Origins and Mechanisms of Diadromy in Fishes

生态学方法：对几个双栖物种进行生态学研究，如白斑鲑、马苏鲑鱼、银鲑、水蛭、日本鳗鱼、淡水石雕鱼、淡水虾虎鱼和三刺鱼。求解了它们的生长、运动、繁殖和变形等生活史参数。生理途径：睾酮的使用促进了马苏鲑鱼和幼鲑的上游洄游行为，抑制了它们的下游洄游行为，表明睾酮在决定马苏鲑鱼向海洄游或在河流中定居的过程中起着重要作用。高剂量的睾酮会引起雄鼠的颤抖和雌鼠的挖掘行为。寄生虫学研究方法：二生淡水鳗安圭拉寄生于单基因的假活动藻属，该属与宿主鱼一起适应了从海洋到淡水的生活。日本鳗鲡和澳大利亚鳗鲡两种鳗的假活动线虫的ITS区碱基序列具有较低的同源性，表明日本鳗鲡和澳大利亚鳗鲡的假活动线虫是分别在日本和澳大利亚独立共同进化的。群体遗传学方法：对半尾鱼分子系统发育的估计表明，阿玉鱼独特的两性特征可能首先起源于半尾鱼谱系。对42个同工酶位点的遗传变异分析表明，内陆红鲑和远洋红鲑之间不存在遗传多态性，而在红鲑中有2个位点存在高多态性。在进化过程中，陆锁事件可能导致遗传变异性的降低。建模方法：采用数学建模的方法研究了双穴居鱼类迁徙策略的进化及其与其他性状的协同进化。考虑了卵的大小和迁徙时间的共同进化，并讨论了其与双穴居鱼物种形成的相关性。

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.