A microsatellite analysis of the western Canadian mountain pine beetle (Dendroctonus ponderosae) epidemic: phylogeography and long distance dispersal patterns

Abstract

The mountain pine beetle (MPB) is an eruptive insect that is currently causing an outbreak of record size in Western Canada. A lack of long distance MPB dispersal data has limited our understanding of and ability to manage MPB epidemics. My goal was to determine the MPBs Western Canadmn population structure. upon wh1ch d1spersal patterns may be supenmposed. I analyzed MPBs from 35 mfested lodgepole pine stands at six microsatellite loc1. The MPB exh1bited strong and s1gmticant Western Canadian population structure. Th1~ population ~tructure wa~ mcongruent w1th the structure of its primary symbiont. 0. £ hn igerwn. but congruent \\1 ith the structure of 1ts primary host, P.contorta. Novel fungal selection pres~ure~ ha"Ve probably caused the discrepancy in beetle/fungus phylogeography. A result of Western Canadmn MPB population structure alternately contrasts and supports population structure~ previou~ly reported for Scolytids, including MPBs. The partitioning of MPB populatiOn structure into a Northern and Southern group is most likely the result of postglacial recolonization and differences in MPB population dynamics. Primarily using my genetic data, I inferred the historical movement patterns of the MPB in Western Canada. I found no evidence that the epidemic spread from an epicenter in Tweedsmuir Provincial Park. My data support multiple sources for the current epidemic; I suggest that regional population expansions have caused the rapid escalation in the severity of the current epidemic. MPB movement patterns and atmospheric wind data were concordant; winds in Western Canada are predominantly westerly or southwesterly. which was the predominant direction of inferred movements amo ng MPB populations. In contrast, current MPB population structure best fits a 30-year climatic suitabi lity distribution for a historical as II opposed to the most current ( 1971 -2000) period. The population genetics of long distance MPB dispersal. an evolutionary theory for MPB population dynamics. and MPB "range expansion" are extensively d1scussed. Potential biases and research limitations are noted. Based on my results and inferences. future areas of investigation are noted.An executive summary. with management recommendations. is prov1ded as a conclusion.

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

“…Calaps et al (2002) used randomly amplified polymorphic DNA (RAPD) markers to study MPB and found no evidence for population structure. However, this study might have been affected by the fungal DNA, as the initial DNA extractions were performed on whole beetles and did not control for fungal contamination (see Bartell 2008). Further, the small sample size per population (15) may also not be adequate to detect genetic differentiation.…”

“…Some population genetic studies, that utilized methods such as mitochondrial and nuclear sequencing, showed the role of geographic barriers on population dynamics of bark beetles (see Bartell 2008). Duan et al (2004) analyzed the population genetic structure of Tomicus piniperda in 12 populations in Yunnan (southern China) and one in Jilin (northern China) using mitochondrial cytochrome oxidase {COI and COIT) and nuclear internal transcribed spacer 2 (ITS2) of ribosomal DNA (rDNA) and 28S-rDNA sequences, and compared the results to those obtained in France.…”

“…Mock et al (2007) found evidence of genetic structuring of MPB and a broad isolation-by-distance pattern. Bartell (2008) used microsatellite markers to study the population genetic structure of MPB and generated many informative results. The sampling design in his study was uniform over a large geographical area.…”

“…The sampling design in his study was uniform over a large geographical area. Bartell (2008) (Goldstein & Schlotterer 2001). It is believed that microsatellites evolve through slipped-strand impairing (Levinson & Gutman 1987), uneven recombination, or a combination of both (Jakupciak & Wells 1999;Wells, 1996).…”

“…In the first study I conduct a detailed population genetic analysis on the MPB in western Canada using a dataset of 15 genomic microsatellite markers. The objective of this study was to increase the resolution of the population genetic structure of MPB described in Bartell (2008) and to understand dispersal of MPB in western Canada. The objective of the second study was to develop a suite of microsatellite markers within, or closely linked to, the coding loci of the MPB genome (i.e., genie microsatellite markers or EST-derived microsatellite markers) in order to increase the marker coverage available for future MPB genetic/genomic research.…”