Phylogeographic origin of Apatania zonella (Trichoptera) in Iceland

The purpose of our study was to analyze the origin of the Icelandic population of the Holarctic caddisfly Apatania zonella, a species with a highly skewed sex ratio. Biological diversity in Iceland, as in the Arctic, has been shaped by the glacial periods of the Pleistocene, but Iceland's geographic isolation contributes to its low diversity. Many species at high latitudes in the northern hemisphere have diverged allopatrically during glacial periods and expanded their distribution following the retreat of the glaciers. Genetic patterns of various species reflect these climate changes, but freshwater insects show patterns that differ from those of many vertebrate and terrestrial species. To analyze the origin of the Icelandic population we assessed sequence variation of the mitochondrial cytochrome c oxidase subunit I (COI) gene in specimens from Iceland and throughout its distribution range. We included sequences from different species for a further comparison. We also assessed sequence variation in 3 nuclear introns for a subset of the sample. We partitioned variation at the molecular level among and within groups and reconstructed and dated phylogenetic trees based on Bayesian and maximum likelihood methods. The molecular variation was highly structured at the large geographical scale and within Iceland. The analysis defined 2 major lineages, Nearctic and Palaearctic, which diverged during the last ice age. Both lineages have colonized Iceland, resulting in high diversity in the Icelandic population. High diversity is also observed in Alaska, and the Alaskan mitochondrial DNA haplotypes are situated close to the center of the genealogical network. The phylogeny of the genus Apatania is not fully resolved, and several species of Apatania cluster within the genealogy of Apatania zonella.