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Phenotypic characterization of Mountain Pine Beetle fungal symbionts under a temperature gradient Zhang, Yiyuan


The Mountain pine beetle (MPB) has symbiotic relationships with Ophiostomatoid fungi (Ophiostomatales, Ascomycota), also known as blue stain fungi. The fungal symbionts associated with MPB contribute to the success of beetle survival, reproduction and outbreaks by providing a number of benefits to beetles. The multi-partite mutualism between fungi and MPB has remained remarkably stable over a long period of evolutionary time without exhibiting strong direct competition. We hypothesize that niche partitioning is a stabilizing mechanism which is important for the maintenance of coexistence and diversity of fungal species. The interspecific and intraspecific phenotypic characteristics of three fungal symbionts from a wide geographic and environmental range were investigated under different temperatures in vitro. The study found that three fungal species are differentially adapted to temperatures. The interspecific comparison indicates that Grosmannia clavigera and Leptographium longiclavatum were able to grow better at lower temperatures than Ophistoma montium, while Ophistoma montium displayed greater tolerance to extreme high temperatures. The intraspecific variation within species showed that isolates of the same species from different genetic groups have different temperature tolerances. Leptographium longiclavatum exhibited greater variability in response to temperature than Grosmannia clavigera and Ophistoma montium. The phenotypic data agrees with the genetic population structures of three fungi species. My research indicated that differential temperature tolerances of three fungal species may mediate competition among symbionts, thus influencing dynamics and compositions of the symbiosis in naturally attacked trees. Different growth responses to variable environmental conditions allow the competing species to capture resources at different times without expending energy on direct competition. By maintaining multipartite relationships with these fungi species, bark beetles are more likely to obtain benefits provided by different species of fungi under fluctuating environmental conditions. The complementarity of these nutritional symbionts could facilitate the colonization of new habitats and a broad ecological amplitude for MPB.

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