Compete then Care: Shifts in Male Reproductive Strategies Over the Life Course in a Polygynous Mammal

Abstract

In polygynous species, there is often intense intra-sexual competition over access to females and high reproductive skew, and males invest more in mating effort than parenting effort. However, the benefits of investments in mating effort and parenting effort may change systematically over the course of males’ lives. In many polygynous mammalian species, there is an ∩-shaped relationship between age, condition, and resource holding power as middle-aged males that are in prime physical condition outcompete older and younger males. As males age, and their competitive abilities decline, males might benefit from reallocating investment from mating effort to parenting effort. We examined the effects of male age and paternity on the likelihood that male olive baboons, Papio anubis, would invest in parenting effort. Male baboons compete for high ranking positions in the group, and there is an ∩-shaped relationship between male age and dominance rank. High ranking males sire more infants than lower ranking males. Males and lactating females often form close ties (primary associates), and females’ primary associates are likely to be the sires of their infants. Males are attentive to their primary associates’ distress, support them in conflicts, and buffer their infants from rough handling and harassment. Here, we show that males are more likely to become the primary associates of lactating females as they age and their competitive abilities decline. These results suggest that fitness benefits derived from male parental investment may favor an extended post-reproductive lifespan in species in which males can identify their own offspring and positively affect their welfare.

Keywords: male reproductive strategy, baboon, mating effort, parenting effort, life history