Gender differences in survival and antipredatory behavior in stalk-eyed flies

Abstract

Exaggerated eye span of stalk-eyed flies is a classic example of the evolution of an extravagant male ornament resulting from sexual selection. Increased male eye span may entail costs associated with production and/or maintenance, including potential locomotor costs that may increase predation risk. However, behavioral responses by individuals may alter the relationship between a morphological trait and performance, increasing expected overall fitness. Antipredator behavior and survival of male and female Teleopsis dalmanni were quantified during pairwise interactions between individual flies and an actively foraging, generalist arachnid predator (Phidippus audax). Male and female flies were compared under the assumption that female stalk length is closer to the optimum set by natural selection. There were significant differences in behaviors between the sexes, with males spending more time engaged in aggressive actions. Interestingly, males also exhibited increased survival relative to females. Within males, survivors did not differ from nonsurvivors in any of the morphological measures, including eye span, but there was a significant difference in abdomen bobbing, grooming, and flight. These results highlight the importance of behavior in the ability of stalk-eyed flies to effectively elude predators, but they do not support the hypothesis that male stalk-eyed flies suffer increased predation due to exaggerated eyestalks.