北海道におけるトミヨ属魚類3種の地理的分布と形態変異

抄録

The patterns of geographic distribution and morphological variation of three species of ninespine sticklebacks (Pungitius tymensis, P.pungitius and P.sinensis) in Hokkaido, Japan, were investigated.The range of geographic distribution of P.tymensis was essentially restricted to thefollowing three areas, Teshio District of the northern part of Hokkaido, Ishikari District of thecentral part of Hokkaido and Kushiro-Nemuro District of the eastern part of Hokkaido.Onthe other hand, P.pungitius and P.sinensis were distributed more widely and continuously onHokkaido, compared with the distribution of P.tymensis.P.pungitius was distributed continuouslyin the rivers of the Pacific slope from Nemuro District to Iburi District of the central part ofHokkaido, though, discontinuously in the rivers along the Japan Sea and the Okhotsk Sea slopes.In most rivers facing the Nemuro Straits, P.pungitius was not collected.P.sinensis was distributedin only a few rivers of the Pacific slope from Tokachi District to the Oshima Peninsula ofthe southern part of Hokkaido, but was continuously distributed in the rivers facing the TsugaruStraits, the Okhotsk Sea and the Nemuro Straits.
In three rivers examined (Osatsu, Fukunaga and Bettoga) P.tymensis exninntea more of anupstream distribution than did P.pungitius and/or P.sinensis.In two rivers (Fukunaga andBettoga), P.pungitius and P.sinensis did not occur together along the lengths of the river, butwere distributed with a different range respectively.The morphological characteristics of P.tymensis were quite different from the other two species and its meristic characters varied less thanthose of P.pungitius and P.sinensis.Difference in morphology between P.pungitius and P.sinensis was not significant except for number of lateral plates.The number of vertebrae, in bothP.pungitius and P.sinensis decreased gradually from north to south on the Japan Sea slope, thoughthe other meristic characters did not indicate such a geo-cline.The patterns of geographic variationswere most similar between the two species in the rivers of the Japan Sea slope.
Comparison of morphological characteristics and distribution patterns suggest that P.tymensisis distinguished as an independent species from P.pungitius and P.sinensis.Although thecomparative study does not necessarily show that P.pungitius and P.sinensis are different speciesfrom each other, it does not show that they are completely identical.The latter two species showdifferent distribution patterns in the coexisting rivers and are distributed contiguously and allopatricalyin Hokkaido.It is supposed, therefore, that P.pungitius and P.sinensis in Hokkaidoshould be distinguished from each other at a lower taxonomic level than species.