| Research Abstract |
The Tokara Strait, usually regarded as a boundary of the Oriental and Palearetic faunal realms, is considered to have been consistently interrupting dispersals of terrestrial fauna since its initial formation in the late Tertiary. However, several lineages of terrestrial animals are actually distributed on both sides of this strait, making interesting subjects from view points of historical biogeography and population systematics. To elucidate the dispersal and isolation of terrestrial animals across the Tokara Strait, we examined for several vertebrates the relative degrees of differentiations among populations around this strait. Quantitative morphological and allelic data were analyzed for distances among populations.
Results have indicated that in most lineages examined, such as Ateuchosaurus pellopleurus, Gekko hokouensis and Eumeces marginatus, populations in both sides of the strait showed very little variation. This indicates the occurrence of oversea dispersals across the strai
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t in an unexpectedly high frequency in these lineages. This results strongly suggest the possible overstimation of the isolation effect of insularization upoiv the terrestrial organisms in other areas of the Ryukyus and Taiwan, where the Kuroshio Current, seemingly the most influensive agent of orga-nismal dispersals in this region, is dominant as in the Tokara Strait.
Some taxonomic groups showing more sporadic distributions on both sides of the strait have been considered as remnants of landbridge dispersals prior to the formation of the Tokara Strait. However, our studies have revealed that there are no sister-relationships between representatives of both sides of the strait in some of such taxa (e.g., Cistoclemmys, including the fossil taxa), and that others (e.g., Pelodiscus sinensis), surely showing close genetic affinities, have been transported artificially across the strait. Such a result circumstantially support the frequent seacurrent-aided dispersal hypothesis for the former three lineages by confirming the long history of the Tokara Strait. Less
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