Department of Biology, Section for Ecology and Evolution, University of Copenhagen, Universitetsparken 15, Building 3, 1st floor, 2100, Copenhagen East, Copenhagen, Denmark.
Department of Biology, Section of Microbiology, University of Copenhagen, Universitetsparken 15, Building 1, 1st floor, 2100, Copenhagen East, Copenhagen, Denmark.
BMC Evol Biol. 2020 Dec 9;20(1):163. doi: 10.1186/s12862-020-01727-z.
Monoculture farming poses significant disease challenges, but fungus-farming termites are able to successfully keep their monoculture crop free from contamination by other fungi. It has been hypothesised that obligate gut passage of all plant substrate used to manure the fungal symbiont is key to accomplish this. Here we refute this hypothesis in the fungus-farming termite species Macrotermes bellicosus.
We first used ITS amplicon sequencing to show that plant substrate foraged on by termite workers harbour diverse fungal communities, which potentially could challenge the farming symbiosis. Subsequently, we cultivated fungi from dissected sections of termite guts to show that fungal diversity does not decrease during gut passage. Therefore, we investigated if healthy combs harboured these undesirable fungal genera, and whether the presence of workers affected fungal diversity within combs. Removal of workers led to a surge in fungal diversity in combs, implying that termite defences must be responsible for the near-complete absence of other fungi in functioning termite gardens.
The rapid proliferation of some of these fungi when colonies are compromised indicates that some antagonists successfully employ a sit-and-wait strategy that allows them to remain dormant until conditions are favourable. Although this strategy requires potentially many years of waiting, it prevents these fungi from engaging in an evolutionary arms race with the termite host, which employs a series of complementary behavioural and chemical defences that may prove insurmountable.
单一栽培种植会带来严重的疾病挑战，但真菌养殖白蚁能够成功地使它们的单一栽培作物免受其他真菌的污染。有人假设，将用于给真菌共生体施肥的所有植物基质强制性地通过肠道是实现这一目标的关键。在这里，我们反驳了真菌养殖白蚁物种 Macrotermes bellicosus 中的这一假设。
我们首先使用 ITS 扩增子测序表明，白蚁工蚁觅食的植物基质含有多种潜在的真菌群落，这可能对养殖共生体构成挑战。随后，我们从白蚁肠道的解剖部位培养真菌，表明真菌多样性在肠道通过过程中不会减少。因此，我们研究了健康的蚁巢是否存在这些不受欢迎的真菌属，以及工蚁的存在是否会影响蚁巢内的真菌多样性。移除工蚁会导致蚁巢中真菌多样性激增，这意味着白蚁的防御机制必须对功能正常的白蚁花园中几乎完全不存在其他真菌负责。
当蚁群受到破坏时，其中一些真菌的迅速增殖表明，一些拮抗剂成功地采用了一种坐以待毙的策略，使它们能够保持休眠状态，直到条件有利。尽管这种策略可能需要多年的等待，但它阻止了这些真菌与白蚁宿主进行进化军备竞赛，白蚁宿主采用了一系列互补的行为和化学防御措施，这些措施可能是无法克服的。
