Long-term occurrence of hybrids between Japan Sea and Pacific Ocean forms of threespine stickleback, <Emphasis Type="Italic">Gasterosteus aculeatus</Emphasis>, in Hokkaido Island,Japan |
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Authors: | Miho Yamada Masahito Higuchi Akira Goto |
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Institution: | (1) Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan;(2) Fisheries Division, Niigata Prefectural Goverment, Niigata 950-8570, Japan |
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Abstract: | The distribution patterns of two genetically divergent forms (Japan Sea and Pacific Ocean forms) of Gasterosteus aculeatus and their hybrids in the Hokkaido Island, Japan were investigated. Hybrid frequencies and the mating pattern of natural F1-hybrids
and backcrosses, were examined by using allozyme analysis. The distribution patterns matched those previously reported. All
three sympatric localities in eastern Hokkaido Island included hybrids between the two forms in each year examined. A low
frequency of hybrids of sticklebacks has been maintained in areas of sympatry of the two forms in Hokkaido Island for several
years. The proportion of F1-hybrids was significantly lower than expected by random mating in six samples from four sympatric
populations, suggesting form-assortative mating. Mating crosses of natural F1-hybrids existed in both patterns. Natural F1-hybrids
backcrossed more frequently with Pacific Ocean form than Japan Sea form. However, the proportions of backcross individuals
in two of three samples were not significantly different from the expected proportions by random mating between F1-hybrids
and their parent forms. In other samples, despite the Pacific Ocean form predominant in a population, F1-hybrid predominantly
backcrossed with the Japan Sea form. These results support the hypothesis of gene flow from Pacific Ocean to Japan Sea forms. |
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Keywords: | Gasterosteus aculeatus Allozyme analysis Sympatric forms Hybrid Backcross individual Introgression |
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