- NSF-PAR ID:
- 10399608
- Date Published:
- Journal Name:
- Evolution
- Volume:
- 77
- Issue:
- 2
- ISSN:
- 1558-5646
- Page Range / eLocation ID:
- 437-453
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Isolation by environment (IBE) is a population genomic pattern that arises when ecological barriers reduce gene flow between populations. Although current evidence suggests IBE is common in nature, few studies have evaluated the underlying mechanisms that generate IBE patterns. In this study, we evaluate five proposed mechanisms of IBE (natural selection against immigrants, sexual selection against immigrants, selection against hybrids, biased dispersal, environment-based phenological differences) that may give rise to host-associated differentiation within a sympatric population of the redheaded pine sawfly, Neodiprion lecontei, a species for which IBE has previously been detected. We first characterize the three pine species used by N. lecontei at the site, finding morphological and chemical differences among the hosts that could generate divergent selection on sawfly host-use traits. Next, using morphometrics and ddRAD sequencing, we detect modest phenotypic and genetic differentiation among sawflies originating from different pines that is consistent with recent, in situ divergence. Finally, via a series of laboratory assays – including assessments of larval performance on different hosts, adult mate and host preferences, hybrid fitness, and adult eclosion timing – we find evidence that multiple mechanisms contribute to IBE in N. lecontei. Overall, our results suggest IBE can emerge quickly, possibly due to multiple mechanisms acting in concert to reduce migration between different environments.more » « less
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Abstract Speciation is facilitated by “magic traits,” where divergent natural selection on such traits also results in assortative mating. In animal populations, diet has the potential to act as a magic trait if populations diverge in consumed food that incidentally affects mating and therefore sexual isolation. While diet‐based assortative mating has been observed in the laboratory and in natural populations, the mechanisms causing positive diet‐based assortment remain largely unknown. Here, we experimentally created divergent diets in a sexually imprinting species of mouse,
Peromyscus gossypinus (the cotton mouse), to test the hypothesis that sexual imprinting on diet could be a mechanism that generates rapid and significant sexual isolation. We provided breeding pairs with novel garlic‐ or orange‐flavored water and assessed whether their offspring, exposed to these flavors in utero and in the nest before weaning, later preferred mates that consumed the same flavored water as their parents. While males showed no preference, females preferred males of their parental diet, which is predicted to yield moderate sexual isolation. Thus, our experiment demonstrates the potential for sexual imprinting on dietary cues learned in utero and/or postnatally to facilitate reproductive isolation and potentially speciation.Open Research Badges This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available at
https://doi.org/10.5061/dryad.n1qq6v3 . -
Abstract Divergent host use has long been suspected to drive population differentiation and speciation in plant‐feeding insects. Evaluating the contribution of divergent host use to genetic differentiation can be difficult, however, as dispersal limitation and population structure may also influence patterns of genetic variation. In this study, we use double‐digest restriction‐associated
DNA (ddRAD ) sequencing to test the hypothesis that divergent host use contributes to genetic differentiation among populations of the redheaded pine sawfly (Neodiprion lecontei ), a widespread pest that uses multiplePinus hosts throughout its range in eastern North America. Because this species has a broad range and specializes on host plants known to have migrated extensively during the Pleistocene, we first assess overall genetic structure using model‐based and model‐free clustering methods and identify three geographically distinct genetic clusters. Next, using a composite‐likelihood approach based on the site frequency spectrum and a novel strategy for maximizing the utility of linkedRAD markers, we infer the population topology and date divergence to the Pleistocene. Based on existing knowledge ofPinus refugia, estimated demographic parameters and patterns of diversity among sawfly populations, we propose a Pleistocene divergence scenario forN. lecontei . Finally, using Mantel and partial Mantel tests, we identify a significant relationship between genetic distance and geography in all clusters, and between genetic distance and host use in two of three clusters. Overall, our results indicate that Pleistocene isolation, dispersal limitation and ecological divergence all contribute to genomewide differentiation in this species and support the hypothesis that host use is a common driver of population divergence in host‐specialized insects. -
Premise Divergence depends on the strength of selection and frequency of gene flow between taxa, while reproductive isolation relies on mating barriers and geographic distance. Less is known about how these processes interact at early stages of speciation. Here, we compared population‐level differentiation in floral phenotype and genetic sequence variation among recently diverged
Castilleja to explore patterns of diversification under different scenarios of reproductive isolation.Methods Using target enrichment enabled by the Angiosperms353 probe set, we assessed genetic distance among 50 populations of four
Castilleja species. We investigated whether patterns of genetic divergence are explained by floral trait variation or geographic distance in two focal groups: the widespreadC. sessiliflora and the more restrictedC. purpurea species complex.Results We document that
C. sessiliflora and theC. purpurea complex are characterized by high diversity in floral color across varying geographic scales. Despite phenotypic divergence, groups were not well supported in phylogenetic analyses, and little genetic differentiation was found across targeted Angiosperms353 loci. Nonetheless, a principal coordinate analysis of single nucleotide polymorphisms revealed differentiation withinC. sessiliflora across floral morphs and geography and less differentiation among species of theC. purpurea complex.Conclusions Patterns of genetic distance in
C. sessiliflora suggest species cohesion maintained over long distances despite variation in floral traits. In theC. purpurea complex, divergence in floral color across narrow geographic clines may be driven by recent selection on floral color. These contrasting patterns of floral and genetic differentiation reveal that divergence can arise via multiple eco‐evolutionary paths. -
Abstract The genetic architecture of local adaptation has been of central interest to evolutionary biologists since the modern synthesis. In addition to classic theory on the effect size of adaptive mutations by Fisher, Kimura and Orr, recent theory addresses the genetic architecture of local adaptation in the face of ongoing gene flow. This theory predicts that with substantial gene flow between populations local adaptation should proceed primarily through mutations of large effect or tightly linked clusters of smaller effect loci. In this study, we investigate the genetic architecture of divergence in flowering time, mating system‐related traits, and leaf shape between
Mimulus laciniatus and a sympatric population of its close relativeM. guttatus . These three traits are probably involved inM. laciniatus’ adaptation to a dry, exposed granite outcrop environment. Flowering time and mating system differences are also reproductive isolating barriers making them ‘magic traits’. Phenotypic hybrids in this population provide evidence of recent gene flow. Using next‐generation sequencing, we generate denseSNP markers across the genome and map quantitative trait loci (QTL s) involved in flowering time, flower size and leaf shape. We find that interspecific divergence in all three traits is due to fewQTL of large effect including a highly pleiotropicQTL on chromosome 8. ThisQTL region contains the pleiotropic candidate gene TCP4 and is involved in ecologically important phenotypes in otherMimulus species. Our results are consistent with theory, indicating that local adaptation and reproductive isolation with gene flow should be due to few loci with large and pleiotropic effects.