二點赤鋸鍬形蟲(鍬形蟲科)之共生酵母菌

Abstract

鍬形蟲科(Lucanidae)是舉世聞名的昆蟲，但關於其生態知識所知甚少。雌成蟲具有儲菌器(mycangia)，其中儲藏之木糖發酵酵母菌有助於幼蟲消化朽木物質。Scheffersomyces被認為是鍬形蟲主要的共生酵母菌，且傳遞於世代間。雌蟲於產卵時將酵母菌塗抹在卵上或周邊介質，並在幼蟲腸道及隧道中移生。化蛹期間，酵母菌被保存在蛹室壁內，新羽化的雌蟲藉由後羽化行為重新獲得菌種。由於鍬形蟲在木材分解與生態保育具有重要性，迫切需要相關研究。本研究調查台灣之二點赤鋸鍬形蟲(Prosopocoilus astacoides blanchardi)，雌成蟲於野外採集並在實驗室內繁殖。酵母菌從儲菌器、卵巢、幼蟲腸道、隧道及蛹室壁中分離培養，並經過物種鑑定、菌落形成單位計算、木糖利用能力測試。從雌成蟲及蛹室壁內及獲得的酵母菌差異相當大，包含Scheffersomyces spp.、Candida spp.及Meyerozyma guilliermondii等。本研究可能為首次在鍬形蟲卵巢中發現酵母菌存在之記錄。幼蟲腸道及隧道之分析結果則相似且均一，以Scheffersomyces spp.及Spathaspora spp.為主。依據親緣關係之結果，從本種鍬形蟲取得之Scheffersomyces屬酵母可能為新種。從所有樣本取得的大多數酵母菌皆可利用木糖。結果顯示二點赤鋸鍬形蟲之共生酵母菌不具物種專一性，垂直傳遞之菌種對幼蟲生存可能並非必須，但所有的共生酵母菌對幼蟲消化具有一定程度之幫助。

Stag beetles (Lucanidae) are world-famous insects, but knowledge about their ecology is limited. Females have mycangia, which harbor xylose-fermenting yeasts that help larvae digest their woody diet. Scheffersomyces yeasts are considered the main symbionts of lucanids, and are transmitted across generations. Yeasts are spread by females on substrates near the eggs and colonize the larval gut and tunnels. During pupation, the yeasts are stored in the cocoon walls, and acquired again by newly eclosed female adults through post-eclosion behaviors. Due to the importance of lucanids in wood decomposition and conservation, related studies are urgently needed. This research investigates Prosopocoilus astacoides blanchardi in Taiwan. Female adults were collected from the wild and reproduced in the laboratory. Yeasts were cultured from the mycangium, ovary, larval gut, tunnels, and cocoon walls. Species identification, CFU calculation, and xylose-utilizing ability tests were done. Yeasts isolated from females and cocoon walls varied greatly. Scheffersomyces spp., Candida spp., and Meyerozyma guilliermondii were found. This study might be the first record of yeast presence in lucanid ovaries. Results of larval gut and tunnels were uniform and similar: Scheffersomyces spp. and Spathaspora spp. were dominant. According to the phylogenic results, the dominant Scheffersomyces species found in this lucanid might be a new species. Most of the collected fungi could utilize xylose. The results suggest that the associations with yeast symbionts in Prosopocoilus astacoides blanchardi are not species-specific. The vertically transmitted yeasts may not be necessary for larval survival, but all yeast symbionts contribute to larval digestion to some degree.