Hormonal independence of courtship behavior in the male garter snake

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.

Section: Androgensmentioning

confidence: 78%

The relationship between plasma steroid hormone concentrations and the reproductive cycle in the Northern Pacific rattlesnake, Crotalus oreganus

Lind

Husak

Eikenaar

et al. 2010

“…Field studies on the common garter snake (Thamnophis sirtalis) from various parts of its expansive range in North America show that levels of circulating androgens (e.g., T) in males at the time of spring emergence are often equiva lent to levels obtained in fall just prior to hibernation (Krohmer et al, 1987;Moore et al, 2000b;Clesson et al, 2002; but see Crews, 1984;Crews et al, 1984;Crews and Moore, 2005), with a relatively rapid decline to basal levels following the brief (days to several weeks) mating season. Despite the fact that determination of levels of plasma sex steroids from free-living garter snakes (e.g., Manitoba pop ulations) during hibernation has not been possible due to their inaccessibility, comparison of levels at the time of ingress (fall) and egress (spring) suggests that they are sta ble throughout the period of hibernation.…”

Section: Discussionmentioning

confidence: 99%

“…Over 20 years ago, Crews (1984) and Crews et al (1984) (see overviews by Moore and Lindzey, 1992;Crews and Moore, 2005) proposed the associated-dissociated model of reproduction, wherein the mating system of the redsided garter snake (T. sirtalis parietalis) was emphasized as relatively unique among vertebrates. This was the case because, during the spring mating season, there was initial evidence from one population (Manitoba) that hormone secretion was decoupled or "dissociated" from sexual behavior (but see Krohmer et al, 1987).…”

Section: Discussionmentioning

confidence: 99%

Winter profile of plasma sex steroid levels in free-living male western diamond-backed rattlesnakes, Crotalus atrox (Serpentes: Viperidae)

Schuett

Repp

Taylor

et al. 2006

Recent Weld studies on the reproductive ecology of western diamond-backed rattlesnakes (Crotalus atrox) from populations in southern Ari typically inaccessible, but in southern Arizona, where environmental conditions are typically mild during winter, adult males frequently bask at or near the entrances of communal dens. Basking activity, therefore, oVers a unique logistical opportunity to assess the complete annual proWle of plasma sex steroid levels in males of a temperate reptile in nature. From November to February, we measured levels of plasma T, DHT, and E2 in adult male C. atrox that were located basking at communal dens. Additionally, cloacal, core body, and ambient air temperatures were obtained to investigate potential relationships between body temperatures and levels of sex steroids. Mean levels of T, DHT, and E2 were rela tively high, and the concentration hierarchy was T > DHT > E2. Mean levels of T, DHT, and E2 showed no signiWcant variation across the four months of sampling; however, E2 levels decreased progressively. In the annul cycle, sex steroid levels during winter were not basal when com pared to values obtained during the active season. Mean cloacal temperatures of basking males were signiWcantly higher than core body tem peratures of non-basking males (inside dens) from November-December, and in February, which suggests that one function of winter basking is to elevate body temperatures. Steroid levels, nonetheless, were not signiWcantly correlated with cloacal temperatures. We suggest that future Weld studies of male C. atrox should: (a) investigate sex steroid levels in non-basking individuals and (b) test whether elevated levels of sex ste roids during winter facilitate the large increases that occur in early spring, which are coincident with the second mating season. Our Wndings on the reproductive biology of C. atrox and other viperids are discussed in the context of the associated-dissociated model of reproduction.

“…Of particular interest in C. atrox are seasonal differences in the association of hormone profiles with reproductive events. Crews (1984) and Crews et al (1984) categorize reproduction in vertebrates as either ''associated'' (mating behavior coincides with gonadal activity) or ''dissociated'' (mating behavior does not coincide with gonadal activity). In C. atrox, females show an E2 peak during the mating/vitellogenesis period in the spring, but have no increase in E2 during the fall mating season, indicating that E2 is probably associated with vitellogenesis and not with mating in C. atrox.…”

Section: Discussionmentioning

confidence: 99%

Seasonal steroid hormone levels and their relation to reproduction in the Western Diamond-backed Rattlesnake, Crotalus atrox (Serpentes: Viperidae)

Taylor

DeNardo

Jennings

2004

107

We report seasonal variation in steroid hormone levels in blood samples from free ranging Western Diamond backed Rattle snakes (Crotalus atrox), and the relationship between these hormones and events in the reproductive cycle. At a field site in the Sonoran Desert of south central Arizona, we collected monthly blood samples over the course of two active seasons from 17 ra diotelemetered females, and over three active seasons from 103 randomly encountered males. We used radioimmunoassay to measure plasma levels of 17b estradiol, progesterone, corticosterone, and testosterone in samples from females, and corticosterone and testosterone in samples from males. Non reproductive females have consistently low levels of circulating 17b estradiol, pro gesterone, and testosterone throughout the year. In reproductive females, 17b estradiol levels increase dramatically and testosterone levels increase modestly during vitellogenesis in April and May, while progesterone levels increase dramatically at ovulation in June and then steadily decline until parturition in August. Corticosterone levels appear relatively constant in non reproductive females, whereas reproductive females show increased levels at the end of gestation. Plasma testosterone levels in males are low in early summer and are elevated during spring and late summer, corresponding to the two mating periods of C. atrox. Plasma cortico sterone levels in males did not vary seasonally and were not related to testosterone levels.