Genetic effects of forest fragmentation on a rainforest restricted lizard (Scincidae: Gnypetoscincus queenslandiae)

Abstract

The amount and distribution of polymorphism at four allozyme loci and mitochondrial DNA was assessed in samples from populations of the prickly skink, Gnypetoscincus queenslandiae, located in rainforest fragments and in nearby continuous forest within the Wet Tropics World Heritage Area, north-eastern Australia. The aim was to assess the effects of recent anthropogenic fragmentation in the context of episodic, long-term, natural rainforest fragmentation. Both the allozyme loci and mtDNA were strongly influenced by historical processes. Skinks from the southern Atherton Tableland, whether in fragments or continuous forest, had reduced heterozygosity and overall there was a pattern of isolation by distance. For mtDNA there was a marked phylogeographic dichotomy between highly diverse east Atherton continuous forest sites and the near uniform central and southern Atherton sites. These two mtDNA lineages meet and introgress in rainforest fragments at the headwaters of the North Johnstone River, east Atherton Tableland. There was no strong trend towards reduced diversity within fragments, but there was slightly greater divergence among fragments than continuous-forest sites and both central and east Atherton fragments had significant inbreeding coefficients, whereas sites in continuous forest did not. Overall, however, the genetic structure of the populations appears to be dominated by historical (natural) rather than current (anthropogenic) fragmentation and this complicates attempts to assess the effects of the latter. Further studies are needed and these should focus on historically, as well as geographically, matched sites and should employ high mutation rate genetic markers, such as microsatellites, which will more rapidly approach equilibrium with current processes.