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 re...