The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
David W Pfennig - One of the best experts on this subject based on the ideXlab platform.
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genetic accommodation in the wild evolution of gene expression plasticity during character displacement
Journal of Evolutionary Biology, 2017Co-Authors: Nicholas A Levis, Antonio Serratocapuchina, David W PfennigAbstract:Ecological character displacement is considered crucial in promoting diversification, yet relatively little is known of its underlying mechanisms. We examined whether evolutionary shifts in gene expression plasticity (‘genetic accommodation’) mediate character displacement in spadefoot toads. Where Spea bombifrons and S. multiplicata occur separately in Allopatry (the ancestral condition), each produces alternative, diet-induced, larval ecomorphs: omnivores, which eat detritus, and carnivores, which specialize on shrimp. By contrast, where these two species occur together in sympatry (the derived condition), selection to minimize competition for detritus has caused S. bombifrons to become nearly fixed for producing only carnivores, suggesting that character displacement might have arisen through an extreme form of genetic accommodation (‘genetic assimilation’) in which plasticity is lost. Here, we asked if we could infer a signature of this process in regulatory changes of specific genes. In particular, we investigated whether genes that are normally expressed more highly in one morph (‘biased’ genes) have evolved reduced plasticity in expression levels among S. bombifrons from sympatry compared to S. bombifrons from Allopatry. We reared individuals from sympatry vs. Allopatry on detritus vs. shrimp and measured the reaction norms of nine biased genes. Although different genes displayed different patterns of gene regulatory evolution, the combined gene expression profiles revealed that sympatric individuals had indeed lost the diet-induced gene expression plasticity present in allopatric individuals. Our data therefore provide one of the few examples from natural populations in which genetic accommodation/assimilation can be traced to regulatory changes of specific genes. Such genetic accommodation might mediate character displacement in many systems. This article is protected by copyright. All rights reserved.
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Geographic variation in mimetic precision among different species of coral snake mimics.
Journal of evolutionary biology, 2017Co-Authors: Christopher K. Akcali, David W PfennigAbstract:Batesian mimicry is widespread, but whether and why different species of mimics vary geographically in resemblance to their model is unclear. We characterized geographic variation in mimetic precision among four Batesian mimics of coral snakes. Each mimic occurs where its model is abundant (i.e. in 'deep sympatry'), rare (i.e. at the sympatry/Allopatry boundary or 'edge sympatry') and absent (i.e. in Allopatry). Geographic variation in mimetic precision was qualitatively different among these mimics. In one mimic, the most precise individuals occurred in edge sympatry; in another, they occurred in deep sympatry; in the third, they occurred in Allopatry; and in the fourth, precise mimics were not concentrated anywhere throughout their range. Mimicry was less precise in Allopatry than in sympatry in only two mimics. We present several nonmutually exclusive hypotheses for these patterns. Generally, examining geographic variation in mimetic precision - within and among different mimics - offers novel insights into the causes and consequences of mimicry.
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Batesian mimicry promotes pre- and postmating isolation in a snake mimicry complex.
Evolution, 2015Co-Authors: David W Pfennig, Christopher K. Akcali, David W. KikuchiAbstract:We evaluated whether Batesian mimicry promotes early-stage reproductive isolation. Many Batesian mimics occur not only in sympatry with their model (as expected), but also in Allopatry. As a consequence of local adaptation within both sympatry (where mimetic traits are favored) and Allopatry (where nonmimetic traits are favored), divergent, predator-mediated natural selection should disfavor immigrants between these selective environments as well as any between-environment hybrids. This selection might form the basis for both pre- and postmating isolation, respectively. We tested for such selection in a snake mimicry complex by placing clay replicas of sympatric, allopatric, or hybrid phenotypes in both sympatry and Allopatry and measuring predation attempts. As predicted, replicas with immigrant phenotypes were disfavored in both selective environments. Replicas with hybrid phenotypes were also disfavored, but only in a region of sympatry where previous studies have detected strong selection favoring precise mimicry. By fostering immigrant inviability and ecologically dependent selection against hybrids (at least in some habitats), Batesian mimicry might therefore promote reproductive isolation. Thus, although Batesian mimicry has long been viewed as a mechanism for convergent evolution, it might play an underappreciated role in fueling divergent evolution and possibly even the evolution of reproductive isolation and speciation.
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does character displacement initiate speciation evidence of reduced gene flow between populations experiencing divergent selection
Journal of Evolutionary Biology, 2010Co-Authors: Amber M Rice, David W PfennigAbstract:Character displacement ‐ trait evolution stemming from selection to lessen resource competition or reproductive interactions between species ‐ has long been regarded as important in finalizing speciation. By contrast, its role in initiating speciation has received less attention. Yet because selection for character displacement should act only where species co-occur, individuals in sympatry will experience a different pattern of selection than conspecifics in Allopatry. Such divergent selection might favour reduced gene flow between conspecific populations that have undergone character displacement and those that have not, thereby potentially triggering speciation. Here, we explore these ideas empirically by focusing on spadefoot toads, Spea multiplicata, which have undergone character displacement, and for which character displacement appears to cause post-mating isolation between populations that are in sympatry with a heterospecific and those that are in Allopatry. Using mitochondrial sequence data and nuclear microsatellite genotypes, we specifically asked whether gene flow is reduced between populations in different selective environments relative to that between populations in the same selective environment. We found a slight, but statistically significant, reduction in gene flow between selective environments, suggesting that reproductive isolation, and potentially ecological speciation, might indeed evolve as an indirect consequence of character displacement. Generally, character displacement may play a largely underappreciated role in instigating speciation.
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parallel evolution and ecological selection replicated character displacement in spadefoot toads
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Amber M Rice, Aaron R Leichty, David W PfennigAbstract:Ecological character displacement—trait evolution stemming from selection to lessen resource competition between species—is most often inferred from a pattern in which species differ in resource-use traits in sympatry but not in Allopatry, and in which sympatric populations within each species differ from conspecific allopatric populations. Yet, without information on population history, the presence of a divergent phenotype in multiple sympatric populations does not necessarily imply that there has been repeated evolution of character displacement. Instead, such a pattern may arise if there has been character displacement in a single ancestral population, followed by gene flow carrying the divergent phenotype into multiple, derived, sympatric populations. Here, we evaluate the likelihood of such historical events versus ongoing ecological selection in generating divergence in trophic morphology between multiple populations of spadefoot toad (Spea multiplicata) tadpoles that are in sympatry with a heterospecific and those that are in Allopatry. We present both phylogenetic and population genetic evidence indicating that the same divergent trait, which minimizes resource competition with the heterospecific, has arisen independently in multiple sympatric populations. These data, therefore, provide strong indirect support for competition’s role in divergent trait evolution.
Frank T Burbrink - One of the best experts on this subject based on the ideXlab platform.
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Hard and soft Allopatry: physically and ecologically mediated modes of geographic speciation
Journal of Biogeography, 2010Co-Authors: R. Alexander Pyron, Frank T BurbrinkAbstract:Aim Three common patterns have emerged in comparative phylogeographic analyses at many barriers: (1) a potential geographic pseudocongruence of lineage divergences; (2) a disconnect between the inference of temporally clustered, relatively recent timing for observed speciation events, and dates spanning a broader, apparently random time-scale; and (3) an apparent prevalence of speciation with recent or continuing gene flow. It is unclear if there is a unifying explanation for these phenomena. We argue that the interaction between geographic barriers to dispersal and ecological limits on the distribution of species can explain these patterns. We suggest that these patterns can be explained by the presence of a continuum between two underlying processes, here termed ‘hard’ and ‘soft’ allopatric divergence, which result from the interplay between organismal ecology and the physioecological nature of geographic barriers. Location Examples from North America. Methods We examine comparative phylogeographic divergences in 18 groups of terrestrial vertebrates at two major biogeographic features in North America ‐ the Mississippi River Embayment and the Cochise Filter Barrier ‐ to test predictions made by this hypothesis. Results We find support for the two distinct processes of hard and soft Allopatry, and note several examples exhibiting characteristics of both. Hard Allopatry is caused by physical barriers promoting divergence as a function of consistent geographic isolation. Soft Allopatry is caused by ecological processes that isolate populations geographically in allopatric refugia through niche conservatism, or across ecological transition zones through niche divergence, but which may be periodic or inconsistent through time.
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Hard and soft Allopatry: physically and ecologically mediated modes of geographic speciation
Journal of Biogeography, 2010Co-Authors: R. Alexander Pyron, Frank T BurbrinkAbstract:Aim Three common patterns have emerged in comparative phylogeographic analyses at many barriers: (1) a potential geographic pseudocongruence of lineage divergences; (2) a disconnect between the inference of temporally clustered, relatively recent timing for observed speciation events, and dates spanning a broader, apparently random time-scale; and (3) an apparent prevalence of speciation with recent or continuing gene flow. It is unclear if there is a unifying explanation for these phenomena. We argue that the interaction between geographic barriers to dispersal and ecological limits on the distribution of species can explain these patterns. We suggest that these patterns can be explained by the presence of a continuum between two underlying processes, here termed ‘hard’ and ‘soft’ allopatric divergence, which result from the interplay between organismal ecology and the physioecological nature of geographic barriers. Location Examples from North America. Methods We examine comparative phylogeographic divergences in 18 groups of terrestrial vertebrates at two major biogeographic features in North America ‐ the Mississippi River Embayment and the Cochise Filter Barrier ‐ to test predictions made by this hypothesis. Results We find support for the two distinct processes of hard and soft Allopatry, and note several examples exhibiting characteristics of both. Hard Allopatry is caused by physical barriers promoting divergence as a function of consistent geographic isolation. Soft Allopatry is caused by ecological processes that isolate populations geographically in allopatric refugia through niche conservatism, or across ecological transition zones through niche divergence, but which may be periodic or inconsistent through time.
Fabienne Van Rossum - One of the best experts on this subject based on the ideXlab platform.
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Lineages of Silene nutans developed rapid, strong, asymmetric postzygotic reproductive isolation in Allopatry.
Evolution; international journal of organic evolution, 2017Co-Authors: Hélène Martin, Pascal Touzet, Mathilde Dufay, Cécile Godé, Eric Schmitt, Emna Lahiani, Lynda F. Delph, Fabienne Van RossumAbstract:Reproductive isolation can rise either as a consequence of genomic divergence in Allopatry or as a byproduct of divergent selection in parapatry. To determine whether reproductive isolation in gynodioecious Silene nutans results from allopatric divergence or from ecological adaptation following secondary contact, we investigated the pattern of postzygotic reproductive isolation and hybridization in natural populations using two phylogeographic lineages, western (W1) and eastern (E1). Experimental crosses between the lineages identified strong, asymmetric postzygotic isolation between the W1 and the E1 lineages, independent of geographic overlap. The proportion of ovules fertilized, seeds aborted, and seeds germinated revealed relatively little effect on the fitness of hybrids. In contrast, hybrid mortality was high and asymmetric: while half of the hybrid seedlings with western lineage mothers died, nearly all hybrid seedlings with E1 mothers died. This asymmetric mortality mirrored the proportion of chlorotic seedlings, and is congruent with cytonuclear incompatibility. We found no evidence of hybridization between the lineages in regions of co-occurrence using nuclear and plastid markers. Together, our results are consistent with the hypothesis that strong postzygotic reproductive isolation involving cytonuclear incompatibilities arose in Allopatry. We argue that the dynamics of cytonuclear gynodioecy could facilitate the evolution of reproductive isolation.
Edmund D. Brodie - One of the best experts on this subject based on the ideXlab platform.
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toxicity and population structure of the rough skinned newt taricha granulosa outside the range of an arms race with resistant predators
Ecology and Evolution, 2016Co-Authors: Michael T J Hague, Charles T. Hanifin, Amber N. Stokes, Lelena A Avila, Andrew W Snedden, Edmund D. BrodieAbstract:: Species interactions, and their fitness consequences, vary across the geographic range of a coevolutionary relationship. This spatial heterogeneity in reciprocal selection is predicted to generate a geographic mosaic of local adaptation, wherein coevolutionary traits are phenotypically variable from one location to the next. Under this framework, allopatric populations should lack variation in coevolutionary traits due to the absence of reciprocal selection. We examine phenotypic variation in tetrodotoxin (TTX) toxicity of the Rough-Skinned Newt (Taricha granulosa) in regions of Allopatry with its TTX-resistant predator, the Common Garter Snake (Thamnophis sirtalis). In sympatry, geographic patterns of phenotypic exaggeration in toxicity and toxin-resistance are closely correlated in prey and predator, implying that reciprocal selection drives phenotypic variation in coevolutionary traits. Therefore, in Allopatry with TTX-resistant predators, we expect to find uniformly low levels of newt toxicity. We characterized TTX toxicity in northwestern North America, including the Alaskan panhandle where Ta. granulosa occur in Allopatry with Th. sirtalis. First, we used microsatellite markers to estimate population genetic structure and determine if any phenotypic variation in toxicity might be explained by historical divergence. We found northern populations of Ta. granulosa generally lacked population structure in a pattern consistent with northern range expansion after the Pleistocene. Next, we chose a cluster of sites in Alaska, which uniformly lacked genetic divergence, to test for phenotypic divergence in toxicity. As predicted, overall levels of newt toxicity were low; however, we also detected unexpected among- and within-population variation in toxicity. Most notably, a small number of individuals contained large doses of TTX that rival means of toxic populations in sympatry with Th. sirtalis. Phenotypic variation in toxicity, despite limited neutral genetic divergence, suggests that factors other than reciprocal selection with Th. sirtalis likely contribute to geographic patterns of toxicity in Ta. granulosa.
Karin S. Pfennig - One of the best experts on this subject based on the ideXlab platform.
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Why do species co-occur? A test of alternative hypotheses describing abiotic differences in sympatry versus Allopatry using spadefoot toads.
PloS one, 2012Co-Authors: Amanda J. Chunco, Todd Jobe, Karin S. PfennigAbstract:Areas of co-occurrence between two species (sympatry) are often thought to arise in regions where abiotic conditions are conducive to both species and are therefore intermediate between regions where either species occurs alone (Allopatry). Depending on historical factors or interactions between species, however, sympatry might not differ from Allopatry, or, alternatively, sympatry might actually be more extreme in abiotic conditions relative to Allopatry. Here, we evaluate these three hypothesized patterns for how sympatry compares to Allopatry in abiotic conditions. We use two species of congeneric spadefoot toads, Spea multiplicata and S. bombifrons, as our study system. To test these hypotheses, we created ecological niche models (specifically using Maxent) for both species to create a map of the joint probability of occurrence of both species. Using the results of these models, we identified three types of locations: two where either species was predicted to occur alone (i.e., Allopatry for S. multiplicata and Allopatry for S. bombifrons) and one where both species were predicted to co-occur (i.e., sympatry). We then compared the abiotic environment between these three location types and found that sympatry was significantly hotter and drier than the allopatric regions. Thus, sympatry was not intermediate between the alternative allopatric sites. Instead, sympatry occurred at one extreme of the conditions occupied by both species. We hypothesize that biotic interactions in these extreme environments facilitate co-occurrence. Specifically, hybridization between S. bombifrons females and S. multiplicata males may facilitate co-occurrence by decreasing development time of tadpoles. Additionally, the presence of alternative food resources in more extreme conditions may preclude competitive exclusion of one species by the other. This work has implications for predicting how interacting species will respond to climate change, because species interactions may facilitate survival in extreme habitats.