Seasonal Steroid Hormones in Relation to Vitellogenesis, Mating, and Pregnancy in Free-Ranging Pygmy

Lind, Craig M.

craig.lind@stockton.edu

Department of Natural Science and Mathematics Stockton University

Galloway, New Jersey, USA

Moore, Ignacio T.

Vernasco, Ben J. Department of Biology

Virginia Tech

Blacksburg, Virginia, USA

Farrell, Terence M. Department of Biology

Stetson University

DeLand, Florida, USA

Steroid hormones regulate reproductive investment and play a critical role in mediating the reproductive response to both short (e.g. seasonal) and long-term environmental change. Laboratory studies typically examine the mechanistic relationships between steroids and reproductive processes under tightly controlled conditions and may fail to identify any seasonal modulation of regulatory mechanisms. Thus, field-based research remains important in testing the predictions of laboratory studies under the full range of environmental conditions experienced by an organism. In snakes, seasonal relationships between steroids and male reproduction are prevalent. However, comparatively less work has been conducted on free-ranging female snakes. We described seasonal estradiol, corticosterone, and plasma metabolites (total protein, albumin, phosphorus, and glucose) in relation to seasonal events of the reproductive cycle in free-ranging Pygmy Rattlesnakes, Sistrurus miliarius. We expected elevated estradiol and plasma metabolites during the spring vitellogenic season. Based on previous studies, we did not expect elevated estradiol during the fall breeding season or during pregnancy. We also predicted that corticosterone would be elevated during late pregnancy and hypothesized that corticosterone may play a role in parturition. In S. miliarius, plasma estradiol and metabolites were significantly elevated during both the breeding vitellogenic seasons. However, no palpable follicles were observed in the fall and no breeding behavior was observed in the spring, suggesting that the link between estradiol and these processes may be seasonally uncoupled. As predicted, corticosterone was elevated during late pregnancy compared to early pregnancy, postpartum, and compared to non-reproductive females sampled in the field. Corticosterone was not associated with elevated estradiol in any season. Our results indicate the potential for seasonal modulation of endocrine regulatory mechanisms in pygmy rattlesnakes and highlight the need for further study of the seasonal regulation of reproductive processes in female snakes.