Genetic differentiation of ninespine sticklebacks in Japan and adjacent countries

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We applied mitochondrial DNA (mtDNA) RFLP analysis to trace the maternal lineages of two ninespine stickleback species, Pungitius tymensis and P. pungitius, in which occasional natural hybridization was detected. In this study, mtDNA restriction site variation within each of the introgressed and pure populations was also analyzed, to examine the past population sizes. MtDNA phylogenies resolved two divergent phylogenetic groups A and B. Both allopatric and sympatric populations of P. pungitius fall within group A. In contrast, P. tymensis appeared paraphyletic; all group B haplotypes were possessed by only P. tymensis, but six of seven populations in the northern and central Hokkaido carried group A mtDNA haplotypes, which were very close to the mtDNA haplotypes observed in syrupattic P. pungitius populations. These observations suggest that the group A mtDNA haplotypes of P. tymensis originated and introgressed from sympatric P. pungitius, and that the introgressed mtDNA haplotypes ha … More ve a polyphyletic origin in each region. The lack of the mtDNA variation in the 'pure' populations and the high incidences of the mtDNA introgression in the northern and central Hokkaido regions may be due to a warmer climate than the other regions.We also used RFLP analysis of entire mitochondrial DNA (mtDNA) to examine phylogeography and origin of the intraspecific lateral plate dimorphism in the freshwater type of ninespine sticklebacks, Pungitius pungitius and P. sinensis species complex. The survey with seven restriction enzymes was carried out on the populations of this species collected from 41 localities across the species range and six Pungitius populations collected from the coast of the Sea of Okhotsk in Rissia were appended. UPGMA dendrogram among 54 mtDNA haplotypes revealed the existence of six clustering groups differing from each other by approximately 1.2-1.5% in sequence divergences in Japan. Comparison of the geographic distribution patterns of these groups suggests the patterns shoud beclassified into two broad categories, one with the extensive dispersals and the other with the localized distributions of the constituent haplotypes. The former groups were also carried mainly in the populations with completely plated morph, but the latter groups were in partially plated morph. It appears that the twice glacial dispersals of polymorphic ancestors from northern regions and an interglacial isolation played an important role in the formation of present distributions of the two morphs in Japan. Less