Sexual isolation promotes divergence between parapatric lake and stream stickleback

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 in outdoor mesocosms allowing for natural reproductive behavior reveal that mating occurs preferentially between partners of the same than of the opposed 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 behavior (body size, breeding coloration, nest size). Analyzing size differences among the individuals in the mating trials further indicates ...

物种形成可由栖息于不同生态环境的种群间的适应性分化所启动，但基于性别的生殖障碍如何助力该过程，目前仍未得到充分阐释。本研究针对中欧康斯坦茨湖盆地（Lake Constance basin）内栖息于相邻湖泊与溪流生境的三棘刺鱼（threespine stickleback）生态型（ecotype）间的性隔离展开检验。在可允许自然生殖行为发生的室外中型实验生态系统（outdoor mesocosms）中开展的交配实验表明，相较于异种生态型个体，交配更倾向于发生在同种生态型的配对个体之间。与随机交配相比，该性隔离可使不同生态型间的基因流降低约36%。这一性隔离强度相对较弱的结果颇为出人意料，因为对比两种生态型的雄性个体可见，其在通常被认为与生殖行为相关的性状（体型、繁殖体色、巢尺寸）上存在显著分化。对交配实验中个体间体型差异的进一步分析显示……