The eastern grey kangaroo (Macropus giganteus) is one of the largest existing marsupials. It exhibits a polygamous mating system, established social structuring, and sexual size dimorphism. As an evolutionary response, males exhibit traits that influence their ability to successfully reproduce. In eutherian species, these can include weaponry, a larger body size and/or higher testosterone concentrations. Limited research has been performed on marsupials, impeding the development of evolutionary theories surrounding this extant mammalian lineage. The present study aimed to identify factors influencing male reproductive success in a free-ranging New South Wales eastern grey kangaroo population.
Candidate male body weight, skeletal size, testes size, and testosterone and glucocorticoid concentrations were investigated as potential influential factors. Paternity was assigned to a total of 89 offspring across four breeding seasons, representing male reproductive success. As predicted, body size, indicated by body weight, leg length, testes size and testosterone, significantly influenced male reproductive success. Foot length and glucocorticoid measures had no influence. Such information contributes to the development of broad evolutionary theories across all extant mammalian lineages, as well as providing valuable information to aid the management of wild and captive populations.