The tale of the founder founder: assessing the origin of a recently established fish in Icelandic waters

Abstract

The geographic origin of an alien species is an important aspect of a species’ invasion history 55 used for classification and management plans but can additionally deliver information on 56 introduction pathways that require the attention of managers and scientists. The invasion 57 history of European flounder (Platichthys flesus), an alien flatfish species first documented in 58 Icelandic waters in 1999, has not been fully elucidated. There have been different hypotheses 59 on the European flounder’s origin and introduction pathway, suggesting either a potentially 60 natural arrival from the Faroe Islands or an introduction via ballast water from the coasts of 61 northwestern Europe. To clarify the geographic origin of European flounder found in Iceland, 62 we used microsatellite analysis of purposefully collected samples from 14 sites around Iceland 63 and reference data stemming from previously published research of flounder population 64 structure in the Faroese and other European populations. Our results indicate that the Faroese 65 population is the most likely source of the European flounder found in Iceland. There was 66 weak IBD between Icelandic samples and the Faroese population. Additionally, we identified 67 9 hybrids between alien European flounder and native European plaice (Pleuronectes 68 platessa) and further documented signatures of introgression between the species. European 69 flounder x European plaice hybrids are commonly found throughout the overlapping native 70 range of both species but has previously not been documented in Iceland.