Evidence of genetic segregation in the apogamous fern species Cyrtomium fortunei (Dryopteridaceae)
In apogamous ferns, all offspring from a parent are expected to be clonal. However, apogamous ‘species’ frequently demonstrate a large amount of morphological and genetic variations. Cyrtomium fortunei composed of four varieties (C. fortunei var. fortunei, var. clivicola, var. intermedium, and var. atropunctatum), is all reported to be apogamous triploids, but demonstrates large and continuous morphological variation. In previous studies, we showed that considerable genetic diversity was observed in many local populations of the apogamous fern ‘species’. We hypothesized that genetic segregation has occurred, because neither sexual type nor intraspecific polyploidy have been observed in C. fortunei in Japan. Of 732 progeny examined (250 gametophytes and 482 sporophytes), obtained from a parental sporophyte whose pgiC genotype was estimated as aab, 11 (4.4%) gametophytes and 8 (1.7%) sporophytes showed a different genotype (aaa) from that of the parent sporophyte. We showed that genetic segregation occurs in apogamous C. fortunei in relatively high frequency. Moreover, we could first show that the segregation frequency in gametophytes is significantly higher than that in sporophytes of the next generation (χ 2 = 4.90, P = 0.027). It may suggest the existence of deleterious genes, which are expressed during the morphogenesis and growth of sporophytes.
KeywordsApogamy Cyrtomium fortunei Deleterious genes Genetic segregation Ploidy
We are grateful to Dr. T. Sugawara and Dr. H. Kato of Makino Herbarium, Tokyo Metropolitan University, Dr. Y. Yatabe-Kakugawa, Botanical Gardens, University of Tokyo, Dr. S. Matsumoto of the National Science Museum, Tsukuba, and Dr. S. Masuyama for their valuable suggestions and advice during the course of this study. We are also grateful to Dr. H. Ishikawa, Kitasato University, for showing us his unpublished data. This study is partly supported by a Grant-in-Aid for Scientific Research (#21370037) from the Japan Society for the Promotion of Science to N.M.
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