Weta affairs : an investigation into the population structure and possible hybridisation of two tree weta species (hemideina) in Canterbury.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Recently, hybridisation has been increasingly recognised as contributing to the extinction of species; with the risk especially high for rare species hybridising with more common species. Such risks have raised concerns for the Banks Peninsula tree weta, Hemideina ricta, which is restricted to the eastern half of Banks Peninsula and in some areas lives in sympatry with the more widespread Canterbury species, H. femorata. A previous genetics study found evidence of hybridisation between these two species. However, conclusions made by this study were likely limited by its small sample size. To further assess the risk hybridisation poses to the conservation of these species, a larger genetic study was undertaken. With hybridisation between H. ricta and H. femorata previously hypothesized to be a rare event, modelling of likely sympatric zones was undertaken to optimize the sampling effort. The results of genetic analysis on the resulting samples were consistent with the previous study, in that they suggest hybridisation does occur but is fairly rare. To help determine what processes are maintaining the distinction between the two species, the current study has expanded to incorporate observations of mating behaviour and egg hatching experiments. As well as potential risks from hybridisation, H. ricta and H. femorata have also suffered habitat loss. The Canterbury region has been transformed by the introduction of exotic plant species, fire and logging, with only small patches of native bush remaining. The loss and fragmentation of the native forest is likely to impact the forest fauna such as the tree weta. A previous study of a closely related species H. maori, in a naturally fragmented habitat, determined that dispersal between suitable habitat patches was fairly limited. Therefore, similar to their habitat, H. ricta populations may be small and isolated. Such populations are prone to the fixation of deleterious alleles as well as a loss of genetic diversity. Deleterious traits not only have a short term negative impact but a lack of genetic variation can prevent adaptation in the long term. In the past, studies of population structure have included the influence of intrinsic factors, such as dispersal capabilities but neglected extrinsic factors, such as the environment. The current study uses microsatellite markers to determine the population structure of both species and where possible, maps of land-cover are analyzed for a correlation with genetic structure.