The reproductive biology of male cottonmouths (Agkistrodon piscivorus): do plasma steroid hormones predict the mating season?

ABSTRACT

To better understand the proximate causation of the two major types of mating seasons described for North American pitvipers, we conducted a field study of the cottonmouth (Agkistrodon piscivorus) in Georgia from September 2003 to May 2005 that included an extensive observational regime and collection of tissues for behavioral, anatomical, histological, and hormone analysis. Enzyme immunoassays (EIA) of plasma samples and standard histological procedures were conducted on reproductive tissues. Evidence from the annual testosterone (T) and sexual segment of the kidney (SSK) cycle and their relationship to the spermatogenic cycle provide correlative evidence of a unimodal mating pattern in this species of pitviper, as these variables consistently predict the mating season in all snake species previously examined under natural conditions. In most reptiles studied to date, high plasma levels of T and corticosterone (CORT) coincide during the mating period, making the cottonmouth an exception to this trend; we suggest two possible explanations for increased CORT during spring (regulation of a spring basking period), and decreased CORT during summer (avoiding reproductive behavioral inhibition), in this species.