Life in the slow lane? Demography and life histories of male and female sifaka (Propithecus verreauxi verreauxi)

Abstract

A 16-year study of wild, unprovisioned sifaka Propithecus verreauxi verreauxi at Beza Mahafaly in southwest Madagascar provides estimates of age-speci®c fertility, mortality, and dispersal in a population of 426 marked animals, and longitudinal records of individual life histories. Sifaka females give birth for the ®rst time later and live longer, for their size, than mammals in other orders; they also give birth later and continue reproducing longer, for their size, than other primates. Theory postulates that these features, commonly referred to as bet-hedging, evolve in unpredictable environments in association with widely varying infant survival and a trade-off between reproductive effort and adult survival. The climate of south-west Madagascar is highly unpredictable compared to almost all other regions in the tropics with similar average rainfall, and we argue that sifaka females are bet-hedgers par excellence. Male sifaka, in contrast, become reproductively active at an earlier age than females, and are less likely to have long lives than females. The atypical direction of this asymmetry between males and females re¯ects a`slowing down' of female life histories rather than a`speeding up' of male life histories. Two other unusual features of sifaka biology and behaviour may be linked to the unpredictability of Madagascar's climate: intense local competition between females, and a sex ratio at birth strongly biased in favour of males in most years. In drought years, reproductive females must cope with suddenly intensi®ed resource constraints. This, in turn, may strongly limit the number of`breeding slots' available over the long-term for females.

The lemur syndrome unresolved: extreme male reproductive skew in sifakas (Propithecus verreauxi), a sexually monomorphic primate with female dominance

“…First, an unexpectedly large proportion (in our sample 37%) of multi-male groups are in fact single-male groups because all but one adult male were natal males, who apparently delayed natal dispersal long after sexual maturity (Richard et al 2002). Previous short-term behavioral studies or censuses could not identify these adult males as natal, thereby underestimating assessments of males' monopolization potential (cf.…”

“…Given this observed reproductive skew in favor of dominant males, it remains puzzling why subordinate males do not attempt takeovers more often. One possibility is that they are queuing for the alpha position (Kokko and Johnstone 1999;Cant and English 2006), as for example mountain gorillas (Bradley et al 2005) or spotted hyenas (East and Hofer 2001), but adult mortality rates are low, and sifaka life span may reach up to 30 years (Richard et al 2002). The potential success of this tactic can therefore not be evaluated with the available data.…”

“…In addition, breeding competition among female lemurs is unusually intense, including targeted aggression and eviction of close relatives (Vick and Pereira 1989;Pereira and Leigh 2003). Explaining this combination of traits-the "lemur syndrome"-has long posed a challenge to evolutionary anthropologists, and several hypotheses have been proposed to explain the even sex ratio, the lack of male-biased sexual dimorphism, and the evolution of female dominance (van Schaik and Kappeler 1996;Jolly 1998;Wright 1999;Richard et al 2002). In this study, we test predictions of relevant key hypotheses for the first time with reproductive skew theory.…”

“…Verreaux's sifakas (Propithecus verreauxi) are 3-kg arboreal lemurs that live in groups of typically one to three adult females and about the same number of adult males (Richard et al 2002). Dispersal is strongly male-biased (Richard et al 1993), and males provide no paternal care apart from occasional infant grooming (Grieser 1992;Bastian and Brockman 2007).…”

Mate-Guarding as a Male Reproductive Tactic in Propithecus verreauxi

“…Sifakas are arboreal lemurs that live in multi-male multi-female groups comprising 2-13 individuals (Richard et al 1993) with variable adult sex ratios (Richard 1985). Female dominance and female philopatry are the norm, although females have occasionally been observed to disperse (Jolly 1966;Kubzdela 1997;Richard 1987;Richard et al 1993Richard et al , 2002. Females become receptive once per year (Brockman 1994;Brockman and Whitten 1996) for a period of ≤96 h (Brockman 1999) during a short mating season from January until March.…”