The costs of risky male behaviour: sex differences in seasonal survival in a small sexually monomorphic primate

Abstract

Male excess mortality is widespread among mammals and frequently interpreted as a cost of sexually selected traits that enhance male reproductive success. Sex differences in the propensity to engage in risky behaviours are often invoked to explain the sex gap in survival. Here, we aim to isolate and quantify the survival consequences of two potentially risky male behavioural strategies in a small sexually monomorphic primate, the grey mouse lemur Microcebus murinus: (i) most females hibernate during a large part of the austral winter, whereas most males remain active and (ii) during the brief annual mating season males roam widely in search of receptive females. Using a 10-year capture-mark-recapture dataset from a population of M. murinus in Kirindy Forest, western Madagascar, we statistically modelled sexspecific seasonal survival probabilities. Surprisingly, we did not find any evidence for direct survival benefits of hibernation-winter survival did not differ between males and females. By contrast, during the breeding season males survived less well than females (sex gap: 16%). Consistent with the 'risky male behaviour' hypothesis, the period for lowered male survival was restricted to the short mating season. Thus, sex differences in survival in a promiscuous mammal can be substantial even in the absence of sexual dimorphism.

Are personality differences in a small iteroparous mammal maintained by a life-history trade-off?

“…Males that reach an age of 3 years are the heaviest and acquire the highest reproductive share of up to five offspring per reproductive season [20]. Given low annual survival probabilities of only 0.49 in the natural population [21], the future reproductive value of these males in their prime is low. Hence, these males may increase investment in reproductive effort and express risk-taking behaviour [35,36].…”

“…In contrast to females, male future reproductive value is strongly age-dependent, which might facilitate high boldness as a potential terminal investment strategy. Increased 'risky male behaviour', particularly during the short annual mating season, is costly, however, because it reduces male survival probability by up to 25 per cent compared with females [21].…”

“…Whereas females reproduce in their first year, the chances of not yet fully grown yearling males fathering offspring are low because male reproductive success is determined by body mass [20]. Annual survival rate is low, resulting in an average life span of 2 -3 years, and only a few individuals reach 10 years of age in natural populations [21]. Hence, individuals of different sex and age classes vary in current and future fitness expectations, which, according to the life-history hypothesis, should lead to predictable patterns of stable individual differences in behavioural traits.…”

Senescence or selective disappearance? Age trajectories of body mass in wild and captive populations of a small-bodied primate

“…In this study, we simultaneously assess the influences of intrinsic 'background' mortality, extrinsic hazard and nonrandom mortality of lower quality individuals in creating the observed patterns of FS and lifespan in a species that experiences high EM under natural conditions [30]. We employ long-term body mass (BM) data from one captive and two wild populations (10-18 years covering 7-16 cohorts) of the grey mouse lemur (Microcebus murinus) to characterize variation in body condition.…”

Convenience polyandry or convenience polygyny? Costly sex under female control in a promiscuous primate

“…In addition, energetic costs are presumably not the only mating costs, and probably not the most significant ones from an evolutionary perspective. Males probably pay extra costs compared with females (for instance, in the form of search costs or injuries during male -male fights), and they pay such costs on repeated occasions, which ultimately translate into a pronounced male-biased mortality during the mating season in the wild [70]. Overall, these results add to the increasing body of evidence suggesting that the costs of reproduction are more balanced among the sexes than previously thought, which might be particularly true in weakly dimorphic species with scramble competition mating systems [71].…”