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

本研究旨在解决一年生多倍体蕨类水蕨Ceratopteris thalictroides（L.）布朗在日本：（1）在日本的当地居群中，本种在形态上的变化到何种程度？(2)地方居群间的形态变异具有什么样的适应意义？(3)什么样的特征在当地种群的形态变异中起了重要作用？(4)地方种群间的形态变异与其遗传变异有多大程度的联系？通过三年的调查研究，得出以下结论：（1）地方居群间形态变异具有明显的地理渐变。也就是说，北方地区的植株比南方地区的植株更小，形状更简单。关于（2）：北方型，其特征是营养生长期较短，非常适合日本北方的水稻栽培模式。关于（3）：由于当地的人口显示了高比率的配子体自交接近0.9，近亲繁殖可能是占主导地位的本种。高度近交和每年定殖的特性可能促进了上述北方型在北方地区的建立。关于（4）：日本群体中存在两种类型的遗传变异。一个具有同源多倍体起源的等位酶成分，另一个具有异源多倍体起源的等位酶成分。前者仅局限于岛南部地区。冲绳，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.