Systematics and evolution of predatory flower flies (Diptera: Syrphidae: Syrphinae ) based on exon-capture sequencing

Syrphidae, one of the most species-rich dipteran families, provides important ecosystem services such as pollination, biological control of pests, recycling of organic matter, redistributions of essential nutrients, among others. Flower fly adults show a common feeding strategy on pollen and nectar, but their larval feeding habits are strikingly diverse. In the present study high-throughput sequencing was used to capture and enrich exons as a genome reduction method for the first time for any Diptera group. With the help of the BaitFisher software, we developed a new bait kit (SYRPHIDAE1.0) to target 1945 CDS regions belonging to 1312 orthologous genes. This new bait kit was successfully used to exon-capture the targeted loci in 121 flower fly species across the different subfamilies of Syrphidae. We analyzed different amino acid and nucleotide data sets (1302 loci and 154 loci) with the Maximum Likelihood and the Multispecies Coalescent approaches. Our maximum-likelihood and coalescent-based analyses resolved highly supported similar topologies, although the degree of the SRH (global stationary, reversibility and homogeneity) conditions varied greatly between amino acid and nucleotide data sets. The sisterhood of Pipizinae and Syrphinae is recovered in all our analyses, confirming a common origin of taxa feeding on soft-bodied arthropods. Based on our results, we define Syrphini stat.rev. to include the genera Toxomerus and Paragus. Our divergence estimate analyses with BEAST inferred the origin of the Syrphidae in the Lower Cretaceous and the diversification of predatory flower flies occurred around the K-Pg boundary.食蚜蝇科（Syrphidae）是物种多样性最高的双翅目（Diptera）类群之一，可为生态系统提供诸多重要服务，包括传粉、害虫生物防治、有机质循环以及必需营养物质再分配等。食蚜蝇成虫普遍以花粉和花蜜为食，但其幼虫的取食习性却呈现出显著的多样性。本研究首次针对双翅目类群，采用高通量测序（high-throughput sequencing）技术以外显子捕获富集作为基因组简化方法。借助BaitFisher软件，我们开发了一款全新的诱饵试剂盒（SYRPHIDAE1.0），可靶向覆盖1312个直系同源基因（orthologous genes）的1945个编码区（CDS）序列。该新型诱饵试剂盒成功实现了对食蚜蝇科不同亚科共121种食蚜蝇的目标位点外显子捕获。本研究分别采用最大似然法（Maximum Likelihood）与多物种溯祖分析法（Multispecies Coalescent），对两套数据集（分别包含1302个位点与154个位点的氨基酸序列数据集、核苷酸序列数据集）开展分析。尽管氨基酸与核苷酸数据集的SRH（global stationary, reversibility and homogeneity）条件满足程度存在显著差异，但基于最大似然法与溯祖分析得到的拓扑结构均高度相似且支持率极高。所有分析均恢复出管蚜蝇亚科（Pipizinae）与食蚜蝇亚科（Syrphinae）的姊妹群关系，证实了以软躯体节肢动物为食的类群具有共同起源。基于本研究结果，我们将食蚜蝇族（Syrphini）的分类地位予以修订（stat.rev.），将Toxomerus属与Paragus属纳入该族。借助BEAST软件开展分化时间估计分析，结果显示食蚜蝇科起源于早白垩世，而捕食性食蚜蝇的类群分化大致发生在白垩纪-古近纪（K-Pg）界线前后。