Evolution of the Attine Ant-Fungus Symbiosis

小行星9707209 在美洲热带地区，更有趣的共生现象是蚁族（蚁科）的切叶蚁和蕈类（担子菌纲）的真菌之间的相互作用。在这种相互作用中，切叶蚁维持着新切下的树叶的“花园”，而真菌则在上面照料和收获作为食物。有大约200种左右描述的切叶阿蒂尼蚂蚁，并且已知该组的高级成员保持广泛的花园，其中真菌的繁殖与接种物从父母到后代巢的严格垂直传播有关。这种食物接种物的专性传播提出了一个有趣的问题，即蚂蚁的突变变化和进化多样化是否反映在其栽培真菌的变化和多样化上，并导致物种形成和共同进化的联合模式。这种相互作用更为复杂，因为其他种类的原始阿蒂尼蚁在为花园采集真菌时是机会主义的，并且可能会定期从野生资源中收获新鲜的接种物。哪些蚂蚁群体经常这样做，哪些已经切换到强制性的生长和传播模式，哪些以中间方式行事，这些都是没有答案的问题。相应地，Lepiotaceae真菌的哪些种属与各种蚂蚁群体在接种物摄取和传播的“开放”或“封闭”系统中相关也是未知的。马里兰州大学的Ulrich Mueller博士和他的同事Smithsonian的Ted Schultz以及波多黎各大学的Stephen Reynner进行了初步的分子DNA分析，为研究这一概念上具有挑战性的共生现象打开了一扇重要的技术大门。分子方法在真菌的研究中是特别必要的，因为栽培形式很少，如果有孢子，在没有孢子的结构，分类鉴定是困难的，如果不是不可能的。来自核或线粒体基因的诊断DNA标记有望解决这一问题，同时提供可用于推断真菌之间系统发育或谱系关联的数据。 这个由昆虫学家和真菌学家组成的合作团队继续在中美洲和南美洲进行实地收集，以增加迄今为止收集到的近140种蚂蚁物种，并同时从蚂蚁巢中收集真菌材料。与巴西和阿根廷同事的实地工作将有助于在南美洲富裕地区收集。对蚂蚁和那些在培养中能被诱导产生孢子的真菌进行分子DNA测序和形态学分析，将提供更多的分类学和系统发育学信息。相关的蚂蚁和真菌的系统发育模式和生态栖息地的研究将创建一个可访问的热带陆地生态系统中的共生体进化模型，其丰富的相互作用与珊瑚礁共生体，涉及珊瑚和光合腰鞭毛虫。

9707209 Mueller Among the more fascinating cases of symbiosis in the American tropics is the interaction between leafcutter ants of the tribe Attini (Family Formicidae) and fungi of the mushroom family Lepiotaceae (Basidiomycetes) in which the ants maintain "gardens" of freshly cut leaves on which the fungi are tended and harvested for food. There are some 200 or so described species of leafcutter Attini ants, and advanced members of the group are known to maintain extensive gardens in which propagation of the fungi is obligately linked to strict vertical transmission of inocula from parent to offspring nests. This obligate transmission of food inocula raises the intriguing question whether mutational changes and evolutionary diversification in the ants is mirrored by change and diversification in their cultivated fungi, and leads to conjoint patterns of speciation and coevolution. The interaction is known to be even more complicated because other groups of putatively primitive Attini ants are opportunistic in their acquisition of fungi for their gardens, and may regularly harvest fresh inocula from wild sources. Which ant groups do this regularly, which have switched over to the obligate mode of growth and transmission, and which act in an intermediate fashion are all unanswered questions. Correspondingly, which species and genera of Lepiotaceae fungi are associated with the various ant cohorts in "open" or "closed" systems of inocula uptake and transmission are also unknown. Preliminary molecular DNA analyses by Dr. Ulrich Mueller at the University of Maryland and his colleagues Ted Schultz at the Smithsonian and Stephen Rehner at the University of Puerto Rico have opened a major technological door to the study of this conceptually challenging case of symbiosis. Molecular methods are particularly necessary in study of the fungi because the cultivated forms rarely if ever sporulate, and in the absence of spore-bearing structures, taxonomic identification is difficult if not impossible. Diagn ostic DNA markers, from nuclear or mitochondrial genes, hold hope for solving this problem, while providing data that can be used to infer phylogenetic or genealogical associations among the fungi. This collaborative team of entomologists and mycologists continues field collecting in Central and South America, to augment the nearly 140 ant species thus far collected, and in parallel to collect fungal material from ant nests. Field work with Brazilian and Argentinian colleagues will facilitate collecting in rich areas in South America. Molecular DNA sequencing and morphological analyses of the ants and of those fungi that can be induced to sporulate in culture will provide additional taxonomic and phylogenetic information. Study of the phylogenetic patterns and ecological habitats of associated ants and fungi will create an accessible model of symbiont evolution in tropical terrestrial ecosystems, comparable in its richness of interactions with the coral reef symbioses involving corals and photosynthetic dinoflagellates.