Abstract:
According to Bergmann’s rule, organisms that live in colder regions usually have a larger body size, in contrast to those in warmer climates. Conversely, Allen’s rule proposes that animals living in cold environments generally have shorter limbs, ears, and other appendages compared with related species in warmer environments. Here, we investigated the geographic variation in body size and limb length of male Minshan’s Toads (Bufo minshanicus) across nine different elevations on the eastern Tibetan plateau to assess the validity of Allen’s rule and Bergmann’s rule. Our results found that mean male body size decreases with increasing altitude, which does not conform to Bergmann’s rule. We also found a clear negative linear correlation between altitude and limb lengths after accounting for snout–vent length, supporting Allen’s rule. The shorter relative limb length and decreased surface-to-volume ratio of the extremities that we found in Minshan’s Toads might improve thermoregulatory capacity in cooler climates through slower heating and cooling. However, selective pressures from alternative climatic factors (e.g., annual mean temperature, potential evapotranspiration, and water deficit) could be responsible for the reduction in extremity length at higher elevations.