Maternal costs of reproduction in the southern snow skink, Niveoscincus microlepidotus

Viviparous reproduction is associated with many potential costs that may contribute to the need to adopt a number of physiological and behavioral tradeoffs. Costs are divided into two main categories, survival and fecundity, and these may manifest as locomotory, thermoregulatory, and metabolic costs. Animals must balance these costs with the benefits of reproduction to evolve a successful life-history. To increase our understanding of the life-histories of viviparous reptiles, this study investigated the changes in mobility, thermoregulatory behavior, thermal physiology, and metabolism during pregnancy in Niveoscincus microlepidotus. Niveoscincus microlepidotus is a small (3 - 5g) alpine specialist, restricted to altitudes above 1080 m in Tasmania, Australia. Its preferred microhabitat is open heathlands, alpine forests, and dolerite boulder-fields. This species has an unusual reproductive cycle that makes it an ideal study species for this type of study. Ovulation and mating occur in spring to early summer, gestation takes place during summer and early autumn. The fully developed embryos are held through the winter hibernation and parturition occurs the following spring. Mating does not occur until the next spring. This biennial reproductive mode allows pregnant and non-pregnant females to be studied simultaneously. This study has shown that female Niveoscincus microlepidotus decrease body temperature during pregnancy. Presumably, this is in order to slow embryonic development until just prior to the commencement of hibernation. This may have substantial advantages for reducing the costs of pregnancy to the pregnant female and any costs to the neonates. It has also been shown that Niveoscincus microlepidotus incurs a significant decrease in mobility during pregnancy, which is exaggerated by high temperature and therefore increasing costs as gestation continues. However, it was also found that this species may temporally shift its physiological optimal performance temperature to minimise the decrease in performance seen at higher temperatures. Many of the costs of reproduction associated with impaired locomotory ability are thereby decreased .. This study also examined changes in the standard metabolic rate (SMR) and active metabolic rate (AMR) associated with viviparous pregnancy. This was accomplished by measuring oxygen consumption for SMR and biological elimination of the rubidium86 isotope for AMR. It was shown that there was a significant increase in SMR that reached a peak in late pregnancy, and AMR was significantly higher in pregnant females than non-pregnant females. This suggests that there is a significant metabolic cost associated with pregnancy in female N. microlepidotus. The rubidium86 isotope was proved to be a useful method for determining active metabolic rates in the field, minimising many of the problems inherent in other radionucelotide metabolic techniques. This study has shown that Niveoscincus microlepidotus uses a range of physiological and behavioral adaptations to minimise the costs of reproduction. Thereby, N. microlepidotus has therefore evolved a successful life-history that has allowed it to thrive in its variable alpine microhabitat.