Female lizards (Eremias argus) reverse Bergmann’s rule across altitude

The evolution of body size within and among species is predicted to be
influenced by multifarious environmental factors. However, the specific
drivers of body size variation have remained difficult to understand
because of the wide range of proximate factors that covary with ectotherm
body sizes across populations with varying local environmental conditions.
Here, we used female Eremias argus lizards collected
from different populations across their wide range in China and
constructed linear mixed models to assess how climatic conditions and/or
available resources at different altitudes shape the geographical patterns
of lizard body size across altitude. Lizard populations showed significant
differences in body size across altitudes. Furthermore, we found that
climatic and seasonal changes along the altitudinal gradient also
explained variations in body size among populations. Specifically, body
size decreased with colder and drier environmental conditions at high
altitudes, reversing Bergmann’s rule. Limited resources at high altitudes,
measured by the low vegetative index, may also constrain body
size. Therefore, our study demonstrates that multifarious
environmental factors could strongly influence the intraspecific variation
in organisms’ body size.