Ecological and molecular phylogenetic analysis of the distribution expansion process of spider mites in Southeast and East Asia

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We studied the variation in diapause capacity and the mitochondrial DNA (COI) variation in two species of spider mites (Tetranychus urticae and T.kanzawai) for populations collected from Southeast and East Asia, to elucidate their distribution expansion patterns over the area. Japanese T.uritice (green form) populations showed a clinal change in diapause percentage and populations in the South had a very low diapause capacity. This low diapause capacity was also observed in all populations from Southeast and East Asia. The mites are known to originate from the Mediterranean areas and to have expanded its distribution range over the world within a short period. The present phylogenetic analysis based on COI gene confirmed that all populations from the areas studied are included in a single cluster with very little variation in the COI sequences. The results combined showed that T.urticae is an invasive species in Asia, including Japan, and in the process of distribution expansion the mi … More tes lost its diapause capacity, while they obtained high dispersal capacity, to adjust warm climates with continuous food availability.Most Japanese T.kanzawai populations, except those from Okinawa Islands, exhibited diapause percentages higher than 90%. Diapause percentages varied greatly among populations from Taiwan. This genetically diversified diapause capacity was also observed in populations from northern Vietnam. While populations from Thailand, including those from in the North, showed very low diapause capacity, populations from West Jawa, Indonesia and those from Manila, Philippines maintained high diapause capacity, in spite of their distribution in the tropics. Thus, in T.kanzawai no clear relationship was observed between dipause capacity and latitude and diapause was not subject to natural selection. The phylogenetic analysis based on the COI sequences showed that all populations from Honshu and southward, including those from Korea, Taiwan, Vietnam, and Thailand were genetically homogeneous and formed a single clade. However, populations from northern Hokkaido had 13 haplotypes, thus showing a comparatively high genetic differentiation. The results above implied that T.kanzawai originates in northern area and has expanded its distribution range to southern areas very recently. Less