| Research Abstract |
Japanese freshwater sculpins consist of 6 Cottus and 1 Trachidermus species, with various types of life-cycles, namely, catadromous, amphidromous, lacustrine land-locked and fluvial land-locked. In the present research, biochemical genetic and ecological studies of 6 Cottus species were carried out to understand the phylogenetic relationship and life-history evolution among the species, and the results were listed below.
1) Based on genetic similarity, the Cottus species were classified into following two major groups ; the first group originated from the Siberian Region or differentiated in Japan (C. Pollux, C. Amblystomopsis, C. Nozawae) and the second group originated from the Korea peninsula (C. Reinii, C. Hangiongensis).
2) A comparison of egg size, larval size, clutch size and early life-style among 6 Cottus species showed that their reproductive and life-history styles were characterized as following four distinct types ; the high productive with small eggs and non-direct developm
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ent for lacustrine land-locked C. Reinii, the intermediate productive with small eggs and nondirect development for catadromous C. Kazika, the intermediate productive with middle size of eggs and non-direct development for amphidromous C. Pollux, C. Hangiongensis and C. Amblystomopsis, and the low productive with large eggs and direct development for fluvial land-locked C. Pollux, and C. Nozawae.
3) The fluvial land-locked C. Pollux and C. Nozawae are thought to be speciated from the amphidromous C. Pollux respectively, and the lacustrine land-locked C. Reinii to be derived from C. Hangiongensis. The former mode of speciation might have occurred polypatrically and coincidentally with fluvial land-locking. These suggest that in Cottus species the life-history styles have evolved from the amphidromous life to the lacustrine or fluvial life.
4) Within a population of C. hangiongensis, a life-history variation was found along the course of a river. Such variation is thought to be maintained in relation to the habitat heterogeneity and be magnified in male by the polygynous mating system. Less
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