Divergence And Comparative Phylogeography Of Ficus Pumila And Its Pollinating Wasps(Wiebesia Spp.)

Coevolution was thought as an important factor to promote diversity of herbivorous insects. However, incongruence topology of phylogenetic trees between insects and their host plants were frequently observed in recent studies, suggesting that cospeciation was not the sole mechanism, and other factors such as host shift, also played an critical role in the diversification of insects. In addition, geological events also contributed to the diversification of insects. Uplifts of mountains and formation of straits or rivers led to the isolation and divergence of populations. And climatic fluctuations drove the range shifts of species, resulting in the changing of population genetic structure.Fig trees and their pollinating wasps constitute perhaps the most obligate mutualisms in nature, providing ideal systems to understand the role of geological evens in insects’ speication and in shaping genetic structure of host plants and insects. Previous observations suggested that a fig tree is pollinated by a specific pollinating wasp, i.e.,"one-to-one" rule. However, recent studies using molecular markers found increasing number of exceptions, indicating that "one fig-to-multiple fig wasps" or "multiple figs-to-one fig wasp" may be more common. The interaction between Ficus pumila and its pollinating wasps(Wiebesia spp.) is one of these exceptions. Ficus pumila is pollinated by three cryptic wasp species, which are sister species, hinting that they diverged in one host species.To explore how geological events shape the divergence of F. pumila and Wiebesia spp., we used molecular makers to study the distribution pattern of these cryptic pollinators and to decipher their genetic structures. And we also studied their genetic responses to geological events by comparing phylogeographical patterns of the two intimately interacting partners. Two cryptic pollinators coexist in Zhoushan Archipelago. To understand the way of their coexistence, we observed their emergence phenologies. Finally, we got following conclusions.1) There are three cryptic pollinators in our study range, i.e., Wiebesia spp.1,2and3. They are mainly distributing in allopatry. Mountains are main boundaries of Wiebesia spp.1and2. Wiebesia sp.3is mainly located in Zhoushan Archipelago, where it is in sympatric with Wiebesia sp.1, and it was also found in a mainland population, i.e., Ningde. Besides, in Taiwan, Wiebesia sp.3is the sole pollinator of F. pumila var. awkeotsang. This study also confirmed that the formation of Taiwan Strait and the uplift of Wuyi Mountain were the key factors of divergence and speciation of the F. pumila and its pollinating wasps.2) We observed two or three crops per year for male F. pumila, corresponding with two or three generations per year of the pollinators. In Zhoushan Archipelago, where two species coexist, we found that Wiebesia sp.1emerged earlier than Wiebesia sp.3. They could coexist in one plant, but diverged in phenology. We found only one case that a fig synconium contained both fig wasps. Fig plants were usually occupied by the same pollinating wasp in different years, hinting that the phenology of E pumila was induced by the pollinators. However further studies are needed.3) Due to their obligate dependence on each other, F. pumila and Wiebesia spp. were affected by the same geological events. However, their genetic structures were quite different, a results of different dispersal abilities.According to their population genetic structures and population demographics, we inferred multiple refugia and different postglacial dispersal rutes for F. pumila and Wiebesia spp. Wiebesia sp.1had two potential glacial refugia, located at the northern part of Nanling Mountains in Hunan province, and the west of Wuyi Mountain. Postglacial recolonization from the first refugium was limited in Hunan province by topography. While populations in the second refugium expanded along Wuyi Mountain and Xianxia Mountains, and also to island habitats.There were several potential refugia of Wiebesia sp.2. A refugium was located in south coast of China. High genetic diversity in west populations indicated this place was also a potential refugium. The high genetic divergence between wasps in Hainan Island and the other mainland populations provided evidence for Hainan or nearby place as a glacial refugium. In addition, Taiwan was also a refugium. Islands were the potential refugia of Wiebesia sp.3. Taiwan was one of the palces as a shelter for Wiebesia sp.3in glacial period, because Wiebesia sp.3is the pollinator of F.pumila. var. awkeotsang. Meanwhile, if Wiebesia sp.3had dispersed to the islands of northern part before LGM, then this place was another potential refugium.F. pumila had the same refugia as Wiebesia spp., but showed different dispersal routes. Populations in east of Wuyi Mountain were originated from the south coast refugium, and complicated dispersal patterns in west populations were shaped by the topography.