Lieu: Brunoy

Male reproductive success results from the probabilities to access females before copulation and to fertilize females’ ova after copulation. Although traits contributing to these two components of reproductive success can be potential distinct targets of selection, no study has distinguished selection acting on secondary sexual characters from selection acting on primary sexual characters, which respectively underlie mating access and fertilization success. Taking advantage of a long-term captive breeding program for a polyandrous bird species, the houbara bustard, we were able to access unique longitudinal records of male primary and secondary sexual characters, including five sperm traits and an index of courtship activity measured on 3115 individuals over 15 years. For the first time, we aimed at quantify the strength and direction of selection acting on traits involved in pre- and post-copulatory events, using a regression-based approach to examine multivariate selection. Our analysis revealed opposite patterns of selection for primary and secondary sexual characters, as courtship activity was under negative directional selection but the number of spermatozoa per ejaculate and the proportion of normal spermatozoa were under positive directional selection. Sperm motility and ejaculate volume appeared to be negatively correlated. Hence, our results suggest an evolutionary trade-off between traits promoting mating access and traits promoting fertilization success, supporting that both pre- and post-copulatory selection should always been considered when studying reproductive success and the evolution of mating systems.