RESUMEN
Theory predicts trade-offs between pre- and post-copulatory sexually selected traits. This relationship may be mediated by the degree to which males are able to monopolize access to females, as this will place an upper limit on the strength of post-copulatory selection. Furthermore, traits that aid in mate monopolization may be costly to maintain and may limit investment in post-copulatory traits, such as sperm performance. Australian painted dragons are polymorphic for the presence or absence of a yellow gular patch ('bibs'), which may aid them to monopolize access to females. Previous work has shown that there are physiological costs of carrying this bib (greater loss of body condition in the wild). Here, we show that male painted dragons use this bright yellow bib as both an inter- and intrasexual signal, and we assess whether this signal is traded off against sperm performance within the same individuals. We found no relationship between aspects of bib colour and sperm swimming velocity or percentage of motile sperm and suggest that the bib polymorphism may be maintained by complex interactions between physiological or life-history traits including other sperm or ejaculate traits and environmental influences.
Asunto(s)
Lagartos , Conducta Sexual Animal , Espermatozoides/fisiología , Animales , Australia , Color , Femenino , Masculino , Pigmentación , Conducta SexualRESUMEN
Natural selection and post-copulatory sexual selection, including sexual conflict, contribute to genital diversification. Fundamental first steps in understanding how these processes shape the evolution of specific genital traits are to determine their function experimentally and to understand the interactions between female and male genitalia during copulation. Our experimental manipulations of male and female genitalia in red-sided garter snakes (Thamnophis sirtalis parietalis) reveal that copulation duration and copulatory plug deposition, as well as total and oviductal/vaginal sperm counts, are influenced by the interaction between male and female genital traits and female behaviour during copulation. By mating females with anesthetized cloacae to males with spine-ablated hemipenes using a fully factorial design, we identified significant female-male copulatory trait interactions and found that females prevent sperm from entering their oviducts by contracting their vaginal pouch. Furthermore, these muscular contractions limit copulatory plug size, whereas the basal spine of the male hemipene aids in sperm and plug transfer. Our results are consistent with a role of sexual conflict in mating interactions and highlight the evolutionary importance of female resistance to reproductive outcomes.