天空島嶼 (sky island) 指的是受到地理環境所分隔的高海拔棲地，棲息在天空島嶼之上的物種在長期地理隔離之下，不同島嶼的族群就可能逐漸產生基因上的分歧。台灣高山田鼠 (Microtus kikuchii) 為台灣特有種，主要分佈範圍在台灣海拔2500公尺以上的山區，本研究檢視台灣高山田鼠的族群遺傳結構是否會受到台灣山區地理結構的影響，不同山區族群呈現明顯的遺傳分化，以及根據物種分布海拔所推算出來的最小成本路徑 (least-cost path) 是否比直線距離對於遺傳距離有更高的解釋度。本研究樣本採集自全台灣21個地點，利用粒線體DNA之控制區域 (D-loop) 和細胞色素b基因 (cyt-b) 序列，以及Y染色體DBY7、DBY11、DBY14序列作為分子遺傳標記，建構親緣關係樹與最小網狀關係圖 (network) 進行分析。結果顯示台灣高山田鼠族群有明顯的族群遺傳結構，可分為8個不同的系群，且各系群皆有特定的地理分布範圍，推測在過去間冰期，台灣高山田鼠分布被限制在數量極多的高山避難所之中，並在各個避難所內逐漸產生分化。而最小成本路徑對於遺傳距離有更高的解釋度，推測台灣高山田鼠的遷移可能受到了低海拔環境的阻礙。貝式天際線 (Bayesian skyline plot) 分析的結果，顯示台灣高山田鼠在最末次冰期發生族群擴張，並在冰河期結束後呈現族群大小縮減的情形。而北大武山地區的族群與其它地區的族群已出現明顯的遺傳分化，推測因為北大武山與其他山系相連接的最低鞍低至海拔1700公尺以下，進而導致長期的地理隔離。 Sky islands are high-elevation habitats that are geographically subdivided and isolated among different mountain ranges. Populations of different sky islands will differentiate genetically from each other after long-term geographical isolation. Taiwan voles (Microtus kikuchii) are endemic to Taiwan. They are mainly distributed on mountain ranges above 2500 m in elevation. This research examined whether population genetic structure of Taiwan voles were affected by Taiwan’s mountain topology and populations between different mountain regions would exhibit significant genetic differentiation. Furthermore, least-cost path derived from Taiwan voles’ elevation distribution was expected to have more explanation power in variations of pair-wise genetic distance than Euclidean distance. Population fluctuations of Taiwan voles in the past were also investigated. This study used the mitochondria DNA control region, cytochrome b gene and Y chromosome DNA DBY7, DBY11 and DBY14 gene sequence as molecular markers to reconstruct phylogenetic trees and networks of specimens collected from 21 different localities. Phylogenetic analysis showed that Taiwan voles have significant genetic structure and could be separated into eight lineages. Population subdivision was correlated with mountain range location and topographic structure. Taiwan voles likely were isolated in multiple high mountain refugia during interglacial periods and gradually diverged among these refugia. Higher correlation with genetic distance of least cost path than Euclidean distance suggests that low-elevation habitats likely interfere with dispersals of Taiwan voles. Bayesian skyline plots showed that population of Taiwan voles expanded during the last glacial period and reduced thereafter. The population in the mountain Peitawu has significant genetic differentiation from the other populations. This likely was caused by long-term geographical isolation from populations of the other parts of Taiwan due to saddles of < 1700 m elevation connecting Mountain Peitawu and the other mountain ranges.
