Condition Dependence of Sexual Dimorphism in the Antler Fly, Protopiophila litigata

Abstract

In this thesis, I investigate the relationship between two variables for which persistent directional sexual selection is an evolutionary driver: condition dependence and sexual dimorphism. This joint dependence on sexual selection predicts that among traits within a given species, greater dimorphism should be associated with stronger condition dependence. Very few studies have tested this prediction, and those that have focus on species with highly exaggerated and strongly dimorphic traits between the sexes. Here, I quantified variation in a suite of morphological traits in a dipteran species – the antler fly, Protopiophila litigata – in which sexual dimorphism is less extensive. I manipulated condition via different larval diets and then quantified the effects on adult body size and shape in both sexes. Across traits, I found that the extent of sexual dimorphism was positively associated with the strength of condition dependence in males but not in females. These results suggest a shared developmental basis to condition dependence and sexual dimorphism in body shape, and suggest that this has arisen via sexual selection in males despite the absence of extremely dimorphic shared traits.