FINKLER, MS; CULLUM , KA: Interspecific and sex-related differences in metabolism and post-reproductive energy reserves in spring-breeding Ambystomid salamanders.

We investigated potential differences in post-reproductive metabolism and energy reserves between male and females of three species of spring breeding Ambystomid salamanders (Ambystoma maculatum, A. texanum, and A. tigrinum). Size-adjusted O₂ consumption rates did not differ among species or between sexes, but CO₂ production rates were higher in A. tigrinum than in the other two species, and male A. tigrinum and A. texanum had higher CO₂ production rates than did female conspecifics. Across species, respiratory quotients were significantly higher in males (0.93) than in females (0.86), suggesting that males rely more on carbohydrates for aerobic respiration than do females. Size-adjusted total body triglycerides were higher in males than in females in A. maculatum, but not in the other two species. In both sexes, triglyceride contents were lower in A. tigrinum than in A. texanum. Free glucose contents did not differ among species or between sexes. Among species A. maculatum had lower relative glycogen contents than did either A. tigrinum or A. texanum. Estimated stored energy for combined glycogen and triglyercide contents was higher in male A. maculatum and A. tigrinum than in females. These findings indicate notable differences in the use of available energy substrates between male and female ambystomid salamanders, and suggest possible sex-based differences in the energetic cost of metabolism in at least some species of salamander that could contribute to life history characteristics such as size dimorphism, differences in age of sexual maturity, asynchronous arrival times at breeding areas, and differential survival between the sexes.