Oestrus in a secretive species: endogenous estradiol varies throughout the shed cycle and influences attractiveness in wild northern watersnakes (Nerodia sipedon)

Abstract

Oestrogen (e.g., 17β-estradiol, E2) stimulates vitellogenesis, female sexual behaviour, and induces sex pheromone production throughout vertebrates. Therefore, the quantification of its role in any one these may prove challenging; particularly in taxa such as snakes where mating coincides with vitellogenesis. Studies examining steroid hormones in snakes are further confounded by the typical sampling interval (monthly) which is likely insufficient to observe the brief hormone fluctuations associated with an oestrus period. Thus, the relationship between oestrus and endogenous sex steroids in snakes remains equivocal. We sampled plasma E2 of 12 radio-equipped free-ranging adult female northern watersnakes (Nerodia sipedon) twice weekly during the 2008–2009 mating periods. Reproductive females experienced a large E2 surge coincident with shedding, movement, and male accompaniment indicating that endogenous E2 is involved in oestrus, a phenomenon that has previously not been documented in snakes.