多次跨島播遷與基因交流驅動菲律賓特有雙葉塔冠角蟬種群的多樣化

Abstract

海洋島嶼因其獨特的獨立性、特有性和相對年輕等特徵被廣泛認為是研究演化的天然實驗室。擁有豐富的動物相和超過7,000個島嶼的菲律賓群島，為研究島嶼生物多樣性提供了寶貴的機會。本研究調查了菲律賓特有東亞塔冠角蟬種群Pyrgonota bifoliata的多樣化，推測它們的多樣化主要是受到更新世冰期循環的影響，抑或是早期板塊活動或現有的島嶼界線所造成。藉由簡化基因組定序（RADseq）資料，我訂出12個P. bifoliata物種群的分類操作單元。這些分類操作單元的分化事件發生在更新世冰期循環期間，顯示更新世複合島群（PAIC）可能影響了它們的多樣化。然而祖先分布重建結果顯示了數個PAIC之間的播遷事件，暗示著海洋島嶼和PAIC之間的海洋隔離並未強烈地阻礙P. bifoliata角蟬的播遷。此外，我們使用近似貝葉斯計算與隨機森林（ABC-RF）方法推測了島嶼內、島嶼間、以及PAIC間的譜系分化情境。結果顯示，不論島嶼內或島嶼間分化分化的族群，在末次冰盛期後至今仍持續地有基因交流。在PAIC之間的物種分化的初期也偵測到遺傳交流。因此這篇研究結果顯示，跨海播遷與持續的基因流推動了P. bifoliata物種群的多樣化。此外，長距離跨海播遷可能比以前想像的更頻繁。Oceanic islands have been widely recognized as valuable natural laboratories for studying evolution due to their unique characteristics of isolation, endemism, and relative youth. The Philippines archipelagos, with their diverse fauna and over 7,000 islands, offer a valuable opportunity to investigate island biodiversity. This study investigates the diversification of the Pyrgonota bifoliata species complex, which consists of endemic treehoppers in the Philippines. The objective is to assess whether their diversification was predominantly shaped by Pleistocene glaciation cycles, which cyclically connected and fragmented the Pleistocene Aggregate Island Complex (PAIC) through fluctuating sea levels, or if other factors like ancient tectonic activities and current island boundaries played significant roles. Using restriction site-associated DNA sequencing (RADseq) data, we identified 12 operational taxonomic units within the P. bifoliata species complex, with divergence occurring during the Pleistocene glaciation cycle. This suggests that PAICs may have influenced their diversification. However, our ancestral range reconstruction results also unveiled several instances of dispersal between PAICs, implying that the oceanic barriers between islands and PAICs may not have strongly impeded dispersal. Furthermore, we inferred the demographic history of within and between islands population divergence, as well as between PAIC speciation, using the approximated Bayesian computation random forest (ABC-RF) framework. The outcomes of the ABC-RF analysis reveal the presence of continuous gene flow, even after the last glacial maximum when the PAIC broke up into separate islands, in both within island and between islands population divergence scenarios. Additionally, gene flow was also detected at the initial stages of speciation between PAICs. Overall, our findings suggest that overseas dispersal with continuous gene flow drove the diversification of the P. bifoliata species complex. Moreover, our results suggest that long-distance dispersal, possibly through rafting on vegetation, may occur more frequently than previously thought.