Selection of physiological and metabolic adaptations to food deprivation in the Pyrenean newt Calotriton asper during cave colonisation

Food restriction is one of the major and most common constraints that subterranean animals face in their biotope. Cave-dwelling organisms thus have to cope with fasting periods that can extend from a month to a year. However, adaptive fasting resistance previously found in subterranean fauna has only been highlighted by direct comparisons with phylogenetically distant epigean organisms, which could severely impact conclusions. Here we report physiological and metabolic responses to 42 days of fasting followed by 10 days of refeeding in two populations (one subterranean and one epigean) of Calotriton asper. In the fed state (control), the hypogean population exhibited a hypometabolism together with higher glycogen (+ 25% in liver and muscles) and triglyceride stores (+ 50% in muscles). During the fasting period, cave individuals exhibited a 20% decrease in VO₂ whereas epigean individuals experienced no significant change. In addition, the energetic reserves always remained higher in the hypogean population. According to phylogenic and biogeographic data, cave colonization by this species dates back to less than 10,000 years, suggesting a rapid selection of adaptive traits related to fasting. This study strongly suggests that cave colonization induces a decrease in metabolism together with a higher capacity to accumulate energy reserves and therefore to withstand unpredictable fasting periods.