樹蕨專一性附生蕨類之演化與生態學初探

First Insights into the Ecology and Evolution of Epiphytic Tree Fern Specialists

林大鈞(Ta-Chun Lin)

指導教授 ： 王俊能

共同指導教授 ： 黃曜謀(Yao-Moan Huang)

國立臺灣大學/生命科學院/生態學與演化生物學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201900409

摘要

附生演化發生於多個不同陸生植物類群當中，是為適應新生代被子植物優勢森林的重大演化趨勢。附生植物在探索被子植物所提供的嶄新生態棲位的過程中快速多樣化。然而，有些附生植物並不長在被子植物上，卻只長在樹蕨類的根幔上。透過化石證據顯示「蕨類長在樹蕨上」這樣的關係早在新生代附生植物多樣化大發生之前就已存在，且被認為是植物界最早的附生現象。因此本研究假定蕨類在樹蕨上的附生現象可能是個早於新生代的附生起源。本研究透過分子親緣譜系分析的方法針對具有樹蕨專一性附生蕨類的屬重建其棲地演化的歷史以探究此一假說，包括二囊松葉蕨屬、長片蕨屬、多脈蕨屬與針葉蕨屬。此外本研究探討樹蕨專一性附生蕨類的生態學以了解生理與環境因子對此一宿主偏好的形塑。結果顯示二囊松葉蕨與多脈蕨的樹蕨附生可以追溯至新生代以前，二囊松葉蕨的樹蕨專一性附生遺傳自中生代古遠的祖先特徵，而其他三屬則來自新生代近期的棲位收縮。這個棲位收縮亦作用於配子體世代。且在連孢針葉蕨的案例中，此樹蕨專一性附生蕨類之配子體具有最差的乾旱抗性，可能是導致其棲地使用受限於潮濕的樹蕨上的原因。此結果一反附生演化牽涉到乾旱抗性提升的觀念，因而，樹蕨專一性附生蕨類可能是一個不同於一般附生演化的案例。

關鍵字

附生植物 ； 附生 ； 配子體 ； 宿主專一性 ； 樹蕨

並列摘要

Epiphytism has become an important evolutionary trend among different land plant lineages to adapt to the angiosperm-dominated forests in the Cenozoic. These epiphytes have been rapidly diversified through exploring novel niches provided by angiosperm trees. Nonetheless, some epiphytes in ferns are found never on angiosperm hosts but grow only on the root-mantle-covered trunks of tree ferns. From fossil records, such a “fern-on-tree-fern” relationship was suggested as the earliest plant epiphytism, and can be traced back to the time period much earlier than the known episodes of rapid diversification of epiphytes in the Cenozoic. Based on these findings, I hypothesized that tree fern epiphytism have an ancient origin earlier than the Cenozoic angiosperm epiphytism. To test this hypothesis, I reconstructed the habitat evolution history of four fern genera with tree fern specialists, including Tmesipteris, Abrodictyum, Polyphlebium and Vaginularia. In addition, I studied the ecology of tree fern specialist ferns in Taiwan to better understand what environmental and developmental factors likely shape their host specificity. The results indicate that Tmesipteris and Polyphlebium each has the origin time of tree fern epiphytism earlier than the Cenozoic. Tree fern specialists in Tmesipteris inherited the ancient habitat state from their Mesozoic common ancestor, while tree fern specialists in other three genera evolved through recent niche contractions in the Cenozoic. The niche contraction act on both sporophytic and gametophytic stages. In the case of tree fern specialist Vaginularia junghuhnii, gametophytes of the tree fern specialist perform the worst drought resistance among the vittarioid relatives, which is opposite to the general idea of evolution of epiphytism involving the improvement of drought resistance in the epiphytic environments, and may be the reason for the restricted distribution only on moist tree fern trunks. That is, the evolution of tree fern specialists may be a different phenomenon of evolution of epiphytism.

並列關鍵字

epiphytes ； epiphytism ； gametophytes ； host specificity ； tree ferns

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