台灣茅毛珍珠菜族群遺傳結構之研究

Abstract

茅毛珍珠菜（Lysimachia mauritiana Lam.）?一年生或多年生草本植物。分佈於日本、韓國、中國大陸、琉球、菲律賓、密克羅尼西亞、美拉尼西亞、波里尼西亞、夏威夷、印度、模?西斯、以及台灣。在台灣則?許多小族群散生於北部、東部、南部及綠島、蘭嶼、澎湖等離島之海濱，呈不連續之分佈。本研究顯示，茅毛珍珠菜屬於混合式的交配系統，不論自花授粉或異株異花授粉皆可稔，不行無性繁殖，在沒有昆蟲的媒介下有自花授粉的可能。八個採樣族群用15個引子做RAPD，共出現271條條帶，由所呈現的條帶型式來看，不同族群間確有差異，族群間確有遺傳上的分化，族群相似度由0.551至0.853，群叢分析樹狀圖顯示，八個族群大致上區分?北部海濱、鵝鸞鼻－蘭嶼、三仙台－澎湖等三個群叢。以同功異構?電泳檢視茅毛珍珠菜族群內及族群間的遺傳歧異度與分化程度，共染出13種酵素，觀察到22個基因座。多型性基因百分比（P）最高的是石門的族群，約22.7％，其餘族群只有4.5?13.6％，平均?9.64％，各基因座平均對偶基因個數（A）從1.4?1.0，平均?1.13個，皆遠低於一般的一至二年生，侷限分佈之雙子葉植物種類。而平均異質結合度（HO）?從0.045?0.086，平均期望異質結合度（HE）?從0.023?0.111，顯示出其族群內異質結合的比例很低，大部份基因座均已同質化。但族群間的比較則是在同一基因座，出現了不同的同質對偶基因（圖5），這使得族群間歧異度非常高，由F-statistics所得到的整體的FST?高達0.854，顯示出遺傳變異只有不到15％是族群內的，而超過85％是族群間的。由上述結果，我們得知台灣茅毛珍珠菜族群呈現出族群內變異少，族群間高度分化的遺傳結構。由FST?所推算的Nm?只有0.043，顯示族群間幾乎沒有基因流傳。創始者效應（founder effect）、基因漂變、及瓶頸效應的共同作用，很可能就是造成本省茅毛珍珠菜，成?族群內同質度高而族群間高度分化的遺傳結構的最重要因素。

Lysimachia mauritiana Lam. is an annual or perennial herb distributed in Japan, Korea, Mainland China, Ryukyu archipelago, the Philippines, Micronesia, Melanesia, Polynesia, the Hawaiian islands, India, Mauritius, and Taiwan. In Taiwan, many small and isolated populations are distributed on the seashores of Green island, Orchid island, Penghu islands and along the northern, eastern, and southern coastlines of the main island. The subject of this study is to be informed about the population genetic structure of Taiwanese L. mauritiana and the evolutionary determinants which affect it. Results from reproductive biology experiments show that L. mauritiana belongs to mixed mating type. It is self-or outcross-compatible, with no evidence of apomixis. Mechanical self-pollination could happen. According to the band patterns of the result from RAPD, all eight populations are different from each other genetically and there are genetic differentiations among populations. The population identities ranged from 0.551 to 0.853. Results from cluster analysis showed that these eight populations could be divided into three clusters: northren coastal region, Oluanpi-Orchid island, and Sanhsientai-Penghu. Starch gel electrophoresis was also used to analyze the allozyme variation of 22 loci of 13 isozymes. The average percentage of polymorphic loci (P) is 9.64% and the average number of alleles per locus (A) is 1.13. Both P and A values are lower than those cited for other plants of restricted distributions and indicate the homogenization of most loci. The average observed heterozygosities (HO) ranged from 0.045 to 0.086, and the average expected heterozygosities (HE) ranged from 0.023 to 0.111. Both HO and HE indicate the low rate of heterozygotes and thus low genetic diversity within populations. On the other hand, different populations possess different alleles in the same locus so the genetic diversity among populations is very high. FST value from F-statistics based on allele frequencies is 0.854. This means that among- population variation contributes to approximately 85% of total genetic variation, while within- population variation makes up only 15%. Variation in population genetic structure is low variation within populations, but high among populations. Nm value is 0.043, indicating there is hardly any gene flow between populations. Founder effect, genetic drift, and bottleneck effect could be the most important determinants of the population genetic structure of Taiwanese L. mauritiana.