Spatial genetic structure of the mountain pine beetle (Dendroctonus ponderosae) outbreak in western Canada: historical patterns and contemporary dispersal

Abstract

Environmental change has a wide range of ecological consequences, including species extinction and range expansion. Many studies have shown that insect species respond rapidly to climatic change. A mountain pine beetle epidemic of record size in North America has led to unprecedented mortality of lodgepole pine, and a significant range expansion to the northeast of its historic range. Our goal was to determine the spatial genetic variation found among outbreak population from which genetic structure, and dispersal patterns may be inferred. Beetles from 49 sampling locations throughout the outbreak area in western Canada were analysed at 13 microsatellite loci. We found significant north-south population structure as evidenced by: (i) Bayesian-based analyses, (ii) north-south genetic relationships and diversity gradients; and (iii) a lack of isolation-by-distance in the northernmost cluster. The north-south structure is proposed to have arisen from the processes of postglacial colonization as well as recent climate-driven changes in population dynamics. Our data support the hypothesis of multiple sources of origin for the outbreak and point to the need for population specific information to improve our understanding and management of outbreaks. The recent range expansion across the Rocky Mountains into the jack/lodgepole hybrid and pure jack pine zones of northern Alberta is consistent with a northern British Columbia origin. We detected no loss of genetic variability in these populations, indicating that the evolutionary potential of mountain pine beetle to adapt has not been reduced by founder events. This study illustrates a rapid range-wide response to the removal of climatic constraints, and the potential for range expansion of a regional population.

Temperature-driven range expansion of an irruptive insect heightened by weakly coevolved plant defenses

“…These results provide a mechanistic link between two major environmental threats, transport of invasive species and climatedriven range expansions, in that lack of coevolved defense is an important driver of each (41,42,51). Mountain pine beetle has also expanded its northern range, where it is attacking lodgepole pines in historically unexposed areas, and has spread eastward to breach the geophysical barrier of the Rocky Mountains to attack hybrid lodgepole-jack pine, Pinus banksiana, in Alberta, Canada (7,56). Previous dispersal events likely deposited small numbers of beetles in these habitats, but populations quickly collapsed because of Allee effects.…”

Geographically variable response of Dendroctonus ponderosae to winter warming in the western United States

“…Some modifications to the ecoregion boundaries were made so that their boundaries closely approximated the geographic extent of interbreeding populations of D. ponderosae. Relatively large ecoregions (e.g., Coast Range, Middle Rockies, North Rockies, and Southern Rockies) were subdivided into separate regions based upon the underlying pine forest distribution and topographic features (e.g., river canyons, deserts, and mountains) known to affect movement of D. ponderosae populations (Mock et al 2007;Chen and Walton 2011;Gayathri Samarasekera et al 2012). For example, we created five subregions from the Ecoregion Level III classification of ''Middle Rockies'' to correspond to geographically distinct, forested areas (i.e., Black Hills, Big Horn mountains, Central mountains, Yellowstone Ecosystem, and the western Montana mountains) (Fig.…”

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

“…The MPB has been migrating for the past 8000 years, following a northerly expansion of its host tree species. As temperature increased, expansion has been extraordinarily rapid in the past few decades, so rapid that no loss of genetic variability was detected in expanding populations (Samarasekera et al 2012). Our model explains the role of weather in this expansion, and predicts that the pace of population growth in Alberta and northern BC will continue to increase.…”

“…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).…”