Thermal Aspects of Melanistic and Striped Morphs of the Snake Elaphe quadrivirgata

Abstract

Temperature is a critical factor limiting various aspects of the biology of ectotherms. In addition to environmental factors, coloration and body size are two physical properties that influence ectotherms' body temperature (T_[b]). I compared the influences of these properties on thermal aspects of the two morphs of the color-dimorphic snake (E. quadrivirgata) under experimental conditions. First, I fitted T_[b] data during heating to the von Bertalanffy equation, but considered parameter values of the equilibrium temperature obtained to be biologically meaningless. Alternatively, I limited the data for comparison of the morphs to T_[b]≤35℃, which was the Tb at which snakes began to move vigorously in the experiment. The rate of T_[b] increase was significantly greater in the melanistic morph than in the striped morph. Heating rate was negatively correlated with body size in both morphs. The interaction of body size and heating rate did not significantly differ between the two morphs. The possibility of linkage, due to thermal advantage, between small body size and the prevalence of melanism in the population studied is briefly discussed. Rapid increase of T_[b] is biologically advantageous because snakes with such ability would be released from various time and environmental constraints associated with thermoregulation under particular environmental conditions.