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,
  • Source
    • "Th e rarity of dispersal events would lead to isolation of small populations of siblings for long periods until subsequent dispersal events or range shift s due to climate cycles (see Hotchkiss and Juvik, 1999 ) cause sympatry of morphologically diverged populations (i.e., species ). Under this model, geographic isolation of populations would lead to genetic and phenotypic divergence through the accumulation of novel mutations independently in each population, and by natural selection and/or genetic drift ( Mayr, 1942 , 1963 ; Turelli et al., 2001 ; Gavrilets, 2004 ; Schluter, 2009 ). Reproductive barriers between geographically isolated populations would then arise as a byproduct of divergence ( Dobzhansky, 1936 ; Rice and Hostert, 1993 ; Schluter, 2001 ; Turelli et al., 2001 ). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Premise of the study: Recent reviews of reproductive isolation (RI) in plants propose that boundaries between closely related species are maintained predominantly through prezygotic mechanisms. However, few experimental studies have explored how boundaries are maintained in long-lived species. Hawaiian Cyrtandra presents an intriguing challenge to our understanding of RI, as it comprises 60 shrub or small tree species that are almost exclusively restricted to wet forests, where sympatry of multiple species is common. Methods: We assessed the relative strengths of pre- and postzygotic barriers among four species of Cyrtandra occurring at the extremes of the main Hawaiian Island's natural island-age gradient, Kaua'i (4.7 Myr) and Hawai'i Island (0.6 Myr), to contrast the strengths and stages of reproductive isolation among species at different stages of divergence. Key results: A combination of F1 seed germination, F1 seedling survival, and F1 seedling growth isolated (61-91%) three of the species from sympatric relatives. In contrast, the fourth species was isolated (59%) from its sympatric relative through phenological differences alone. Significant postzygotic barriers in between-island crosses were also observed in one species. Conclusions: Results suggest that boundaries between sympatric Cyrtandra species in Hawaii are maintained predominantly through postzygotic barriers. Observations from between-island crosses indicate that postzygotic barriers can arise in allopatry, which may be important in the initial divergence of populations. Future studies of RI in Cyrtandra should include a broader range of species to determine if postzygotic isolating barriers are foremost in the maintenance of species boundaries in this large genus.
    American Journal of Botany 11/2015; DOI:10.3732/ajb.1500288 · 2.60 Impact Factor
  • Source
    • "Rapid species diversification has been attributed to a few key causes, including selection on ecologically relevant traits (Grant and Grant 2008; Gavrilets and Losos 2009; Schluter 2009) and evolution of social signaling traits, which are involved in inter-and intraspecific interactions (Masta and Maddison 2002; Mendelson and Shaw 2005; Maia et al. 2013). However, singular forms of selection may not be able to drive speciation to completion (Nosil et al. 2009; Servedio and Bürger 2014). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Species diversification often results from divergent evolution of ecological or social signaling traits. Theoretically, a combination of the two may promote speciation, however, empirical examples studying how social signal and ecological divergence might be involved in diversification are rare in general and typically do not consider range overlap as a contributing factor. We show that ecologically distinct lineages within the Australian sand dragon species complex (including Ctenophorus maculatus, Ctenophorus fordi, and Ctenophorus femoralis) have diversified recently, diverging in ecologically relevant and social signaling phenotypic traits as arid habitats expanded and differentiated. Diversification has resulted in repeated and independent invasion of distinct habitat types, driving convergent evolution of similar phenotypes. Our results suggest that parapatry facilitates diversification in visual signals through reinforcement as a hybridization-avoidance mechanism. We show that particularly striking variation in visual social signaling traits is better explained by the extent of lineage parapatry relative to ecological or phylogenetic divergence, suggesting that these traits reinforce divergence among lineages initiated by ecologically adaptive evolution. This study provides a rare empirical example of a repeated, intricate relationship between ecological and social signal evolution during diversification driven by ecological divergence and the evolution of new habitats, thereby supporting emergent theories regarding the importance of both ecological and social trait evolution throughout speciation.
  • Source
    • "A key issue in macroevolution is how ecology affects speciation and extinction to generate differences in species richness among clades (Schluter 2009). Ecological opportunity is a key potential part of this relationship, and refers to how niche space constrains the richness of clades using these niches (Valentine 1980; Wellborn and Langerhans 2015). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Hexapoda, the insects and their relatives, includes over half of all described species. Because large proportions of this diversity cluster within a small set of phytophagous groups, dietary substrates have been proposed to shape patterns of richness within the clade through antagonistic coevolution and zones of ecological opportunity. Here we explore these processes in the context of a recent dated phylogeny of Hexapod families. Our results indicate phylogenetic clustering of specialized ecologies, such as phytophagy and parasitism, but reveal no consistent associations between the use of particular dietary substrates and clade richness. We also find no evidence that diets expected to promote antagonistic coevolution are consistently associated with elevated species richness or that sister clades differing in dietary state are associated with greater-than-expected differences in richness. We do, however, identify variation in the age of, and transition rates among, dietary states that are likely to play a role in the observed heterogeneity in richness among dietary classes. Based on these findings, we suggest remaining circumspect about the generality of adaptive zones based on broad dietary groupings as an explanation for hexapod richness and suggest that richness heterogeneity may be better explained by origination and transitions rates as well as variation within dietary categories.
    The American Naturalist 10/2015; 186(6). DOI:10.1086/683461 · 3.83 Impact Factor
Show more