| Summary: | 碩士 === 東海大學 === 生命科學系 === 99 === Geographic isolation has been proposed as a major force in speciation. Allopatric mode of speciation emphasizes the prominent role of physical barriers and restriction of gene flow on population divergence. Under allopatric model, gene flow is considered as an impediment for speciation. The question of how much historical gene flow has occurred in diverged natural populations and species is largely unknown. In this study, we investigated the level of historical gene flow during the speciating process of two sibling species pairs of Euphaea damselflies, E. formosa + E. yayeyamana and E. decorata + E. ornata, using two mitochondrial and ten unclear loci. The reconstructed species phylogeny based on cox2 and arr genes indicated that E. formosa + E. yayeyamana, and E. decorata + E. ornata, are both valid sister species pairs. The results of multilocus analyses rejected the strict isolation model in E. formosa and E. yayeyamana, and E. decorata and E. ornata. Moderate to large two directional gene flows were detected between E. formosa and E. yayeyamana, but there is little evidence of gene flow between E. decorata and E. ornata. The divergence time of E. decorata and E. ornata was estimated at approximately 0.511 Mya, which was more recent than the split of E. formosa and E. yayeyamana (1.145 Mya). We concluded that the model of speciation with gene flow best describe the observed sequence variation in E. formosa and E. yayeyamana, whereas the model of allopatric speciation without gene flow is more appropriate for E. decorata and E. ornata.
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