Studies on the origin of apogamy and speciation of Cornopteris

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This study on the origin of apogamy in plants obtained the following results :1. Cornopteris christenseniana propagated in an artificial environment (Fern Garden) in the University of Tokyo Botanical Gardens, although it is considered to be a natural triploid sterile fern derived by hybridization between C. crenulatoserrulata and C. decurrenti-alata. It indicates that C. christenseniana is able to reproduce in such a condition.2. An electrophoretic analysis of allozyme variations and a molecular phylogenetic analysis of chloroplast DNA showed that most of young plants propagated by apogamy from mature plants of C. christenseniana grown in or near the Fern Garden. By contrast, hybridization between the parental species is not involved in propagation of C. christenseniana in the Fern Garden. Furthermore, the results showed that some plants of C. christenseniana, which were transplantedサfrom various localities, were derived by hybridization involving C. crenulatoserrulata as mother and the others, involving C. decurrenti-alata as mother, indicating multiple origins of C. christenseniana.3. Observations of sporogenesis indicated that C. christenseniana produces a few viable unreduced spores in a different sporogenetic pathway from that of Dopp-Manton and Braithwaite apogamy systems.4. C. christenseniana is considered to be a species complex consisting of populations which are various in the frequencies of viable spore and gametophyte production, ranging from a high (about 80 %) to a low (about 1 %) frequency.5. Our results support the hypothesis that different mutations are involved independently in the origin of unreduced sporogenesis and apogamy in the gametophyte generation (sensu stricto), as compared with the single-gene hypothesis.