Unraveling the evolutionary dynamics of high symbiont diversity in the fungus-farming ant genus Apterostigma: A phylogenomic approach

最著名的真菌种植蚂蚁是Atta和Acromyrmex属的切叶蚂蚁，它们是新世界热带地区主要的植物收获动物。这些蚂蚁利用植物的叶子来培育一种单一的、最近进化的真菌物种，然后吃掉它们。然而，有一种鲜为人知的食真菌蚁属（Apterostigma），其真菌种类的多样性超过了所有其他食真菌蚁的总和。近缘种的无翼柱体培育出近缘类群的真菌，但在4000万年的无翼柱体蚂蚁和真菌的共同进化过程中，向远缘类群的重大转变发生了多次。这项研究旨在更好地了解切叶蚁和它们所培育的真菌的共同进化。这包括发展关于无翼蚁物种及其相关真菌的数量、多样性和分布的新知识，以及确定蚂蚁和真菌之间的进化关系。要解决的问题包括：为什么割叶蚁属（Apterostigma）的真菌种类比所有其他种植真菌的蚂蚁（割叶蚁和不割叶蚁）的总和更多样化？为什么一些无柱头蚁种只培育几种彼此密切相关的真菌，而另一些则培育多种只是远亲的真菌？这项研究的结果可能对整个社会有益，因为真菌养殖蚂蚁为达尔文农业和达尔文医学等新兴领域提供了一个罕见的非人类模型系统，这些领域旨在通过研究类似的自然系统来改善人类农业和疾病管理。最近，从与切叶蚁生活在一起的真菌和细菌物种中分离和描述了几种抗生素和抗疟醌，使它们的生物学与健康问题特别相关。此外，一些与切叶蚁有关的真菌已经成为更有效的生物燃料生产的模型。本研究将通过对蚂蚁和真菌在自然界分布的巢穴进行全面的实地收集，并通过比较基于蚂蚁和真菌基因组数据的系统发育分析，记录无翼蚁及其真菌品种中共物种形成模式的存在或不存在。研究人员将利用超保守遗传元件（UCEs）的定向富集来推断物种水平的系统发育。这些系统发育将用于测试共同进化和真菌物种保真度的假设，以及宿主蚂蚁物种之间随时间的流动性。基因组UCE数据也将用于解决物种边界（识别物种）在未知的类群中。这对于重建物种特异性抗真菌协同进化相互作用以及修改蚂蚁分类和生成不同蚂蚁物种的图像识别密钥至关重要。

The best known fungus-farming ants are the leaf-cutting ants of the genera Atta and Acromyrmex, which are the dominant plant harvesting animals of the New World tropics. These ants use plant leaf cuttings in order to cultivate a single, recently evolved fungal species, which they then eat. However, a more poorly known group of fungus-farming ants in the genus Apterostigma, cultivate a greater diversity of fungal species than all other fungus-farming ants combined. Closely related species of Apterostigma cultivate closely related groups of fungi, but major shifts to distantly related fungal groups have occurred multiple times during 40 million years of co-evolution between Apterostigma ants and fungus. This research aims to better understand the co-evolution of leaf-cutting ants and the fungi they cultivate. This includes developing new knowledge about the numbers, diversity and distribution of Apterostigma ant species and their associated fungi, as well as determining the evolutionary relationships among both ants and fungi. Questions to be addressed include: Why do leaf-cutting ants in the genus Apterostigma cultivate a greater diversity of fungal species than all other fungus-farming ants (leaf-cutting and non-leaf-cutting) combined? Why do some Apterostigma ant species cultivate only a few fungi that are closely related to each other, while others cultivate diverse fungi that are only distant relatives? The results from this research may benefit society in general because fungus-farming ants provide a rare non-human model system for the emerging fields of Darwinian agriculture and Darwinian medicine, which aim to improve human agriculture and disease management through the study of analogous natural systems. Recently several antibiotics and antimalarial quinones have been isolated and described from fungi and bacterial species living in association with leaf-cutting ants, making their biology particularly relevant to issues of health. Further, some fungi associated with leaf-cutting ants have become models for more efficient biofuel production.This research will proceed by comprehensive field collecting of ants and fungi from nests throughout their distributions in nature, and documenting the presence or absence of co-speciation patterns in Apterostigma ants and their fungal cultivars, by comparing phylogenetic analyses based on genomic data for both ants and fungi. The researchers will employ targeted enrichment of Ultra-Conserved genetic Elements (UCEs) to infer the species-level phylogenies. These phylogenies will be used in testing hypotheses of co-evolution and fungal species fidelity and mobility among host ant species over time. The genomic UCE data will also be used to resolve species boundaries (identify species) among poorly known species-complexes of Apterostigma ants. This is essential for reconstructing species-specific ant-fungus co-evolutionary interactions as well as for revising ant taxonomy and producing pictorial identification keys to various ant species.