Spatial Community Structure of Mountain Pine Beetle Fungal Symbionts Across a Latitudinal Gradient

Abstract

Symbiont redundancy in obligate insect–fungal systems is thought to buffer the insect host against symbiont loss and to extend the environmental conditions under which the insect can persist. The mountain pine beetle is associated with at least three well-known and putatively obligate ophiostomatoid fungal symbionts that vary in their environmental tolerances. To better understand the spatial variation in beetle–fungal symbiotic associations, we examined the community composition of ophiostomatoid fungi associated with the mountain pine beetle as a function of latitude and elevation. The region investigated represents the leading edge of a recent outbreak of mountain pine beetle in western Canada. Using regression and principal components analysis, we identified significant spatial patterns in fungal species abundances that indicate symmetrical replacement between two of the three fungi along a latitudinal gradient and little variation in response to elevation. We also identified significant variation in the prevalence of pair-wise species combinations that occur within beetle galleries. Frequencies of pair-wise combinations were significantly different from what was expected given overall species abundances. These results suggest that complex processes of competitive exclusion and coexistence help determine fungal community composition and that the consequences of these processes vary spatially. The presence of three fungal symbionts in different proportions and combinations across a wide range of environmental conditions may help explain the success of mountain pine beetle attacks across a broad geographic range.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-011-9841-8) contains supplementary material, which is available to authorized users.

Fungal Frequency and Mite Load Trends Interact with a Declining Mountain Pine Beetle Population

“…A faster MPB development may allow its incursion into cooler latitudes and elevations, as well as population increments in these areas as a greater portion of the population survives the shorter season. Specifically, the blue-stain L. longiclavatum promoted a faster MPB larvae development in Canada [19], where the fungus was shown to increase in frequency in direct relation to the increase in latitude [21]. Thus, in northerly latitudes, the MPB may be benefitting from its more frequent association with L. longiclavatum [21].…”

“…Specifically, the blue-stain L. longiclavatum promoted a faster MPB larvae development in Canada [19], where the fungus was shown to increase in frequency in direct relation to the increase in latitude [21]. Thus, in northerly latitudes, the MPB may be benefitting from its more frequent association with L. longiclavatum [21]. Although the 2000's MPB epidemic expansion to new latitudes and elevations in both the Colorado Rockies and Alberta is considered to have been caused by warmer winter temperatures, there is no good quantification of non-prevailing MPB incursions into novel areas.…”

“…Analyses of the effects of temperature on the stability of the above two blue-stain fungi have shown that beetle movement between warm and cold habitats, as well as variations in their attack densities, can help explain the prevalence of both species in the symbiosis [31]. Thus, a fungal redundancy in the system may occur [10,21], but studies of fungal community trends during changing MPB populations have not been performed.…”

“…Within a tree, the variation in the relative abundances of blue-stain species may be influenced by the collection period after initial insect attacks. This variation may be due to site latitude, the beetle developmental state on the tree, and site temperature at the time of collection [17,21,27,28]. As an example, Ophiostoma montium, which is more tolerant of warmer temperatures, has been found predominantly in MPB populations attacking during warmer periods [17].…”

“…Lee, J.J. Kim and C. Breuil was first documented in Canada during the epidemic at the turn of the century. This species has been associated with cooler areas within the distribution of the beetle [21]. Another, Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer and Wingfield can influence MPB success by obtaining its needed carbon from limonene [22], a component of the oleoresin that is toxic to the beetle [23][24][25].…”