The effect of thermal stress on the mating behavior of three Drosophila species.

Selection may act on the weakest link in fitness to change how a species adapts to an environmental stress. For many species, this limitation may be reproduction. After adult Drosophila melanogaster, Drosophila simulans, and Drosophila mojavensis males were exposed to varying levels of thermal stress well below those that endanger life, courtship and mating frequency declined. The regression coefficients of both courtship and mating success did not differ significantly between D. melanogaster and D. simulans males. In contrast, significant differences were present between the two cosmopolitan species and D. mojavensis. Courtship frequency decreased at a much slower rate in D. mojavensis than in D. melanogaster and D. simulans, and while heat-stressed D. mojavensis males continued to court, many did not mate. In the cosmopolitan species, courting males almost always mated successfully. Courtship behaviors, including wing waving, were observed in D. mojavensis at temperatures that prohibited flight, while flight, courtship, and mating were knocked out simultaneously in D. melanogaster. One possible explanation for decreased flight ability and courtship success may be the reduced heat shock response in the flight muscle tissue because Hsp70 expression was lowest in the thoracic tissue of both D. melanogaster and D. mojavensis.