidolon, Gnatholepis thompsoni, Elacatinus evelynae, Dendrobium loddigesii Dendrobium devonianum, Dysoxylum binectariferum, Nothofagus antarctica, Nothofagus dombeyii, Nothofagus nervosa, Nothofagus obliqua, Sula nebouxii, and Sula variegata. This article also documents the addition of 39 sequencing primer pairs and 15 allele specific primers or probes for Paralithodes camtschaticus.
Molecular Ecology Resources 03/2010; 10(2):404-408. · 3.06 Impact Factor
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ABSTRACT: Climate in alpine habitats has undergone extreme variation during Pliocene and Pleistocene epochs, resulting in repeated expansion and contraction of alpine glaciers. Many cold-adapted alpine species have responded to these climatic changes with long-distance range shifts. These species typically exhibit shallow genetic differentiation over a large geographical area. In contrast, poorly dispersing organisms often form species complexes within mountain ranges, such as the California endemic ice-crawlers (Grylloblattodea: Grylloblattidae: Grylloblatta). The diversification pattern of poorly dispersing species might provide more information on the localized effects of historical climate change, the importance of particular climatic events, as well as the history of dispersal. Here we use multi-locus genetic data to examine the phylogenetic relationships and geographic pattern of diversification in California Grylloblatta.
Our analysis reveals a pattern of deep genetic subdivision among geographically isolated populations of Grylloblatta in California. Alpine populations diverged from low elevation populations and subsequently diversified. Using a Bayesian relaxed clock model and both uncalibrated and calibrated measurements of time to most recent common ancestor, we reconstruct the temporal diversification of alpine Grylloblatta populations. Based on calibrated relaxed clock estimates, evolutionary diversification of Grylloblatta occurred during the Pliocene-Pleistocene epochs, with an initial dispersal into California during the Pliocene and species diversification in alpine clades during the middle Pleistocene epoch.
Grylloblatta species exhibit a high degree of genetic subdivision in California with well defined geographic structure. Distinct glacial refugia can be inferred within the Sierra Nevada, corresponding to major, glaciated drainage basins. Low elevation populations are sister to alpine populations, suggesting alpine populations may track expanding glacial ice sheets and diversify as a result of multiple glacial advances. Based on relaxed-clock molecular dating, the temporal diversification of Grylloblatta provides evidence for the role of a climate-driven species pump in alpine species during the Pleistocene epoch.
BMC Evolutionary Biology 01/2010; 10:163. · 3.52 Impact Factor
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ABSTRACT: Growth of alpine glaciers during the Pleistocene had profound effects on montane landscapes in North America and the organisms now inhabiting alpine ecosystems. Biogeography of this region has often been viewed as a system of sky islands despite the fact that species richness patterns deviate from a strict island biogeographic model. One explanation is that alpine species are not in equilibrium because of late Quaternary geographic range shifts. Genetic data can provide evidence of nonequilibrium dynamics and the distributional shifts that occur during glaciation events in alpine landscapes. Using mitochondrial and nuclear sequence data, we examine the evolutionary history of butterflies in the Parnassius phoebus complex. We test explicit, alternative models of the biogeographic history of Parnassius smintheus and Parnassius behrii, including an equilibrium island model, ancestral radiation and fragmentation, an expanding alpine archipelago and an alpine archipelago refuge model. Our results support the alpine archipelago refuge model, in which alpine butterflies undergo population contraction during glacial climates followed by population expansion during interglacial phases. While butterflies can disperse between distant mountain ranges during glacial periods, gene flow is rare. We find evidence of recent connectivity between California and Colorado, population expansion events following deglaciation approximately 20,000 years B.P., and small population sizes during the last glacial period. An analysis of lineage splitting suggests that morphological differences in P. smintheus and P. behrii are the result of late Pleistocene divergence (approximately 48,000 years B.P.) with limited gene flow. Our results demonstrate that spatially complex and nonequilibrium population dynamics influence alpine diversity patterns.
Molecular Ecology 08/2009; 18(16):3471-85. · 5.52 Impact Factor
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ABSTRACT: Biological invasions are typically the outcome of complex patterns of introduction, establishment, and spread, and genetic
methods are excellent tools to resolve such histories for non-native organisms. The mealy plum aphid, Hyalopterus pruni, is an invasive pest of dried plum in California. We examined nine microsatellite loci and DNA sequences from three mitochondrial
genes (1,148bp) in populations throughout the native and invaded ranges of H. pruni to assess key invasion parameters, including geographic origins of invasive populations, number of introductions, and levels
of genetic diversity and gene flow. Our results provide evidence for multiple invasions of H. pruni into North America, suggesting that aphids in California may have been introduced from Spain, and aphids in the eastern United
States and Vancouver, Canada were likely introduced from central or northern Europe. H. pruni populations in California were characterized by low genetic diversity relative to native populations, while the two other
North American populations were less genetically impoverished. Gene flow among introduced populations was low, but does appear
to occur with some regularity. These findings provide a framework for more detailed studies of H. pruni, but also represent a model for how population genetics approaches can be used to study invasion biology and aid the development
of optimized management methods for agricultural pests.
Biological Invasions 01/2009; 11(2):299-314. · 2.90 Impact Factor
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ABSTRACT: We have isolated and characterized 17 microsatellite loci for the endemic Hawaiian planthopper Nesosydne chambersi (Delphacidae), a member of a large Hawaiian Nesosydne radiation. Thirty individuals from one population and 10 individuals from two populations across the species' range were tested to investigate polymorphism. The observed loci contained two to nine alleles per locus. Expected heterozygosity within this species ranged from 0.2 to 0.85. These markers will be used to assess intraspecific differentiation and population structure within N. chambersi.
Molecular Ecology Resources 11/2008; 8(6):1436-8. · 3.06 Impact Factor
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ABSTRACT: The flora and fauna of oceanic islands have inspired research since the early scientific explorations. Islands can be considered 'nature's test tubes'- simple systems with multiple replicates. Our research has used the simplicity of island systems to understand ecological community dynamics and to compare the properties of island communities with those in more complex mainland systems. Here, we present three topics: (i) current patterns of biodiversity on isolated islands of the Pacific; (ii) current patterns of disturbance and invasion on islands; and (iii) future trajectories inferred from these patterns. We examine features of islands (in particular, topography and isolation) that have allowed for given levels and distribution of endemicity. The extent to which island communities are impacted by, resist or accommodate disturbance and/or invasions by nonindigenous species appears to be dictated to a large extent by properties of the native communities and how these communities were originally assembled. Accordingly, patterns of disturbance and invasion are very different for high (montane) islands that are extremely isolated compared to those that are nearer to a source of natural migrants. As with all biotas, those on islands are dynamic entities. However, the unique aspect of islands is their isolation, and extreme isolation has largely been lost over the course of the last few centuries due to the development of transportation routes. We argue that such a modified dynamic will affect the future of the biota and the processes that gave rise to the biota. Specifically for isolated habitats, ecological processes will become increasingly more likely to generate biodiversity than evolutionary processes which have been relatively more important in the past. In the short term, island biotas and other similar biotas that occur in montane habitats may fare well as species are often abundant locally in the habitat to which they are indigenous, and may demonstrate considerable resistance and resilience to invasion. However, island biotas - and other biotas that show high local endemism - will likely not fare well in the face of prolonged disturbance. The biotas in these areas generally display a relatively low dispersal capacity; therefore, under conditions of long-term habitat modification, isolated biotas are likely to be swamped by non-natives, which - simply because of random processes and higher propagule pressure - will move more readily into available habitats. Thus, despite the importance of incorporating the evolutionary process into conservation efforts, we must also be careful to evaluate the likely form that the processes will take when the context (specifically, extent of isolation) has been highly modified.
Molecular Ecology 02/2008; 17(1):45-57. · 5.52 Impact Factor
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ABSTRACT: Over the past several decades biologists' fascination with plant-herbivore interactions has generated intensive research into the implications of these interactions for insect diversification. The study of closely related phytophagous insect species or populations from an evolutionary perspective can help illuminate ecological and selective forces that drive these interactions. Here we present such an analysis for aphids in the genus Hyalopterus (Hemiptera: Aphididae), a cosmopolitan group that feeds on plants in the genus Prunus (Rosaceae). Hyalopterus currently contains two recognized species associated with different Prunus species, although the taxonomy and evolutionary history of the group is poorly understood. Using mitochondrial COI sequences, 16S rDNA sequences from the aphid endosymbiont Buchnera aphidicola, and nine microsatellite loci we investigated population structure in Hyalopterus from the most commonly used Prunus host species throughout the Mediterranean as well as in California, where the species H. pruni is an invasive pest. We found three deeply divergent lineages structured in large part by specific associations with plum, almond, and peach trees. There was no evidence that geographic or temporal barriers could explain the overall diversity in the genus. Levels of genetic differentiation are consistent with that typically attributed to aphid species and indicate divergence times older than the domestication of Prunus for agriculture. Interestingly, in addition to their typical hosts, aphids from each of the three lineages were frequently found on apricot trees. Apricot also appears to act as a resource mediated hybrid zone for plum and almond associated lineages. Together, results suggest that host plants have played a role in maintaining host-associated differentiation in Hyalopterus for as long as several million years, despite worldwide movement of host plants and the potential for ongoing hybridization.
Evolution 07/2007; 61(6):1353-67. · 5.15 Impact Factor
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ABSTRACT: Global warming is predicted to affect the evolutionary potential of natural populations. We assessed genetic diversity of 25 populations of desert bighorn sheep (Ovis canadensis nelsoni) in southeastern California, where temperatures have increased and precipitation has decreased during the 20th century. Populations in low-elevation habitats had lower genetic diversity, presumably reflecting more fluctuations in population sizes and founder effects. Higher-elevation habitats acted as reservoirs of genetic diversity. However, genetic diversity was also affected by population connectivity, which has been disrupted by human development. Restoring population connectivity may be necessary to buffer the effects of climate change on this desert-adapted ungulate.
Molecular Ecology 01/2007; 15(14):4295-302. · 5.52 Impact Factor
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ABSTRACT: The success of invasive species appears to be a paradox: despite experiencing strong population bottlenecks, invasive species are able to successfully establish in new environments. We studied how the walnut husk fly, Rhagoletis completa, was able to successfully colonize California from the Midwestern United States, by examining genetic diversity and diapause variation of native and introduced fly populations. Climate plays an important role in the successful establishment of introduced insects, because insect diapause is highly dependent upon external climatic conditions. We examined if: (1) fly populations show signs of a population bottleneck, (2) native and introduced flies differ in diapause length when exposed to California and Midwestern climatic conditions, and (3) population genetic diversity is related to variation in diapause length. We assessed if fly diapause conformed more to a model of establishment by local adaptation or to a model of a highly plastic "general-purpose genotype". Our results indicate that only two populations close to the original introduced location showed signs of a population bottleneck, and native and introduced populations did not differ in genetic diversity. Genetic diversity increased in the northern introduced populations, suggesting that multiple introductions have occurred. Flies emerged about 2 weeks earlier under the Midwestern treatment than the California treatment, and introduced flies emerged about a week earlier than native flies. All flies emerged when walnuts are typically available in California. Although variance in diapause length differed between populations, it did not vary between populations or regions. Furthermore, genetic diversity was not associated with diapause variation. Therefore, multiple introductions and a "general-purpose genotype" appear to have facilitated the fly's invasion into California.
Oecologia 11/2006; 149(4):656-67. · 3.41 Impact Factor
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ABSTRACT: Acetylcholinesterase (Ace) is the molecular target of organophosphate (OP) insecticides, and two mutations that confer different levels of OP insensitivity have previously been identified in the olive fly, Bactrocera oleae. Numerous sensitive and two insensitive alleles (including one convergent acquisition) are described from the entire worldwide distribution of the fly. Most of the variation is harbored in the native range of the species and in the Middle East and consists of numerous low-frequency sensitive alleles. The insensitive alleles likely came to high frequency more recently in the Mediterranean region or in the Middle East, reaching frequencies as high as 100% in some populations, and determined a corresponding decline in overall genetic variation. We hypothesize that the major force that shaped the current distribution of resistant and non-resistant acetylcholinesterase alleles is natural selection, likely responsible for the high frequency of insensitive alleles in areas where organophosphates have been used extensively. We also discuss a role for historical contingency, that can explain why sensitive alleles are absent altogether in the species ancestral range and present in areas of recent expansion, such as California, despite the limited use of OPs.
Insect Biochemistry and Molecular Biology 08/2006; 36(7):593-602. · 3.25 Impact Factor
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ABSTRACT: The rapid expansion of road networks has reduced connectivity among populations of flora and fauna. The resulting isolation is assumed to increase population extinction rates, in part because of the loss of genetic diversity. However, there are few cases where loss of genetic diversity has been linked directly to roads or other barriers. We analysed the effects of such barriers on connectivity and genetic diversity of 27 populations of Ovis canadensis nelsoni (desert bighorn sheep). We used partial Mantel tests, multiple linear regression and coalescent simulations to infer changes in gene flow and diversity of nuclear and mitochondrial DNA markers. Our findings link a rapid reduction in genetic diversity (up to 15%) to as few as 40 years of anthropogenic isolation. Interstate highways, canals and developed areas, where present, have apparently eliminated gene flow. These results suggest that anthropogenic barriers constitute a severe threat to the persistence of naturally fragmented populations.
Ecology Letters 09/2005; 8(10):1029 - 1038. · 17.56 Impact Factor
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ABSTRACT: The olive fly, Bactrocera oleae, is the major pest of olives in most commercial olive-growing regions worldwide. The species is abundant in the Mediterranean basin and has been introduced recently into California and Mexico, creating problems for quarantine protection and international trade. Here, we use nuclear microsatellite markers and mitochondrial sequences to examine the history of olive fly range expansion and colonization. Sampled populations span the current distribution of the olive fly worldwide, including South and Central Africa, Pakistan, Mediterranean Europe and Middle East, California, and Mexico. The Pakistani populations appear to be genetically well differentiated from the remaining populations, though rooting the origins of the species is problematic. Genetic similarity and assignment tests cluster the remaining populations into two genetic groups--Africa and a group including the Mediterranean basin and the American region. That Africa, and not the Mediterranean, is the origin of flies infesting cultivated olive is supported by the significantly greater genetic diversity at microsatellite loci in Africa relative to the Mediterranean area. The results also indicate that the recent invasion of olive flies in the American region most likely originated from the Mediterranean area.
Molecular Ecology 09/2005; 14(9):2729-38. · 5.52 Impact Factor
