Pathogen-induced hatching and population-specific life-history response to waterborne cues in brown trout (Salmo trutta)
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Hatching is an important niche shift, and embryos in a wide range of taxa can either accelerate or delay this life-history switch in order to avoid stage-specific risks. Such behavior can occur in response to stress itself and to chemical cues that allow anticipation of stress. We studied the genetic organization of this phenotypic plasticity and tested whether there are differences among populations and across environments in order to learn more about the evolutionary potential of stress-induced hatching. As a study species, we chose the brown trout (Salmo trutta; Salmonidae). Gametes were collected from five natural populations (within one river network) and used for full-factorial in vitro fertilizations. The resulting embryos were either directly infected with Pseudomonas fluorescens or were exposed to waterborne cues from P. fluorescens-infected conspecifics. We found that direct inoculation with P. fluorescens increased embryonic mortality and induced hatching in all host populations. Exposure to waterborne cues revealed population-specific responses. We found significant additive genetic variation for hatching time, and genetic variation in trait plasticity. In conclusion, hatching is induced in response to infection and can be affected by waterborne cues of infection, but populations and families differ in their reaction to the latter.
KeywordsAdditive genetic variation Fish embryo Induced hatching Niche shift Phenotypic plasticity Reaction norm Salmonid
We thank the members of the Fisheries Inspectorate Bern for their support, and especially U. Gutmann, J. Gutruf, C. Küng, M. Schmid, and H. Walther for permissions, for catching and taking care of the adult fish, and for assistance during the preparations of the in vitro fertilizations. Thanks also to G. Brazzola, P. Christe, M. dos Santos, S. Einum, N. Perrin, A. Ross-Gillespie, R. Stelkens, C. van Oosterhout, and L. Wilkins for help in the field and/or useful discussions, T. Bakker, K. Warkentin and two reviewers for comments on the manuscript, and the Swiss National Science Foundation and the Foundation Maison de la Rivière for financial support.
Permissions for handling embryos were granted by the local authority (i.e., the Fishery Inspectorate of the Bern canton). The manipulations of the adults were part of the yearly hatchery program of the Bern canton. Experimental manipulations on embryos were performed prior to yolk sac absorption. All manipulations comply with the current law of the country in which they were performed (Switzerland).
Conflict of interest
The authors declare that they have no conflict of interest.
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