Sexual selection, viability and sexual differences

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Males of many animal species sport elaborate weaponry or ornamentation used in competing for and attracting mates. Although such traits were explained by Darwin to have evolved via sexual selection, we still lack a full understanding of why this type of selection is usually greater on males than on females. To address this we study exceptional species that show 'reversed' sexual selection, i.e. sexual competition among females. Thus we can understand patterns of sexual selection in general. The proposed research focuses on sex-specific secondary sexual structures, such as ornaments, with a main question being why sex-specific ornamentation is rare in females even in 'role-reversed' species. Predictions come from new developments in theory of how these traits evolve in females. We will test predictions using statistical analyses of selection - not only sexual selection but also viability selection through predation on ornamented individuals. Studies will be conducted over several seasons in order to examine variation in selection. Our organisms are several orthopterans (crickets and allies) and dipterans (flies) with ornamented females that show sexual competition in securing mating meals (gifts) provided by males. Projects will use mate choice experiments and will examine the intensity and form of multivariate sexual selection on the female traits both (i) estimating female mating success (number of copulations thus gifts received) in some cases using DNA markers (being developed in another lab) and (ii) examining viability selection (via spider web predation) on females with different sized ornaments. For one of our study groups, a genus with many species that vary in degree of female ornamentation, molecular-genetic evolutionary trees (from collaborators) will be used to test hypotheses about ornament evolution. Our species with sexual selection on females will be compared to related species with male sexual selection in projects examining sexual selection and viability selection on male-specific traits such as weaponry and mate-attracting songs. Lab work will confirm the fact that mating gifts in our study species are of significant value to females.