Reproduction (mating) in copperhead snakes (Agkistrodon contortrix) in the most northern populations occurs during a brief period from mid-July to late August. The mating system is best characterized as a scramble mate-search competition, with males competing indirectly in locating and courting as many as females as possible during the month and a half-long reproductive season. There is, however, considerable variation in mating success among males, with some males mating with three or more females during a single season and other males obtaining no matings at all.
Using data collected in the field over the course of three field seasons, we are investigating potential proximate determinants driving male mating success, including plasma steroid levels, body size, home range size, and movement levels. Determining the factors that lead to elevated male mating success will provide valuable insight into the mating system of these animals and the evolution of mating systems among squamate reptiles in general. Update: now published
During the reproductive season in copperhead snakes (Agkistrodon contortrix) females may mate with more than one male and single litters, numbering from four to fourteen neonates, may have genetic contributions from more than one male. Using DNA fingerprinting, we are the prevalence of multiple paternity across litters. Eventually, we intend to incorporate male plasma steroid levels, body size, and spatial parameters as predictors of male representation in multiple-sired litters.
Observations of multiple paternity lead to additional interesting evolutionary questions that we intend to address in the future, including females control of fertilization (sperm selection) and sperm competition among males, as well as the possibility of first or last male precedence.
While we have spent the past twelve years intensively studying the spatial ecology of copperhead snakes in northern populations, virtually nothing is known of the life history of southern populations. Using radio-telemetry and GIS technology, we are beginning to gather data on habitat use and movement patterns.
Seasonal movements and habitat usage are two components of an animal’s behavior that must be known before the natural history and ecology of the animal can be accurately understood. Gathering these data for snakes presents a challenge because of their secretive and often fossorial nature. In recent years, the use of radio-telemetry to monitor snake movements has proven to be a valuable field method and can potentially provide an abundance of ecological, behavioral, and natural history data.
We are using radio-telemetry to determine which habitats are particularly important to the biology of this species, the frequency each habitat type is used and the components of the preferred habitat that are necessary for maintaining the species (e.g. availability of open areas, basking sites, food, winter retreats, etc.).
In addition, we are interested in how individuals use their population’s range over time. For instance, do males typically move greater distances than females? At what time of year do long-range movements take place? Are movements at all correlated with mating season? Lastly, developments in the miniaturization of thermal data logging sensors now allows for continual monitoring of body temperatures in free-ranging snakes and we wish to incorporate such sensing technology into our study.
Facultative parthenogenesis (FP)—asexual reproduction by bisexual species—has been observed in a variety of captive multi-cellular organisms, but only recently has FP been shown in captive snakes, varanid lizards, birds and sharks. Based on captive observations, FP appears widespread in squamate reptiles (snakes, lizards and amphisbaenians), and although its occurrence in nature seemed inevitable, the task of detecting FP in wild individuals of any species was deemed formidable. Unlike the approximately 80 taxa of unisexual (obligate parthenogenic) reptiles, amphibians and fishes that exist in nature, it was only recently that FP was documented in the wild.
Snakes have traditionally been thought of as being asocial. However, many snake species frequently form conspecific aggregations. Pregnant females often aggregate during and after gestation, and groups of females and their newborn young are often observed in the field, particularly among pitviper snakes.
Female pitvipers show behaviors representative of parental care and often remain with newborn offspring until they have shed. In addition, aggregations of adult individuals are often seen outside of the reproductive season. There are a number of potential benefits to both adults and newborns from aggregations, including enhanced defense against predators.
Kin selection theory predicts that the benefits of aggregations, such as predator defense, will be greater when groups are composed of related individuals, rather than unrelated individuals. Our study focused on whether kin recognition occurs in a representative pitviper species, the northern copperhead, Agkistrodon contortrix.