A TEST OF THE GLACIAL REFUGIUM HYPOTHESIS USING PATTERNS OF MITOCHONDRIAL AND NUCLEAR DNA SEQUENCE VARIATION IN ROCK...

Area of Science:

• Evolutionary Biology
• Genetics
• Paleoclimatology

Background:

• The glacial refugium hypothesis (GRH) posits that glacial periods drive intraspecific diversification by isolating populations in ice-free refugia.
• Understanding population structure and divergence patterns is crucial for evolutionary biology.

Purpose of the Study:

• To test the GRH predictions for rock ptarmigan (Lagopus mutus) evolutionary divergence during the late Pleistocene Wisconsin glaciation.
• To examine subspecies distributions, population genetic structure, and phylogenetic relationships across North America and the Bering Sea.

Main Methods:

• Analysis of sequence variation in mitochondrial control region, Gapdh intron, and ITS1 across 26 rock ptarmigan populations.
• Examination of subspecies distributions and concordance with identified glacial refugia.
• Phylogenetic analysis to estimate divergence times of lineages.

Main Results:

• Mitochondrial control region and Gapdh intron sequences revealed strong population and phylogeographic structure in rock ptarmigan.
• Morphologically distinct subspecies distributions aligned with five Nearctic and one Icelandic refugium, with five refugia showing concordance with haplotype distributions.
• Phylogenetic lineage divergence predated the last glacial maximum for most lineages, and evidence suggested two unknown Bering Sea refugia supported populations.

Conclusions:

• Results strongly support the glacial refugium hypothesis for rock ptarmigan, with divergence occurring in multiple refugia during the Wisconsin glaciation.
• Geographic variation in rock ptarmigan reflects recolonization patterns after glacial retreat.
• The GRH provides a plausible explanation for similar biogeographic patterns observed in other Nearctic vertebrates.