Morphological and physiological aspects of digestive processes in the graminivorous primate Theropithecus gelada—a preliminary study

Abstract

Hindgut fermentation has been suggested to contribute significantly to the digestive process in the gelada (Theropithecus gelada). We therefore hypothesized that in an in vitro fermentation test (Hohenheim gas test, using gas production as measure of microbial digestion) inoculum based on fresh gelada feces would degrade grass to a similar degree as zebra (Equus burchelli chapmani) feces and to a higher degree than that of hamadryas baboons (Papio hamadryas). Additionally, morphology of gelada tongue, salivary glands, stomach, and intestine were examined in this study. Gas production was measured between 4 and 96 hr using animal feces incubated with 200 mg of air-dry hay or mixed concentrate sample. For grass hay, 12-hr gas production was as follows: T. gelada (19.9 ml)>Papio (18.4 ml)>Equus (15.7 ml). After 24 hr, gas production changed: Papio (35.1 ml)>T. gelada (31.9 ml)>Equus (27.9 ml). At 96 hr, Papio was unexpectedly the most effective species with the highest gas production (53.1 ml)>zebra (51.2 ml)>gelada (49.4 ml). With a concentrate standard, 12-hr gas production was as follows: T. gelada (38.5 ml)>Equus (36.8 ml) = Papio (36.4 ml). At 24 hr, gas production differed: Papio (51.7 ml)>Equus (47.0 ml) = T. gelada (46.8 ml). At 96 hr, zebra was the most effective species with the highest gas production (63.9 ml)>Papio (60 ml) = T. gelada (59.9 ml). In conclusion, the results show that the microbial population present in gelada feces is able to ferment forage and concentrate substrates in vitro, although this fermentation did not occur with the expected effectiveness. Future studies should therefore focus also on the bacteria species involved.

Diet of Theropithecus from 4 to 1 Ma in Kenya

“…The δ 13 C values of tooth enamel from modern and fossil browsers are about −12‰ in open forests through grasslands, whereas grazers have δ 13 C values near 2‰, and mixed feeders have intermediate values (16)(17)(18)(19). We note that mammals from closed canopy forests are even more depleted in 13 C than those mammals from open forests (20). Previous studies using isotopes in fossil primates show dietary preferences from pure C 3 -derived to predominantly C 4 -derived diets (21)(22)(23)(24)(25)(26)(27).…”

“…The diet of Homo was consistently depleted in 13 C compared with Theropithecus (26), with little overlap in the range of δ 13 C values. Although Homo consumed a mixed C 3 -C 4 diet, its reliance on C 4 resources was considerably less than Theropithecus.…”

“…Today, a single species of Theropithecus is restricted to montane regions in Ethiopia; Papio is found throughout most of Africa. Modern baboons in Africa have δ 13 C 1750 values that indicate a diet dominated by C 3 diet resources (Fig. 2), but some baboons show a component of C 4 -based resources in their diets.…”

“…During the Pliocene, Theropithecus was thought to have occupied an ecological niche that is dominated today by ungulates, many of which are ruminants; thus, Theropithecus may have shared some of the dietary features of ungulates (such as being capable of chewing and digesting large volumes of low-quality, high-fiber, and/or highly siliceous vegetation), although Theropithecus did not have the benefit of hooves or ruminant digestion (11). Modern geladas are able to masticate grass as effectively as an equid, and they can also ferment cellular material from grass in their hindguts but less effectively than a zebra, which may have aided in this adaptation (6,12,13). Even with the richness of the genus's fossil record and the many paleoecological and functional anatomical studies that have speculated on the respective habitat and dietary preferences of the T. brumpti and T. oswaldi lineages, many questions remain about their respective dietary specializations and how they may have contributed to the eventual extinction of both lineages.…”

“…Stable isotope ratios of 13 C/ 12 C are ideally suited to test this hypothesis because of the difference in isotope ratios between C 3 plants (most dicots) and C 4 plants (grasses and sedges, both of which are monocots) in the tropics; the dietary distinction between C 3 and C 4 plant-derived foods is preserved in the fossil record of Africa for most of the past 10 Ma (14,15). The δ 13 C values of tooth enamel from modern and fossil browsers are about −12‰ in open forests through grasslands, whereas grazers have δ 13 C values near 2‰, and mixed feeders have intermediate values (16)(17)(18)(19).…”