Geographic variation and adaptation in the Tasmanian metallic skink (Niveoscincus metallicus)

Species occupying broad geographic ranges tend to display reproductive and physiological traits that compensate for environmental constraints. This thesis examines these traits in the metallic skink, Niveoscincus metallicus. The metallic skink is the most widespread of all Tasmanian reptiles. It is a small (2-5 g) skink, found throughout Tasmania, and on most of its offshore islands, occurring from sea level to alpine elevations, in a range of habitat types. It also has a limited mainland distribution, in southern Victoria. This thesis provides a detailed examination of thermal biology and life history adaptation within this species. The thesis is presented in three main sections, each dealing with an important aspect of adaptation on a geographic scale. In the first section (Chapter 3) I examine the phylogenetic history of N. metallicus across its entire distributional range, using restriction fragment length polymorphism analysis (12s-16s rRNA gene) and nucleotide sequence divergence information (16s rRNA sequence). These analyses revealed five phylogenetically distinct subtypes of N metallicus, four of which are found within Tasmania. I selected four field sites from within the distributional range of one of these subgroups for a detailed study of inter-population variation. These sites covered the altitudinal range of the species (two high altitude and two low altitude sites). Within each altitude group, sites were chosen to represent open (little tree cover) and closed (complex tree cover) habitats. The second section of work (Chapters 4 and 5) investigates thermoregulatory adaptation in N metallicus. As part of this work I examined microhabitat occupation for lizards at all four sites. I found that animals at high altitude bask overtly on rock surfaces while those at low altitude are more covert and bask on logs. These differences represent behavioural adaptations to variation in the thermal environment evident between high and low altitude sites. The importance of acclimatization and genetic adaptation to the thermal physiology and performance of N. metallicus was examined in a series of field and laboratory experiments. Preferred body temperatures did not differ between sites. Nevertheless, thermal adaptation does occur in this species. Animals from high altitude tolerate significantly lower environmental temperatures, and can sprint significantly faster at extreme body temperatures. These differences appear to represent genetic adaptation, and thus data from this study support the \labile\" view of thermal adaptation. The third section to this thesis (Chapters 6 and 7) presents an examination of life history adaptation across my four field sites. Life history was found to vary with altitude; however habitat effects were also evident. High altitude females live significantly longer than do low altitude lizards and mature one year later; however no variation in adult body size or size at maturity was detected. Relative clutch mass is highest at low altitude; however trade-offs between offspring size and litter size are evident between low altitude populations. This trade-off appears to result from predatory induced effects. High altitude young are born with significantly larger abdominal fat reserves a characteristic of some advantage to young which must hibernate within two months of birth. Evidence from this and previous studies on N. metallicus and from research on the sister species N. ocellatus indicates that life history traits are phenotypically plastic and do not represent evolved adaptations to environmental constraints. An ability to utilize phenotypic life history responses may be of adaptive significance to species such as N. metallicus occupying wide geographic and/or climatic ranges as it allows these animals to exploit fluctuating environments and adapt life history traits to suit present environmental conditions."