Body Size Increases with Elevation in Pyrenean Newts ( Calotriton asper )

Abstract

Phenotypic variation along environmental gradients—particularly in body size—occurs in a variety of species. Larger-bodied individuals are usually found in colder climates, as predicted by Bergmann’s rule. In ectotherms, this pattern remains controversial. Among thermoconformers, smaller body sizes are expected in colder climates because these species might have relatively shorter warm-up times (advantageous in cold climates), whereas the reverse pattern can be expected in thermoregulators (heat-balance hypothesis). In amphibians, additional factors like humidity and thermal niche might also contribute to body-size variation. Following Allen’s rule, there can also be a negative relationship between temperature and relative limb length. Here, we described associations among temperature, precipitation, body size, and relative limb length in Calotriton asper. We expected individuals from higher elevations (colder climates) to be smaller when compared to lowelevation conspecifics. We found an influence of temperature on body-size variation but, contrary to expectations, salamanders from colder climates were larger compared to low-elevation populations, which corroborates with the heat-balance hypothesis. In accordance with the converse water-availability hypothesis, we also demonstrated that precipitation was related to body-size variation in this species. Finally, our results supported the predictions of Allen’s rule. This trend could be the result of evolutionary responses to harsh environments, driven by either local adaptation, plasticity processes, or a combination of both.