How melanism affects the sensitivity of lizards to climate change

The impact of climate change on global biodiversity is firmly established,
but the differential effect of climate change on populations within the
same species is rarely considered. In ectotherms, melanism (i.e. darker
integument due to heavier deposition of melanin) can significantly
influence thermoregulation, as dark individuals generally heat more and
faster than bright ones. Therefore, darker ectotherms might be more
susceptible to climate change. Using the color-polyphenic lizard
Karusasaurus polyzonus (Squamata: Cordylidae), we hypothesized that, under
future climatic projections, darker populations will decrease their
activity time more than brighter ones due to their greater potential for
overheating. To test this, we mechanistically modeled the body
temperatures of 56 individuals from five differently-colored populations
under present and future climate conditions. We first measured
morphological traits and integumentary reflectance from live animals, and
then collected physiological data from the literature. We used a
biophysical model to compute activity time of individual lizards as proxy
for their viability, and thereby predict how different populations will
cope with future climate conditions. Contrary to our expectations, we
found that all populations will increase activity time and, specifically,
that darker populations will become relatively more active than bright
ones. This suggests that darker populations of K. polyzonus may benefit
from global warming. Our study emphasizes the importance of accounting for
variation between populations when studying responses to climate change,
as we must consider these variations to develop efficient and specific
conservation strategies.