Mutual mate choice: When it pays both sexes to avoid inbreeding

Conventional sex roles imply choosy caring females and non-discriminating competing males. However, growing experimental data as well as theoretical models suggest that male choosiness is more common than expected, even in non-sex role reversed species. In particular, selectivity of a sex is predicted to evolve in association with high mate availability, high variation in mate quality and high reproductive effort. Here we investigate the selectivity of males and females in a non-sex role reversed species, the cockroach Blattella germanica, with caring females and competing males. We demonstrate that males and females base their mate choice on different criteria and at different steps during the mating sequence. Males assess their relatedness with females during antennal contacts and choose to court non-sibling females more vigorously. In turn, females base their mate choice on male’s courting vigour. This mutual mate choice provides shared benefits by both partners by ultimately leading to close inbreeding avoidance and associated embryonic lethality observed in inbred matings. We experimentally identify that female choosiness can be explained by their high investment in reproduction (embryonic parental care), their low potential reproductive rate and by male high quality variance (relatedness). On the contrary, male selectivity seems to be a primarily a consequence of female quality variance. Our study provides experimental supports to theoretical predictions of evolutionary models and highlights the need to consider both male and female selectivity, even in non-sex role reversed species.