Shifts in Male Reproductive Tactics over the Life Course in a Polygynandrous Mammal

In polygynous and polygynandrous species, there is often intense male-male competition over access to females, high male reproductive skew, and more male investment in mating effort than parenting effort [ 1 ]. However, the benefits derived from mating effort and parenting effort may change over the course of males’ lives. In many mammalian species, there is a ∩-shaped relationship between age, condition, and resource holding power as middle-aged males that are in prime physical condition outcompete older males [ 2–8 ] and sire more infants [ 9–12 ]. Thus, males might derive more benefits from parenting effort than mating effort as they age and their competitive abilities decline [ 13 ]. Alternatively, older males may invest more effort in making themselves attractive to females as mates [ 14 ]. One way that older males might do so is by developing relationships with females and providing care for their offspring [ 14, 15 ]. Savannah baboons provide an excellent opportunity to test these hypotheses. They form stable multi-male, multi-female groups, and males compete for high ranking positions. In yellow and chacma baboons ( Papio cynocephalus and P. ursinus ), there is a ∩-shaped relationship between male age and dominance rank [ 12 ], and high rank enhances paternity success [ 12,  16 ]. Lactating female baboons form close ties (“primary associations” hereafter) with particular males [ 15–20 ], who support them and their infants in conflicts [ 15, 19 ] and buffer their infants from rough handling [ 20 ]. Females’ primary associates are often, but not always, the sires of their current infants [ 16,  20–22 ].