FEMALE CHOICE RESPONSE TO ARTIFICIAL SELECTION ON AN EXAGGERATED MALETRAIT IN A STALK-EYED FLY

Quantitative genetic models for the evolution of exaggerated male trai ts 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 choi ce. Here we use a stalk-eyed fly, Cyrtodiopsis dalmanni (Diptera:Diops idae), which exhibits pronounced sexual dimorphism in eye span, to eva luate these predictions. Field observations reveal that each evening f emales aggregate while males disperse among roosting sites where matin g occurs. A positive regression between male relative eye span and the number of females in an aggregation suggests that sexual selection ac ts on male eye span. Mate choice experiments in the lab, using flies a fter 13 generations of bidirectional selection on male relative eye sp an, reveal that females from long eye-span lines and an unselected pop ulation preferred long eye-span males. Short eye-span line females, ho wever, preferred short eye-span males, demonstrating a genetic correla tion 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 indep endent of egg number, thereby providing no evidence that mate choice i mpairs female survival or fecundity.