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ABSTRACT Microbial symbionts play crucial roles in host nutrition, defence, and detoxification. However, host‐symbiont interactions are context‐dependent, and environmental stressors can disrupt these benefits. Diverse hosts, including corals, insects and leguminous plants, have been shown to suffer under thermal stress due to the negative impact of high temperatures on their symbionts. This failure is often linked to a symbiont's poor transcriptional regulation of heat shock genes, causing vulnerability at high temperatures. In the bug‐Caballeroniamodel system, insect performance at elevated temperatures varies based on the hosted symbiont species. Here, we explore the underlying mechanisms that drive this variation using comparative metatranscriptomics and two symbionts with contrasting host outcomes at high temperatures. We evaluated both host and symbiont transcriptional responses to elevated temperature, testing the hypothesis that symbionts conferring improved host outcomes at high temperatures will have more upregulated heat shock genes under thermal stress compared to those conferring worse host outcomes. Our findings reveal that host transcription did not change with different symbionts but rather only at different temperatures. Furthermore, symbionts had distinct gene expression profiles across temperatures. At 36°C, the heat‐resistant symbiont not only increased expression of heat shock genes but surprisingly upregulated flagellar genes, which are normally turned off during symbiosis. This suggests that symbiont, not host, transcription underlies host benefits at low versus high temperatures and ultimately furthers our understanding of context dependence in the outcomes of symbiotic associations.
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Microbial symbionts buffer hosts from the demographic costs of environmental stochasticity
Abstract Species' persistence in increasingly variable climates will depend on resilience against the fitness costs of environmental stochasticity. Most organisms host microbiota that shield against stressors. Here, we test the hypothesis that, by limiting exposure to temporally variable stressors, microbial symbionts reduce hosts' demographic variance. We parameterized stochastic population models using data from a 14‐year symbiont‐removal experiment including seven grass species that hostEpichloëfungal endophytes. Results provide novel evidence that symbiotic benefits arise not only through improved mean fitness, but also through dampened inter‐annual variance. Hosts with “fast” life‐history traits benefited most from symbiont‐mediated demographic buffering. Under current climate conditions, contributions of demographic buffering were modest compared to benefits to mean fitness. However, simulations of increased stochasticity amplified benefits of demographic buffering and made it the more important pathway of host–symbiont mutualism. Microbial‐mediated variance buffering is likely an important, yet cryptic, mechanism of resilience in an increasingly variable world.
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- PAR ID:
- 10520110
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 27
- Issue:
- 5
- ISSN:
- 1461-023X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/ele.14438
