Leclerc Jean-Baptiste, Pinto Silva Jennifer, Detrain Claire
Unit of Social Ecology, Université Libre de Bruxelles, CP 231, Boulevard du Triomphe, 1050 Brussels, Belgium.
R Soc Open Sci. 2018 Jul 11;5(7):180267. doi: 10.1098/rsos.180267. eCollection 2018 Jul.
As entomopathogens are detrimental to the development or even survival of insect societies, ant colonies should avoid digging into a substrate that is contaminated by fungal spores. Here, we test the hypotheses that ant workers (i) detect and avoid fungus-infected substrates and (ii) excavate nest patterns that minimize their exposure to entomopathogenic spores. Small groups of workers were allowed to dig their nest in a two-dimensional sand plate of which one half of the substrate contained fungal spores of , while the other half was spore-free. We found that the overall digging dynamics of nests was not altered by the presence of fungus spores. By contrast, the shape of the excavated areas markedly differed: control nests showed rather isotropic patterns, whereas nests that were partially dug into a fungus-contaminated substrate markedly deviated from a circular shape. This demonstrates that the sanitary risks associated with a digging substrate are key factors in nest morphogenesis. We also found that colonies were able to discriminate between the two substrates (fungus-infected or not). Furthermore, some colonies unexpectedly showed a high consistency in excavating mainly the infected substrate. This seemingly suboptimal preference for a contaminated soil suggests that non-lethal doses of fungal spores could help ant colonies to trigger 'immune priming'. The presence of fungi may also indicate favourable ecological conditions, such as humid and humus-rich soil, that ants use as a cue for selecting suitable nesting sites.
由于昆虫病原体对昆虫群落的发育甚至生存有害，蚁群应避免挖掘被真菌孢子污染的基质。在此，我们检验以下假设：蚂蚁工蚁（i）能够检测并避开被真菌感染的基质，以及（ii）挖掘巢穴模式以尽量减少其暴露于昆虫病原孢子的风险。让小群工蚁在二维沙盘里挖掘巢穴，其中一半基质含有某种真菌的孢子，而另一半没有孢子。我们发现真菌孢子的存在并未改变巢穴的整体挖掘动态。相比之下，挖掘区域的形状明显不同：对照巢穴呈现出较为各向同性的模式，而部分挖掘到被真菌污染基质中的巢穴则明显偏离圆形。这表明与挖掘基质相关的卫生风险是巢穴形态发生的关键因素。我们还发现蚁群能够区分这两种基质（是否被真菌感染）。此外，一些蚁群意外地表现出高度一致性，主要挖掘被感染的基质。这种对污染土壤看似次优的偏好表明，非致死剂量的真菌孢子可能有助于蚁群引发“免疫预激发”。真菌的存在也可能表明存在有利的生态条件，如潮湿且富含有腐殖质的土壤，蚂蚁以此作为选择合适筑巢地点的线索。
