Elevated testosterone levels during nonbreeding-season territoriality in a fall-breeding lizard, Sceloporus jarrovi.

In many vertebrates, seasonal activation of sexual and territorial behaviors coincides with seasonal gonadal activation and is caused by the increase in sex steroid hormones. Both male and female Sceloporus jarrovi are territorial, but in this species territorial behavior is seasonally activated in late April, months before seasonal gonadal maturation, which occurs in August prior to the fall mating season. Measurements of seasonal changes in circulating levels of the sex steroid hormones testosterone, progesterone, and estradiol indicated that testosterone levels in both sexes are elevated when territorial behavior is expressed, even during the period of nonbreeding-season territoriality during the summer. This suggests that a nonbreeding season behavior is activated by a sex steroid hormone in this species.