Population-genetic structure in the New Zealand caddisfly Orthopsyche fimbriata revealed with mitochondrial DNA

Nucleotide sequences of 422 base pairs of the cytochrome c oxidase subunit I (COI) gene were used to assess phylogeographic structure in the New Zealand hydropsychid caddisfly Orthopsyche fimbriata. A hierarchical examination of populations from 16 streams at different spatial scales in the central and northern North Island of New Zealand found 23 haplotypes. Most regions were characterised by unique haplotypes with genetically differentiated populations at the 70+ km scale. Haplotype diversity was high (0.5-0.8) at most sites, but low (0.2-0.3) in Northland and zero at some central sites. Analyses of molecular variance found significant genetic diversity among regions (66%) and among catchments (55%). Most population pair-wise FST tests were significant, with non-significant pairwise tests among sites in the central region and pairs of sites between neighbouring streams. The levels of sequence divergence are interpreted as the result of divergence of relict populations in multiple refugia, leading to the evolution of regionally unique haplotypes. The low diversity in some central region populations is interpreted as resulting from recolonisation following extinctions associated with historical volcanic events.