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Greater knowledge of how host–microbiome interactions vary with anthropogenic environmental change and influence pathogenic infections is needed to better understand stress-mediated disease outcomes. We investigated how increasing salinization in freshwaters (e.g. due to road de-icing salt runoff) and associated increases in growth of nutritional algae influenced gut bacterial assembly, host physiology and responses to ranavirus exposure in larval wood frogs (Rana sylvatica). Elevating salinity and supplementing a basic larval diet with algae increased larval growth and also increased ranavirus loads. However, larvae given algae did not exhibit elevated kidney corticosterone levels, accelerated development or weight loss post-infection, whereas larvae fed a basic diet did. Thus, algal supplementation reversed a potentially maladaptive stress response to infection observed in prior studies in this system. Algae supplementation also reduced gut bacterial diversity. Notably, we observed higher relative abundances of Firmicutes in treatments with algae—a pattern consistent with increased growth and fat deposition in mammals—that may contribute to the diminished stress responses to infection via regulation of host metabolism and endocrine function. Our study informs mechanistic hypotheses about the role of microbiome mediation of host responses to infection that can be tested in future experiments in this host–pathogen system
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Tradeoffs between elemental homeostasis and growth govern freshwater phytoplankton responses to salinization
Abstract Anthropogenic salinization resulting from road salt application can degrade aquatic environments by altering the structure and function of phytoplankton communities, ultimately reducing flows of resources through aquatic food webs. However, physiological mechanisms underlying taxon‐specific responses to salinization are often poorly linked to higher‐order ecosystem dynamics, limiting our ability to predict community responses to salinization. To this end, we tested hypotheses derived from Subsidy‐Stress and Ecological Stoichiometry theory by growing two cosmopolitan genera,Dolichospermum(prokaryotic, cyanobacteria) andScenedesmus(eukaryotic, green algae), across NaCl gradients and contrasting differences in their growth rates, degree of Na homeostasis, and cellular C : N : P ratios. We found mixed support for the subsidy‐stress hypothesis, with only stress responses observed for both species. Instead, growth declines appeared to be linked to stoichiometric tradeoffs between growth and homeostatic regulation, with stronger homeostatic Na regulation coinciding with a greater reduction inScenedesmusgrowth rates and higher variation in their stoichiometric C : N : P ratios across NaCl gradients. Nonhomeostatic Na regulation allowedDolichospermumto sustain higher growth rates, which appeared to constrain variation in their stoichiometric C : N : P ratios along with their stronger physiological regulation of intracellular P storage molecule production. Differences in phytoplankton growth responses were consistent with stoichiometric theory and field observations documenting shifts from green algae to cyanobacteria in response to freshwater salinization. Our results suggest that these shifts could take place below existing North American chronic threshold limits, resulting in decreased production at higher trophic levels by reducing phytoplankton biomass production rates and inducing nutritional stress in consumers.
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- PAR ID:
- 10629796
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 70
- Issue:
- 8
- ISSN:
- 0024-3590
- Format(s):
- Medium: X Size: p. 2026-2038
- Size(s):
- p. 2026-2038
- Sponsoring Org:
- National Science Foundation
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