The Relationship Between Plasma Steroid Hormone Concentrations and the Reproductive Cycle of the Northern Pacific Rattlesnake, Crotalus oreganus

Abstract

The Relationship Between Plasma Steroid Hormone Concentrations and the Reproductive Cycle in the Northern Pacific Rattlesnake, Crotalus oreganusCraig M. LindTo gain a better understanding of the role of steroid hormones in vertebrate reproduction, we quantified steroid hormone concentrations in a free ranging population of the Northern Pacific rattlesnake, Crotalus oreganus. Plasma steroid hormone concentrations were quantified for both male and female snakes throughout the active season (Mar-Oct). We measured testosterone (T), 5α-dihydrotestosterone (DHT), and corticosterone (B) concentrations in male and female snakes. 17β-estradiol (E2) and progesterone (P) were measured in females only. We also observed breeding behaviors (e.g. consortship, courtship, and copulation) in the field and measured testis and follicle size in male and female snakes from museum collections. Our results indicate that C. oreganus in central California utilizes a bimodal pattern of breeding, with mating and agonistic behavior occurring in the spring and the late summer/fall. Each breeding season corresponds with elevated or highly variable androgen (T and DHT) levels. Several female snakes had high E2 concentrations in the spring and fall, coincident with vitellogenesis and mating. Females with high E2 concentrations also had high T and DHT concentrations. Corticosterone concentrations in males are not related to either time of year or concentrations of any other hormones quantified. This suggests that the breeding season in this population may not demand a significant increase in energy mobilization by glucocorticoids. Measurements of testis volume show that testes are regressed in the spring when the majority of breeding was observed in this population and reach peak volume in August and September during spermatogenesis. Multiple regression analyses revealed that in female snakes, P is positively correlated with T and DHT, and E2 is correlated with T. Since these results are strictly descriptive, experimental studies are needed to identify the functional significance of these results.

Stress Ecology of the Pacific Rattlesnakes (Crotalus Oreganus and Crotalus Helleri)

“…In both groups, CORT levels at all time points averaged below 100 ng/ml, which is similar to baseline field levels previously reported for C. oreganus (Lind et al 2010;Holding et al 2014a). This is despite our observations that treatment snakes often rattled in response to activation of the shaker unit, and one treatment snake defecated after the first vibrator activation.…”

“…The magnitude of elevated baseline CORT in the treatment snakes at this sample is within normal baseline levels based on reports from several species of free-ranging rattlesnakes, including the sister species C. oreganus (Holding et al 2014a;Schuett et al 2004;Lutterschmidt et al 2009, Lind et al 2010. As baseline CORT varies within inidividuals, within a population, and across seasons in these studies, it is difficult to attribute a specific value of baseline CORT to achieve a general classification of "chronically stressed".…”

“…CORT levels were determined via radioimmunoassay of plasma as described in Lind et al (2010). Briefly, samples were extracted in dichloromethane, then dried in a 40° C water bath under nitrogen gas.…”

Evaluation of Seasonal Serum Level of Estradiol and Progesterone Hormones in Iranian Female Caucasian Viper

“…These hormones have all been implicated as role players in the production of breeding behavior and/or vitellogenesis in female reptiles. There was a large amount of within-season variation in the concentrations of all quantified hormones [12]. In general, the relationship between steroid hormones and reproduction in snakes shows that plasma estradiol (E2) is high during vitellogenesis that reflects its role in stimulating the production of vitellogenin by liver.…”

“…While both hormones level are low in non-fertile females during the year. In studies of the reproductive cycle of rattlesnakes in North Crotalus oreganus [12] showed that different concentrations of progesterone do not differ in females. But it is likely that during pregnancy in the summer, P4 concentration is high.…”