An ecological approach to understanding obesity in captive lemurs

Obesity is associated with other serious health problems, e.g. reproduction issues and reduced lifespan, so is a concern in captive animals. Some lemur species seem prone to extreme weight gain and potential obesity in captivity, yet for others a healthy body condition is typical. Understanding the basis for proneness to obesity is fundamental to successfully addressing it, and to improve health and welfare. Madagascar, to which all lemurs are native, is characterised by poor plant productivity, pronounced seasonality, and unpredictable inter-year climatic variation. Adaptations to this environment may result in some species being especially “thrifty” (storing fat when food is available) and thus obesity-prone under well-provisioned captive conditions. Wild lemurs also vary in arboreality, which increases the mass-dependent costs of locomotion, and could explain why some species consistently maintain lower fat levels. Alternatively, predation risk might be the driver, as excess weight impedes escape. Controlling for species' statistical non-independence, we tested these hypotheses by exploring relationships between species-typical ecological predictors, and deviation from wild-type body mass. Weight records and corresponding husbandry were collected using a survey, yielding useable data on 675 adult animals representing 13 species from 183 collections worldwide. Data on species-typical wild biology were collated from published literature and online climate databases. We found tentative support for one hypothesis: species that experience unpredictable, large between-year variation in rainfall tended to have larger captive weight gain (T2, 10=1.92, R2=0.29, λ=<0.01, P=0.084). Based on this we discuss practical recommendations to address unwanted weight gain; the need to validate ‘body mass ratio’ as a proxy for obesity; and whether the ‘obesity’ observed in these species truly represents obesity in the pathological sense.