Reduction of the metabolic level by phenotypic plasticity involved in
cave colonization by the Pyrenean newt Calotriton asper
Abstract
To test the hypothesis whether a lower metabolic rate is expected in
cave organisms compared to surface ones due to an adaptation to food
scarcity in subterranean environments, we measured the oxygen
consumption rates of individuals from hypogean (i.e. subterranean) and
epigean (i.e. surface) populations of the troglophilic newt Calotriton
asper. We found that epigean individuals exhibit higher rates than
hypogean ones and showed that when we acclimated epigean C. asper to
cave conditions, these individuals reduced their oxygen consumption. We
compared the metabolic levels of hypogean and epigean C. asper
acclimated and non-acclimated to the cave, with the obligate cave
salamander Proteus anguinus as wells as two epigean species: an urodel
(Ambystoma mexicanum) and a fish (Gobio occitaniae). As predicted, we
find differences between hypogean and epigean species, and that the
troglophilic C. asper exhibited in-between performances. We argue then
that this shift of the metabolic level observed between epigean C. asper
non-acclimated and acclimated to the cave is not directly due to the
food availability in our experiments but to a stasis of the temperature.
However we then discuss that this adjustment of the metabolic level
under a temperature close to the thermal optimum may secondarly allow
individuals to cope with the food limitations of the subterranean
environement.