Glacial vicariance in the Pacific Northwest: evidence from a lodgepole pine mitochondrial DNA minisatellite for multiple genetically distinct and widely separated refugia

Abstract

The Canadian side of the Pacific Northwest was almost entirely covered by ice during the last glacial maximum, which has induced vicariance and genetic population structure for several plant and animal taxa. Lodgepole pine (Pinus contorta Dougl. ex. Loud.) has a wide latitudinal and longitudinal distribution in the Pacific Northwest. Our main objective was to identify relictual signatures of glacial vicariance in the population structure of the species and search for evidence of distinct glacial refugia in the Pacific Northwest. A maternally inherited mitochondrial DNA minisatellite-like marker was used to decipher haplotype diversity in 91 populations of lodgepole pine located across the natural range. Overall population differentiation was sizeable (G(ST) = 0.365 and R(ST) = 0.568). Four relatively homogeneous groups of populations, possibly representative of as many genetically distinct glacial populations, were identified for the two main subspecies, ssp. latifolia and ssp. contorta. For ssp. contorta, one glacial lineage is suggested to have been located at high latitudes and possibly off the coast of mainland British Columbia (BC), while the other is considered to have been located south of the ice sheet along the Pacific coast. For ssp. latifolia, two genetically distinct glacial populations probably occurred south of the ice sheet: in the area bounded by the Cascades and Rocky Mountains ranges, and on the eastern side of the Rockies. A possible fifth refugium located in the Yukon may have also been present for ssp. latifolia. Zones of contact between these ancestral lineages were also apparent in interior and northern BC. These results indicate the role of the Queen Charlotte Islands and the Alexander Archipelago as a refugial zone for some Pacific Northwest species and the vicariant role played by the Cascades and the American Rocky Mountains during glaciation.

Glacial refugia and modern genetic diversity of 22 western North American tree species

“…Neither Pinus ponderosa nor Pseudotsuga menziesii projections suggest stable habitat north or west of the continental ice. The phylogeography of interior and coastal subspecies of Pinus contorta is somewhat more complex, with genetic data suggesting additional refugia either in Beringia or along the Pacific coast, possibly in the area of Haida Gwaii [9,10]. The potential for refugia west or north of the continental ice is supported in our GFDL model projections in particular, which show extensive Pinus contorta habitat along the Pacific Coast and in Beringia, the most stable of which appears in Haida Gwaii and western Alaska (electronic supplementary material, figure S1N).…”

“…[13]). There is some fossil and genetic evidence that refugia west of the continental ice contained tree species, allowing for rapid recolonization of northern coastal areas [9,10]. Similarly, white spruce and certain other boreal tree species may have found habitat in ice-free Beringia, allowing southward post-glacial recolonization routes [5,6,14].…”

“…Pinus contorta (lodgepole pine), Pinus ponderosa (ponderosa pine), Pseudotsuga menziesii (Douglas fir). These could have emerged through east-west separation of populations by the coastal Cascade Mountains throughout cycles of glaciations and de-glaciation [8][9][10]. On the other hand, many temperate tree species of the Pacific northwest with disjunct coastal and interior populations show little or no genetic differentiation, e.g.…”

Species delimitation and biogeography of two fir species (Abies) in central China: cytoplasmic DNA variation

“…Although some ptDNA haplotypes were species specific, the three most common ptDNA haplotypes (H1, H2 and H5), along with the three common mitotypes (M1, M2 and M4), were widely shared across both species (Figure 1). Shared polymorphisms across closely related species appear to be common in fir, pine and spruce genera of the Pinaceae (for example, see Tsumura and Suyama, 1998;Godbout et al, 2008;Jaramillo-Correa et al, 2008;Du et al, 2009). Sharing might result from introgression following secondary contact between long diverged species or, alternatively, to the maintenance of ancestral polymorphisms due to incomplete lineage sorting within recently diverged species (Wiens, 2007;de Queiroz, 2007).…”

Individual-Based Modeling: Mountain Pine Beetle Seasonal Biology in Response to Climate

“…This irruptive species attacks and kills most Pinus species in western North America (Wood 1982). Genetic data suggest that MPB migrated north following the postglacial Holocene recolonization of British Columbia by several Pinus species (Richardson et al 2002;Mock et al 2007;Godbout et al 2008;Samarasekera et al 2012). Recent warming has increased the speed of this MPB migration into new regions in Alberta, British Columbia, the Yukon, and Northwest Territories, Canada Safranyik et al 2010;Cudmore et al 2010;de la Giroday et al 2012), with exposure to at least one new host tree species, jack pine (Pinus banksiana) (Cullingham et al 2011).…”