Repeatability of Female Reproductive Traits in Pigmy Rattlesnakes (Sistrurus miliarius)

Abstract

The consistency of a trait's expression within individuals reflects both its maximal possible heritability and that trait's susceptibility to the influence of temporal variation in environmental conditions. A lack of repeatability in reproductive traits may also result if there are ontogenetic changes in female reproductive effort. In a decade-long study, we collected data on the reproductive traits (including female SVL, female postpartum condition, litter size, total litter mass, mean offspring mass, and birth date) of free-ranging Pigmy Rattlesnakes in central Florida. We captured and held the study snakes in field enclosures for several weeks before parturition each year. A total of 24 females produced two or more litters during the course of the study. We determined the repeatability for each reproductive trait. Our results indicated that four of the six reproductive traits had high and statistically significant repeatability despite annual variation in environmental conditions. A lack of growth in adult Sistrurus miliarius and the ability of females to skip reproduction in some years appear to foster the high repeatability of reproductive traits. Our research and previous studies indicate that many, but not all, reproductive traits in female snakes are highly repeatable. The repeatability of a few traits, particularly post-partum female condition, is likely to depend strongly on the reproductive mode of the species.