Infected connections: Unraveling the impact of a bacterial symbiont on ant-aphid partnership
(2025) PLoS One — Vol. 20, n° 6, p. e0326875 (2025)
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- Authors
Jossart, Margaux 
- Abstract
- 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.
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Jossart, M., Hance, T., & Detrain, C. (2025). Infected connections: Unraveling the impact of a bacterial symbiont on ant-aphid partnership. PLoS One, 20(6), e0326875. https://doi.org/10.1371/journal.pone.0326875 (Original work published 2025)