Phylogeography and Population Genetics of New Zealand Leaf Litter Weevils

Abstract

The leaf litter layer in New Zealand forests is home to a rich native invertebrate community. Despite their diversity, the biology of these fauna has been little studied, including their evolutionary history and population genetic structure. This thesis aims to provide a multifaceted genetic study of native leaf litter inhabiting weevil species, by investigating genetic patterns at multiple spatial scales. Population genetics methods were used to investigate the genetic structure of the species Geochus politus along the urban-rural gradient spanning Waitakere Ranges Regional Parkland and suburbs of west Auckland. The objective at this scale was to determine whether differences in population genetic differentiation and diversity would be observed between sites in continuous forest and those in urban areas. Seven microsatellite markers were developed and screened across individuals from nine sampling locations. Pairwise FST values, a principal coordinates analysis, and a Structure analysis all demonstrated that the most urban site was strongly differentiated from the others. Differentiation was also observed among sampling locations within continuous forest, suggesting that both urbanisation and other landscape variables are influencing gene flow between these locations. Measures of heterozygosity and allelic richness were similar across sampling locations including those in more urban areas, highlighting the potential for urban reserves to harbour significant levels of diversity, and emphasising the importance of maintaining these sites. A phylogeographic study at a national scale was conducted to explore spatial genetic patterns at a broader level. This focussed on the genus Etheophanus, the species of which are collectively distributed across most of New Zealand. The aims of this study were to both delimit the species boundaries within Etheophanus, and to investigate phylogeographic patterns within each species relative to their distributions and infer potential causative processes. A molecular phylogeny was reconstructed utilising sequences from the mitochondrial cytochrome oxidase subunit I (COI) and the nuclear 28S gene regions. Species formed monophyletic clades consistent with how they had been morphologically delimited. High levels of structuring were observed within E. striatus and the E. nitidellus/E. optandus complex, suggesting the presence of cryptic species in these groups, which is consistent with other studies of leaf litter invertebrates. Phylogeographic patterns indicated colonisation of E. striatus from the South to North Island, and the potential presence of a climate refuge in south Westland, a finding which has also been uncovered in other studies of forest beetles. This thesis not only contributes to our understanding of leaf litter fauna, but also explores the genetic responses of these weevils to environmental change, enhances our taxonomic understanding of these groups, and adds to the growing genetic resources available for the native New Zealand insect biota.