天然紀念物的隔離族群在保育上的困境與建議—以台灣鮭及三棘鱟為例

在基因交流受到限制時，隔離對族群常導致嚴重的親代自交與遺傳多樣性的流失。天然紀念物的隔離族群的其中一項保育困境，在於同時增加族群數量與遺傳多樣性，以避免適應性的流失與滅絕危機的增加。台灣鮭是陸封型鮭魚，在最後一次的最大冰期後被隔離在台灣的高山溪流，近年來更受到棲地劣化的威脅。日本和台灣的三棘鱟隔離的族群也面臨相似的挑戰，有些族群的粒線體控制區間和細胞色素c氧化酶基因I(COI)，甚至完全失去遺傳多樣性。我們整理遺傳多樣性流失的前因後果，包括隔離在演化和生態時間尺度的影響、棲地破壞或族群直接被捕、大量低遺傳變異的人工繁殖個體的引入。我們也對復育隔離族群提供原則性建議和針對台灣鮭和三棘鱟各自不同情境下的實務性建議，包括最大化人工繁殖用之親代的遺傳變異、避免基因污染、保護親代健全及提升子代存活率，以及維護棲地連通性與品質。總而言之，進行遺傳多樣性進行定期的監測是相當重要的，以找出族群長期存活所需的遺傳多樣性的最低閥值，與找出避免遺傳均質化的環境變因，並改善原有或復育己破壞的棲地。以增加族群的適應性，並減少地方性干擾和氣候變遷造成的極端環境的衝擊。

關鍵字

天然紀念物；隔離族群；三棘鱟；台灣鮭；遺傳多樣性；復育

並列摘要

With restricted gene flow, isolation typically leads to great inbreeding and loss of genetic diversity for population. One of the f rises on conservation for a fragmented population of the two natural monuments is to increase both genetic diversity and population size from losing fitness and raising the risk of extinction. Formosa Landlocked salmon, Oncorhynchus masou formosanum is a landlocked salmon isolated in high-mountain streams since last glacial maximum and recently threaten by habitat degradation in Taiwan. Horseshoe crabs, Tachypleus tridentatus face to the similar challenge with isolated populations in Japans and Taiwan, and some of them even totally lose their genetic diversity revealed by mitochondrial control region. We integrate the cause and consequence of losing genetic diversity including effect of isolation in evolutionary and ecological time scale, habitat degradation or overharvested and large reintroduction with lowly genetic diversity recruits. We also recommend the principles and practical applications for recovery of isolated population depending on each situation of O. masou formosanum and T. tridentatus. Those recommendations include maximizing genetic diversity of parents for propagation, avoiding genetic contamination, protecting parents and increasing survival rate of descendants, and maintaining the connectivity and quality of habitat. To sum up, it is important to monitor genetic diversity in time and space to define the threshold of minimum genetic diversity for long-term survival of population and environmental factors of avoiding genetic homogenization, and to improve original or restore destroyed habitat to increase their fitness to prevent from local disturbance and extreme environment increased by climate change.

並列關鍵字

natural monument ； fragmented population ； Tachypleus tridentatus ； horseshoe crab ； Oncorhynchus masou formosanum ； Formosa Landlocked salmon ； genetics diversity ； restoration

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天然紀念物的隔離族群在保育上的困境與建議—以台灣鮭及三棘鱟為例

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