A single case study of mycetangia-associated fungi and their abilities to assimilate wood-associated carbon sources in the ship timber beetle Elateroides flabellicornis (Coleoptera: Lymexylidae) in Japan

摘要

Ship timber beetles (Coleoptera: Lymexylidae) grow symbiotic fungi of the genus Alloascoidea in wood. The female adults possess fungus-carrying organs (mycetangia) and deposit the symbiont onto wood during oviposition. The larvae acquire the symbiont, excavate a tunnel into wood, and feed on the symbiont growing on the tunnel walls. As lymexylids use wood as a larval habitat, it is possible that the fungal symbionts can utilize indigestible wood-associated sugars. However, their abilities to assimilate wood-associated carbon sources remain unknown. In addition, no lymexylid-associated fungal communities have been reported except for Elateroides dermestoides. Here, I report that the ship timber beetle E. flabellicornis originating from Japan harbored five fungal species. When microbial isolation was conducted from mycetangia of a female adult of E. flabellicornis, colonies of filamentous fungi and yeasts were recovered. DNA analyses revealed that they were Alloascoidea sp., Ambrosiozyma llanquihuensis, Ambrosiozyma sp., Cyberlindnera sp., and Saccharomycopsis sp. When wood-associated carbon assimilation abilities of four of the five fungal species: Alloascoidea sp., Am. llanquihuensis, Cyberlindnera sp., and Saccharomycopsis sp., were tested, the abilities were variable among them. Only Saccharomycopsis sp. assimilated galactose and galacturonic acid. Alloascoidea sp. and Cyberlindnera sp. strongly assimilated xylan from corn. Saccharomycopsis sp. and Cyberlindnera sp. assimilated cellobiose. All of the fungi assimilated glucose, mannose, and xylose. These results suggest that the association with multiple fungal species with various carbon assimilation abilities may help the larvae of E. flabellicornis to achieve efficient nutrient intake in space-limited tunnels within nutrient-poor wood.