瀕危條紋球背象鼻蟲的物種判定研究與蘊含的保育意義

Abstract

海洋性島嶼是產生新種和豐富特有性的高生產力棲地，主要歸因於地理隔離、族群量小與在地適應等特性。然而島嶼物種的分化時間短和細微的形態或生態分化可能蒙蔽物種鑑定，因此島嶼上的隱蔽特有種可能被低估。瀕危的條紋球背象鼻蟲 Pachyrhynchus sonani Kôno, 1930 (Coleoptera: Curculionidae: Entiminae: Pachyrhynchini)是棲息於台灣—呂宋島鏈中綠島與蘭嶼的特有種，族群間存在多樣的色彩與寄主植物變異，因此衍生出物種界線與隱蔽多樣性程度的問題。本研究結合形態(體型大小及形狀、生殖器形狀、色彩與鱗片)、遺傳(四組基因與RAD-seq)和生態(寄主植物與島嶼來源)多樣性的整合物種判別方法來測試條紋球背象鼻蟲的物種界線。結果顯示除了色彩光譜外，所有雄蟲的形態特徵在兩島嶼間重疊，但統計上顯著不同；相反地，兩族群間的雌蟲形態極少分化。兩島嶼間的條紋球背象鼻蟲族群在寄主植物頻率顯著不同，遺傳分群與親緣關係分析建立其為兩個有效的演化種。整合物種判別分析支持綠島和蘭嶼條紋球背象鼻蟲族群為兩個獨立物種。我將綠島族群描述為新種P. jitanasaius sp. nov. Chen& Lin 並建議將其列為瀕危物種。本研究結果顯示，在這兩島嶼上的特有生物的島間種化事件可能比之前所知的更加普遍，並強調小型海洋性島嶼的隱蔽多樣性可能仍然被大量低估。

Oceanic islands are productive habitats for generating new species and high endemism, which is primarily due to their geographical isolation, smaller population sizes and local adaptation. However, the short divergence times and subtle morphological or ecological divergence of insular organisms may obscure species identity, so the cryptic endemism on islands may be underestimated. The endangered weevil Pachyrhynchus sonani Kôno, 1930 (Coleoptera: Curculionidae: Entiminae: Pachyrhynchini) is endemic to Green Island and Orchid Island of the Taiwan-Luzon Archipelago and displays widespread variation in coloration and host ranges, thus raising questions regarding its species boundaries and degree of cryptic diversity. I tested the species boundaries of P. sonani using an integrated approach that combined morphological (body size and shape, genital shape, coloration and cuticular scale), genetic (four genes and restriction site-associated DNA sequencing, RAD-seq) and ecological (host range and island of origin) diversity. The results indicated that all of the morphological data sets for male P. sonani, except for the colour spectrum, reveal overlapping but statistically significant differences between islands. In contrast, the morphology of the female P. sonani showed minimum divergence between island populations. The populations of P. sonani on the two islands were significantly different in their host ranges, and the genetic clustering and phylogenies of P. sonani established two valid evolutionary species. Integrated species delimitation combining morphological, molecular and ecological characters supported two distinct species of P. sonani from Green Island and Orchid Island. The Green Island population was described as P. jitanasaius sp. nov. Chen& Lin, and it is recommended that its threatened status be recognized. Our findings suggest that the inter-island speciation of endemic organisms inhabiting both islands may be more common than previously thought, and they highlight the fact that the cryptic diversity of small oceanic islands may still be largely underestimated.