Testing a invasive species hypothesis on Platypus quercivorus, a vector insect of the Japanese oak wilt by DNA analysis among regional populations

点击翻译按钮获取中文摘要

Before starting this project, Platypus quercivorus was recorded from Japan, India, Indonesia, New Guinea, and Taiwan. We collected the species from Thailand and Vietnam, which is the new record of the distribution of this species. We found that two types were distributed in Japan, which were thought to be two independent species ("Japan-Sea type" and "Pacific -Ocean type" in this MS). These two types differed from each other morphologically and genetically. These morphological and genetic differences coincided. Regarding the "Japanese-Sea type" two populations were recognized by DNA analysis: mainland population and central Ryukyu population. Genetic distance between the two populations was farthest among four regional populations by DNA analysis including Thai and Indonesian populations. The mainland population was most close to Thai population, and the central Ryukyu population was to the Indonesian. It was difficult to explain this result by natural pattern. The mainland population was introduced from Thailand after the last glacier age probably by human activity. On contrary, the pathogenic fungus, Raffaelea quercivora did not varied so much as P quercivorus did: R. quercivora that was collected from P quercivorus in Taiwan and Japan were classified into one trade. We hypothesized an origin of the Japanese oak wilt disease as follows: Japan-Sea-type P quercivorus that were introduced from Thailand after glacier age were hijacked by R. quercivora carried by the Pacific-Ocean type at southern Kyushu, in which these two types coexist. Because Quercus crispula is highly susceptible to R. quercivora and because reproduction rate of P quercivorus is high in dead Q. crispula, epidemics of the Japanese oak wilt spread rapidly and the distribution range of the Thai population of the "Japan-Sea-type" P. quericovrus expanded fast