Large Shift in Symbiont Assemblage in the Invasive Red Turpentine Beetle

Stephen J Taerum,Donald R Owen,Jiang-Hua Sun,Michael J Wingfield,Tuan A Duong,Nicole M Gerardo,Nancy Gillette,Z Wilhelm De Beer

doi:10.1371/journal.pone.0078126

Abstract

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 (Dendroctonus valens) 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 D. valens 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 (Ophiostoma floccosum) was shared between western North America and China, and three species (Grosmannia koreana, Leptographium procerum, and Ophiostoma abietinum) were shared between eastern North America and China. Ophiostoma floccosum and O. abietinum have worldwide distributions, and were rarely isolated from D. valens. However, G. koreana and L. procerum are primarily limited to Asia and North America respectively. Leptographium procerum, which is thought to be native to North America, represented >45% of the symbionts of D. valens in eastern North America and China, suggesting D. valens may have been introduced to China from eastern North America. These results are surprising, as previous population genetics studies on D. valens based on the cytochrome oxidase I gene have suggested that the insect was introduced into China from western North America.

Highlights

Symbionts greatly influence the success and impact of many human-mediated species invasions [1,2,3,4]
Bark beetles were rolled onto 2% malt extract agar (MEA; 20 g agar and 20 g malt extract per 1 L water) containing 0.5 g cycloheximide, which is selective for fungi in the order Ophiostomatales
Few ophiostomatalean species were shared between the three populations, more species were shared between ENA and China than between WNA and China

Summary

Introduction

Symbionts greatly influence the success and impact of many human-mediated species invasions [1,2,3,4]. Mutualistic symbionts can facilitate invasive species or enhance the damage they cause (i.e., invasional meltdown [5]). Successful plant invasions often depend on co-invading or newly adopted mychorrhizae [6] or endophytes [7,8,9], while plants that lose their mutualists can have lowered fitness in invaded environments [10]. Invasive forest insects can benefit from microbial symbionts that allow the insects to aggressively colonize naive hosts [11]. Some coinvading commensalists, mutualists, and pathogens can indirectly influence the success of invasive species by outcompeting native symbionts that would reduce the invader’s fitness, or by inhibiting the invader’s competitors or predators [15,16]

Methods

Results

Conclusion