Material and Energy Balance of some Captive and Free-ranging Reptiles in Western France

Abstract

Abstract Rates of turnover of water, energy and sodium were measured in free-ranging and enclosed Lacerta viridis and Vipera aspis at a site in Western France in late summer. Rates of CO2 production did not differ significantly between free-ranging Lacerta and those maintained in large outdoor enclosures and averaged 0.371 ± 0.056 mL(g.hr)-1 which was significantly greater (P < 0.05) than the rate of 0.152 ± 0.02 mL(g.hr)-1 recorded for Vipera aspis living in similar outdoor enclosures. Rates of water, but not sodium, turnover were significantly greater in free-ranging than in enclosed Lacerta (12.03 ± 1.21 mL(100g.day)-1 versus 7.46 ± 1.03 mL(100g.day)-1 respectively), suggesting that the free-ranging individuals, which were captured along a canal, had access to a source of free water not linked with their diet. Field Metabolic Rates (FMR) of Lacerta were positively and significantly correlated with the rate of water turnover and analysis of influx and efflux data indicate that this lizard requires on the average approximately 8mL(100g.day)-1 of water to maintain its hydric balance. A similar analysis suggests that this species requires roughly 1meq(kg.day)-1 of sodium for the maintenance of electrolyte balance. Rates of sodium and water turnover were significantly correlated in captive Lacerta, the diet of which was supplemented daily with mealworms and crickets, but the correlation in the case of animals living by the canal was not significant, indicating again that sources of water and sodium intake were independent in these individuals. Rates of water and sodium turnover were low in the vipers maintained in external enclosures and both elements were in negative balance, as would be expected with non-feeding animals. The data reveal a small but significant intake of sodium however, which was not identified. A regression of water intake versus rate of weight loss suggest that Vipera aspis requires an intake of approximately 2.5mL(100g.day)-1 to maintain hydric balance under these conditions. The data reported here for FMR's and rates of water turnover are compared with those for other lizards in the literature and suggest that Lacerta viridis falls mid-way between desert and tropical species studied to date. Further work with temperate-living species should prove of value in delineating the physiological capacities of terrestrial reptiles.