Data from: 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 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 also caution against inferring strong sexual isolation from the observation of strong population divergence in sexually relevant traits.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这一过程，目前仍未得到充分阐释。本研究针对中欧康斯坦茨湖流域相邻湖泊与溪流生境中的三棘刺鱼（threespine stickleback）生态型之间的性隔离展开检验。在可模拟自然繁殖行为的室外中型实验生态系统（mesocosms）中开展的交配试验显示，相较于不同生态型的个体，试验对象更倾向于与同生态型的配偶进行交配。与随机交配相比，这类性障碍可使两种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后发现，二者在诸多通常被认为与繁殖行为相关的性状（体型、繁殖色、巢穴大小）上均存在显著分化。通过对交配试验中个体体型差异的分析进一步证实，选型交配（assortative mating）与生态型间的体型差异并无关联。综上，本研究证实，基于性别的生殖障碍与其他已知生殖障碍共同推动了湖溪生境三棘刺鱼的种群分化，但同时也提醒学界，切勿仅凭与繁殖相关性状的显著种群分化，就推断其对应的性隔离强度同样强劲。