Evolution

Not Continental Drift

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Science  04 Jun 2010:
Vol. 328, Issue 5983, pp. 1209
DOI: 10.1126/science.328.5983.1209-a
CREDIT: ANDREW FORBES

A number of genes that have been identified among different species and habitats may be drivers of sympatric speciation—that is, speciation occurring within a population without physical isolation. These genes are generally believed to cause population-level divergence under strong selection, and hence it is expected that closely linked genes will experience genetic separation, resulting in “genomic islands” of divergence. However, in light of ongoing gene flow, the remaining genomic landscape is expected to remain relatively homogenous.

Michel et al. tested this hypothesis in a model organism for sympatric speciation, Rhagoletis flies, that utilize different host species—apple versus hawthorn flies, diverging approximately 150 years ago. Surveying the genomes of apple and hawthorn flies across a latitudinal gradient and mimicking natural conditions inducing diapause and eclosion, the authors found that large portions of the genome are divergent and are not merely islands linked to the putative drivers of divergence. Based on these results, they conclude that loci located throughout the genome are under selection and that these differences are not due to genetic drift. This supports the view that genomic continents of divergence may occur even during early stages of speciation.

Proc. Natl. Acad. Sci. U.S.A. 107, 10.1073/pnas.1000939107 (2010).

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