Population genetics and biogeography of the lungwort lichen in North America support distinct Eastern and Western gene pools

Populations of species with large spatial distributions are shaped by
complex forces that differ throughout their ranges. To maintain the
genetic diversity of species, genepool-based subsets of widespread species
must be considered in conservation assessments. In this study, the
population genetics of the lichenized fungus Lobaria pulmonaria and its
algal partner, Symbiochloris reticulata , were investigated to determine
population structure, genetic diversity, and degree of congruency in
eastern and western North America. Data loggers measuring temperature and
humidity were deployed at selected populations in eastern North America to
test for climatic adaptation. To better understand the role Pleistocene
glaciations played in shaping population patterns, a North American,
range-wide species distribution model was constructed and hindcast to
22,000 years before present and at 500-year time slices from then to the
present. The presence of two gene pools with minimal admixture was
supported, one in the Pacific Northwest and one in eastern North America.
Western populations were significantly more genetically diverse than
eastern populations. There was no evidence for climatic adaptation among
eastern populations, though there was evidence for range-wide adaptation
to evapotranspiration rates. Hindcast distribution models suggest that
observed genetic diversity may be due to a drastic Pleistocene range
restriction in eastern North America, whereas a substantial coastal
refugial area is inferred in the west. Taken together the results show
different, complex population histories of L. pulmonaria in eastern and
western North America, and suggest that conservation planning for each
gene pool should be considered separately.