Female choice response to artificial selection on an exaggerated male trait in a stalk-eyed fly

Quantitative genetic models for the evolution of exaggerated male traits through female mate choice predict that selection on male ornaments should cause a correlated response in female preferences. Furthermore, female selectivity should be inversely related to costs of mate choice. Here we use a stalk-eyed fly, Cyrtodiopsis dalmanni (Diptera: Diopsidae), which exhibits pronounced sexual dimorphism in eye span, to evaluate these predictions. Field observations reveal that each evening females aggregate while males disperse among roosting sites where mating occurs. A positive regression between male relative eye span and the number of females in an aggregation suggests that sexual selection acts on male eye span. Mate choice experiments in the lab, using flies after 13 generations of bidirectional selection on male relative eye span, reveal that females from long eye-span lines and an unselected population preferred long eye-span males. Short eye-span line females, however, preferred short eye-span males, demonstrating a genetic correlation between female preference and a sexually selected male trait. Eye span of the largest male in a field aggregation correlated positively with female age, as estimated by amount of eye pigment, and was independent of egg number, thereby providing no evidence that mate choice impairs female survival or fecundity. 1.