Natal-to-juvenile pelage change in free-living François’ (Trachypithecus francoisi) and Cat Ba langurs (T. poliocephalus)

Abstract

This article discusses the timing, patterning, and implications of natal pelage loss for two species of limestone-dwelling Asian colobines – François’ (Trachypithecus francoisi) and Cat Ba (Trachypithecus poliocephalus) langurs. It considers why some primate species, such as those in the Trachypithecus genus, are born with a flamboyant, orange natal coat and what purpose it may serve in promoting allocare and reducing the threat of infanticide. With 11-12 months of observation of each species, this study assesses the pattern of natal coat loss for three François’ langur infants living in Mayanghe Nature Reserve (China) and three Cat Ba langur infants living on Cat Ba Island (Vietnam). There was conflicting evidence for our first hypothesis, as the pattern of natal coat loss is similar in both species, although the timing is sped up in François’ langur infants. Using previous data on these species, and confirming our second hypothesis, there does appear to be an association between increased independence and decreased group member interest in infants that were progressively developing an adult coat colouration, suggesting that the coat does signal dependence and promote allocare. Finally, in analysing the pattern of where the natal coat is lost first, observations suggests that both species of langurs may be using a paternity cloaking approach to avoiding infanticide. Ultimately, it is unclear if François’ and Cat Ba langurs are experiencing different degrees of infanticidal threat given the contradictory evidence, nor is it known how or if their divergent patterns of development are related to habitat quality.