Do Host‐associated Gut Microbiota Mediate the Effect of an Herbicide on Disease Risk in Frogs?

Sarah A. Knutie, Caitlin R. Gabor, Kevin D. Kohl, Jason R. Rohr

Research output: Contribution to journalArticlepeer-review

Abstract

<p> <ol> <li> Environmental stressors, such as pollutants, can increase disease risk in wildlife. For example, the herbicide atrazine affects host defences (e.g. resistance and tolerance) of the amphibian chytrid fungus <em> Batrachochytrium dendrobatidis </em> ( <em> Bd </em> ), but the mechanisms for these associations are not entirely clear. Given that pollutants can alter the gut microbiota of hosts, which in turn can affect their health and immune systems, one potential mechanism by which pollutants could increase infection risk is by influencing host&hyphen;associated microbiota. </li> <li> Here, we test whether early&hyphen;life exposure to the estimated environmental concentration (EEC; 200 &mu;g/L) of atrazine affects the gut bacterial composition of Cuban tree frog ( <em> Osteopilus septentrionalis </em> ) tadpoles and adults and whether any atrazine&hyphen;induced change in community composition might affect host defences against <em> Bd </em> . We also determine whether early&hyphen;life changes in the stress hormone corticosterone affect gut microbiota by experimentally inhibiting corticosterone synthesis with metyrapone. </li> <li> With the exception of changing the relative abundances of two bacterial genera in adulthood, atrazine did not affect gut bacterial diversity or community composition of tadpoles (in vivo or in vitro) or adults. Metyrapone did not significantly affect bacterial diversity of tadpoles, but significantly increased bacterial diversity of adults. </li> <li> Gut bacterial diversity during <em> Bd </em> exposure did not predict host tolerance or resistance to <em> Bd </em> intensity in tadpoles or adults. However, early&hyphen;life bacterial diversity negatively predicted <em> Bd </em> intensity as adult frogs. Specifically, <em> Bd </em> intensity as adults was associated negatively with the relative abundance of phylum Fusobacteria in the guts of tadpoles. </li> <li> Our results suggest that the effect of atrazine on <em> Bd </em> infection risk is not mediated by host&hyphen;associated microbiota because atrazine does not affect microbiota of tadpoles or adults. However, host&hyphen;associated microbes seem important in host resistance to <em> Bd </em> because the early&hyphen;life microbiota, during immune system development, predicted later&hyphen;life infection risk with <em> Bd </em> . Overall, our study suggests that increasing gut bacterial diversity and relative abundances of Fusobacteria might have lasting positive effects on amphibian health. </li> </ol></p>
Original languageAmerican English
JournalJournal of Animal Ecology
Volume87
DOIs
StatePublished - Mar 1 2018

Keywords

  • atrazine
  • bacteria
  • Batrachochytrium dendrobatidis
  • chytrid fungus
  • corticosterone
  • Fusobacteria
  • Osteopilus septentrionalis
  • stress

Disciplines

  • Biology
  • Integrative Biology

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