Control of length of the courtship season in the red-sided garter snake, Thamnophis sirtalis parietalis: the role of temperature
The influence of temperature on the length and intensity of the courtship season was examined in both field and laboratory populations of red-sided garter snakes (Thamnophis sirtalis parietalis) over a 2-year period. Snakes were exposed to fluctuations in temperature following emergence from hibernation and activation of courtship behavior. In the field, males were exposed to four temperature regimens: extended hibernation (0L:24D, 4 ± 1.5 °C), cool (14L:10D, 12 ± 2.3° C), warm (14L:10D, 28 °C:ambient), or control (ambient temperatures and light). Control animals exhibited courtship behavior fluctuating in intensity with daily ambient temperatures. Animals exhibited high intensity courtship behavior when exposed to warm conditions following emergence from either natural hibernation or a secondary period of laboratory hibernation. Animals placed in the cool regimen were active but exhibited very little courtship behavior. Animals maintained under the cool regimen for 14 days did not initiate courtship behavior when placed in the warm regimen. Studies conducted in the laboratory support the field results. However, whereas animals maintained under the cool regimen for 14 days and then placed in the warm regimen exhibited dramatically reduced courtship behavior, animals placed in the warm regimen after 21 days under the cool regimen initiated courtship of normal intensity and duration. Following the end of all courtship behavior, males exposed to conditions of hibernation for a brief period reinitiated courtship behavior. These data suggest that the areas of the central nervous system critical for the perception of temperature fluctuations and initiation of courtship behavior remained sensitive in late spring. Following the end of the courtship season, females exposed to a brief period of hibernation also reinstated courtship behavior in noncourting males. These data suggest that the length of the courtship season ultimately may be controlled by the presence of attractive females.