It’s Tough Out There: Variation in the Toughness of Ingested Leaves and Feeding Behavior Among Four Colobinae in Vietnam

Abstract

Colobines are similar in their exploitation of a high percentage of leaf matter. However, this observation obfuscates interesting differences among genera of Southeast Asian colobines in morphology and behavior that may be reflected in the degree to which they rely on mastication or gut volume and gut retention time when ingesting and digesting leaves. We detail the use of a laboratory-based method to measure the mechanical properties of foods selected and processed by 4 captive species of Southeast Asian Colobinae -Pygathrix nemaeus, Pygathrix cinerea, Trachypithecus delacouri, and Trachypithecus laotum hatinhensis-at the Endangered Primate Rescue Center (EPRC), Vietnam. We also detail a field method that quantifies chewing rates and chewing behavior via a consumer-grade video camera and laptop computer. Observations in the captive setting permit a degree of experimental control that is not possible in the wild, and the location of the EPRC in the primates' habitat country permitted us to provide leaves that they encounter and eat in the wild. We collected toughness data with a portable tester designed by Lucas et al. The average toughness of selected leaves does not differ among the taxa, nor does the length of time spent chewing foods. However, there are differences in feeding rate, with Trachypithecus spp. chewing foods twice as fast as Pygathrix spp. Our findings suggest that Trachypithecus spp. emphasize comminution of food by mastication, while Pygathrix spp. emphasize the comminution of leaf matter Int J Primatol (in the stomach. The hypothesis is supported by data on molar size, gut mass, and gut morphology. We provide new insights into dietary variation among primate species and detail methods that are typically conducted only in a laboratory setting. We augment the findings with additional data on activity, feeding rates, and tooth morphology.

Patch depletion behavior differs between sympatric folivorous primates

“…This difference may instead have a basis in digestive physiology. Red colobus have an extra chamber in their stomach, called a presaccus, which may function for storage and preliminary digestion of food for more efficient processing (Chivers 1994;Stevens and Hume 1995;Caton 1998;National Research Council 2003;Wright et al 2008). Guerezas lack this chamber and frequently rest for extensive periods of time in a patch between feeding bouts and before moving to another patch to feed, a behavior that is much less common among red colobus.…”

Relationships between the diet and dentition of Asian leaf monkeys

“…Another avenue of inquiry, which may aid in the interpretation of the dental patterns outlined here, and add additional weight to the ingestive versus digestive folivore hypothesis (Wright et al, 2008a), is the study of gut passage rate or mean retention time (e.g., Dierenfeld et al, 1992;Edwards and Ullrey, 1999;Nijboer et al, 2007). In addition, as noted by Kirkpatrick (1998), colobines potentially adapt to new diets or to seasonal changes in diet by the same method as other foregut fermenters: through rapid changes in proportions of gut microorganisms (Bauchop, 1978).…”

Trachypithecus delacouri (Primates: Cercopithecidae)

“…Larger molars and larger, deeper mandibles, combined with differences in stomach morphology noted above, enable 2 Pygathrix species to chew more slowly than T. delacouri to extract similar food value (Wright et al 2008a(Wright et al , 2008b. By chewing much more rapidly for about the same amount of time, T. delacouri relies more on dental mastication and oral comminution of foods before exposure to stomach microbes in its tripartite stomach.…”