A number of peramelid (bandicoot and bilby) species have been negatively affected since European settlement with introduced predators, competition from introduced species and altered habitat all being implicated in their decline or extinction. Peramelids are broadly classified as omnivores and possess relatively uncomplicated gastrointestinal tracts. However, variation in diet and morphology of the gastrointestinal tract exists between species. Differences among species’ preferences for habitat, their geographic distribution, phylogeny, and variation in diet or a combination of these may account for some of these differences. The majority of research on peramelids has focussed on three species, Isoodon macrourus, Perameles nasuta and Macrotis lagotis. Despite this, significant gaps exist in our understanding of the nutritional physiology of peramelids. Given the seasonally variable diet of I. macrourus (northern brown bandicoot), it was hypothesised that basic gastrointestinal attributes, such as gut morphology, histology, passage rate of ingesta, as well as gut microbial populations would change with diet to maximise nutrient capture by the bandicoot.
This research investigated the effect of dietary treatment on the digestive performance, morphology, histology and bacterial profile of the gastrointestinal tract of captive I. macrourus. The bacterial profiles of faecal samples from free-living I. macrourus were also examined. Three experimental diets were tested during this research, herbivorous, omnivorous and insectivorous. The bandicoots consumed between 23.9 and 35.5 g DM/d. The bandicoots maintained or gained liveweight when fed the omnivorous and insectivorous diets. The herbivorous diet had lower nutritive value than the insectivorous and omnivorous diets which was reflected in the significantly lower apparent digestibilities of dry matter (P < 0.0001), organic matter (P < 0.0001), gross energy (P < 0.0001), total lipid (P < 0.0001), total nitrogen (P < 0.0001) and acid detergent fibre (P < 0.003). The poorer nutrititive value of the herbivorous diet resulted in a decrease in liveweight of the captive I. macrourus, however the bandicoots fed the herbivorous diet were able to partly compensate for the reduced nutritive value by consuming significantly more feed (P < 0.02) than bandicoots on the insectivorous or omnivorous diets. As expected, the results for the omnivorous diet were between those for the insectivorous and herbivorous diets. The solute marker, Co-EDTA, was retained significantly longer in bandicoots fed the insectivorous diet (P = 0.025) than bandicoots fed the herbivorous diet. The mean retention time of the particle marker, Cr-CWC, did not differ in bandicoots fed the three experimental diets.
On three occasions I. macrourus fed the herbivorous diet were observed to be coprophagic. This may have been a mechanism for coping with a nutritively poor diet. Coprophagy may have resulted in the consumption of microbial protein which would have incidentally increased nitrogen intake, leading to reduced liveweight losses in these animals. Coprophagy may also have affected the ingesta retention results of the I. macrourus in this study by bandicoots re-consuming markers.
In the histology study, the first description of the gastrointestinal tract, from stomach to colon, of adult I. macrourus was provided. Dietary treatment had minimal effect on the histology of the gastrointestinal tract of I. macrourus. An unusual feature of the small intestine was that the long villi were folded into a zig-zag formation. Although it is possible that this observation was an artefact of preservation and has not been previously reported in I. macrourus, it has been observed in the long-nosed bandicoot, Perameles nasuta and other mammals such as bats and rats. The functional benefit that this feature would convey is unknown.
This research has presented a preliminary investigation into the bacteria present in the gastrointestinal tract of captive I. macrourus and the faeces of free-living bandicoots of this species. The bacterial profiles generated from captive (gastrointestinal) and free-living (faeces) I. macrourus were diverse. The small intestine differed in its bacterial profile from the remainder of the intestinal tract (caecum, proximal colon and distal colon). Seventeen bacterial species were identified in this research from the faeces of free-living I. macrourus, approximately half of these were Clostridium species. Kluyvera ascorbata and some Citrobacter species are considered to be pathogenic and were identified in the faeces of free-living I. macrourus. These bacterial species could have been consumed during foraging but may form part of the core bacteria for I. macrourus.
In conclusion, I. macrourus has the ability to rapidly adapt to changing diets, with minimal effect on the morphology and histology of the gastrointestinal tract. The hindgut has been confirmed as the main site for microbial fermentation in this species. The bacterial profiles from the hindgut segments, caecum, proximal colon and distal colon, were more similar to each other than to the small intestine.