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ABC; anadromous fish; British Isles; phylogeographical hypothesis testing; statistical phylogeography
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.
