The role of gene expression in ecological speciation.
Bottom Line: Gene expression may be associated with ecologically important phenotypes not evident from morphology and play a role during colonization of new environments.We also find clear examples of gene expression having effects on phenotypic traits and adaptive genetic divergence, but links to the evolution of reproductive isolation itself remain indirect.The study of gene expression has promise for increasing our understanding ecological speciation, particularly when integrative approaches are applied.
Affiliation: Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada.Show MeSH
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Mentions: Darwin's finches arose via adaptive radiation on the Galapagos Islands.138 Beak morphology diverged adaptively among populations and species in response to divergent selection stemming from competition and use of seeds of differing size and hardness.139,140 Beak morphology might also contribute to reproductive isolation via song divergence141 or due to selection against immigrants and (intermediate) hybrids.142,143 Among species, higher levels of the bone morphogenetic protein 4 (Bmp4) expression are correlated with deeper beak shapes and over-expression of Bmp4 in chick embryos altered beak development in the predicted direction.144 These results provide compelling evidence that gene expression variation from Bmp4 affects morphological divergence among species of Darwin's finches (Fig. 3). Similar results occur for another gene, calmodulin (CaM145). However, due to a lack of common garden or mapping studies, there is as of yet no evidence that heritable differences in beak morphology are affected by Bmp4 or CaM. The mutations underlying beak size differences in Darwin's finches have not been identified. Thus, although there is good evidence that regulatory changes underlie morphological divergence among species of Darwin's finches, the ultimate link between gene expression and genetically based reproductive isolation (= speciation) is yet to be made.
Affiliation: Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada.