Department of Botany and Biodiversity Research, University of Vienna, Vienna, Austria.
Department of Microbiology and Ecosystem Science, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.
BMC Biol. 2024 May 14;22(1):112. doi: 10.1186/s12915-024-01897-y.
Fungi and ants belong to the most important organisms in terrestrial ecosystems on Earth. In nutrient-poor niches of tropical rainforests, they have developed steady ecological relationships as a successful survival strategy. In tropical ant-plant mutualisms worldwide, where resident ants provide the host plants with defense and nutrients in exchange for shelter and food, fungi are regularly found in the ant nesting space, inhabiting ant-made dark-colored piles ("patches"). Unlike the extensively investigated fungus-growing insects, where the fungi serve as the primary food source, the purpose of this ant-fungi association is less clear. To decipher the roles of fungi in these structures within ant nests, it is crucial to first understand the dynamics and drivers that influence fungal patch communities during ant colony development.
In this study, we investigated how the ant colony age and the ant-plant species affect the fungal community in the patches. As model we selected one of the most common mutualisms in the Tropics of America, the Azteca-Cecropia complex. By amplicon sequencing of the internal transcribed spacer 2 (ITS2) region, we analyzed the patch fungal communities of 93 Azteca spp. colonies inhabiting Cecropia spp. trees. Our study demonstrates that the fungal diversity in patches increases as the ant colony grows and that a change in the prevalent fungal taxa occurs between initial and established patches. In addition, the ant species significantly influences the composition of the fungal community in established ant colonies, rather than the host plant species.
The fungal patch communities become more complex as the ant colony develops, due to an acquisition of fungi from the environment and a substrate diversification. Our results suggest a successional progression of the fungal communities in the patches during ant colony growth and place the ant colony as the main driver shaping such communities. The findings of this study demonstrate the unexpectedly complex nature of ant-plant mutualisms in tropical regions at a micro scale.
真菌和蚂蚁属于地球上陆地生态系统中最重要的生物。在热带雨林贫瘠的营养环境中，它们形成了稳定的生态关系，这是一种成功的生存策略。在全球范围内的热带蚁-植物互惠关系中，居住在蚁巢中的蚂蚁为宿主植物提供防御和养分，以换取庇护和食物，真菌经常出现在蚂蚁筑巢的空间中，栖息在蚂蚁制造的深色堆（“斑块”）中。与广泛研究的真菌养殖昆虫不同，真菌是这些昆虫的主要食物来源，而这种蚂蚁-真菌的共生关系的目的不太明确。为了解析这些蚂蚁巢穴结构中的真菌作用，首先了解影响蚂蚁群体发育过程中真菌斑块群落的动态和驱动因素至关重要。
在这项研究中，我们研究了蚁群年龄和蚁-植物物种如何影响斑块中的真菌群落。作为模型，我们选择了美洲热带地区最常见的共生关系之一，即 Azteca-Cecropia 复合体。通过对内部转录间隔区 2（ITS2）区域的扩增子测序，我们分析了栖息在 Cecropia 树上的 93 个 Azteca spp. 蚁群的斑块真菌群落。我们的研究表明，随着蚁群的生长，斑块中的真菌多样性增加，并且在初始和成熟斑块之间，优势真菌类群发生变化。此外，蚂蚁物种对成熟蚁群中真菌群落的组成有显著影响，而不是宿主植物物种。
由于从环境中获取真菌和基质多样化，随着蚁群的发展，真菌斑块群落变得更加复杂。我们的结果表明，在蚁群生长过程中，真菌群落会在斑块中经历一个演替过程，并将蚁群作为塑造这些群落的主要驱动力。本研究的结果表明，在微观尺度上，热带地区的蚁-植物互惠关系出乎意料地复杂。
