Does date of birth or a capacity for facultative placentotrophy influence offspring quality in a viviparous skink, Niveoscincus microlepidotus?

Abstract

Niveoscincus microlepidotus is a viviparous lizard that exhibits biennial reproduction: births in spring optimise offspring survival in this species’ alpine habitat. Over three annual activity seasons, we investigated the hypothesis that date of birth influences offspring characteristics. In the first year of our study, there was no effect of date of birth on any offspring characteristic measured. In the second year, later-born offspring grew significantly faster. In the third year, later-born offspring were significantly longer and heavier at birth. These varying results may be attributable to differences in basking opportunities for the gestating females due to annual variations in spring weather patterns. To test the hypothesis that both lecithotrophic (yolk) and placentotrophic nutrients support embryos during their extended gestation, we determined the degree of placentotrophy for this species. The mean dry neonate : dry egg ratio of 0.755 indicates that this species is predominantly lecithotrophic. Only in the first year of the study did the data suggest a potential for facultative placentotrophy in this species. We therefore suggest that in N. microlepidotus lecithotrophic nutrition is converted into embryonic fat bodies that support the embryo in utero over winter until spring parturition.