Genetic diversity and differentiation in the leaf litter weevil Geochus politus across an urban-rural gradient

Urban reserves have the potential to retain relatively high biodiversity. However, populations of the taxa within them can have reduced genetic diversity and, if gene flow between populations is inhibited by urbanised surroundings, can become genetically differentiated. Here we determine whether differences in population genetic differentiation and diversity can be observed in the leaf litter inhabiting weevil Geochus politus along the urban-rural gradient spanning Waitākere Ranges Regional Parkland and suburbs of west Auckland, New Zealand. Nine microsatellite markers were developed and screened across 300 individuals from nine sampling locations. Pairwise FST values, a principal coordinates analysis, and Bayesian estimates of population structure all demonstrated that the most urban site was strongly differentiated from the others. This site also had the lowest heterozygosity and highest FIS values, potentially indicating a loss of genetic variation and a greater degree of inbreeding, although not to a dramatic extent. 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. This study highlights the potential for urban reserves to harbour significant diversity and emphasises the importance of maintaining these sites.