What does mitogenomics tell us about the evolutionary history of the <i>Drosophila buzzatii</i> cluster (<i>repleta</i> group)?

The Drosophila repleta group is an array of more than 100 species endemic to the “New World”, many of which are cactophilic. The ability to utilize decaying cactus tissues as breeding and feeding sites is a key aspect that allowed the successful diversification of the repleta group in American deserts and arid lands. Within this group, the Drosophila buzzatii cluster is a South American clade of seven closely related species in different stages of divergence, making them a valuable model system for evolutionary research. Substantial effort has been devoted to elucidating the phylogenetic relationships among members of the D. buzzatii cluster, including molecular phylogenetic studies that have generated ambiguous results where different tree topologies have resulted dependent on the kinds of molecular marker used. Even though mitochondrial DNA regions have become useful markers in evolutionary biology and population genetics, none of the more than twenty Drosophila mitogenomes assembled so far includes this cluster. Here, we report the assembly of six complete mitogenomes of five species: D. antonietae, D. borborema, D. buzzatii, two strains of D. koepferae and D. seriema, with the aim of revisiting phylogenetic relationships and divergence times by means of mitogenomic analyses. Our recovered topology using complete mitogenomes supports the hypothesis of monophyly of the D. buzzatii cluster and shows two main clades, one including D. buzzatii and D. koepferae (both strains), and the other containing the remaining species. These results are in agreement with previous reports based on a few mitochondrial and/or nuclear genes, but conflict with the results of a recent large-scale nuclear phylogeny, indicating that nuclear and mitochondrial genomes depict different evolutionary histories.repleta果蝇类群（Drosophila repleta group）是一类分布于新大陆的超过100个物种的集合，其中多数为嗜仙人掌性物种。以腐烂仙人掌组织作为繁殖与取食场所的能力，是该类群得以在美洲沙漠与干旱地区成功辐射演化的关键因素。该类群中的巴氏果蝇支簇（Drosophila buzzatii cluster）是分布于南美洲的一个演化支，包含7个亲缘关系紧密且处于不同分化阶段的物种，使其成为演化研究的宝贵模型系统。学界已投入大量精力阐明巴氏果蝇支簇内各物种的系统发育关系，其中多项分子系统发育研究得出了模糊的结果——不同分子标记的选择会导致得到不同的系统树拓扑结构。尽管线粒体DNA区域已成为演化生物学与群体遗传学中常用的分子标记，但目前已组装完成的20余个果蝇线粒体基因组（mitogenome）中，尚无一个属于该支簇。本研究报道了5个物种的6个完整线粒体基因组的组装结果，分别为：安东奈果蝇（D. antonietae）、博博雷马果蝇（D. borborema）、巴氏果蝇（D. buzzatii）、柯氏果蝇（D. koepferae）的2个品系，以及塞列马果蝇（D. seriema）；本研究旨在通过线粒体基因组学分析，重新探讨该支簇的系统发育关系与分化时间。基于完整线粒体基因组得到的系统树拓扑结构，支持巴氏果蝇支簇为单系群的假说，并显示出两个主要演化支：一支包含巴氏果蝇与柯氏果蝇（两个品系），另一支包含其余物种。该结果与此前基于少量线粒体和/或核基因的研究结论一致，但与近期一项大规模核基因组系统发育研究的结果相悖，这表明核基因组与线粒体基因组所呈现的演化历史存在差异。