Data from: The cost of reinforcement in Drosophila yakuba

When the ranges of two species overlap and the species can hybridize, some individuals may waste gametes on inviable or infertile hybrids. In these cases, enhanced reproductive isolation may evolve as a byproduct of selection against maladaptive hybridization in a process called reinforcement. On the slopes of the African island of São Tomé, Drosophila yakuba and its endemic sister species D. santomea have a well-demarcated hybrid zone. D. yakuba females from within this zone, but not from outside it, show an increase in gametic isolation from males of D. santomea. To understand why reinforced gametic isolation does not spread to the whole geographic range and stays confined to areas of secondary contact, we studied the associated costs of reinforced gametic isolation in D. yakuba by using a combination of natural collections and experimental evolution. We found that D. yakuba males from sympatric populations sire fewer progeny than allopatric males when the female involved in the mating is an allopatric female. The results here shown suggest that the advantageous nature of reinforcement in D. yakuba is local, as its associated costs (i.e., reduced male fertility) might prevent its dispersal outside the hybrid zone.

当两个物种的分布范围发生重叠且二者可发生杂交时，部分个体可能会将配子浪费在无法存活或不育的杂交后代上。在此类场景中，针对适应不良杂交的选择所产生的副产物，可能会演化出增强的生殖隔离，这一过程被称为强化作用（reinforcement）。
在非洲圣多美岛的山坡上，雅库巴果蝇（Drosophila yakuba）及其特有近缘物种圣多美果蝇（D. santomea）存在一个界限清晰的杂交带。该杂交带内的雅库巴果蝇雌蝇（而非杂交带外的个体），与圣多美果蝇雄蝇交配时的配子隔离程度有所提升。
为阐明强化的配子隔离为何未能扩散至整个地理分布范围，且仅局限于二次接触区域，我们结合自然采集与实验演化手段，对雅库巴果蝇中强化配子隔离的相关成本展开了研究。
我们发现，当交配对象为异地种群的雌蝇时，来自同域种群的雅库巴果蝇雄蝇所产生的后代数量，少于异地种群的雄蝇。
本研究结果表明，雅库巴果蝇中强化作用的优势仅具有局域性，其伴随的成本（即雄蝇育性下降）或可阻止该性状扩散出杂交带。