Digestive retention times for Allen's swamp monkey and L'Hoest's monkey: data with implications for the evolution of cercopithecine digestive strategy.

Primates access energy from plant fiber via bacterial fermentation in either a modified forestomach ('foregut'), a caecocolic ('hindgut') chamber of the large intestine, or both. Longer digestive retention times allow for more complete fermentation; as such, primates that consume an herbivorous diet high in fiber are expected to have both relatively and absolutely longer retention times than those mammals that rely on more readily digestible plant foods, such as fruit. We used particulate markers to measure the digestive retention times of captive Allen's swamp monkeys [Allenopithecus nigroviridis (Pocock, 1907)] (n= 3) and L'Hoest's monkey (Cercopithecus lhoesti P. Sclater, 1899) (n= 2). Results indicate mean retention times of 23.2-29.4 h and 23.2-24.0 h for C. lhoesti and A. nigroviridus, respectively. Results from this study, in combination with previously published data on digestive retention times in other primate species, indicate that cercopithecines differ from other primate taxa by having lengthier retention times that can be predicted by body mass alone. These data are consistent with the hypothesis that relatively lengthy retention times are a primitive trait for Cercopithecinae.