Genetic Variation in Tuatara (Sphenodon) Populations, as Inferred from Microsatellite DNA Markers

Abstract

The tuatara (Sphenodon) is an endemic New Zealand reptile, once distributed throughout the mainland, but now confined to 35 island populations. This severe range contraction is associated with human colonization. This thesis examines patterns of genetic diversity within fourteen isolated tuatara populations, and characterises genetic relationships among these populations using microsatellite DNA markers. In addition, investigate the impact of island size and introduced predators on the genetic variation within these populations. Microsatellite DNA markers are shown to be an excellent tool for population genetics of tuatara. Isolated populations were screened at six microsatellite loci (first developed by Chambers and MacAvoy, 2000), using PCR to amplify the loci, which were then genotyped by automated electrophoretic scoring. The genotypic data obtained were combined with data from previous tuatara population analyses for three further islands using the same loci (Sainsbury, 2000; Lawrence, 2002), providing a large data-set for analysis of genetic diversity in tuatara populations. Individual populations were characterised by their unique profiles of microsatellite genetic diversity. Some populations exhibit effects of inbreeding (severe in one case), particularly those on smaller islands. On islands that were once inhabited by kiore the small remaining relict tuatara populations exhibit surprisingly high levels of the ancestral variation, but arc expected to be severely affected by genetic drift over the next few generations. Data analyses indicate that populations are significantly differentiated (F ST>0.260; R ST>0.156). However, various phylogenetic analyses do not provide any consistent pattern of population structuring, grouping North Brother tuatara with the Poor Knights and Little Barrier populations. The clearly evident distinctiveness of each tuatara population suggests that each should be managed as a separate conservation unit. Careful management of those remaining individuals from kiore-associated islands, and from small bottlenecked populations, is required to increase numbers and prevent severe loss in genetic variation by genetic drift and inbreeding.