Data for: Body size and substrate use affect ventral, but not dorsal, brightness evolution in lizards

Substrate properties can affect the thermal balance of organisms, and the
colored integument, alongside other factors, may influence heat transfer
via differential absorption and reflection. Dark coloration may lead to
higher heat absorption and could be advantageous when substrates are cool
(and vice versa for bright coloration), but these effects are rarely
investigated. Here, we examined the effect of substrate reflectance,
specific heat capacity (cp), and body size on the dorso-ventral brightness
using 276 samples from 12 species of cordylid lizards distributed across
26 sites in South Africa. We predicted, and found, that bright ventral
colors occur more frequently in low cp (i.e. drier, with little
energy needed for temperature change) substrates, especially in larger
body-sized individuals, possibly to better modulate heat transfer with the
surrounding environment. By contrast, dorsal brightness was not associated
with body size nor any substrate thermal property, suggesting selection
pressures other than thermoregulation. Ancestral estimation and
evolutionary rate analyses suggest that ventral brightness rapidly
differentiated within the Cordylinae starting 25 Mya, coinciding with an
aridification period, further hinting at a thermoregulatory role for
ventral colors. Our study indicates that substrate properties can have a
direct role in shaping the evolution of ventral brightness in ectotherms.