Dataset for Body size impacts critical thermal maximum measurements in lizards

Understanding the mechanisms behind critical thermal maxima (CTmax, the
high body temperature at which neuromuscular coordination is lost) of
organisms is central to understanding ectotherm thermal tolerance. Body
size is an often overlooked variable that may affect interpretation of
CTmax, and consequently, how CTmax is used to evaluate mechanistic
hypotheses of thermal tolerance. We tested the hypothesis that body size
affects CTmax and its interpretation in two experimental contexts. First,
in four Sceloporus species, we examined how inter- and intra-specific
variation in body size affected CTmax at normoxic and
experimentally-induced hypoxic conditions, and cloacal heating rate under
normoxic conditions. Negative relationships between body size and CTmax
were exaggerated in larger species, and hypoxia-related reductions in
CTmax were unaffected by body size. Smaller individuals had faster cloacal
heating rates and higher CTmax, and variation in cloacal heating rate
affected CTmax in the largest species. Second, we examined how body size
interacted with the location of body temperature measurements (i.e.,
cloaca versus brain) in Sceloporus occidentalis, then compared this in
living and deceased lizards. Brain temperatures were consistently lower
than cloacal temperatures. Smaller lizards had larger brain-cloacal
temperature differences than larger lizards, due to a slower cloacal
heating rate in large lizards. Both live and dead lizards had lower brain
than cloacal temperatures, suggesting living lizards do not actively
maintain lower brain temperatures when they cannot pant. Thermal inertia
influences CTmax data in complex ways, and body size should therefore be
considered in studies involving CTmax data on species with variable sizes.