Digestive Physiology of the Ground Cuscus (Phalanger gymnotis), a New Guinean Phalangerid Marsupial

Abstract

Digestive-tract morphology and function were studied in the ground cuscus (Phalanger gymnotis), reported to be the most frugivorous of eight species of New Guinean phalangerid marsupials. When offered a mixed diet of fruit and foliage, captive animals selected a diet of more than 90% fruit. Fibre digestibility was low and variable, but apparent digestibilities of both dry matter (90%) and energy (87%) were high, and intake of digestible energy was similar to that of the Australian phalangerid Trichosurus vulpecula (common brushtail possum) in captivity. The small intestine of P. gymnotis was the longest and heaviest region of the gastrointestinal tract, but the stomach contained more digesta. The total nitrogen content of digesta was low in the stomach and small intestine, but increased four-fold in the hindgut, because of microbial activity. No difference in nitrogen concentration or in the proportions of small or medium particles was found along the hindgut, but the caecum contained a smaller proportion of large particles than the distal colon. The transit time of a large particle marker was much longer than that of a solute marker, but mean retention times (MRTs) of the two markers did not differ. Both transit times and MRTs were long relative to those reported in T. vulpecula. Although fermentation rates in the caecum and proximal colon were similar to those in T. vulpecula on a foliage diet, fluid volumes were less than one-third those of T. vulpecula, and, consequently, daily production of short-chain fatty acids (SCFAs) was less than half that in T. vulpecula, and contributed only 5% of digestible energy intake (v. 15% in T. vulpecula). These results are consistent with reports that the natural diet of P. gymnotis is based largely on fruit rather than on foliage.