Threespine sticklebacks are a classic case of speciation caused by natural selection. Photo by wolfpix.This week at The Molecular Ecologist, my friend and collaborator Chris Smith writes, with two coauthors, about a new study simulating adaptive speciation in the face of gene flow, and the effects of linkage among genes involved in the adaptive divergence:
Models of speciation that involve ongoing gene flow remain controversial because gene flow is expected to homogenize differences between populations. However, genome-level effects may facilitate speciation with gene flow. For example, selection against immigrants may have the effect of reducing realized gene flow, even at loci that are not under divergent selection (Rundle & Nosil 2005). This global reduction in gene flow and increased divergence across the genome due to divergent selection is termed ‘Genome Hitchhiking’ (Feder et al. 2012). Genome hitchhiking may be enhanced by fitness epistasis – multiple loci interacting synergistically to cause reductions in fitness that are greater than selection acting on any one locus.
It turns out that speciation is more probable in models that don't treat genes like independently evolving beans in a beanbag, bearing out a classic criticism of simple speciation models made most prominently by Ernst Mayr. However, true linkage among the selected genes isn't necessary, either. All in all, this is an exciting new development for those of us who think natural selection might be important in forming new species, so you should definitely go read the whole thing.◼