臺灣北部產萼形柱珊瑚的族群遺傳結構 與共棲菌相多樣性

Abstract

珊瑚是建造地球上生物多樣性最高的生態系－珊瑚礁生態系的關鍵生物，然而隨著氣候變遷造成全球暖化，珊瑚的死亡率大幅上升。因此，為了維護珊瑚礁生態系寶貴的生物多樣性，必須了解珊瑚族群在不同地理區域中的遺傳多樣性、結構以及族群之間的連接性，以指引後續的保育規劃。除了族群遺傳資訊，珊瑚與眾多微生物具有緊密的共生關係，在這之中，細菌是多樣性與豐富度最高的微生物類群，參與珊瑚宿主的生理代謝、免疫等重要功能。此外，珊瑚共棲菌落組成具有高度的動態變化，隨著環境、地域、珊瑚宿主健康狀態等因子快速變動，可做為評估珊瑚健康狀態的重要指標之一。因此結合珊瑚的遺傳結構與共棲菌落組成，將有助於了解族群的現況，提供後續的保育規劃參考。台灣北部海域具有複雜地形與洋流，如此多變的環境下，使台灣的珊瑚生態系以三貂角作為分界（Chen’s Line），呈現南北不同的珊瑚礁群聚型態。分界線以北為非礁型珊瑚群聚、以南則是熱帶珊瑚礁群聚。然而目前仍不清楚在南北相異的珊瑚礁群聚環境下，珊瑚的族群遺傳結構以及共棲細菌群落的分化模式。為此，本論文以廣泛分布且常用於珊瑚研究的萼形柱珊瑚（Stylophora pistillata）為對象，設立六處樣點，分別為Chen’s Line 以北的鼻頭、望海巷，位於交界處的馬崗，以南的龜山島、豆腐岬、墾丁，每個樣點收集 30~36 個，總計 214 個珊瑚群體，以 MIG-seq 技術獲取珊瑚遺傳資訊並建構族群遺傳結構，並搭配珊瑚杯孔型態評估是否存在隱蔽種；細菌群落資料則以 16S rRNA V6–V8 區段的擴增子定序獲取。本研究結果顯示，萼形柱珊瑚可區分為兩個展現初期分化的遺傳分群，且兩者仍存有一定程度的基因交流，顯示分化程度尚未達到隱蔽種的水準，此外，在族群結構方面，兩個遺傳分群的分布模式與珊瑚群落分界線並不一致，其中一個遺傳分群僅出現在最北（望海巷）與最南（墾丁）的樣點。另一方面，台灣的萼形柱珊瑚族群相對其他洋區，展現高度的連接性，其背後的原因可歸因於台灣周遭複雜的洋流系統。在共棲細菌群落方面，菌相組成受到主要受到環境異質性影響，不同的樣點展現出相異的共棲菌落。雖然樣點是影響菌相的主要因子，然而珊瑚宿主的基因型亦會形塑共棲菌相，萼形柱珊瑚的遺傳分群與共棲菌落呈現譜系共生（phylosymbiosis）現象，顯示珊瑚與共棲微生物之間可能具有協同適應環境變化的潛力。此外，儘管採集的珊瑚樣本皆為健康的群體，然而與環境汙染、白化相關的菌株在超過半數的樣本中被觀察到，顯示本研究的樣點有遭受壓力的可能。

Corals are the key organisms that build coral reef ecosystems, the most biodiverse ecosystems on Earth. However, climate change leads to global coral reef decline, highlighting the urgency of coral conservation. Understanding the genetic connectivity and diversity of coral populations and coral microbiome is needed to guide conservation efforts. Population genetic structure could help managers to evaluate the resilience of population, while coral-associated bacteria play important roles in coral holobiont physiology, immunity, and stress response, which could serve as an indicator to evaluate the physiological state of coral. There is a biogeographic boundary called “Chen’s Line” that separates tropical reefs in the south from non-reefal coral communities in the north. But little is known about how this boundary affects coral population structure and their microbiomes. This study examined Stylophora pistillata populations across six sites along this latitude, including two north of Chen’s Line (Bitou, Wanghaixiang), one at the boundary (Magang), and three to the south (Guishan Island, Dufu Cape, Kenting) by using MIG-seq to genotype 214 colonies and compared coral genetic data with corallite morphological traits, while bacterial communities were obtained through 16S rRNA (V6–V8) sequencing. The results revealed that there were two genetic clusters which showed evidence of incipient speciation. The distribution of genetic clusters did not match Chen’s Line. Besides, both negative FIS and low FST, indicating high geneflow, which may be due to strong and highly variable current systems around Taiwan. Microbial communities differed significantly across locations, mainly due to environmental differences, but also showed links to host genetics. Evidence of phylosymbiosis suggests co-adaptive relationships between corals and their bacteria. Overall, bleaching and stress-associated bacteria are found in most samples, indicating the potential of stress among these sites.