Evidence for Ecological Speciation and Its Alternative

Biodiversity Research Centre and Zoology Department, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Science (Impact Factor: 33.61). 03/2009; 323(5915):737-41. DOI: 10.1126/science.1160006
Source: PubMed


Natural selection commonly drives the origin of species, as Darwin initially claimed. Mechanisms of speciation by selection fall into two broad categories: ecological and mutation-order. Under ecological speciation, divergence is driven by divergent natural selection between environments, whereas under mutation-order speciation, divergence occurs when different mutations arise and are fixed in separate populations adapting to similar selection pressures. Tests of parallel evolution of reproductive isolation, trait-based assortative mating, and reproductive isolation by active selection have demonstrated that ecological speciation is a common means by which new species arise. Evidence for mutation-order speciation by natural selection is more limited and has been best documented by instances of reproductive isolation resulting from intragenomic conflict. However, we still have not identified all aspects of selection, and identifying the underlying genes for reproductive isolation remains challenging.

Download full-text


Available from: Dolph Schluter, Oct 10, 2015
104 Reads
  • Source
    • "Adaptive divergence is thought to proceed as a balance between divergent selection and homogenizing gene flow (Levene 1953; Hagen 1967; Endler 1973; Bell 1982) and hence may reach various stages. This has long been recognized at the phenotypic level (Tregenza 2002; Moore et al. 2007; Hendry 2009; Schluter 2009). More recently, theoretical and empirical studies have improved our understanding of the genomic architecture at various stages of adaptation as well (Pinho and Hey 2010; Yeaman and Otto 2011; Yeaman and Whitlock 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Local adaptation is often obvious when gene flow is impeded, such as observed at large spatial scales and across strong ecological contrasts. However, it becomes less certain at small scales such as between adjacent populations or across weak ecological contrasts, when gene flow is strong. While studies on genomic adaptation tend to focus on the former, less is known about the genomic targets of natural selection in the latter situation. In this study, we investigate genomic adaptation in populations of the three-spined stickleback Gasterosteus aculeatus L. across a small-scale ecological transition with salinities ranging from brackish to fresh. Adaptation to salinity has been repeatedly demonstrated in this species. A genome scan based on 87 microsatellite markers revealed only few signatures of selection, likely owing to the constraints that homogenizing gene flow puts on adaptive divergence. However, the detected loci appear repeatedly as targets of selection in similar studies of genomic adaptation in the three-spined stickleback. We conclude that the signature of genomic selection in the face of strong gene flow is weak, yet detectable. We argue that the range of studies of genomic divergence should be extended to include more systems characterized by limited geographical and ecological isolation, which is often a realistic setting in nature.
    Ecology and Evolution 09/2015; 5(18). DOI:10.1002/ece3.1671 · 2.32 Impact Factor
  • Source
    • "Recent studies using multilocus data provide increasing evidence that divergent selection is more common than previously thought (Rundle and Nosil 2005; Schluter and Conte 2009; Via 2012; Shafer and Wolf 2013). Divergent selection reduces overall gene flow between populations, leading to a pattern of isolation by environment (IBE), which can eventually affect all loci and result in ecological speciation (Nordborg and Innan 2002; Nosil et al. 2009; Schluter 2009; Strasburg et al. 2012; Orsini et al. 2013; Shafer and Wolf 2013). However, when speciation is incomplete, divergent selection would only act on particular areas of the genome, resulting in mosaic patterns of genetic differentiation, where different parts of the genome will show different degrees of genetic differentiation between incipient species (Via and West 2008; Via 2012; Feder et al. 2014). "
    [Show abstract] [Hide abstract]
    ABSTRACT: We explored the role of isolation by environment in a white pine species complex: Pinus flexilis, Pinus strobiformis and Pinus ayacahuite distributed from Canada to Central America. We predict that species differentiation would match genetic structure of candidate genes associated with significant differences in climatic niche in the species complex. To test this prediction, we sequenced five candidate genes for drought tolerance and three housekeeping genes, in individuals from across the entire range of each species. We performed neutrality tests, estimated genetic differentiation and performed partial mantel correlations, to test for isolation by environment in the species complex. Our results show that different loci vary in degrees of genetic differentiation within species and contrast in patterns of differentiation among species. This is considered to be a mosaic pattern of genetic differentiation. There was also significant isolation by environment in candidate genes. P. flexilis was genetically differentiated for candidate genes and P. ayacahuite for housekeeping genes. There was also an overall pattern of shared ancestral polymorphism followed by independent evolution. Nonetheless, all loci together recovered groups that correspond to the recognized taxonomy. In conclusion, the pattern of isolation by environment in candidate genes support the idea of ecologically driven differentiation of this species complex, especially in the case of P. flexilis. The observed difference in housekeeping genes between P. strobiformis and P. ayacahuite can be due to limited gene flow. The mosaic pattern of differentiation suggests that speciation is recent and ecological differences could be a factor in the diversification of pines in North America.
    Evolutionary Ecology 08/2015; DOI:10.1007/s10682-015-9785-4 · 2.52 Impact Factor
  • Source
    • "In addition to sexual dimorphism, classic work has shown that color divergence can be caused by adaptation to local environments to optimize camouflage and sexual signaling (Endler 1978, 1980). More recent advances have demonstrated that, under certain conditions, distinct local environments driving intraspecific diversification in camouflage and sexual signals can lead to reproductive isolation among populations (reviewed in Boughman 2002; Schluter 2009; Stevens 2013). Although many studies assume that conspicuous coloration is costly to survival, surprisingly few have directly tested whether it does increase the risk of attack from predators across varying local environments, instead relying on measurements of relative degrees of matching against different backgrounds (e.g., Rosenblum et al. 2004; Stuart-Fox et al. 2004; Hoekstra et al. 2005; Rosenblum 2006; Rosenblum et al. 2010; Marshall and Stevens 2014; McLean et al. 2014; but see for example Vignieri et al. 2010). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Animal coloration is strikingly diverse in nature. Within-species color variation can arise through local adaptation for camouflage, sexual dimorphism and conspicuous sexual signals, which often have conflicting effects on survival. Here, we tested whether color variation between two island populations of Aegean wall lizards (Podarcis erhardii) is due to sexual dimorphism and differential survival of individuals varying in appearance. On both islands, we measured attack rates by wild avian predators on clay models matching the coloration of real male and female P. erhardii from each island population, modeled to avian predator vision. Avian predator attack rates differed among model treatments, although only on one island. Male-colored models, which were more conspicuous against their experimental backgrounds to avian predators, were accordingly detected and attacked more frequently by birds than less conspicuous female-colored models. This suggests that female coloration has evolved primarily under selection for camouflage, whereas sexually competing males exhibit costly conspicuous coloration. Unexpectedly, there was no difference in avian attack frequency between local and non-local model types. This may have arisen if the models did not resemble lizard coloration with sufficient precision, or if real lizards behaviorally choose backgrounds that improve camouflage. Overall, these results show that sexually dimorphic coloration can affect the risk of predator attacks, indicating that color variation within a species can be caused by interactions between natural and sexual selection. However, more work is needed to determine how these findings depend on the island environment that each population inhabits.
    Ecology and Evolution 07/2015; 5(18). DOI:10.1002/ece3.1650 · 2.32 Impact Factor
Show more