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Strong selection on male plumage in a hybrid zone between a hybrid bird species and one of its parents
Author(s) -
Bailey R. I.,
Tesaker M. R.,
Trier C. N.,
Sætre G.P.
Publication year - 2015
Publication title -
journal of evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.289
H-Index - 128
eISSN - 1420-9101
pISSN - 1010-061X
DOI - 10.1111/jeb.12652
Subject(s) - biology , plumage , cline (biology) , hybrid zone , introgression , sparrow , reproductive isolation , hybrid , evolutionary biology , zoology , assortative mating , sexual selection , genetics , genetic variation , gene flow , mating , population , demography , gene , botany , sociology
Homoploid hybrid speciation ( HHS ) requires reproductive barriers between hybrid and parent species, despite incomplete reproductive isolation ( RI ) between the parents. Novel secondary sexual trait values in hybrids may cause prezygotic isolation from both parents, whereas signals inherited by the hybrid from one parent species may cause prezygotic isolation with the other. Here we investigate whether differences in male plumage function as a premating barrier between the hybrid Italian sparrow and one of its parent species, the house sparrow, in a narrow Alpine hybrid zone. Italian sparrow male plumage is a composite mosaic of the parental traits, with its head plumage most similar to its other parent, the Spanish sparrow. We use geographical cline analysis to examine selection on three plumage traits, 75 nuclear single nucleotide polymorphisms ( SNP s) and hybrid indices based on these SNP s. Several SNP s showed evidence of restricted introgression in the Alps, supporting earlier findings. Crown colour exhibited the narrowest plumage cline, representing a 37% (range 4–65%) drop in fitness. The cline was too narrow to be due to neutral introgression. Only crown colour was significantly bimodal in the hybrid zone. Bimodality may be due to RI or a major QTL , although fitness estimates suggest that selection contributes to the pattern. We discuss the implications with respect to HHS and the species status of the Italian sparrow.

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