北美高山絹蝶在第四紀的氣候循環中的生物地理學研究

文獻來源：Schoville SD & Roderick GK. 2009. Alpine biogeography of Parnassian butterflies during Quaternary climate cycles in North America. Molecular Ecology. 18(1): 3471-3485. [Abstract]

更新世的冰河消長對於北美洲高山的地景，以及現居高山生態系的生物有深遠的影響。雖然物種豐度的模式偏離了島嶼生物地理學的預測，但在生物地理學上北美高山仍常被視為空中島嶼。原因之一即為受第四紀末期的地景變遷影響，造成了高山生物非平衡的群聚動態以及地理分布的變動，此可從遺傳資料中獲得證據。此研究利用粒線體DNA的COI片段以及核DNA的wingless與EF1a片段做分析、推測福布絹蝶（Parnassius phoebus）種複合群的演化歷史。作者對Parnassius smintheus與Parnassius behrii生物地理分布的變動歷史進行了多項測試，結果支持高山島嶼避難所模式，意即高山蝶類族群於冰河期縮減，並隨著間冰期的來到而擴張。雖然蝴蝶有能力於冰河期時在高山之間進行長距離的播遷，但事實上基因交流卻很少。此研究發現加州與科羅拉多州的高山棲地曾於間冰期形成連結，接著蝴蝶族群就於約兩萬年前快速擴張，進入上次冰河期後又縮減成小族群。研究譜系分枝的結果顯示P. smintheus與P. behrii的形態差異源自於更新世末期（約四萬八千年前），由於不順暢的基因交流造成分化所形成。此研究結果說明了空間的異質性與非平衡的族群動態影響了高山的生物多樣性。

Abstract
Growth of alpine glaciers during the Pleistocene had profound effects on montane landscapes in North America and the organisms now inhabiting alpine ecosystems. Biogeography of this region has often been viewed as a system of sky islands despite the fact that species richness patterns deviate from a strict island biogeographic model. One explanation is that alpine species are not in equilibrium because of late Quaternary geographic range shifts. Genetic data can provide evidence of nonequilibrium dynamics and the distributional shifts that occur during glaciation events in alpine landscapes. Using mitochondrial and nuclear sequence data, we examine the evolutionary history of butterflies in the Parnassius phoebus complex. We test explicit, alternative models of the biogeographic history of Parnassius smintheus and Parnassius behrii, including an equilibrium island model, ancestral radiation and fragmentation, an expanding alpine archipelago and an alpine archipelago refuge model. Our results support the alpine archipelago refuge model, in which alpine butterflies undergo population contraction during glacial climates followed by population expansion during interglacial phases. While butterflies can disperse between distant mountain ranges during glacial periods, gene flow is rare. We find evidence of recent connectivity between California and Colorado, population expansion events following deglaciation ∼20 000 years B.P., and small population sizes during the last glacial period. An analysis of lineage splitting suggests that morphological differences in P. smintheus and P. behrii are the result of late Pleistocene divergence (∼48 000 years B.P.) with limited gene flow. Our results demonstrate that spatially complex and nonequilibrium population dynamics influence alpine diversity patterns.