The genomic landscape underlying phenotypic integrity in the face of gene flow in crows

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Science  20 Jun 2014:
Vol. 344, Issue 6190, pp. 1410-1414
DOI: 10.1126/science.1253226

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Crows of a feather flock together

Closely related species with overlapping ranges typically evolve genetic barriers to prevent crossbreeding. Poelstra et al. sequenced genes from two species of central European crows: gray-bodied hooded crows and black carrion crows (see the Perspective by de Knijff). Although most of the genomes shared genes between the two species, one region that affected coat color and color vision differed. The authors suggest that black and gray-coated crows prefer to mate with birds like themselves.

Science, this issue p. 1410; see also p. 1345


The importance, extent, and mode of interspecific gene flow for the evolution of species has long been debated. Characterization of genomic differentiation in a classic example of hybridization between all-black carrion crows and gray-coated hooded crows identified genome-wide introgression extending far beyond the morphological hybrid zone. Gene expression divergence was concentrated in pigmentation genes expressed in gray versus black feather follicles. Only a small number of narrow genomic islands exhibited resistance to gene flow. One prominent genomic region (<2 megabases) harbored 81 of all 82 fixed differences (of 8.4 million single-nucleotide polymorphisms in total) linking genes involved in pigmentation and in visual perception—a genomic signal reflecting color-mediated prezygotic isolation. Thus, localized genomic selection can cause marked heterogeneity in introgression landscapes while maintaining phenotypic divergence.

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