Genetic variation among Japanese populations of Platypus quercivorus (Coleoptera: Platypodidae), an insect vector of Japanese oak wilt disease, based on partial sequence of nuclear 28S rDNA

Abstract

The ambrosia beetle, Platypus quercivorus, is an insect vector of the Ascomycete fungus, Raffaelea quercivora, the causal agent of Japanese oak wilt disease. In this study, we compared the nucleotide sequences (937-955 bp) of the nuclear 28S rDNA fragment, including the D1 and D2 expansion segment, among local populations of the beetle in Japan. Sequence analysis of 81 beetles from 32 collection sites ranging from the Ryukyu Islands to northern Honshu Island showed seven types of sequences, many of which were separated among different geographic areas. Phylogenetic analysis showed that these sequence types were separated between two deeply divergent genetic groups, suggesting the necessity for taxonomic reexamination of this species. DNA typing of beetles and oak wilt status at the collection sites indicated that several genetically divergent beetle populations are associated with the incidence of the disease. This is the first investigation of genetic variation in the ambrosia beetle across Japan.

Isolation and characterization of 10 new microsatellite loci in the ambrosia beetlePlatypus quercivorus

“…Nine out of 10 primer pairs succeeded in achieving amplification for Type 2, which belongs to the same genetic group (group A) as Type 1 (Hamaguchi and Goto 2010). Eight of these gave polymorphic bands.…”

“…Because the sequence differences among Types 4a, 4b, 4c, and 4d were because of intra-individual polymorphic sites only, and these types were distributed in the same regions (Hamaguchi and Goto 2010), reproductive or geographic isolation may not exist among them. We therefore treated all Type 4s as one type for the amplification test.…”

“…They were divided into two deeply divergent genetic groups: group A (Types 1 and 2) and group B (Types 3, 4a, 4b, 4c and 4d). Hamaguchi and Goto (2010) also reported that, except for Types 4a, 4b, 4c and 4d that coexist, the different types were distributed in different regions. Among these types, Type 1 is especially important from the viewpoint of management because it was predominantly distributed across wide areas on Honshu and Kyushu Islands where most of the serious damage caused by the disease has been observed (Hamaguchi and Goto 2010).…”

“…The markers reported by Takahashi et al (2008) are also likely to be from P. quercivorus Type 1 because the other types are not found in the northern part of Honshu Island (Hamaguchi and Goto 2010) from which their samples were collected.…”

“…Takahashi et al (2008) recently reported 12 microsatellite markers for the beetle; however, these markers had only a moderate number of polymorphisms (the number of alleles ranged from two to six), and the development of additional markers is needed for detailed analyses. Hamaguchi and Goto (2010) recently reported seven genetic types for 28S rDNA among individuals of P. quercivorus in Japan. They were divided into two deeply divergent genetic groups: group A (Types 1 and 2) and group B (Types 3, 4a, 4b, 4c and 4d).…”