Seasonal changes in sex and adrenal steroid hormones of gopher tortoises (Gopherus polyphemus)

We sampled a population of gopher tortoises (Gopherus polyphemus) from May to October 1997 to determine seasonal cycles of steroid hormones (testoster one, T; 17 beta-estradiol, E; and progesterone, P) and related them to obse rvations of mating behavior. In males, plasma T levels peaked in July and A ugust and remained elevated through October. This coincides with the report ed time of peak mating and spermatogenesis, indicating that males display a n associated pattern of reproduction. In females, E levels were high in Sep tember and October. Plasma T levels in females were elevated in May, decrea sed to basal levels in June and July, and rose again in August and Septembe r. Elevated E and T levels correspond to the reported time of peak vitellog enic activity, indicating that females also display an associated cycle. Pl asma P in females remained basal throughout the active season, suggesting t hat ovulation occurs in late winter. We also determined levels of corticost erone (B) to assess the influence of capture stress on tortoises and correl ated B levels with tortoise activity patterns and sex steroid levels. We fo und no seasonal variation in levels of B in males or females. Plasma B leve ls were not correlated with levels of T or E, but were positively correlate d with female P levels. Further, we found no relationship between plasma B levels in males and mean distance moved, mean number of burrows used, or me an home range size. However, there was a significant negative correlation b etween plasma B levels and male body size. In females, there was no relatio nship between B levels and mean distance moved, but B levels were significa ntly negatively correlated with the number of burrows females occupied. Las tly, there was no relationship between levels of B and the number of minute s required to obtain blood from an animal. However, B levels increased with the length of time that a tortoise spent in a trap, suggesting that trappe d tortoises do exhibit capture stress. (C) 2000 Academic Press.