Age negatively impacts reproduction in high-ranking male rhesus macaques on Cayo Santiago, Puerto Rico.

Based on sexual selection theory, the reproductive potential of male primates is expected to be limited by access to fertile females. Alpha males, the highest ranking males in a social group, are predicted to have better access to mates and produce more offspring until they are no longer dominant, which usually corresponds with age. Little is known about male reproductive senescence independent of rank changes in nonhuman primates. Here, we examine variation in the reproductive success of high-ranking male rhesus macaques on Cayo Santiago. We recorded behavioral data for 21 adult males across 9 social groups during the 2013 mating season. Additionally, we used paternity data from the long-term database to determine the number of offspring each subject sired over his lifetime and during the study period. Older high-ranking males in stable groups had fewer offspring than younger high-ranking males in stable groups in 2013. The low reproductive output for the older males was not a result of lower mating effort, and reproductive output in 2013 was not predicted by total prior reproductive success. Our results provide novel evidence of post-copulatory reproductive senescence in high-ranking male nonhuman primates.