title: Unique mitochondrial DNA lineages in Irish stickleback populations: cryptic refugium or rapid recolonization?
abstract: Repeated recolonization of freshwater environments following Pleistocene glaciations has played a major role in the evolution and adaptation of anadromous taxa. Located at the western fringe of Europe, Ireland and Britain were likely recolonized rapidly by anadromous fishes from the North Atlantic following the last glacial maximum (LGM). While the presence of unique mitochondrial haplotypes in Ireland suggests that a cryptic northern refugium may have played a role in recolonization, no explicit test of this hypothesis has been conducted. The three-spined stickleback is native and ubiquitous to aquatic ecosystems throughout Ireland, making it an excellent model species with which to examine the biogeographical history of anadromous fishes in the region. We used mitochondrial and microsatellite markers to examine the presence of divergent evolutionary lineages and to assess broad-scale patterns of geographical clustering among postglacially isolated populations. Our results confirm that Ireland is a region of secondary contact for divergent mitochondrial lineages and that endemic haplotypes occur in populations in Central and Southern Ireland. To test whether a putative Irish lineage arose from a cryptic Irish refugium, we used approximate Bayesian computation (ABC). However, we found no support for this hypothesis. Instead, the Irish lineage likely diverged from the European lineage as a result of postglacial isolation of freshwater populations by rising sea levels. These findings emphasize the need to rigorously test biogeographical hypothesis and contribute further evidence that postglacial processes may have shaped genetic diversity in temperate fauna.
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast Belfast, U.K ; Lovén Centre-Tjärnö, Department of Biology and Environmental Sciences, University of Gothenburg Gothenburg, Sweden.
authors.forename: Mark
authors.initials: M
authors.lastname: Ravinet
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast Belfast, U.K ; Instituto de Ciencias Naturales Alexander Von Humboldt, Universidad de Antofagasta Chile.
authors.forename: Chris
authors.initials: C
authors.lastname: Harrod
authors.affiliation: GEOMAR|Helmholtz Centre for Ocean Research Duesternbrooker weg 20, 24105, Kiel, Germany ; Max Planck Institute for Evolutionary Biology August Thienemannstr. 2, 24306, Ploen, Germany.
authors.forename: Christophe
authors.initials: C
authors.lastname: Eizaguirre
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast Belfast, U.K.
authors.forename: Paulo A
authors.initials: PA
authors.lastname: Prodöhl
keywords: ABC; British Isles; anadromous fish; phylogeographical hypothesis testing; statistical phylogeography