whole_WapstraErik1997_thesis.pdf (13.98 MB)
Life history and reproductive variation in the spotted skink, Niveoscincus ocellatus (Gray 1845)
thesisposted on 2023-05-27, 12:32 authored by Wapstra, E
The spotted skink, Niveoscincus ocellatus is a widely distributed small to medium size skink (3-12 g) which occurs throughout eastern and central Tasmania in a variety of climatic regimes. This thesis provides the first major ecological study of this species and describes in detail the life history and reproductive characteristics of two populations living at the climatic extremes of the species' distribution: a site on the Central Plateau represented the cold extreme and a site at Orford on the east coast represented the warm extreme. Niveoscincus ocellatus is a viviparous species that reproduces annually across its range. It shows an asynchronous gonadal cycle, with maximum male gonadal development in late summer and mating from April to June and August to September. Vitellogenesis occurs predominantly in autumn and continues through winter with ovulation in spring (September to October). Parturition occurs in January in the temperate Orford population, and in February in the subalpine Central Plateau population. In addition to minor variations in the timing of reproductive events between years at each site, N. ocellatus shows a degree of flexibility in the timing of reproductive events between sites. Ovulation and parturition occur approximately one month later at the Central Plateau, but there is little difference in the length of the gestation period between sites. An ability to show flexibility in the timing of reproductive events is undoubtedly responsible, in part, for the widespread distribution of Niveoscincus ocellatus in a range of climatic conditions. Niveoscincus ocellatus displays considerable geographic variation in life history traits. Maturity is delayed at the Central Plateau (3 years) compared to Orford (2 years). As a result, indiv~duals from the Central Plateau mature at a large size and have a larger maximum size. Associated with their larger size and delayed maturity, Central Plateau females produce larger (mass and number of young) clutches than those from Orford. There is no trade-off between clutch size and size of offspring between populations, and females from the Central Plateau produce more (size adjusted) and larger offspring than females from Orforct. Through a series of experiments I show that life history traits of N. ocellatus are phenotypically plastic, and that observed differences in life history traits between sites, and annually within sites, may be explained, at least in part, by phenotypic responses to environmental variables. For example, growth rate of juveniles is positively correlated to basking opportunities in the laboratory and to thermal conditions in field enclosures, but is not influenced by any underlying genetic differences between populations. Offspring growth rate and phenotype are also influenced by other proximate factors, including the basking behaviour of their mothers prior to parturition in the laboratory. Phenotypically plastic responses allow a flexible approach to life history and reproductive strategies and are of adaptive significance to species such as N. ocellatus that occupy a wide geographic and/ or climatic range.
Rights statementCopyright 1997 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Library has additional copy on microfiche. Thesis (Ph.D.)--University of Tasmania, 1998. Includes bibliographical references