Data from: Correlated evolution of male and female reproductive traits drive a cascading effect of reinforcement in Drosophila yakuba

Selection against maladaptive hybridization can drive the evolution of reproductive isolation in a process called reinforcement. While the importance of reinforcement in evolution has been historically debated, many examples now exist. Despite these examples, we typically lack a detailed understanding of the mechanisms limiting the spread of reinforced phenotypes throughout a species' range. Here we address this issue in the fruit fly Drosophila yakuba, a species that hybridizes with its sister species D. santomea and is undergoing reinforcement in a well-defined hybrid zone on the island of São Tomé. Within this region, female D. yakuba show increased postmating-prezygotic (gametic) isolation towards D. santomea when compared with females from allopatric populations. We use a combination of natural collections, fertility assays, and experimental evolution to understand why reinforced gametic isolation in D. yakuba is confined to this hybrid zone. We show that, among other traits, D. yakuba males from sympatric populations sire fewer progeny than allopatric males when mated to allopatric D. yakuba females. Our results provide a novel example of reinforcement acting on a postmating-prezygotic trait in males, resulting in a cascade of reproductive isolation among conspecific populations.

对不适应杂交的选择可推动生殖隔离的演化，这一过程被称为强化（reinforcement）。尽管进化生物学界曾长期围绕强化的重要性展开争论，如今却已积累诸多实证案例。尽管存在这些案例，我们仍普遍缺乏对限制强化表型在物种分布范围内扩散的机制的详细认知。
本研究以雅库巴果蝇（Drosophila yakuba）为研究对象，该物种会与其姊妹物种圣多美果蝇（D. santomea）发生杂交，且在圣多美岛上一处特征明确的杂交带（hybrid zone）中正经历强化过程。在此区域内，与异域种群的雌性雅库巴果蝇相比，同域种群的雌性雅库巴果蝇在与圣多美果蝇交配时，展现出更强的交配后合子前（postmating-prezygotic，配子）生殖隔离。
我们结合自然种群采样、生育力实验（fertility assays）与实验进化（experimental evolution）手段，旨在阐明为何雅库巴果蝇中经强化演化的配子生殖隔离仅局限于该杂交带。研究发现，在诸多性状中，当与异域雌性雅库巴果蝇交配时，同域种群的雄性雅库巴果蝇所产生的后代数量少于异域雄性。我们的研究结果提供了全新案例：强化作用于雄性的交配后合子前性状，进而导致同物种种群间出现连锁的生殖隔离效应。