伊藤氏原始觀音座蓮天然雜交種之研究

Abstract

伊藤氏原始觀音座蓮為臺灣的特稀有蕨類植物，因其具有較大的羽葉及回脈，是原始觀音座蓮屬中最為特殊的成員；而較大的體型及回脈，一般認為是觀音座蓮屬所具有的特徵。由於伊藤氏原始觀音座蓮的外部型態特徵介於二屬之間，而其棲息環境中亦同時生長著觀音座蓮及臺灣原始觀音座蓮，因此推測伊藤氏原始觀音座運可能為觀音座蓮與臺灣原始觀音座蓮二者之天然雜交後代。雜交種的外部形態常介於父母種之間，且其分子遺傳標記具有加成性，故本研究欲以量化的葉部與抱子囊群特徵及篩選具專一性的RAPD分子標記，來探討伊藤氏原始觀音座蓮的雜交起源。 外部形態特徵的結果顯示，伊藤氏原始觀音座蓮在葉長、羽片數、羽月長度、孢子囊群位置及一孢子囊群中所含之孢子囊個數，皆明顯介於觀音座蓮與臺灣原始觀音座蓮之間，且變化範圍幾無重疊；在葉長寬比與葉身長寬比方面，伊藤氏原始觀音座蓮與臺灣原始觀音座蓮無顯著不同，而觀音座蓮則與二種原始觀音座蓮皆有顯著差異。在羽片長寬比方面，伊藤氏原始觀音座蓮的值最大，與觀音座蓮及臺灣原始觀音座蓮皆有極顯著的差異；而觀音座蓮與臺灣原始觀音座蓮之間則無差異。在篩選具專一性的RAPD分子標記方面，於所使用的52個隨機引子中，有5個引子能在PCR中放大出專一性的DNA片段，其中有4條片段可判定為觀音座蓮所特有，13條為臺灣原始觀音座蓮所特有，而伊藤氏原始觀音座蓮則同時具有這17條DNA片段。 無論是外部形態或RAPD分子標記的結果，都支持伊藤氏原始觀音座蓮為一雜交種的推論，且極可能為不孕性之雜交Fl；而其野外族群堆測是由父母種間不斷發生雜交來維持。

Archangiopteris itoi Shieh is a rare endemic fern in Taiwan, and it is the most distinct one in the genus because of its larger fronds and spurious recurrent veinlets that are usually thought to be characters belong to genus Angiopteris. According to above, Ar.itoi is morphologically intermediate between Angiopteris and Archangiopteris. Besides, An. lygodifolia and Ar. somai can also be found at the natural habitat of Ar itoi. We therefore made the hypothesis that Ar. itoi might be the natural hybrid between An. lygodifolia and Ar.somai. Hybrids are often morphologically intermediate between their putative parents, and should exhibit additivity of genetic markers that are specific to each of the putative parents. In this study, the author wants to discuss the hybrid origin of Ar.itoi by employing quantified characters of fronds and sori, and screening species-specific RAPD markers. Characters of Ar.itoi including the total length of frond and pinna, number of pinnae, sorus position, and number of sporangia in a sorus, are significantly intermediate between those of An. lygodiifolia and Ar.somai. The length/width ratios of frond and blade of Ar.itoi are not obviously different from those of Ar.somai, however those of An.lygodiifolia are significantly different from Ar. itoi and Ar.somai. The length/width ratio of pinna of Ar. itoi is higher than the other 2 species, and is significantly different from them. But those of An. 1ygodifolia and Ar somai are almost the same. 52 random primers for PCR were screened, and five primers that gave species-specific products were identified and used for analysis. There were four and thirteen fixed and species-specific markers for An. lygodiifolia and Ar. somai respectively, and all the individuals of Ar. itoi in this study were detected these seventeen species-specific amplified DNA fragments for both An. lygodiifolia and Ar. somai. Both morphology and RAPD markers analyses in this study support the hybrid origin hypothesis of Ar. itoi, and also imply that it might be a sterile F1 from hybridization between An. lygodiifolia and Ar. somai. The population of Ar. itoi in the field might be maintained by constant hybridizations between its parants.