Genomic divergence during speciation: causes and consequences

Abstract

Speciation is a fundamental process responsible for the diversity of life. Progress has been made in detecting individual 'speciation genes' that cause reproductive isolation. In contrast, until recently, less attention has been given to genome-wide patterns of divergence during speciation. Thus, major questions remain concerning how individual speciation genes are arrayed within the genome, and how this affects speciation. This theme issue is dedicated to exploring this genomic perspective of speciation. Given recent sequencing and computational advances that now allow genomic analyses in most organisms, the goal is to help move the field towards a more integrative approach. This issue draws upon empirical studies in plants and animals, and theoretical work, to review and further document patterns of genomic divergence. In turn, these studies begin to disentangle the role that different processes, such as natural selection, gene flow and recombination rate, play in generating observed patterns. These factors are considered in the context of how genomes diverge as speciation unfolds, from beginning to end. The collective results point to how experimental work is now required, in conjunction with theory and sequencing studies, to move the field from descriptive studies of patterns of divergence towards a predictive framework that tackles the causes and consequences of genome-wide patterns.

Figure 1.

Schematic of the (a) island versus (b) continent views of genomic divergence. These views represent ends of a continuum, rather than mutually exclusive hypotheses. For example, ‘continents’ of divergence can be conceptualized as very large islands with variable topography. Outlier status refers to whether a locus would exhibit statistical evidence for unusually high levels of genetic differentiation in an observational genome scan. See text for details. Reproduced with permission from Michel et al. [49], National Academy of Sciences USA.

Figure 2.

A diagrammatic depiction of how integrative approaches might yield an understanding of the ‘natural history of the genome’, and of how speciation and genomic divergence unfolds over time. RI, reproductive isolation (note that further work on the relationship between divergence and RI is sorely needed) [38].