Sexual dimorphism exemplifies the remarkable diversity and aesthetic beauty in nature, with mating signals representing a key aspect of this phenomenon. These signals have evolved to encompass multimodal sensory modalities, and understanding their evolution necessitates exploring the complex interactions among various selective pressures. This dissertation examines the intricate relationship between sexual dimorphism and mating signals, utilizing cuticular hydrocarbons (CHCs) in Drosophila species as a model system. We investigated three pivotal questions: 1) Is there a correlation between the evolution of sexual dimorphism and the evolution of mating signals, and can the degree of sexual dimorphism predict the functional roles of these signals? 2) What genetic mechanisms underlie the evolution of exaggerated female traits? 3) What phenotypic trade-offs are associated with the evolution of mating signals? Employing the Bray-Curtis dissimilarity index, we initially assessed the degrees of sexual dimorphism in CHC profiles across Drosophila species and tested the impact of CHC perception on male courtship interest. Our findings did not support a correlation between the degree of sexual dimorphism and the use of CHCs for mate recognition. Next, we focused on a species exhibiting pronounced sexual dimorphism, identifying a candidate gene with female-biased expression in adult oenocytes, likely responsible for the production of exaggerated female traits. This expression pattern is attributed to cis-regulatory changes, characterized by two specific modules: one related to oenocyte expression and another to sex-biased expression. Lastly, the costs associated with producing methyl-branched cuticular hydrocarbons (mbCHCs) in transgenic D. mojavensis lines was tested. Our findings do not reveal direct developmental trade-offs associated with the production of mbCHCs, but suggest a positive correlation between mbCHC production and reproductive fitness. While mbCHCs are correlated to individual fitness, they have not evolved to function as reliable signals influencing mate preferences. This dissertation contributes to addressing unresolved questions regarding the evolution of sexual dimorphism and mating signals, offering novel insights into the genetic mechanisms and potential evolutionary costs associated with these traits.
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