Regurgitation and remastication in the foregut-fermenting proboscis monkey ( Nasalis larvatus )

Abstract

Although foregut fermentation is often equated with rumination in the literature, functional ruminants (ruminants, camelids) differ fundamentally from non-ruminant foregut fermenters (e.g. macropods, hippos, peccaries). They combine foregut fermentation with a sorting mechanism that allows them to remasticate large particles and clear their foregut quickly of digested particles; thus, they do not only achieve high degrees of particle size reduction but also comparatively high food intakes. Regurgitation and remastication of stomach contents have been described sporadically in several non-ruminant, non-primate herbivores. However, this so-called 'merycism' apparently does not occur as consistently as in ruminants. Here, to our knowledge we report, for the first time, regurgitation and remastication in 23 free-ranging individuals of a primate species, the foregut-fermenting proboscis monkey (Nasalis larvatus). In one male that was observed continuously during 169 days, the behaviour was observed on 11 different days occurring mostly in the morning, and was associated with significantly higher proportions of daily feeding time than on days when it was not observed. This observation is consistent with the concept that intensified mastication allows higher food intake without compromising digestive efficiency, and represents an expansion of the known physiological primate repertoire that converges with a strategy usually associated with ruminants only.

Relationships between the diet and dentition of Asian leaf monkeys

“…Including information on dental eruption sequence may provide additional insight concerning how the dentition wears through time and thereby provide new perspectives on ingestive behavior (see Godfrey et al, 2003). For example, they have been found to regurgitate and remasticate foods (Matsuda et al, 2011), they exhibit marked sex dimorphism in body size (Tables 4 and 5), their incisors, as noted, erupt first and exhibit extensive wear before the adult dentition has fully erupted, and they exhibit large lingual tubercles on the maxillary incisors ( Fig. Regardless, N. larvatus is a case-in-point when considering the complexity of assessing dental function from a general analysis of diet and dental morphology.…”

In Vitro Fermentation of Dietary Carbohydrates Consumed by African Apes and Monkeys: Preliminary Results for Interpreting Microbial and Digestive Strategy

“…Among primates, hindgut fermentation is the ancestral state. Foregut fermentation without rumination has evolved only among the Colobinae (Kay and Davies 1994;Milton 1998;Matsuda et al 2011).…”

Physiological adaptations of ruminants and their potential relevance for production systems

“…This increased chewing efficiency is not achieved by a particular dental design, but by a density-depending sorting mechanism in the forestomach, which separates the small particles from the large ones that are then regurgitated to be masticated again (i.e., rumination) (Lechner-Doll et al, 1991). Although merycism (i.e., regurgitation and re-mastication) and the presence of comparatively fine digesta particles have been reported in non-ruminant foregut fermenters such as kangaroos Vendl et al, 2017) and proboscic monkeys (Nasalis larvatus) (Matsuda et al, 2011;Matsuda et al, 2014), true rumination linked to a sorting mechanism and with a physiologically fixed motor sequence (Gordon, 1968) only evolved twice, in the camelids and the taxonomic ruminants. While there appears to be no functional difference in the forestomach particle sorting mechanism between these two functional ruminant groups (Dittmann et al, 2015b), a major difference between them is the generally lower metabolism and lower feed intake in camelids (Dittmann et al, 2014).…”