Luca Montana

Université de Sherbrooke
Male reproductive success in a polygamous marsupial: a spatial odyssey

Luca Montana, François Rousseu, Dany Garant, Marco Festa-Bianchet

In mammals with a polygamous mating system, male reproductive success can vary with the number and social rank of competitors overlapping its home range, as well as the spatial and temporal distribution of reproductive females. Some of these ecological variables, however, are rarely considered in studies of sexual selection, which often assume that males have equal access to every reproductive female and that variation in reproductive success is entirely the result of male-male competition or mate choice. That approach ignores possible spatial constraints on access to reproductive females. Here, we examine how spatial overlap between individuals influences male relative reproductive success in eastern grey kangaroos (Marcopus giganteus). Eastern grey kangaroos are a dimorphic species with high potential for mate monopolization, because of the long breeding season and the asynchrony of oestruses. However, the mating skew observed among males, in terms of number of paternities, is lower than expected. We show how spatial overlap between male-female pairs has a strong influence on male reproductive success. We propose that the maximum potential reproductive success of a given male can be estimated by the number of reproductive females whose home range overlaps by at least 50% the male home range. This measure reflects how males have unequal opportunities for reproduction and allows to refine the estimation of the relative reproductive success of each male. It also leads to a better assessment and understanding of morphological traits under sexual selection.