Reproductive strategies and sperm competition in the adder, Vipera berus

Abstract

Abstract Reproduction in temperate snakes shows large variation. In males the reproductive cycle is annual, while females have a biennial or longer cycle depending on species and environmental conditions. Ovulation (fertilization) is temporally separated from copulation, allowing sperm competition in polyandric species. This system can, however, be violated by male-mediated renal sex secretion reducing sperm transfer from later matings by contraction of posterior uteri, or by a copulatory plug. Matings can be restricted to one spring or autumn period or can be biannual. Short-term sperm storage between mating and ovulation is the normal case, but sperm can be stored over winter in species with autumn matings, or several years in species lacking aggregation periods or with low population density. In the adder (Vipera berus), precopulatory behaviour in spring includes violent male-male combats and mate guarding, and sex ratio is male-biased because the female reproductive cycle is biennial. During recent years quite different opinions have been expressed concerning adder reproductive behaviour. Main questions have involved the presence or importance of long-term sperm storage, a copulatory plug, multiple paternity in wild populations, male and female choice and whether promiscuity influences offspring viability. We performed DNA fingerprinting of 12 litters of adders in order to find out whether multiple paternity can be determined without collecting fathers and in order to investigate the significance of multiple paternity in wild adders. For each litter we tested the binomial probability that a single father would transmit the observed number of paternal bands in each offspring. In 83% of the litters only one male had sired the offspring, while in the remaining litters more than one father was involved. We conclude that although females may copulate more than once with a single male, multiple paternity is a rare event in the population studied.