Effects of reproduction on survival and growth of female northern water snakes, Nerodia sipedon

Abstract

The cornerstone of life-history theory is the expectation that current reproduction will have a detrimental effect on survival and (or) future reproduction. When fecundity increases with body size, the cost to future reproduction arises through decreased growth of reproductive individuals. We investigated the effects of reproduction on aspects of survival and growth in female northern water snakes (Nerodia sipedon). We did not find a decrease in survival associated with mating despite the conspicuousness of mating aggregations, and pregnancy did not impair locomotor ability. We found evidence of a decrease in over-winter survival of reproductive females related to their emaciated state following parturition. Reproductive females grew less in length than nonreproductive females, but increased similarly in mass. Following parturition, reproductive females weighed less than in the spring, indicating that mass gain prior to parturition was invested in the litter and that most foraging occurred prior to ovulation. Captive reproductive females given food ad libitum grew in length at a rate similar to free-living reproductive females, but increased more in mass. Captive females weighed more after giving birth than in the spring, indicating that unlike that of females in the wild, some of their mass increase was due to energy storage, and also that they continued to feed after ovulation. Consistent with the prediction that smaller females would benefit more than larger females from reproducing less and growing more to increase future fecundity, we found that smaller females participated less in mating aggregations and reproduced less often.