Jossart Margaux, Hance Thierry, Detrain Claire
Unit of Social Ecology, Université Libre de Bruxelles, Brussels, Belgium.
Earth and Life Institute, Biodiversity Research Center, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
PLoS One. 2025 Jun 23;20(6):e0326875. doi: 10.1371/journal.pone.0326875. eCollection 2025.
The multitrophic plant-aphid-ant system is a model widely studied in ecology and evolutionary biology. Within this system, bacterial symbionts can circulate and may modify the relationships between partners. A common symbiont of aphids, Serratia symbiotica, shows a wide variety of strains with different lifestyles, one of them being associated with the aphid gut and found in the digestive tract of aphid-tending ants. This free-living S. symbiotica strain induces fitness costs on its aphid host which can be offset by a lower selective pressure exerted by parasitoids. In this paper, we investigated whether this aphid gut-associated bacterium may alter the mutualistic relationships between Aphis fabae aphids and Lasius niger ants. Aphids infected with S. symbiotica showed a reduced population growth, this negative effect being attenuated in the presence of aphid-tending ants. This bacterium also reduced the ant interest in honeydew-producing aphids: they were less likely to visit plants bearing S. symbiotica-infected aphids, they ingested fewer honeydew droplets and they took a longer time before deciding to feed on released honeydew. The bacterium thus makes honeydew less palatable for ant foragers, most probably by altering its composition. This suggests that the free-living S. symbiotica strain may promote a gradual abandonment of infected aphids by ants and ultimately jeopardize the ant-aphid mutualistic relationship. We speculate about bacteria-induced consequences of reduced ant protection against aphid natural enemies and increased host plant defense as due to a potential redirection of ant foraging towards extrafloral nectaries as an alternative sugar resource.
多营养级植物-蚜虫-蚂蚁系统是生态学和进化生物学中广泛研究的模型。在这个系统中，细菌共生体可以循环并可能改变伙伴之间的关系。蚜虫的一种常见共生体，共生沙雷氏菌，表现出多种具有不同生活方式的菌株，其中一种与蚜虫肠道相关，存在于照顾蚜虫的蚂蚁的消化道中。这种自由生活的共生沙雷氏菌菌株会给其蚜虫宿主带来适合度成本，而寄生蜂施加的较低选择压力可以抵消这一成本。在本文中，我们研究了这种与蚜虫肠道相关的细菌是否可能改变豆蚜与黑蚁之间的互利关系。感染共生沙雷氏菌的蚜虫种群增长减少，在有照顾蚜虫的蚂蚁存在时，这种负面影响会减弱。这种细菌还降低了蚂蚁对分泌蜜露的蚜虫的兴趣：它们不太可能访问带有感染共生沙雷氏菌蚜虫的植物，摄入的蜜露滴更少，并且在决定取食分泌出的蜜露之前花费的时间更长。因此，这种细菌很可能通过改变蜜露的成分，使蜜露对蚂蚁觅食者来说不那么可口。这表明自由生活的共生沙雷氏菌菌株可能会促使蚂蚁逐渐抛弃受感染的蚜虫，并最终危及蚂蚁与蚜虫的互利关系。我们推测，由于蚂蚁觅食可能会转向花外蜜腺作为替代糖源，细菌导致蚂蚁对蚜虫天敌的保护减少以及宿主植物防御增加，从而产生相应后果。
