[1] Hokkaido Univ, Grad Sch Env Sci, Lab Ecol Genet, Sapporo, Hokkaido 060, Japan
[2] Natl Inst Genet, Mammalian Genet Lab, Mishima, Shizuoka, Japan
[3] Tokyo Univ Agr, Setagaya Ku, Dept Bioprod, Tokyo 1568502, Japan
[4] RIKEN, BioResource Ctr, Wako, Saitama, Japan