This paper focuses on the origin of Trichoptera species in Iceland in light of the island biogeography of caddisflies in the North-Atlantic islands, i.e., Greenland, Svalbard, Iceland, Faroe Islands, Shetland, and Orkney, and adjacent larger regions, Norway and Britain. Three of the 12 recorded species have circumpolar distribution, the other nine are Palaearctic. The number of species declines with the distance from the mainland of Europe and is independent of the island sizes. However, the occurrence of species is stochastic, with only a few species common to the more remote islands—e.g., Iceland has 12 species and the Faroe Islands 20, but only 4 species are common to both islands. Studies on phylogeographic patterns of two species, Potamophylax cingulatus and Apatania zonella, show different history based on genetic markers. Potamophylax cingulatus in Iceland is from a western European lineage, distinct from two eastern and southern European lineages that may have diverged in southern refugia during the glacial periods of the latest Ice Age. The ancestors of the Icelandic population have migrated from the Iberian Peninsula up the west cost of Europe to the Faroe Islands and Iceland. The parthenogenetic A. zonella in Iceland originated near the Bering Strait, and has migrated along two routes, one westward through northern Eurasia and the other eastward through North America and Greenland to Iceland, where the two populations meet. Preliminary phylogeographic studies on two other circumpolar species, Limnephilus fenestratus and L. picturatus indicate possible interchanges between North America and Europe, but due to a low number of samples, it is difficult to state where the Icelandic population came from.
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