Coping with environmental stress: The effects of wastewater pollutants on energy stores and leptin levels in insectivorous bats

Abstract

Anthropogenic environmental stress imposes increasing pressure on ecosystems. Wastewater treatment works (WWTWs) are major stressors in urban environments and are associated with high levels of pollutants that bioaccumulate and elicit stress responses in animals such as bats. Stress responses are linked with increased metabolic rate and may result in energy store depletion. In this study we measured the effects of WWTWs on energy stores and leptin levels in the insectivorous bat, Neoromicia nana. Energy stores including glucose, glycogen, lipids and proteins were measured in the storage tissues (liver and pectoral muscles) and blood of bats. Further, lactic acid was measured in the pectoral muscles to provide an indirect measure of anaerobic respiration and stress. Leptin, the hormone associated with satiation, and hypoxia inducible factor 1α (Hif-1α) were measured in the interscapular brown adipose tissue (iBrAT). Bats caught at WWTWs exhibited significantly higher pectoral glucose and lactic acid concentrations than bats at reference sites, indicating a stress induced increase in glucose demand and increased reliance on gluconeogenesis to fuel this response. However, glycogen, lipid and protein stores were not depleted in WWTW bats. This may be due to their fat-rich diet at WWTW sites. Moreover, this high polyunsaturated fatty acid (PUFA) diet may be responsible for the unexpectedly high leptin levels in WWTW bats. Lactic acid concentrations were elevated in the pectoral muscles of bats at WWTW sites, indicating some degree of oxidative stress although there was no increase in iBrAT Hif-1α levels. These results show that in the face of environmental stresses, N. nana is able to maintain energy stores.