Masters Degrees (Zoology)

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Aspects of digestion and physiology in Wahlberg's epauletted fruit bat (Epomophorus wahlbergi)
(2012) Mqokeli, Babalwa R.; Downs, Colleen Thelma.
Degradation of forest environments in South Africa have greatly affected both the plants and animals that interact with these plants. It is therefore important to understand plant-animal interactions in forest ecosystems in an effort to develop strategies for forest conservation. Animal dispersal can assist in the restoration of forest plant diversity and consequently animal diversity. Wahlberg’s epauletted fruit bat (Epomophorus wahlbergi) occurs in the eastern part of South Africa and is known to feed on fruit, nectar, pollen and flowers. It is an important disperser of various indigenous and alien invasive forest fruit species. Little is known about the benefits these bats get from feeding on fruit. Furthermore, the buccal cavity and lingual adaptations of fruit bats in Southern Africa are unknown. This study investigated morphological and physiological adaptations for frugivory in E. wahlbergi. In particular, the palatal and lingual morphological structures of E. wahlbergi were examined by light microscopy and scanning electron microscopy. The results of this study showed that the morphological structures of tongue papillae in E. wahlbergi were similar to that of other fruit and nectar feeding bats. The structural arrangement of tongue papillae in E. wahlbergi probably allows food to move from the anterior part of the tongue and collect at the median line of the posterior part of the tongue, and thereafter move down to the pharynx. These bats had an elongated tongue, wide, flattened molar teeth, and a hard papillae structure observed on the upper palate at the posterior end of the buccal cavity. This papillae structure has not been described previously; and it appears that it is with this structure, together with the palatal ridges, and teeth that E. wahlbergi crushes fleshy fruit to extract the juices when feeding. Consequently palatal and lingual structures of E. wahlbergi showed morphological adaptations for efficiently feeding on fleshy fruit and nectar. South African indigenous and exotic fleshy fruits available to E. wahlbergi are found to be generally hexose dominant. These bats are suggested to have high glucose intake irrespective of sugar concentration to power their high energy demands due to flight. High glucose intake could result in increased blood plasma glucose levels which are detrimental to mammals of small body size. This study investigated the diel variations in blood plasma glucose concentrations of E. wahlbergi. Epomophorus wahlbergi’s blood plasma glucose concentration was lower (5.24 ± 0.38 mm ol/l) at 18h00 before feeding and increased during/after feeding (8.19 ± 1.24 mm ol/l), however bats appeared to regulate it within limits. Their range in concentrations was higher than the normal mammalian blood plasma glucose concentrations range. Consequently these bats appear to regulate their blood plasma glucose concentration although at a range higher than normal mammalian levels and thus reduce the negative consequences associated with hyperglycemia. The data obtained provide a baseline for comparison with free-ranging E. wahlbergi. Proteins are important in a diet to provide the required nitrogen and amino acids necessary for maintaining body tissues. Fruits, however, appear to have energy-rich but protein-limited foods. Frugivores that feed exclusively on fruit may therefore have difficulties in maintaining their protein requirements since fruits are generally high in sugar content but low in protein content. The importance of protein in the diet of E. wahlbergi was determined by measuring diet intake at varying levels of protein in the laboratory. Epomophorus wahlbergi were offered equicaloric 15 % glucose solutions with varying protein concentrations (2.58, 5.68, 7.23 g soy protein/kg H2O) and a solution with no protein. This was repeated using 15 % sucrose instead of glucose solutions. Epomophorus wahlbergi’s volumetric intake of the respective glucose and sucrose solutions varied among individual bats, with total volumetric intake highest for the solution with no protein (control) and lowest at 2.58 g/kg soy protein concentration solution for glucose and 5.68 and 7.23 g/kg soy protein concentration for sucrose. These bats appeared to prefer sugar solutions without or low protein, and their daily protein intake was relatively low. This suggests they have low-protein requirements, and this relates to their characteristic low-protein fruit available in the wild. Feeding and digestive efficiency has been widely studied in frugivorous and/or nectarivorous birds but relatively few studies have been done on bats, particularly African bats. Feeding on a liquid nectar diet and fruit juices could cause physiological challenges for nectarivores and/or frugivores as they have to balance water and energy intake from this liquid diet. Mammalian kidneys have to eliminate salts and nitrogenous wastes, conserve water during water restriction as well as excrete it when ingested in excess. Morphological renal characters are known to be reliable indicators of urinary concentrating abilities in mammals. Short digesta residence time is a digestive trait that is known to be associated with frugivory and this may be a problem since digestive efficiency is a function of the length of digesta retention time. Histological sections of E. wahlbergi kidneys and small intestines were examined under microscopy to determine water regulation and specialization for sugar absorption respectively. Cortex and medulla length measurements were taken to calculate the medulla: cortex ratio (M/C) and the percent medullary thickness (PMT). The observed M/C ratio and PMT of E. wahlbergi is typical of a mesic species. Epomophorus wahlbergi feeds on a watery diet and does not need to concentrate urine; therefore the medulla and cortex were more or less the same size. Analysis of the histological sections showed that the kidney structure of these bats allows efficient water regulation in a mesic environment. The microvilli of E. wahlbergi intestine were relatively long with a large surface area thus serves the purpose for efficient digestion and absorption of sugars in these bats. Future studies need to be done to determine the mechanisms by which these bats regulate their blood plasma glucose levels, and also determine intake on a selection of fruit in order to broaden research to adaptation of these bats on low-protein diets. This study contributes to a greater understanding of the physiological and morphological mechanisms that may affect fruit intake and consequently dispersal. It will contribute to a greater understanding of plant-animal interactions in southern Africa.
Seasonal home range and foraging movements of the Wahlberg's epauletted fruit bat (Epomophorus wahlbergi) in an urban environment.
(2012) Rollinson, Dominic Paul.; Downs, Colleen Thelma.; Coleman, Joy Carol.
Urbanisation through the process of habitat loss and fragmentation has caused drastic changes in ecosystem dynamics around the world. Many species can no longer survive in these urban areas; however there are those species that have been able to survive and in fact thrive in the newly created habitats. With increasing urbanisation it is important that animals are able to adjust to a life in close association with humans. One such group of organisms which has adjusted well to urbanisation is the suborder Megachiroptera (Chiroptera). Some species from this suborder have benefited from increased food and roost resources in certain urban areas. Exotic fruiting plants (introduced purposely and accidentally) as well as increased cultivated gardens have provided additional food sources in some urban environments, while man-made structures, and increased suitable vegetation, have provided additional roosting opportunities. Although these urban dwelling species live in close association with humans, very little is known of their ecology in urban areas. Wahlberg's epauletted fruit bat Epomophorus wahlbergi is one such species of which little is known of its suburban ecology despite its increased presence in many urban areas. This study on the ecology of E. wahlbergi was conducted from February to October 2011 in the urban environment of Pietermaritzburg, South Africa. The aim was to examine foraging movements and habitat use of E. wahlbergi in this urban environment. The objectives were to determine seasonal differences in foraging movements and home range sizes in this urban environment. In addition the roosting dynamics and roost characteristics of E. wahlbergi in this urban environment were determined. In late summer, it was found that individual E. wahlbergi movements ranged considerably, with some bats making extensive flights to different parts of town while others stayed in particular areas throughout; no bats were recorded to have left the urban environment. Some of the larger distances covered in a single night's movements were two and five km. In late summer roosting fidelity varied between individual bats; all the individual bats changed their roosts at least once during late summer. Some individuals had as many as three known daytime roost sites. There was a difference in home range size between the sexes; with females occupying a larger home range size than males. This variation in movement patterns of individual bats suggests that their social interactions, roost site preferences, or dietary preferences vary between individuals in late summer. A significant difference in home range size and habitat use by E. wahlbergi was found between winter and spring, with home range sizes being larger in winter. The increased home range sizes and habitat use in winter were a consequence of bats feeding on the fruits of the alien invasive Syringa (Melia azedarch) with few other trees in fruit. Consequently bats had to move greater distances for food in winter. In spring, fruit availability was greater and more varied including both indigenous and exotic fruits. Consequently in winter, the bats were more reliant on a few fruiting species to meet their dietary requirements than during spring. Bats changed their roosts regularly in summer, winter and spring. There was considerable variation in roost temperatures however roost temperatures were higher than ambient temperatures. Roosts in man-made structures were higher in temperature than those in natural vegetation. This study suggests the importance of temperature in the selection of daytime roosts, however other factors such as predator avoidance and proximity to food resources are also considered in selection of daytime roosts. Within the order Chiroptera, species from the suborder Microchiroptera have generally not been well represented in urban areas, it is important that the reasons for this be better understood. Further research is still required to better understand the ecology of urban dwelling species as well as to understand the reasons why many species are not able to adjust to urban environments.

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Browsing Masters Degrees (Zoology) by Subject "Bats--Food."