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Cottus asper; fish; morphometrics; multiple colonization events; North America; Pacific Northwest; parallel evolution; phylogeography; Pleistocene
Abstract:
Aim Glacial cycles during the Pleistocene may have frequently contributed to
parallel evolution of phenotypes across independently evolving genetic lineages
associated with separate glacial refugia. Previous studies based on morphology
suggested that the prickly sculpin (Cottus asper) survived the Last Glacial Maximum
(LGM) in southern coastal and inland refugia, favouring allopatric divergence
between coastal and inland prickling phenotypes, which vary in the
degree to which spine-like scales cover the body of the fish. Herein, we aimed
to test whether parallel evolution across multiple genetic lineages rather than a
single-lineage origin of highly prickled inland sculpins could serve as an explanation
for the biogeographical distribution of prickling phenotypes.
Location North-western North America, Southeast Alaska and Canada (British
Columbia).
Methods We used data from mitochondrial haplotypes and 19 microsatellite
loci to identify distinct genetic lineages as a basis to interpret patterns of phenotypic
evolution.
Results The occurrence of multiple mtDNA groups suggests that highly prickled
inland phenotypes comprise more than one genetic lineage. Both mtDNA
and microsatellite data are consistent with post-glacial dispersal along the coast
and repeated coastal to inland colonization events, as opposed to inland dispersal
of a single lineage from a southern refugium to northern regions.
Main conclusions Our results suggest that highly prickled inland phenotypes
evolved repeatedly following multiple inland colonization events, probably via
coastal rivers. The prickly sculpin therefore provides an example of recent
(post-glacial) parallel evolution, potentially facilitated by standing genetic variation
already present in the ancestral coastal populations.
