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標題: | 台灣瑞香之性別系統研究 Sexual System of Daphne arisanensis Hayata (Thymelaeaceae) |
作者: | Wei-Jie Huang 黃偉傑 |
指導教授: | 胡哲明(Jer-Ming Hu) |
關鍵字: | 隱性雌雄異株,花部多型性,授粉生物學,自花授粉,瑞香科, cryptic dioecy,floral polymorphism,pollination biology,self-pollination,Thymelaeaceae, |
出版年 : | 2017 |
學位: | 碩士 |
摘要: | 被子植物在性別系統上具有豐富的多樣性,除大多數種類只具單一型兩性花 (hermaphrodite) 外,單性花亦在許多類群獨立演化出現,各種性別系統的演化歷史及其適應意義是植物生殖生物學中的核心問題。台灣瑞香 (Daphne arisanensis Hayata) 為台灣本島產瑞香科 (Thymelaeaceae) 特有種灌木,過去文獻罕有關於其性別系統的紀錄,而據野外觀察,台灣瑞香族群中存在花藥發育不全的雄不孕型,與雌雄花器皆完整的兩性花兩種花型,就此形態而言,暗示台灣瑞香之性別系統可能為雌花兩性花異株 (gynodioecy),然而欲確定其真實的性別系統,仍須進一步檢驗兩種花型個別的生殖潛力,以及花型在族群中的分佈模式。
本研究於2014-2017年沿省道臺14甲線,追蹤梅峰、鳶峰、合歡山、大禹嶺及關原地區台灣瑞香族群的開花型表現,並分別於中海拔關原族群及合歡山周圍高海拔族群進行授粉試驗。結果顯示三年之間沒有植株改變其開花型;雄不孕型花除了在自然授粉及人工授粉下皆正常結實外,於無授粉條件下仍有部分的花朵能夠結實,顯示雄不孕型為具無融合生殖能力 (apomixis) 的雌花;兩性花型則在所有授粉處理下幾乎都無結實,支持兩性花型為功能性的雄花。調查中另有兩株兩性花型植株 (即功能性雄株) 開出少量具不同程度雄不孕的花型,極端雄不孕的形態與雌花相似,且在自然授粉狀態下能夠結實,顯示雄株偶能重建部分的雌性生殖能力,而所有授粉條件下產生的種子皆具有萌芽的潛力。透過活體花粉萌發試驗則發現,雄花的柱頭對自體或異株花粉仍都具有接受性 (receptivity)。不同族群間在形態特徵、花型比例及開花物候上都有高度的變異。相較於關原族群,高海拔族群具有較大的花朵、較長的開花時間、較低的自然結實率以及較低的無融合生殖能力,而兩族群皆觀察到由多種非專一性夜行蛾類進行授粉。 此外,為探討台灣瑞香性別系統可能的演化背景,本研究另於2017年春季陽明山地區,針對同屬中另一兩性花物種白花瑞香 (Daphne kiusiana Miq. var. atrocaulis (Rehder) Maekawa) 進行套袋試驗。結果顯示白花瑞香在隔絕授粉者之下仍有 49% 的花朵能結實,支持瑞香屬植物中普遍具有自發性自花授粉的現象。 綜合上述結果,本研究確認台灣瑞香的性別系統為具滲漏性 (leakiness) 的隱性雌雄異株 (cryptic dioecy),開花特性在不同族群間有高度變異,而此雌雄分化的生殖適應可能與瑞香屬中普遍的自花授粉特性有關。 Angiosperms exhibit great diversity of sexual systems, as the majority of extant species are hermaphrodite, the evolution of unisexuality has drawn attention since Darwin’s age. The reproductive biology of Daphne arisanensis Hayata (Thymelaeaceae), an endemic shrub in Taiwan, had rarely been studied before. Field observations implied that populations of D. arisanensis comprise morphologically bisexual and male-sterile individuals, hence this species may be gynodioecious. However, no unequivocal evidence had been presented yet. To clarify the true sexual system of D. arisanensis, I investigated the spatial and temporal expression of sexuality, and tested the reproductive potential of each floral morph. In this study, phenology surveys were conducted in Meifeng, Yuanfeng, Hehuanshan, Dayuling and Guanyuan during 2014-2017. Pollination experiments were operated in Guanyuan and the Hehuanshan-nearby alpine populations respectively. No individual altered the flowering type in this three-year observation. Male-sterile flowers had the ability to set fruits either with pollination or without fertilization (i.e. apomixis). The gynoecia of morphologically bisexual flowers displayed receptivity to pollens from either itself or other plants, but they hardly set fruits among all pollination treatments. In addition, unusual flowers with different degrees of male-sterility were occasionally found on morphologically bisexual plants. The extremes were quite similar to the typical “female” flowers in male-sterile plants and indeed set fruit under open pollination. The seeds from all kinds of treatments showed germination potential. Great variations in morph ratio, floral traits and floral phenology were found among populations. Compared to the Guanyuan population, individuals in alpine areas showed larger flower size, longer floral lifespan and lower fruit-set rates under both open pollination and apomixis. Various nonspecific nocturnal moths were observed pollinating in both of the populations. To provide materials for inferring the possible evolutionary scenario of the gender divergence in D. arisanensis, I also conducted bagging experiments to another congeneric hermaphroditic species, D. kiusiana Miq. var. atrocaulis (Rehder) Maekawa, in Yangmingshan. The results show that 49% of the bagged flowers had set fruits via autonomous selfing, suggesting that self-pollination may be common in genus Daphne. These findings indicate that the sexual system of D. arisanensis is cryptic and leaky dioecy. The flowering phenology and floral traits varied among populations, and the evolution toward dioecism would probably be correlated with the self-pollination pressure in genus Daphne. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/2371 |
DOI: | 10.6342/NTU201703009 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 生態學與演化生物學研究所 |
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