A Study on the Geographical Differentiation of Ceratopteris Thalictroides Populations in Japan

本研究的目的是解决下列问题，一年生多倍体蕨类Ceratopteris thalictroides （L.）。Brongn。在日本：(1)该物种在日本当地种群中的形态变化程度如何？(2)地方种群间形态变异具有怎样的适应意义？(3)哪些特定的特征对建立地方种群间的形态变异起了重要作用？(4)地方种群间的形态变异与遗传变异的关联程度如何？在三年的调查中，发现并得出以下结论：关于(1)：在地方种群之间的形态变化中可以看出地理上的差异。也就是说，北方地区的植物比南方地区的更小，形状更简单。关于(2)：北方型具有营养生长期较短的特点，很适合日本北部的水稻种植模式。关于(3)：由于一个地方种群的配子体自交率很高，接近0.9，因此该物种可能以近交为主。高近交和年定殖的特殊特征可能促进了上述北方型在北方地区的建立。关于(4)：在日本人群中存在两种类型的遗传变异。一个具有表明同源多倍体起源的同工酶成分，另一个具有表明异源多倍体起源的同工酶成分。前者有限地分布在以色列南部地区。冲绳岛和后者广泛分布在该岛北部地区。

The purpose of the present study is to settle the following problems as to the annual, polyploid fern Ceratopteris thalictroides (L.) Brongn. in Japan : (1) To what degree is this species varied in morphology among local populations in Japan? (2) What adaptive significance does the morphological variation among local populations possess? (3) What specific characteristics have played an important role to establish the morphological variation among local populations? (4) To what degree is the morphological variation among local populations linked with their genetic variation?The followings were revealed and concluded in the investigation during three years.As to (1) : A geographical cline is recognizable in the morphological variation among local populations. That is, plants are smaller and simpler in shape in the northern regions than in the southern regions.As to (2) : The north type, which is characterized by a shorter period of the vegetative growth, is well adapted to the mode of rice cultivation in the north of Japan.As to (3) : Because a local population showed a high rate of gametophytic selfing near to 0.9, inbreeding is probably predominant in this species. Specific characteristics of high inbreeding and annually colonizing may have promoted to establish the above north type in the northern regions.As to (4) : Two types of the genetic variation are present in Japanese populations. One possesses the allozyme components suggesting the autopolyploid origin and the other has those suggesting allopolyploid origin. The former is distributed limitedly in the area on the south of Isl. Okinawa and the latter is widely distributed in the area on the north of that island.