It is generally thought that secondary sexual signals are honest signals of phenotypic and genetic quality. We show that in the three-spined stickleback, however, males investing more in carotenoid-based red coloration carry higher levels of oxidative DNA damage in muscle, testis and sperm possibly due to the competing functions of carotenoids as colorants and antioxidants.

In central Panamanian populations of the harlequin beetle riding pseudoscorpion, Cordylochernes scorpioides, males carrying highly divergent mitochondrial haplogroups (A and B2) differ extensively in the expression of mtDNA genes in testicular tissue. DNA profiling demonstrates that B2-carrying males sire more than three times as many offspring in two-male sperm competition experiments than do A males, and this B2 competitive advantage cannot be explained by female mitochondrial haplogroup or male nuclear genetic background. Despite conferring strong fitness benefits on males, the B2 haplogroup remains rare in central Panamá as a consequence of male inability to transmit mitochondria to offspring (mother's curse).

Bateman’s Paradigm predicts reproductive success and the number of mates is positive for males but not for females, resulting in more intense sexual selection on males vs. females. Many studies fail to corroborate this paradigm, potentially due to parental care. We show that in brood parasitic brown-headed cowbirds (Molothrus ater), which lack parental care in either sex, annual reproductive success increases with the number of mates in males, but not in females; conforming to predictions of the Bateman’s Paradigm. Photo: Marie Read.

Female genitalia have been largely neglected in studies of genital evolution, perhaps due to the long standing belief that they are relatively invariable and therefore taxonomically and evolutionarily uninformative in comparison to male genitalia. Contemporarry studies dispute this point of view, and in this review we synthesise current evidence both for and against sexual selection acting as a driver of female genital evolution. Lastly, we offer directions for future studies in order to expand and refine our knowledge surrounding female genital evolution.