抄録
Variations in several characters were observed in two species of ninespine sticklebacks, Pungitius pungitius Linnaeus and P.sinensis uichenot, for 506 specimens from nine localities in the Tohoku and Hokuriku districts of Honshu, the Main Island of Japan.The localities were isolated from one another, and the two species were distributed allopatrically in all of the localities except for Hiraga.In allopatric populations, specimens of P.pungitius had scutes varying from 5 to 13 in number, except for those from Tendo, which were characterized by larger numbers of degenerated scutes (31 35), and those of P.sinensis had scutes varying from 28 to 35.The arrangement pattern of scutes in P.pungitius was more variable than in P.sinensis.No marked difference was observed between the two species in the number of dorsal spines, dorsal, pelvic and anal soft rays.Geographical, but not cinal, variations were observed in these characters between local populations of each species.Clinal variations were recognized in both species in the length of the last dorsal, pelvic and anal spines.Mean spine lengths in the populations near the coast were the longest and became shorter in localities farther away from the coast.The number of gillrakers in populations of P.pungitius varied from 6 to 12 with their mean number varying between 8.0 and 9.2, and that of P.sinensis varied between 8 and 11 with the mean varying between 9.8 and 10.1.Between the two species the mean significantly differed at the 5%level.
In the sympatric population of Hiraga, though morphological differences between the two species were definitely detected, variation in the number and arrangement pattern of scutes in each species was greater than in the other allopatric populations, and taxonomically intermediate forms were found at a low frequency (9.1%).These facts suggest the possibility that natural hybridization occurs between the two species and introgression results.
