Influence of environmental variation on sexual dimorphism in Drosophila morphology among adaptively diverged populations and in an inter-specific comparative context.

Abstract

Environmental variation, an important source of phenotypic variation, can influence phenotypes, fitness and even rates of evolution. My thesis explores the effects of evolutionary change on the response to different types of environmental variation. In the first study, I examined the evolution of environmental canalization in adaptively diverged populations of Drosophila melanogaster that vary in degree of genetic canalization. I use these populations to test the congruence hypothesis which predicts that genetic canalization is a co-product of the evolution of environmental canalization and thus should be correlated. My results show that, despite adaptive evolutionary changes in morphology and genetic canalization, these populations have similar degree of variability due to environmental variation. In the second study, I explore how both variation in temperature and food quality during development influence patterns of sexual dimorphism in wing morphology in adaptively diverged populations of Drosophila melanogaster. I compare the relative contributions of adaptation, food availability and temperature on sexual size and shape dimorphism of the Drosophila wing. In particular, I focus on how these factors influence size-shape allometry both in general and in a sex-specific manner. My results show that despite the large adaptive divergence and a strong influence of environmental manipulation on wing size and shape, sex-specific patterns of condition dependence remain relatively consistent between the two populations. In the third study, I explore the evolutionary patterns of condition-dependent sexual size dimorphism among 27 different species from the melanogaster species group with varying degrees of sexual size dimorphism. Using food availability manipulations during development, I examine how sexual size dimorphism changes in response to condition at both the intra-specific and the inter-specific level. The results of this study suggest that, although we see a correlation between sexual size dimorphism and condition dependence among traits within most species, sexual dimorphism and condition dependence do not seem to have a correlated evolution among species of the melanogaster species group.