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 ad apts to an environmental stress. For many species, this limitation may be r eproduction. After adult Drosophila melanogaster, Drosophila simulans, and Drosophila mojavensis males were exposed to varying levels of thermal stres s well below those that endanger life, courtship and mating frequency decli ned. The regression coefficients of both courtship and mating success did n ot differ significantly between D. melanogaster and D. simulans males. In c ontrast, significant differences were present between the two cosmopolitan species and D. mojavensis. Courtship frequency decreased at a much slower r ate in D. mojavensis than in D. melanogaster and D. simulans, and while hea t-stressed D. mojavensis males continued to court, many did not mate. In th e cosmopolitan species, courting males almost always mated successfully. Co urtship behaviors, including wing waving, were observed in D. mojavensis at temperatures that prohibited flight, while flight, courtship, and mating w ere 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 lo west in the thoracic tissue of both D. melanogaster and D. mojavensis.