Diademed sifakas (Propithecus diadema) in intact and degraded forest habitat at Tsinjoarivo, Madagascar, show high reproductive success and no evidence that dental senescence or rainfall affects reproductive output

Abstract

Sifakas (genus Propithecus) diverge from other lemurs in their strategy to contend with Madagascar’s highly seasonal climate and maximize reproductive success: they have long lifetimes (presumably to wait out unfavorable times) and extreme dental precocity (to allow weanlings to effectively process tough foods and thereby relieve energetic stress on mothers). However, as sifakas age, dental senescence can contribute to reproductive failure, especially when coupled with unfavorable weather conditions (as shown by King et al., 2005 for P. edwardsi at Ranomafana). To extend the effective life of the teeth, compensatory blades maintain functionality for the female sifaka, but wear may eventually have consequences on infant survival in certain climatic scenarios. We investigate the impacts of climate, age, and dental senescence on the reproduction of another sifaka, Propithecus diadema, in fragmented and intact habitats of Tsinjoarivo, Madagascar. We documented birth and infant survival between 2002 and 2017 across twelve groups, including 73 births, and we used 77 dental casts representing 54 adults to estimate age when exact age was not known. We report that sifakas in Tsinjoarivo do not conform to the expectations that link advanced age with dental and reproductive senescence. Propithecus diadema at Tsinjoarivo show slower tooth wear, higher reproductive output and higher infant survival compared to congeners. Likelihood of birth and infant mortality do not correlate with intrinsic (mother’s age, tooth wear) or extrinsic (rainfall or habitat type) stressors. However, the small number of years without births or with infant deaths limits statistical power. At the local level, this study suggests that the long-term viability of Propithecus diadema at Tsinjoarivo is promising and reproductive output is high, even in disturbed fragments where nutrient intakes are reduced. Further research is needed to contextualize and understand these differences among sites and regions within Madagascar and avoid over-generalizing from single study sites.