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Sexual isolation promotes divergence between parapatric lake and stream stickleback
Author(s) -
Berner D.,
Ammann M.,
Spencer E.,
Rüegg A.,
Lüscher D.,
Moser D.
Publication year - 2017
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.13016
Subject(s) - biology , reproductive isolation , ecotype , stickleback , assortative mating , ecological speciation , parapatric speciation , ecology , mating , gene flow , gasterosteus , population , sexual selection , genetic algorithm , habitat , zoology , evolutionary biology , fishery , genetic variation , fish <actinopterygii> , biochemistry , demography , sociology , gene
Speciation can be initiated by adaptive divergence between populations in ecologically different habitats, but how sexually based reproductive barriers contribute to this process is less well understood. We here test for sexual isolation between ecotypes of threespine stickleback fish residing in adjacent lake and stream habitats in the Lake Constance basin, Central Europe. Mating trials exposing females to pairings of territorial lake and stream males in outdoor mesocosms allowing for natural reproductive behaviour reveal that mating occurs preferentially between partners of the same ecotype. Compared to random mating, this sexual barrier reduces gene flow between the ecotypes by some 36%. This relatively modest strength of sexual isolation is surprising because comparing the males between the two ecotypes shows striking differentiation in traits generally considered relevant to reproductive behaviour (body size, breeding coloration, nest size). Analysing size differences among the individuals in the mating trials further indicates that assortative mating is not related to ecotype differences in body size. Overall, we demonstrate that sexually based reproductive isolation promotes divergence in lake–stream stickleback along with other known reproductive barriers, but we also caution against inferring strong sexual isolation from the observation of strong population divergence in sexually relevant traits.