Slow Lorises (Nycticebus spp.) Really Are Slow: a Study of Food Passage Rates

Abstract

The characteristics of food ingested by a primate affect its assimilation of energy by modulating food passage rate. In general, digestive time increases in folivorous primates and decreases in frugivorous primates when they are fed higher fiber diets but this relationship is understudied in exudativorous primates. We compared the food passage rate of five slow loris species. We studied 34 wild-caught slow lorises (15 Nycticebus coucang, 15 N. javanicus, and 4 N. menegensis) in an Indonesian rescue center and four captive-born slow lorises (2 N. bengalensis and 2 N. pygmaeus) in a UK institution. We fed the Indonesian subjects two different diets: a captive-type diet comprising fruits, vegetables, and insects and a wild-type diet formulated to be similar in nutrients to that consumed by slow lorises in the wild, consisting of gum, insects, vegetables, and nectar. We fed the UK subjects a diet of gum, vegetables, insects, and hard-boiled eggs. We formulated this diet to mimic the wild diet, with notably higher fiber fractions and lower soluble sugars than the previous diet. We measured two variables: the transit time (TT) and the mean retention time (MRT). We mixed 1 tsp. of glitter in bananas or gum as our markers and fed them to the slow lorises immediately before their main diet. We noted the date and time of feeding and of appearances of the marker in feces. We weighed food given and left over for each individual to calculate ingested foods and nutrients. We found that TTs were not affected by diet treatment but MRTs were significantly longer for all species fed the wild-type diet. Our results show that Nycticebus spp. have long MRTs for their body weight, and N. pygmdaeus may have the slowest MRT of all primates in relation to body mass. The digestive flexibility of exudativorous primates should allow them to maximize fermentation opportunities when they ingest more (appropriate) fiber by increasing the amount of time the fiber substrate stays in the large intestine. Exudativorous primates appear to have plastic digestive strategies that may be an adaptation to cope with relatively nutrient-poor staple food sources such as gum. The provision of gum in a captive setting may therefore provide benefits for gut health in slow lorises.