The thermal requirements of ectotherms may vary among species due to adaptation to
different thermal environments. Nevertheless, some of these requirements are evolutionarily
conserved, leading organisms to compensate behaviorally for harsh environmental conditions.
High-mountain systems provide temperature gradients that allow for studies of evolutionary
and plastic variation in thermal ecology under natural conditions. We evaluated the
thermoregulation strategies of Sceloporus grammicus Wiegmann, 1828 at three points
(2600, 3100, and 4150 m above sea level) along an altitudinal gradient. We found that
the thermal quality of the site and the body temperatures of lizards are influenced
by altitude and decrease with increasing elevation. However, lizards from the three
different elevations have similar thermal requirements. High-altitude lizards have
lower thermal accuracy and efficiency indices compared with those from the lower sites,
owing to the low thermal quality of their environment. Nevertheless, they are efficient
in thermoregulation, increasing their body temperature above the ambient temperature.
We found that pregnant females from all three elevations had similar preferred body
temperatures. Compared with nonpregnant females and males, they exhibited lower preferred
temperatures and more accurate thermoregulation. The wide altitudinal distribution
of S. grammicus is thus not caused by variable thermal requirements. Instead, the
wide repertoire of physiological and behavioral strategies of these lizards allows
this species to successfully inhabit contrasting environments.