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bioRxiv · 10.1101/2023.10.15.562412

Mutualist-Provided Resources Increase Susceptibility to Parasites

Yi, E.·Meng, N.·Wood, C. W.
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Abstract

Background and AimsO_LIMutualistic microbes often increase their hosts susceptibility to parasite infection, but the mechanism underlying this pattern remains unknown. C_LIO_LIWe tested two competing hypotheses to identify the cause of this phenomenon. C_LIO_LIFirst, mutualist-provided resources could attract antagonists by making hosts more resource-rich. C_LIO_LISecond, mutualism establishment itself might increase host vulnerability to antagonists by enabling antagonists to exploit host defenses or immune systems, which are often downregulated during mutualism establishment. C_LI MethodsO_LITo test which mechanism underlies increased parasite susceptibility, we experimentally decoupled mutualism establishment and mutualist-provided resources in the legume-rhizobia mutualism. C_LIO_LIWe measured parasite load on Medicago truncatula plants infected with root-knot nematodes in a full-factorial design, in which we independently manipulated rhizobia inoculation (mutualism establishment) and nitrogen availability (mutualist-provided resources). C_LI Key ResultsO_LIIncreased nitrogen availability increased parasite infection. However, its effect was non-linear and was not explained by nitrogen assimilation into plant tissues, indicating that this effect is not driven by parasite attraction to resource-rich hosts. C_LIO_LIWe found little effect of mutualism establishment on susceptibility, as neither rhizobia inoculation nor nodulation without nitrogen fixation significantly increased parasite infection. C_LI ConclusionsO_LIOur results suggest that mutualist-provided resources are an important driver of indirect ecological costs of mutualism, although the mechanism linking mutualist-provided resources and susceptibility to infection remains unknown. C_LI

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Yi, E., Meng, N., Wood, C. W.. 2023-10-18. Mutualist-Provided Resources Increase Susceptibility to Parasites. https://doi.org/10.1101/2023.10.15.562412

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