苦苣苔科大岩桐亞族的三維花冠形狀與二維蜜標樣式分析

Analyses of the 3D Corolla Shape and the 2D Nectar Guide Pattern on Petals in the Subtribe Ligeriinae (Gesneriaceae)

許皓鈞(Hao-Chun Hsu)

指導教授 ： 郭彥甫

國立臺灣大學/生物資源暨農學院/生物機電工程學系/博士(2021年)

https://doi.org/10.6342/NTU202102856

摘要

花冠形狀和蜜標樣式的多樣性，在導引傳粉者的訪花行為和吸引傳粉者視覺偏好中扮演重要角色。傳統上，花冠形狀與蜜標樣式的量化仰賴生物學家的觀察經驗與主觀判斷；近十年，已有許多影像分析工具得以協助生物學家精準地量化花冠形狀與蜜標樣式的變異。然而，大多數影像分析工具未考慮花冠組織特徵的同源性，使得在花冠大小與形狀差異明顯的物種之間難以進行比較分析，進而造成分析結果高估或低估花冠形狀與蜜標樣式的變異。在開花植物中，花冠維管束的形態發生具有同源性，且在近緣物種之間擁有近似的脈型。因此，花冠維管束的脈型能提供花冠組織上同源區域的空間資訊，使得不同花冠大小與形狀的近緣物種間的比較更為客觀。本論文結合影像處理技術與植物組織學技術，提出以花冠維管束為基礎的量化花冠形狀與蜜標樣式方法，應用於苦苣苔科大岩桐亞族的物種。花冠形狀方面，首先以微米級電腦斷層掃取得花冠之三維影像，接著定義花冠輪廓與維管束系統的特徵點，並擷取其三維座標。透過三維幾何形態學析量化特徵點在空間中的主成分變異，進而以視覺化之主成分變異定義與花冠形狀相關的性狀。花瓣蜜標樣式方面，以彩色平板式掃描器分別取得腹側花瓣之新鮮影像及經透明化處理之組織學影像，接著定義花瓣輪廓與維管束系統的軌跡，並擷取其二維座標。透過二維幾何變換將新鮮花瓣影像之蜜標樣式轉換至同源感興趣區域，進而以主成分分析與視覺化之變異定義與蜜標樣式相關的性狀。進一步以量化之變異檢驗花冠形狀與蜜標樣式的種間差異、傳粉者類型關聯性、以及親緣訊息。結果表明，形狀性狀與蜜標樣式性狀在物種間存在顯著差異。在量化的性狀中，花冠管狀區域的曲率與擴張度、蜜標樣式的遠端著色與近端著色與傳粉者類型的相關性顯著。其中，花冠管狀區域的曲率與擴張度在親緣關係中亦呈現顯著的親緣訊息，而蜜標樣式的遠端著色與近端著色在親緣關係中則未偵測到顯著的親緣訊息。此結果暗示花冠管狀區域形狀的變異與傳粉者類型的關聯性反應在大岩桐亞族物種的演化。

關鍵字

花冠筒形狀 ； 花瓣蜜標樣式 ； 花瓣輪廓 ； 花瓣維管束系統 ； 三維幾何形態學分析 ； 二維幾何變換 ； 傳粉者類型

並列摘要

The corolla shape and the nectar guide pattern play an important role in luring the pollinator visiting by regulating the visiting behavior and attracting visual attention. Traditionally, the variation of corolla shape nectar guide pattern was subjectively identified by experienced researchers. In recent decades, many image processing tools have emerged to quantify the variation of corolla shape and nectar guide pattern. However, in most of the proposed tools, the homologous region of the corolla tissue was less emphasized. Thus, the interspecific comparison is difficult to be conducted among the specimens with considerable differences in their size and shape. The quantified variation might be under-or over-estimated. In most flowering plants, the development of petal vascular is homologous. Particularly, some closely related species share a similar petal vasculature. The petal vasculature is, therefore, an ideal indicator for identifying the homologous region on the petal tissue, which enables a comparison analysis to be conducted between the specimen with different shape and size. This dissertation aims to integrate the knowledge of plant histology with the image processing technology. The approaches that quantifying the variation of corolla shape and nectar guide pattern based on the petal vasculature were proposed and applied to the species of subtribe Ligeriinae, family Gesneriaceae. On the aspect of corolla shape, the 3D image of corolla was first captured by a micro-computer tomography. Based on the 3D coordinates of petal contours and vasculatures, the 3D geometric morphometrics analysis was then conducted to quantify and visualize the principal variation of corolla shape. According to the identified variation, the corresponding shape traits were further defined. On the aspect of nectar guide pattern, the 2D images of fresh petal and tissue-cleared petal was captured by a flatbed color scanner, respectively. Based on the 2D coordinates of petal contours and vasculature, the homologous ROI was then proposed and extracted to obtain the unified nectar guide pattern from the specimens through 2D geometric transformation. The principal variation of the collection of homologous ROI was then identified and visualized. The corresponding pattern traits were further defined. The quantified shape and pattern traits were further utilized to assess the interspecific discrepancy, the association with pollination types, and the phylogenetic signals. The result shows that the interspecific discrepancy is significant. Among the defined traits, the tube curvature and tube dilation of corolla shape and the distal and proximal patterning modes of nectar guide pattern are strongly associated with pollination types. Furthermore, strong phylogenetic signals were detected in the tube curvature and tube dilation rather than the distal and proximal patterning modes. This indicates that the variation of corolla shape accompanying the association with pollination types might dominate the evolution of the subtribe Ligeriinae.

並列關鍵字

2D geometric transformation ； 3D geometric morphometrics analysis ； corolla shape ； nectar guide pattern ； petal contour ； petal vasculature ； pollination type

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