| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2004: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2003: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
The nucleotide substitution rate for mitochondrial DNA (mtDNA) is generally much faster than that for nuclear DNA in higher animals, which makes mtDNA useful to detect a difference between closely related species. However, phylogenetic relationships of mtDNA often show conflicts with the species relationships due to ancestral polymorphisms and geographic population subdivisions. For instance, the mitochondrial introgression, which totally disrupts the correspondence between mtDNA and species phylogenies, has been reported repeatedly between closely related species in a sympatric condition.
To clarify the interactive effects of speciation and introgression on the mtDNA evolution, the sequence divergences of mtDNA (cytochrome c oxidase subunit 1 gene) and nuclear DNA (xanthine dehydrogenase and white genes) were investigated for species and subspecies of the Drosophila nasuta subgroup, which includes several closely related species and subspecies on the way of speciation and distributes in various condition from complete allopatry to sympatry depending on the geographic locations. The results show a strong correlation between geographic distances of habitats and sequence divergences of mtDNA, whereas it was not the case of nuclear DNA. Furthermore, evidence of frequent mitochondrial introgressions in the course of the D.nasuta subgroup evolution was indicated. In conclusion, the importance of taking geographic distribution pattern and the potential of introgression into consideration in the phylogenetic studies of mtDNA was suggested.
Furthermore, for better performance of molecular phylogenetic analyses, theoretical studies were conducted to develop the statistical methods for estimating a neutral nucleotide substitution rate from protein coding sequences under a codon selection and a distance matrix for the reconstruction of large phylogenetic trees with the neighbor-joining method.
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