Abstract
BackgroundChanges in wild animal gut microbiotas may influence host health and fitness. While many studies have shown correlations between gut microbiota structure and external factors, few studies demonstrate causal links between environmental variables and microbiota shifts. Here, we use a fully factorial experiment to test the effects of elevated ambient temperature and natural nest parasitism by nest flies (Protocalliphora sialia) on the gut microbiotas of two species of wild birds, the eastern bluebird (Sialia sialis) and the tree swallow (Tachycineta bicolor).ResultsWe find that bacterial communities from the nestlings of each host species show idiosyncratic responses to both heat and parasitism, with gut microbiotas of eastern bluebirds more disrupted by heat and parasitism than those of tree swallows. Thus, we find that eastern bluebirds are unable to maintain stable associations with their gut bacteria in the face of both elevated temperature and parasitism. In contrast, tree swallow gut microbiotas are not significantly impacted by either heat or nest parasitism.ConclusionsOur results suggest that excess heat (e.g., as a result of climate change) may destabilize natural host-parasite-microbiota systems, with the potential to affect host fitness and survival in the Anthropocene.
Highlights
Changes in wild animal gut microbiotas may influence host health and fitness
Composition and diversity of eastern bluebird and tree swallow microbiota The majority of taxa from both eastern bluebirds and tree swallows were represented by seven bacterial phyla
Effects of temperature and nest parasitism on nestling microbiota For alpha diversity, we found that parasitized eastern bluebirds had lower bacterial richness than non-parasitized birds, regardless of heat treatment or life stage
Summary
Changes in wild animal gut microbiotas may influence host health and fitness. Over the past two decades, our knowledge of microbiota patterning as it relates to host evolution (e.g., [8, 9]) and ecology (e.g., [10, 11]) has increased While these studies are useful for identifying important correlations between host intrinsic factors and gut community structure, few studies demonstrate causal links between external forces and changes in the gut microbiota. Understanding how and why gut bacterial communities change in response to specific factors requires careful experimental manipulation In many cases, such causal links have been inferred through the use of germ-free laboratory models that allow for the controlled testing of effector variables. Experimental studies performed on free-ranging wild hosts are even rarer despite a growing body of research suggesting that animal-associated microbiotas may inform wildlife health and conservation [13,14,15]
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