Origins and Mechanisms of Diadromy in Fishes

生态学方法：对白斑鱼、三文鱼、三文鱼、斑点三文鱼、日本鳗鱼、淡水雕像、淡水虎鱼和三刺鱼等几种水栖鱼类进行了生态学研究。生理方法：给予睾酮促进马哈鱼和未成熟鲑鱼的上游迁徙行为，抑制向下迁徙，这表明睾酮在决定马哈鱼向海迁徙或在河流中居住的过程中起着重要作用。高剂量的睾丸素会引起雄性的颤抖和雌性的挖洞行为。寄生虫学方法：与寄主鱼一起适应海洋生活到淡水生活的单殖吸血鳗鱼寄生在潜水淡水鳗鱼身上。日本鳗和澳大利亚鳗两种鳗鱼SRNA ITS区碱基序列的同源性较低，表明日本鳗和澳大利亚鳗是独立进化的。种群遗传学方法：分子系统发育的估计表明，AYU独特的两面性可能最先起源于鳗类。利用42个同工酶基因座的遗传变异分析表明，内陆红鱼和远洋红鱼之间没有发现遗传多态现象，而红鱼在两个基因座上表现出高度的多态现象。在进化过程中，陆锁事件可能会导致遗传变异性的降低。建模方法：通过数学建模研究了水栖鱼类迁徙策略的进化及其与其他性状的协同进化。考虑了卵大小和迁徙时间的共同进化，并讨论了它们与江河鱼类物种形成的关系。

Ecological Approach : Ecological studies were performed for several diadromous species, such as white-spotted charr, masu salmon, coho salmon, dolly verden, Japanese eel, freshwater sculpins, freshwater gobies and threespine stickleback. The life-history parameters concerning their growth, movement, reproduction and metamorphosis were solved.Physiological Approach : Administration of testosterone facilitated the upstream migratory behavior and suppressed the downward migration in the masu salmon smolts and immature kokanee, suggesting an important role of testosterone in determination of the seaward migration or residence in a river. High administration of testosterone induced a quivering in male and a digging behavior in female in the kokanee.Parasitological Approach : Diadromous freshwater eels Anguilla are parasitized with the monogenean Pseudodactylogyrus spp., which have adapted from marine to freshwater life together with the host fish. A lower homology in the base sequence of the ITS region of sRNA between two species of Pseudodactylogyrus on the Japanese eel and Australian eel suggested that the eel Pseudodactylogyrus had co-evolved independently in Japan and Australia, respectively.Population genetic Approach : Estimated molecular phylogeny of the osmerid fishes suggested that the unique amphidromy of ayu might derive first in the osmerid lineage. Genetic variability of 42 isozyme loci between landlocked kokanee and sea-run sockeye salmon revealed that no genetic polymorphism was observed in kokanee, while high polymorphism was detected at two loci in sockeye salmon. Decrease of genetic variability could be caused by land-lock event during evolutional process.Modeling Approach : Evolution of migration strategies of diadromous fish and its coevolution with other traits were studied by mathematical modeling. Coevolution of egg size and timing of migration was considered, and its relevance to speciation of diadromous fish was discussed.