Multiple lineages of the mitochondrial DNA introgression fromPungitius pungitius(L.) toPungitius tymensis(Nikolsky)

Abstract

We applied mitochondrial DNA (mtDNA) restriction fragment length polymorphism analysis to trace the maternal lineages and compare the intrapopulation mtDNA variabilities of two ninespine stickleback species, Pungitius pungitius (L.) and Pungitius tymensis (Nikolsky), in which occasional natural hybridization was detected. mtDNA phylogenies constructed by neighbor-joining and Wagner parsimony methods resolved two divergent clades differing by an average nucleotide divergence of 5.94%. All P. pungitius mtDNA haplotypes fall within a single clade. In contrast, P. tymensis appeared paraphyletic; nine of the 13 mtDNA haplotypes found in P. tymensis were grouped within the P. pungitius clade, but the remaining four were of the other clade. The former nine mtDNA variants were very close to the sympatric P. pungitius mtDNA halotypes. These observations suggest that the nine P. tymensis haplotypes originated and introgressed from sympatric P. pungitius and that the introgressed mtDNA haplotypes have a polyphyletic origin in each region. The high incidences of the mtDNA introgression in northern and central Hokkaido may be due to a warmer climate than that of the other regions. The recipient P. tymensis populations had significantly higher mtDNA variation than those observed in the sympatric donor species populations, suggesting the sudden population growth during or after the mtDNA substitution processes.