對囊蕨屬與單葉對囊蕨多倍體化之生物地理及親緣地理學研究

Abstract

多倍體化(polyploidization)是一種真核生物中普遍的現象。在維管束植物中，多倍體化在蕨類演化中扮演非常特殊的角色，創造現生蕨類基因與物種多樣性。除了蕨類中常見的多倍體事件，相較於開花植物蕨類的核基因組有偏好多倍體演化的趨勢。此外，過去研究暗示多倍體類群在蕨類中有較高的拓殖能力。然而，關於蕨類多倍體的演化建立與生物地理研究相當之少。就族群建立與擴展的角度來說，成功的多倍體演化可能與歷史因子(如：年輕的演化歷史)、生態因子(如：氣候棲位偏移)、生殖因子(如：自交)有關，其中可能伴隨相關的演化適應降低了多倍體類群與二倍體親本之競爭而被滅絕的風險。為了回答蕨類多倍體如何建立與擴展族群的一系列問題，本研究論文使用對囊蕨屬(Deparia, Athyriaceae, Eupolypod Ⅱ, Polypodiales)的多倍體類群做為研究對象。尤其是單葉對囊蕨(Deparia lancea)的六倍體，本論文針對其相關因子之效應做深入的探討。對囊蕨屬的生物歷史地理與多倍體化演化重建顯示－種內的地理擴展的案例皆與多倍體化有關；但在同屬物種間的尺度，多倍體與二倍體類群的遠離散播速率並無發現有顯著之差異。在單葉對囊蕨的多倍體中(即有性的四倍體與六倍體)，歷史因子包括年輕的演化歷史與更新世氣候變遷與地質事件並非這些多倍體地理擴展的限制因子。反之，更新世早期的東亞島弧的海洋隔閡的建立可能為這些多倍體建立的促進因子。此外，這兩個有性之多倍體推斷皆有高於二倍體之傳播速率，暗示這些多倍體都要較高之拓殖能力。在單葉對囊蕨的廣泛六倍體類群中，提升的自交能力是來至於配子器自交之偏向表現與高自交容忍度；相較於氣候棲位擴張，此自交能力的提升應為推動其族群建立與地理擴展的主要角色。此自交能力的提升讓這些六倍體拓殖能力提高，並幫助其氣候區位與實際生態區位的探索擴張。最後，依據推斷之地理分布與起源，提出單葉對囊蕨多倍體形成與建立之生物地理假說此假說，相似於“從源至匯” (source-to-sink)之種化過程。

Polyploidization is a universal phenomenon among eukaryotes. Among vascular plants, polyploidy in ferns play an especially important role greatly contributing to their current genetic and species diversity. This is not only because there is a high occurrence of polyploidy speciation in ferns, but also, at genomic aspects, they have evolved under a much polyploid-preferred manner than flowering plants. In addition, fern polyploids are potentially better colonizers with higher dispersal ability than diploids as implied by many previous studies. Despite these, there has scarce empirical study understanding evolutionary establishment and biogeography of fern polyploids. Regarding to establishment and subsequent expansion, the evolutionary success of a polyploid taxon should be related to different factors that are reproductive (e.g. inbreeding), ecological (e.g. climatic niche shift), in which some adaptation can reduce their extinction risk due to outcompeting by the diploid progenitors, and historical (e.g. young evolutionary age). To answer a series of questions about how ferns polyploids naturally establish and subsequently expand their population, this thesis focused on the polyploid taxa in a terrestrial fern genus Deparia (Athyriaceae, Eupolypod II, Polypodiales), and surveyed the relating factors associating with polyploid establishment and expansion in Deparia lancea, especially for its hexaploids. The reconstructions of historical biogeogeophy and polyploidy evolution based on the whole Deparia phylogeny revealed that all species exhibited infraspecific range expansions concurrent with polyploidization. At the species level, no significant differences of long-distance dispersal rates was detected between polyploid and diploid lineages. In Deparia lancea polyploids (sexual tetraploid and hexaploid), the historical factors, including young evolutionary age and recent climatic/geographical event, seem less limit their range expansion. Instead, I implied the historical event of sea barrier formation isolating East Asia Archipelago during the Early Pleistocene had possibly facilitated their successful establishments. In addition, both sexual polyploidy cytotypes were inferred with higher dispersal rates than diploids suggesting an increased colonization ability in these polyploids. In the widespread line hexaploid of D. lancea, I further demonstrated that an increased inbreeding ability, including inbreeding tending gender expression and higher inbreeding tolerance, rather than broaden climatic niche might play a rather important and primary role for their successful population establishment and subsequent expansion. This increased inbreeding ability should be the major cause contributing to the high oversea colonization ability in these hexaploids, and, thus, assist their exploration in climatic niche as well as potential distribution. Finally, based on inferred distribution and origins, I proposed a biogeographical scenario for the polyploidy formation/establishment in Deparia lancea, which was hypothesized to be similar as a source-to-sink speciation process.