Temperature affects conspecific and heterospecific mating rates in Drosophila

Behavioral mating choices and mating success are important factors in the development of reproductive isolation during speciation. Environmental conditions, especially temperature, can affect these key traits. Environmental conditions can vary across, and frequently delimit species' geographic ranges. Pairing suboptimal conditions with relative rarity of conspecifics at range margins may set the stage for hybridization. Despite the importance of mating behaviors as a reproductive barrier, a general understanding of the interaction between behavioral choices and the environment is lacking, in part because systematic studies are rare. With this report, we begin to bridge that gap by providing evidence that temperature has a significant - but not consistent influence on mating choices and success, and thus on reproductive isolation in Drosophila. We studied mating propensity and success at four different temperatures among 14 Drosophila species in non-choice conspecific mating trials and in heterospecific trials among two Drosophila species triads that are known to regularly hybridize in the wild. We show that mating frequency varies significantly across a 10°C range (from 18°C to 28°C), both in 1:1 mating trials and in high-density en-masse trials, but that the effect of temperature is highly species-specific. We also show that mating frequency is consistently low and that temperature has a moderate effect in some heterospecific crosses. As conspecific mating propensity decreases outside of the optimal thermal range, while heterospecific matings remain constant, the proportion of heterospecific matings at suboptimal temperatures is relatively high. This result indicates that temperature can modulate behavioral choices that impose reproductive barriers and influence the rate of hybridization. More broadly, our results demonstrate that to truly understand how mating choice and reproductive isolation occur in nature, they need to be studied in an environmental context.