Sugar assimilation and digestive efficiency in Wahlberg's epauletted fruit bat (Epomophorus wahlbergi)

Bats: Body mass index, forearm mass index, blood glucose levels and SLC2A2 genes for diabetes

Bats have an unusually large volume of endocrine tissue, with a large population of beta cells, and an elevated sensitivity to glucose and insulin. This makes them excellent animal models for studying diabetes mellitus. We evaluated bats as models for diabetes in terms of lifestyle and genetic factors. For lifestyle factors, we generated data sets of 149 body mass index (BMI) and 860 forearm mass index (FMI) measurements for different species of bats. Both showed negative inter-species correlations with blood glucose levels in sixteen bats examined. The negative inter-species correlations may reflect adaptation of a small insectivorous ancestor to a larger frugivore. We identified an 11 bp deletion in the proximal promoter of SLC2A2 that we predicted would disrupt binding sites for the transcription repressor ZNF354C. In frugivorous bats this could explain the relatively high expression of this gene, resulting in a better capacity to absorb glucose and decrease blood glucose levels.

Digestive adaptations of aerial lifestyles

Flying vertebrates (birds and bats) are under selective pressure to reduce the size of the gut and the mass of the digesta it carries. Compared with similar-sized nonflying mammals, birds and bats have smaller intestines and shorter retention times. We review evidence that birds and bats have lower spare digestive capacity and partially compensate for smaller intestines with increased paracellular nutrient absorption.

The sweet side of life: nectar sugar type and concentration preference in Wahlberg's epauletted fruit bat

Whether nectarivores or frugivores place selective pressure on the plants they feed on, in terms of nectar or fruit traits, is much debated. Globally sugar preferences, concentration preference and digestive ability of avian nectarivores have been extensively researched. In contrast, relatively little is known about mammalian nectarivores or frugivores in terms of these, particularly Old World species. Consequently effect of sugar type and concentration on food preference in Wahlberg's epauletted fruit bat Epomophorus wahlbergi was investigated. Pair-wise choice tests were conducted using equicaloric hexose and sucrose solutions at five different concentrations (5%-25%). It was expected that they would prefer hexose sugars as these are dominant in available indigenous fruits. However, bats preferred hexoses only when offered dilute (5%) concentrations. From 10% to 25% they showed a decrease in volume intake. Their body mass was generally higher and similar after feeding during the night with the exception of 5% concentration where the mean body mass decreased. When E. wahlbergi were offered a range of sucrose or hexose solutions (10%-25%) respectively, they showed no concentration preference in terms of total volume consumed, nor energy intake. These findings suggest that these fruit bats do not appear to act as a selective pressure on sugar composition in Old World fruit. In fruit bats with high energy requirements, dietary flexibility may be an advantage when faced with seasonal and unpredictable fruit availability.