An ecological approach to understanding overweight captive lemurs

Excessive body weight, such as being overweight or obese, is associated with other serious health problems, e.g. reproduction issues and reduced lifespan, and is therefore concerning in captive animals. Some lemur species seem prone to extreme weight gain in captivity, yet for others a healthy body condition is typical. Understanding the basis for susceptibility to captive weight gain 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 prone to weight gain 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 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, and thus food resource unpredictability, tended to have larger captive weight gain (t1, 11=2.04, R2=0.27, λ=<0.001, P=0.07). Based on this we discuss practical recommendations to address unwanted weight gain; the need to establish the appropriateness of the threshold we used to infer obesity; and whether the captive feeding environment might in fact be perceived by some as being unpredictable, thus helping to explain our results.