Circadian Rhythmicity, Respiration and Behavior in Hypogean and Epigean Salamanders

Hervant, F., Mathieu, J. & Durand, J. P.: Circadian rhythmicity, respiration and behavior in hypogean and epigean salamanders. Nat. Croat., Vol. 10, No 3, 141–152, 2001, Zagreb. Comparisons of circadian rhythmicity, behavior, and metabolism between surface and cavedwelling salamanders enable elucidation of evolutionary trends in these processes. The obligate cave-dwelling proteid Proteus anguinus did not show any apparent daily rhythm of activity or resting metabolic rate. In contrast, the surface-dwelling salamandrid Euproctus asper had a circadian SMR and activity cycle. These circadian rhythms possessed an endogenous component. The lives of both salamanders studied were characterized by long periods of inactivity punctuated by bouts of foraging or exploratory/predatory behavior. Proteus anguinus had reduced resting metabolic and spontaneous activity rates (considerably lower than most surface-dwelling amphibians), and therefore appears to be a good example of a vertebrate as a low-energy system. The low metabolic and activity rates of P. anguinus are interpreted as adaptations to a subterranean existence where poor and discontinuous food supplies and/or intermittent hypoxia may be present for long periods.