TY - JOUR
T1 - Winter profile of plasma sex steroid levels in free-living male western diamond-backed rattlesnakes, Crotalus atrox (Serpentes: Viperidae)
AU - Schuett, Gordon W.
AU - Repp, Roger A.
AU - Taylor, Emily N.
AU - Denardo, Dale
AU - Earley, Ryan L.
AU - Van Kirk, Edward A.
AU - Murdoch, William J.
N1 - Funding Information:
We are grateful for the assistance of the Schuett family (Laura, Laudon, and Emory). Chad Montgomery, Jack O’Leile, Ryan Sawby, and Don Swann provided invaluable assistance in the field. Steve Beaupre, Mike Cardwell, Harry Greene, Matthew Grober, Dave Hardy, and Randy Reiserer always made themselves available to discuss rattlesnake biology. Steve Goldberg kindly discussed with us spermatogenesis in C. atrox . Several anonymous reviewers sharpened our focus on several topics and thus improved and earlier version of this manuscript. Funding for this study was by a Research Incentive Award and a Scholarship Research Creative Activities Award (Arizona State University) to G.W.S., and a National Science Foundation Graduate Research Fellowship to E.T. Snakes were collected under Arizona Game & Fish Department scientific collecting permits. This research was approved by the IACUC at Arizona State University (98-429R) to G.W.S. We dedicate this paper to the memory of Timothy Repp, who showed great love for the Sonoran Desert and all of its life.
PY - 2006/10
Y1 - 2006/10
N2 - Recent field studies on the reproductive ecology of western diamond-backed rattlesnakes (Crotalus atrox) from populations in southern Arizona showed significant differences in the concentration of plasma sex steroids (testosterone, T; 5α-dihydrotestosterone, DHT; and 17β-estradiol, E2) throughout the active season (March-October), and peak levels were coincident with the two mating periods (late summer and early spring). There is, however, no information on levels of sex steroids during winter. Similar to most snakes, hibernating individuals of C. atrox are 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, offers a unique logistical opportunity to assess the complete annual profile 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 relatively high, and the concentration hierarchy was T > DHT > E2. Mean levels of T, DHT, and E2 showed no significant 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 compared to values obtained during the active season. Mean cloacal temperatures of basking males were significantly higher than core body temperatures 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 significantly correlated with cloacal temperatures. We suggest that future field studies of male C. atrox should: (a) investigate sex steroid levels in non-basking individuals and (b) test whether elevated levels of sex steroids during winter facilitate the large increases that occur in early spring, which are coincident with the second mating season. Our findings on the reproductive biology of C. atrox and other viperids are discussed in the context of the associated-dissociated model of reproduction.
AB - Recent field studies on the reproductive ecology of western diamond-backed rattlesnakes (Crotalus atrox) from populations in southern Arizona showed significant differences in the concentration of plasma sex steroids (testosterone, T; 5α-dihydrotestosterone, DHT; and 17β-estradiol, E2) throughout the active season (March-October), and peak levels were coincident with the two mating periods (late summer and early spring). There is, however, no information on levels of sex steroids during winter. Similar to most snakes, hibernating individuals of C. atrox are 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, offers a unique logistical opportunity to assess the complete annual profile 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 relatively high, and the concentration hierarchy was T > DHT > E2. Mean levels of T, DHT, and E2 showed no significant 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 compared to values obtained during the active season. Mean cloacal temperatures of basking males were significantly higher than core body temperatures 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 significantly correlated with cloacal temperatures. We suggest that future field studies of male C. atrox should: (a) investigate sex steroid levels in non-basking individuals and (b) test whether elevated levels of sex steroids during winter facilitate the large increases that occur in early spring, which are coincident with the second mating season. Our findings on the reproductive biology of C. atrox and other viperids are discussed in the context of the associated-dissociated model of reproduction.
KW - Associated-dissociated reproduction
KW - Body temperature
KW - Hibernation
KW - Mating season
KW - Pitviper
KW - Reptile
KW - Snake
KW - Steroid hormones
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U2 - 10.1016/j.ygcen.2006.05.005
DO - 10.1016/j.ygcen.2006.05.005
M3 - Article
C2 - 16828091
AN - SCOPUS:33747891076
SN - 0016-6480
VL - 149
SP - 72
EP - 80
JO - General and Comparative Endocrinology
JF - General and Comparative Endocrinology
IS - 1
ER -