Large Shift in Symbiont Assemblage in the Invasive Red Turpentine Beetle

<div><p>Changes in symbiont assemblages can affect the success and impact of invasive species, and may provide knowledge regarding the invasion histories of their vectors. Bark beetle symbioses are ideal systems to study changes in symbiont assemblages resulting from invasions. The red turpentine beetle (<i>Dendroctonus valens</i>) is a bark beetle species that recently invaded China from its native range in North America. It is associated with ophiostomatalean fungi in both locations, although the fungi have previously been well-surveyed only in China. We surveyed the ophiostomatalean fungi associated with <i>D. valens</i> in eastern and western North America, and identified the fungal species using multi-gene phylogenies. From the 307 collected isolates (147 in eastern North America and 160 in western North America), we identified 20 species: 11 in eastern North America and 13 in western North America. Four species were shared between eastern North America and western North America, one species (<i>Ophiostoma floccosum</i>) was shared between western North America and China, and three species (<i>Grosmannia koreana</i>, <i>Leptographium procerum</i>, and <i>Ophiostoma abietinum</i>) were shared between eastern North America and China. <i>Ophiostoma floccosum</i> and <i>O. abietinum</i> have worldwide distributions, and were rarely isolated from <i>D. valens</i>. However, <i>G. koreana</i> and <i>L. procerum</i> are primarily limited to Asia and North America respectively. <i>Leptographium procerum</i>, which is thought to be native to North America, represented >45% of the symbionts of <i>D. valens</i> in eastern North America and China, suggesting <i>D. valens</i> may have been introduced to China from eastern North America. These results are surprising, as previous population genetics studies on <i>D. valens</i> based on the cytochrome oxidase I gene have suggested that the insect was introduced into China from western North America.</p>