Editorial Ecological speciation: Selection and the origin of species

The past 20 years have seen a renaissance in the study of speciation. At the core of this research endeavor is the study of ecological speciation, and substantial evidence has been marshaled revealing that much of the world's biodiversity arises through this process (Seehausen, 2006; Schluter, 2009). Ecological speciation comes about when selection that differs between contrasting environments causes the evolution of reproductive isolation. One of the surprises has been the realization that reproductive isolation can evolve very rapidly, even within tens or hundreds of generations (Hendry et al. 2007). Another key finding is that ecological speciation often proceeds only partway, creating partially isolated species (Nosil et al. 2009). What determines whether it goes to completion? Moreover, its dependence on the environment makes it vulnerable to environmental change, which can actually reverse the speciation process (Taylor et al., 2006; Vonlanthen et al., 2012). Thus, ecological speciation is front and center in our understanding of how the massive ecological changes caused by humans might affect biodiversity and the fabric of life. Ecological speciation is clearly a dynamic evolutionary process. The study of speciation in action has already given us a window on how species are created, revealing the nature of selection driving speciation and the genetic underpinnings of divergent adaptation. This special column on Ecological Speci-ation brings together scientists working on fundamental questions about the creation of biodiversity. A problematic issue for ecological speciation is whether it can proceed in the face of gene flow, because recombination will disrupt the correlation between traits that are divergent adaptations and those that confer reproductive isolation. Thus, much recent work has fo-cused on identifying mechanisms to enhance such correlations , including correlational selection and aspects of genetic architecture such as pleiotropy, physical linkage, and inversions. Several of the papers in the special column explore these points from different perspectives (Podos and colleagues, Hardwick and colleagues , and Rogers and colleagues). Traits that are divergent adaptations and also generate assortative mating can overcome the problem very effectively because they automatically cause reproductive isolation and avoid the problem of recombination. Such traits have been dubbed 'magic traits' (Gavrilets, 2004). Whether they have special properties or commonly facilitate speciation is controversial (Servedio et al., 2011). Two papers in the special column (Podos and colleagues and Hardwick and colleagues) explore mechanisms to connect adaptation and assorative mating. Direct comparisons of magic and non-magic traits in speciation has not …