Abstract
Analyses of genomewide polymorphism data have begun to shed light on speciation and adaptation. Genome scans to identify regions of the genome that are unusually different between populations or species, possibly due to divergent natural or sexual selection, are widespread in speciation genomics. Theoretical and empirical work suggests that such outlier regions may grow faster than linearly during speciation with gene flow due to a rapid transition between low and high reproductive isolation. We investigate whether this pattern could be attributed to neutral processes by simulating genomes under neutral evolution with varying amounts and timing of gene flow. Under both neutral evolution and divergent selection, simulations with little or no gene flow, or with a long allopatric period after its cessation, resulted in faster than linear growth of the proportion of the genome lying in outlier regions. Without selection, higher recent gene flow erased differentiation; with divergent selection, these same scenarios produced nonlinear growth to a plateau. Our results suggest that, given a history of gene flow, the growth of the divergent genome is informative about selection during divergence, but that in many scenarios, this pattern does not easily distinguish neutral and non‐neutral processes during speciation with gene flow.
Highlights
Speciation is responsible for the diversity of life on earth, and understanding its mechanisms is of great interest to evolutionary biologists
Namely those tightly linked to loci causing reproductive isolation between occasionally hybridizing taxa, may be especially resistant to gene flow, while unlinked neutral differences introgress between species
Flaxman et al (2014) predicted speciation in Heliconius to proceed without such a nonlinear transition, because it often involves few genes of large effect (Kronforst & Papa, 2015; Nadeau et al, 2012). To explore whether this faster than linear increase could be produced by processes other than selection interacting with gene flow, we simulated neutral evolution in allopatry and compared it to various scenarios of speciation with gene flow and selection and to Kronforst et al.’s (2013) results for Heliconius
Summary
Speciation is responsible for the diversity of life on earth, and understanding its mechanisms is of great interest to evolutionary biologists. To explore whether this faster than linear increase could be produced by processes other than selection interacting with gene flow, we simulated neutral evolution in allopatry and compared it to various scenarios of speciation with gene flow and selection and to Kronforst et al.’s (2013) results for Heliconius.
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