An examination of factors influencing mating and reproductive success in female Northern Watersnakes (Nerodia sipedon)

For internally-fertilizing taxa to mate, members of the opposite sex must first locate one another. This can be problematic for wide-ranging taxa. Therefore, animals have developed a number of methods with which to communicate with one another over large distances. Snakes emit chemical signals (pheromones) informing conspecifics of their identity, location, and reproductive status. Male snakes alter their movements during the mating period to increase their likelihood of encountering females and this movement has long been viewed as the primary determinant in mate location. Historically, females have been regarded as mostly passive participants in mating system dynamics. However, if males locate females using female pheromonal cues, and these cues are deposited on the substrate as females move through the environment, female actions during the mating period are likely also important determinants of mate location. In some ophidian taxa, shedding enhances female attractivity, yet it is unknown whether the act of shedding increases pheromone volatility, if the pheromone concentration varies throughout the shed cycle, or whether both the volatility and concentration fluctuate. During the mating period, females mate with multiple males resulting in multiple paternity. Upon examining the paternity of multiply-sired litters, it is frequently observed that one male has a distinct advantage over the other mating males. However, it remains unknown whether this is due to phenotypic or genotypic differences of the mating males, a function of mating order, or a combination thereof. I monitored the movement, hormone concentrations, mating behaviors, and shed cycle of 27 free-ranging radio-equipped female Northern Watersnakes (Nerodia sipedon) throughout the 2007-2009 mating periods to examine the influence of these factors on male mate location and reproductive success. The sex steroid hormones of reproductive females fluctuated throughout mating period and the volatility of the sex pheromone likely increased upon shedding. Females increased their movements only during an abbreviated period (thus decreasing their total energetic and mortality costs) coincident with this increased attractivity. Microsatellite DNA paternity analysis on the proximate causes of differential paternity was inconclusive; however, it is evident that females are not simply passive participants in snake mating systems.