Endocrine and immune responses of larval amphibians to trematode exposure
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In nature, multiple waves of exposure to the same parasite are likely, making it important to understand how initial exposure or infection affects subsequent host infections, including the underlying physiological pathways involved. We tested whether experimental exposure to trematodes (Echinostoma trivolvis or Ribeiroia ondatrae) affected the stress hormone corticosterone (known to influence immunocompetence) in larvae representing five anuran species. We also examined the leukocyte profiles of seven host species after single exposure to R. ondatrae (including four species at multiple time points) and determined if parasite success differed between individuals given one or two challenges. We found strong interspecific variation among anuran species in their corticosterone levels and leukocyte profiles, and fewer R. ondatrae established in tadpoles previously challenged, consistent with defense “priming.” However, exposure to either trematode had only weak effects on our measured responses. Tadpoles exposed to E. trivolvis had decreased corticosterone levels relative to controls, whereas those exposed to R. ondatrae exhibited no change. Similarly, R. ondatrae exposure did not lead to appreciable changes in host leukocyte profiles, even after multiple challenges. Prior exposure thus influenced host susceptibility to trematodes, but was not obviously associated with shifts in leukocyte counts or corticosterone, in contrast to work with microparasites.
KeywordsDisease Stress Hormone Immunity Glucocorticoids Amphibian Parasite
We thank B. LaFonte and A. Sangiolo for assistance with experimental infections, tissue collection, and cell counts, B. Ardelli for methodological assistance, as well as J. Bowerman, J. Rohr, M. Venesky, T. Raffel, and J. Mihaljevic for providing amphibian eggs. Critical feedback useful in developing the manuscript was provided by C. Peletier and I. M. Neegan.
This research was supported by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and Canada Foundation for Innovation (JK), the National Science Foundation and National Institutes for Health (PTJJ), a fellowship from the David and Lucile Packard Foundation (PTJJ), a Rubicon fellowship from the Netherlands Organization for Scientific Research (BJH), and a NSERC Undergraduate Student Research Award (USRA) to TMYU.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed, and all procedures performed were in accordance with the ethical standards of the institution at which the studies were conducted. This article does not contain any studies with human participants performed by any of the authors.
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