Maternal allocation of carotenoids increases tolerance to bacterial infection in brown trout
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Life-history theory predicts that iteroparous females allocate their resources differently among different breeding seasons depending on their residual reproductive value. In iteroparous salmonids there is typically much variation in egg size, egg number, and in the compounds that females allocate to their clutch. These compounds include various carotenoids whose functions are not sufficiently understood yet. We sampled 37 female and 35 male brown trout from natural streams, collected their gametes for in vitro fertilizations, experimentally produced 185 families in 7 full-factorial breeding blocks, raised the developing embryos singly (n = 2960), and either sham-treated or infected them with Pseudomonas fluorescens. We used female redness (as a measure of carotenoids stored in the skin) and their allocation of carotenoids to clutches to infer maternal strategies. Astaxanthin contents largely determined egg colour. Neither egg weight nor female size was correlated with the content of this carotenoid. However, astaxanthin content was positively correlated with larval growth and with tolerance against P. fluorescens. There was a negative correlation between female skin redness and the carotenoid content of their eggs. Although higher astaxanthin contents in the eggs were associated with an improvement of early fitness-related traits, some females appeared not to maximally support their current offspring as revealed by the negative correlation between female red skin colouration and egg carotenoid content. This correlation was not explained by female size and supports the prediction of a maternal trade-off between current and future reproduction.
KeywordsTolerance to infection Bacterial infection Pseudomonas fluorescens Salmonidae Astaxanthin
We are grateful to L. Benaroyo, I. Castro, P. Christe, P. Engel, G. Glauser, D. Maitre, Y. Poirier, C. Primmer, T. Reusch, A. Uppal, A. Vallat, J. van der Meer and D. Zeugin for assistance in the field and/or discussion. We thank B. Bracher and U. Gutmann from the Fishery Inspectorate Bern for catching and taking care of the adult fish, C. Küng for permissions, R. Alford and two reviewers for helpful comments, and the Swiss National Science Foundation for funding. This study complied with the relevant ethical regulations imposed by the University of Lausanne, the canton, and the country in which it was carried out.
Author contribution statement
LW, LMC and CW designed the project. LW, LMC, DN and CW sampled the fish, did the in vitro fertilizations and distributed the eggs to 24-well plates. All further manipulations and bacterial infections on the embryos were done by LW and LMC. MH measured embryo length and growth. LM, DO and VV carried out the chemical analyses, DN wrote the macros that were used by LMC to analyse the skin colouration. LW, LMC and CW performed the statistical analyses and wrote the first version of the manuscript that was then critically revised by all other authors.
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