Microsatellite Variation in Mountain Pine Beetle ( Dendroctonus ponderosae Hopkins) in Western Canada: Spatial Genetic Analyses of Neutral Variation and Development of Genic Markers.

The mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, is the most destructive pest of pine forests in western North America. In this study genetic variation of MPB in western Canada was explored both at neutral genomic and gene-linked microsatellite markers. To understand the spatial genetic structure and dispersal patterns, beetles from 49 sampling locations throughout western Canada were analyzed at 13 neutral microsatellite loci. The MPB exhibits significant north-south population structure in western Canada. The decline of genetic diversity from south to north and the lack of isolation by distance in the northernmost cluster are consistent with patterns expected from postglacial recolonization. In terms of dispersal patterns, northern outbreaks are consistent with an expansion out of Tweedsmuir Provincial Park, an early site of infestation in the current epidemic, while southern outbreaks are consistent with multiple centers of origin. To explore the gene-linked variation in the MPB genome, a panel of gene-linked markers was developed by screening an EST database of MPB. Fifty of 79 EST-derived markers developed were found to be polymorphic. A preliminary survey of five EST-derived microsatellite markers show evidence of selection at two loci. The genetic variation at another three loci was comparable with the genetic variation at neutral microsatellite markers. This study showed that the use of EST-derived microsatellites is a promising approach for identifying signatures of selection. Further, the new markers developed will be useful in constructing linkage maps and in performing genome scans and further landscape-scale genomic studies in both MPB and other related bark beetles. --P. ii.