Geographic and annual variation in reproductive cycles in the Tasmanian spotted snow skink, Niveoscincus ocellatus (Squamata : Scincidae)

Abstract

We studied the reproductive cycle of two populations of the spotted snow skink, Niveoscincus ocellatus, over a three-year period. This species is widespread in Tasmania and its distribution overlaps those of other species in the genus that show two distinct reproductive strategies: annual reproduction that is completed within one season, and biennial reproduction in which females carry advanced embryos throughout winter hibernation. We chose populations representative of the climatic extremes of the species' distribution, within these areas of overlap. Niveoscincus ocellatus maintains the same basic reproductive strategy in both populations: summer gestation, primary autumn mating with obligate sperm storage by females, secondary mating in spring, and predominantly spring vitellogenesis and ovulation. In both populations all females reproduce annually, suggesting that reproductive frequency is not constrained by availability of energy. However, we found distinct differences in the timing of ovulation and parturition. Females from our subalpine site ovulated approximately one month later than those from our warmer, lowland site; parturition was delayed by the same period so gestation length was unchanged. The delay in ovulation results in gestation proceeding over the warmest months at the cold site. The annual reproductive cycle of this species appears to constrain its distribution to the lower altitudinal/climatic range of alpine Niveoscincus species. There were minor annual differences in the timing of reproductive events at each site, which we attribute to variation in thermal conditions and the amount of precipitation.