Regulation of Seasonal Gonadal Cycles by Temperature in the Painted Turtle, Chrysemys picta

Abstract

Tests to elucidate the influence of environmental factors in the regulation of the seasonal gonadal cycle in the painted turtle, Chrysemys picta, indicate that temperature represents a major proximate cue for gonadal recrudescence in both sexes. The thermal dependence of the testicular and ovarian cycle is, however, very different. In males, body temperatures above 17 C are required for the initiation of testicular growth, spermatogenesis and testosterone secretion. Complete testicular recrudescence can be stimulated within 7 weeks at 28 C in males with regressed testes starting in either fall or spring, whereas maintenance of males at 17 C or below completely suppresses the testicular cycle. Males exhibit spontaneous testicular regression even under constant warm temperatures. In contrast, warm temperatures (28 C) inhibit follicular growth and cause regression of ovaries. Maximal ovarian growth and ovulation are observed only in spring in females kept at a constant temperature of 17 C or 17 C with several hours of basking daily; follicles grow at lower temperatures (13 C) but ovulation does not occur. These experimental observations may help explain the timing of the teticular and ovarian cycle of C. picta throughout its range.