日本列島におけるオニヤブソテツ複合種(オシダ科)の繁殖様式と種分化に関する種生態学的研究

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The ornamental fern, Cyrtomium falcatum (L. f.) C. Presl native in Eastern Asia naturalized coastal region of the warm-temperate zone in the world. The chromosome number for cytotypes on 186 localities (341 individuals) and the spore-number per sporangium for reproductive mode on 794 localities (2,467 individuals including herbarium specimens and population samples) in Japan were surveyed. Four cytotypes, two sexual diploid (A1: dwarf, A2: normal), one sexual tetraploid (C) and one apogamous triploid (B) were mainly recognized. In central Japan, A1, B and C types show that the habitat segregation among sea-cliff, coastal grassy ground and forest floor are sympatric. While, A1 and A2 types show that the geographic segregation between northern part and southern part in Japan are allopatric. And also, several polyploid hybrids were recognized at contact zones of each cytotype and another apogamous triploid species. There are one sterile triploid (A1×C), one apogamous and sexual tetraploid (A1×B) and four apogamous pentaploid [C×B (♂), C×D (D: C. laetevirens (Hiyama) Nakaike: ♂), C×E (E: C. fortunei (J. Sm.) var. clivicola (Makino) Tagawa: ♂), C×F (F: C. caryotideum (Wall, ex Hook, et Grev.) C. Presl: ♂). The polyhaploid (apogamous dihaploid) was gotten from reduced spores (64 spores in a sporangium) of the tetraploid (A1×B). This apogamous dihaploid considered to make variation of B type as donor of sperm by backcross (hybrid cycle: 3x to 4x to 2x to 3x). Artificial hybrid for genome analysis were synthesized as follow, fertile diploid (A1×A2), sterile triploid (A1×C) and sterile and apogamous tetraploid [C×(A1×B)]. Sexual meiosis of all hybrids including natural apogamous hybrids and dihaploid were analyzed for the basic 4 types, A1, A2, and B types were same genome as AA, AA and AAA respectively, but C type was allotetraploid having AABB (see Fig. 3-5). On the genetic background of agamospory, the apogamy was considered to be one dominant gene from the segregation ratio of gametophytes to originate in reduced-spores of tetraploid hybrid, A1×B. And also linkage of apogamy and diplospory genes considered as to be present, for reason to show diplospory on the almost dihaploid. On the variation of mating systems, ratio of the gametangium formation (mix or separate antheridia with archegonia) and sporophyte formation by intragametophytic selfing test were investigated on the A1, A2 and C types, and one hybrid A1×A2. A2 and C were separate types, but A1 was variable from separate to mix type and the hybrid was intermediate type with the half ratio. Sporophyte formation of the mix types including parent (A1) of the hybrid were high frequencies by self-fertility, but that of separate types were low in A1 and A2 types of diploid or relatively low in C type of tetraploid. And also sporophyte formation of separate types later one month than that of mix type. On the comparative study under the cultivation, dwarf form of A1 type specialized genetically from A2 type was considered as 'Progenesis'. The shape of B type intermediates between A1 and A2 types. While, C type was distinguished from another types with shape of pinna and presence of micro-scale on upper surface of frond. Correlation of the ecological structure and speciation on basic 4 cytotypes of Cyrtomium falcatum complex in Japanese Archipelago were considered from viewpoint of species ecological study (see Fig. 4-1). Most basic A2 type growing subtropical maritime forest with cross mating evolved under K-selection. The A1 type growing warm and cool temperate sea-cliff evolved under r-selection from A2 type, as follows, the first by genetic drift, migrating only grayish indusium strain with self mating, the second by progenesis, shorten the life cycle from three years or more to one or two years. Most widely spread B type growing the coastal forest edge with apogamous reproduction evolved by hybridization at several times or by hybrid cycle from A2 and A1 types under competition environment. The C type growing warm temperate wetly forest floor evolved under K-selection, by hybridization between A2 type and unknown another species of Cyrtomium. Taxonomy of basic 4 types on Cyrtomium falcatum complex was as follows by examination of two holotype specimens. Cyrtomium devexiscapulae (Koidz.) Ching (C type) C. falcatum (L. f.) C. Presl subsp. falcatum (B type) subsp. littorale S. Matsumoto (A1 type) subsp. australe S. Matsumoto (A2 type)
国立科学博物館の論文
2003-12-25

日本列島におけるオニヤブソテツ複合種(オシダ科)の繁殖様式と種分化に関する種生態学的研究

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