Glucose Metabolism Capacity In Fruit Bats (Pteropodidae) And Effects Of Ethanol Concentration In Diet On Food Intake Of Captive Nectarivore Bats (Eonycteris Spelaea)

Chiropetra, commonly called bats, is the second largest order of mammals with relatively high species diversity and various feeding habits. Although increasing people devoted themselves to bat research, we know little about bat’s energy metabolism. In recent years, the prevention and treatment of sugar metabolic diseases as diabetes are facing many difficulties, so some researchers are beginning to focus on fruit bats, which can use rapidly and efficiently high-sugar diet with some possible particular mechanism of sugar utilization and aim to get some hints to improve the modeof dealing with human sugar metabolism diseases. Based on the domestication practices for bats for years, we choose three fruit bats as main research objects, to explore their ecological and behavioral pattern of sugar metabolism and glucose regulation, and the results were as following:Firstly, to test the glucose metabolism ability of fruit bats at rest, we conducted intraperitoneal glucose tolerance test on phytophagous bats, Cynopterus sphinx,Rousettus leschenaultia, Eonycteris spelaea, and insectivorous bats, Hipposideros armiger, Miniopterus schreibersii. We found the rate of glucose metabolism in phytophagous bats was higher than insectivorous bats. And among the fruit bats,glucose metabolism in C. sphinx was faster than E. spelaea. We considered that the comprehensive effects of excess expression of intestinal sucrose and maltase, strong paracellular absorption and the direct fuel with exogenous sugar made fruit bats having a higher metabolic rate of glucose than insectivorous bats. There were also some difference between C. sphinx and E. spelaea of in glucose metabolism due to the distinction in ecological habit and foraging strategy.Secondly, we investigated blood glucose regulation in nectar-feeding bats(E.spelaea) and fruit-eating bats(C. sphinx). We varied the amount of dietary sugar or flight time in the experiments. Blood glucose levels increased with the quantity of glucose ingested. The maximum blood glucose concentrations of C. sphinx exceeded 24mmol/L, which was a very high values ever recorded in the mammals fed sugar quantities similar to their natural diet. However, the blood glucose levels of E. spelaea were always under 15 mmol/L. During normal feeding, blood glucose values decreased with increasing flight time. Blood glucose fell to expected values when E. spelaea spent60-75 percent of their time airborne. In spite of blood glucose levels of C. sphinx were not falling back to the fast level after spent 75 percent of time on air, it did decline a lot.Either fruit bats had evolved some mechanisms to avoid negative health effects of hyperglycaemia, or high activity was the key to balance blood glucose levels during foraging. We suggested that the coevolutionary specialization of bats toward a carbohydrate-rich diet was supported by the high activity and elevated metabolic ratesof these bats. High activity might have conferred benefits to the bats in terms of behavioural interactions and foraging success, and was simultaneously likely to have increased their efficiency as plant pollinators.Finally, we also tested whether ethanol could act as an appetitive stimulant and influenced the quantity of food consumption by captive bats. Fruit bats generally choose to eat nectar or ripe fruits in which ethanol concentration increases as ripening. So, we offered the captive bats different food(sucrose solution) containing 7 level concentrations of ethanol( 0.005, 0.01, 0.05, 0.1, 0.3, 0.5 or 1% respectively), to test whether the bats’ response was positive or negative, i.e., they ate more or less when ethanol in the food increased comparing to control(ethanol free). The results showed that E. spelaea did not change consumption when food contained 0.005% ethanol, but significantly decreased consumption at higher levels of ethanol concentration(≥0.01%),and even when ethanol concentration in food went up to 1%, the food consumption was only 34% that of ethanol free. The results indicated that ethanol in food had a negative influence on food intake, but the reasons for this remained to be tested further.In summary, physiological adaptation plus high-intensity-exercise lifestyle, were necessary for fruit bats to protect from hyperglycemia in spite of taking predominantly sugar-rich food, and this also provideds some implication for therapy and precaution of human hyperglycemia.