Data from: A maladaptive combination of traits contributes to the maintenance of a Drosophila hybrid zone

Drosophila teissieri and D. yakuba diverged approximately 3 mya and are thought to share a large, ancestral, African range [1, 2, 3]. These species now co-occur in parts of continental Africa and in west Africa on the island of Bioko [1, 4]. While D. yakuba is a human commensal, D. teissieri seems to be associated with Parinari fruits, restricting its range to forests [4, 5, 6]. Genome data indicate introgression, despite no evidence of contemporary hybridization. Here we report the discovery of D. yakuba-D. teissieri hybrids at the interface of secondary forests and disturbed, open habitats on Bioko. We demonstrate that hybrids are the F1 progeny of D. yakuba females and D. teissieri males. At high temperatures like those found on Bioko, D. teissieri females are generally less receptive to mating, and in combination with temperature effects on egg lay and egg-to-adult viability, this decreases the potential for gene flow between female D. teissieri and male D. yakuba relative to the reciprocal cross. Field and laboratory experiments demonstrate that F1 hybrids have a maladaptive combination of D. yakuba behavior and D. teissieri physiology, generating additional barriers to gene flow. Nevertheless, analysis of introgressed and non-introgressed regions of the genome indicate that, while rare, gene flow is relatively recent. Our observations identify precise intrinsic and extrinsic factors that, along with hybrid male sterility, limit gene flow and maintain these species. These data contribute to a growing body of literature that suggests the Gulf of Guinea may be a hotspot for hybridization.

泰氏果蝇（Drosophila teissieri）与雅库巴果蝇（Drosophila yakuba）约于300万年前发生分化，被认为拥有共同的广阔祖先非洲分布范围[1,2,3]。目前这两个物种在非洲大陆部分区域以及西非的比奥科岛同域分布[1,4]。尽管雅库巴果蝇为人类共生物种，但泰氏果蝇似乎与巴榄仁属（Parinari）果实相关联，其分布范围仅局限于森林生境[4,5,6]。尽管尚无当代杂交的直接证据，但基因组数据显示二者存在基因渐渗（introgression）。本研究报道了在比奥科岛次生林与受干扰开放生境的交界区域发现的雅库巴果蝇与泰氏果蝇杂交后代。研究证实，这些杂交后代均为雅库巴果蝇雌蝇与泰氏果蝇雄蝇交配产生的F1子代。在比奥科岛的高温环境下，泰氏果蝇雌蝇通常对交配的接受度较低；结合温度对产卵量以及卵至成虫存活率的影响，相较于反交组合，这一特性降低了泰氏果蝇雌蝇与雅库巴果蝇雄蝇之间的基因交流潜力。野外与室内实验均表明，F1杂交后代兼具雅库巴果蝇的行为特征与泰氏果蝇的生理特性，该组合存在适应不良性，进一步为基因交流增添了障碍。不过，对基因组中渐渗区域与非渐渗区域的分析显示，尽管基因交流事件较为罕见，但发生时间相对较近。本研究的观测结果明确了精准的内在与外在因素，结合杂交雄性不育现象，共同限制了基因交流并维持了这两个物种的物种独立性。本研究数据为日益增多的相关研究文献提供了实证支持，这些文献提示几内亚湾（Gulf of Guinea）可能为杂交事件的热点区域。