Metabolism and circadian rhythms of the European blind cave salamander Proteus anguinus and a facultative cave dweller, the Pyrenean newt (Euproctus asper)

Comparisons of circadian rhythmicity, behavior, and metabolism between surf ace- and cave-dwelling salamanders allow evolutionary trends in these proce sses to be elucidated. The proteid Proteus anguinus, an obligate cave-dwell er, showed no apparent daily rhythm of activity or resting metabolic rate. In contrast, the salamandrid Euproctus asper, a surface-dweller/facultative cave-dweller, had a circadian resting metabolic rate and activity cycle. T hese circadian rhythms had an endogenous component. The lives of both studi ed salamanders were characterized by long periods of inactivity punctuated by bouts of foraging or exploratory/predatory behavior. Proteus anguinus ha d reduced resting metabolic and spontaneous activity rates (considerably lo wer than those of most surface-dwelling amphibians), and therefore appears to be a good example of a vertebrate as a low-energy system. The low metabo lic and activity rates of P. anguinus are interpreted as adaptations to a s ubterranean environment, where a poor and discontinuous food supply and (or ) intermittent hypoxia may be present for long period.