Subordinate male meerkats prospect for extra-group paternity: alternative reproductive tactics in a cooperative mammal

Abstract

In cooperatively breeding species, subordinates typically suffer strong constraints on within-group reproduction. While numerous studies have highlighted the additional fitness benefits that subordinates might accrue through helping, few have considered the possibility that subordinates may also seek extra-group matings to improve their chances of actually breeding. Here, we show that subordinate males in cooperative meerkat, Suricata suricatta, societies conduct frequent extraterritorial forays, during periods of peak female fertility, which give rise to matings with females in other groups. Genetic analyses reveal that extra-group paternity (EGP) accrued while prospecting contributes substantially to the reproductive success of subordinates: yielding the majority of their offspring (approx. 70%); significantly reducing their age at first reproduction and allowing them to breed without dispersing. We estimate that prospecting subordinates sire 20-25% of all young in the population. While recent studies on cooperative birds indicate that dominant males accrue the majority of EGP, our findings reveal that EGP can also arise from alternative reproductive tactics employed exclusively by subordinates. It is important, therefore, that future attempts to estimate the fitness of subordinate males in animal societies quantify the distribution of extra-group as well as within-group paternity, because a substantial proportion of the reproductive success of subordinates may otherwise go undetected.

Figure 1

(a) The proportion of time spent by males prospecting in different dominance and dispersal classes. Bars present predicted means±s.e. from the GLMM, controlling for seasonal variables and males prospecting at higher rates as they age (see §3). (b) The seasonal variation in male prospecting closely paralleled that of female fertility. The prospecting profile presents predicted monthly means±s.e. for subordinate natal males (calculated by substituting calendar month in place of the female fertility variable in our prospecting-time GLMM; the profile for subordinate immigrant males was almost identical, just with lower values). The female fertility bars present monthly means±s.e. of dominant female conception probabilities, calculated from our historical data (see §2).

Figure 2

(a) The distribution of intra- and EGP among males of differing dominance and dispersal class (for the 51 offspring that were assigned fathers with greater than 95% confidence: 41 intra-group sirings and 10 extra-group sirings). (b) The probability that subordinate males sired intra- or extra-group offspring before and after dispersal from their natal groups. Bars represent predicted means±s.e. from the GLMM (using 279 offspring assigned with greater than 80% confidence), controlling for variation in each male's tenure in that dispersal class.