Consumption of carotenoids not increased by bacterial infection in brown trout embryos (<i>Salmo trutta</i>)

<div><p>Carotenoids are organic pigment molecules that play important roles in signalling, control of oxidative stress, and immunity. Fish allocate carotenoids to their eggs, which gives them the typical yellow to red colouration and supports their resistance against microbial infections. However, it is still unclear whether carotenoids act mainly as a shield against infection or are used up during the embryos’ immune defence. We investigated this question with experimental families produced from wild-caught brown trout (<i>Salmo trutta</i>). Singly raised embryos were either exposed to the bacterial pathogen <i>Pseudomonas fluorescens</i> or sham-treated at one of two stages during their development. A previous study on these experimental families reported positive effects of egg carotenoids on embryo growth and resistance against the infection. Here, we quantified carotenoid consumption, i.e. the active metabolization of carotenoids into compounds that are not other carotenoid types, in these infected and sham-infected maternal sib groups. We found that carotenoid contents mostly decreased during embryogenesis. However, these decreases were neither linked to the virulence induced by the pathogen nor dependent on the time point of infection. We conclude that egg carotenoids are not significantly used up by the embryos’ immune defence.</p></div

Proportional changes in carotenoid content relative to early fitness-related traits.

<p>Embryo hatching time (a–c) and larval growth (d–f) are shown for change in astaxanthin, lutein, and zeaxanthin. Changes in carotenoid contents are given for sham-treated controls (circles and solid lines) and PF treated samples (triangles and dashed lines). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198834#pone.0198834.t003" target="_blank">Table 3</a> for statistics.</p

The relationship between carotenoid content in eggs and in embryos across maternal half sib families.

<p>Astaxanthin, lutein and zeaxanthin contents were measured before fertilization (“content in eggs”; data from Wilkins et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198834#pone.0198834.ref024" target="_blank">24</a>]) and at a late-eyed development stage (“content in embryos”) in sham-treated controls (circles and solid regression lines) and after exposure to <i>P</i>. <i>fluorescens</i> (PF; triangles and dashed regression lines). Panels a-c show the relationship between carotenoid contents at the two different time points; and panels d-f the absolute changes in carotenoids relative to carotenoid contents before fertilization. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198834#pone.0198834.t001" target="_blank">Table 1</a> for non-parametric statistics (the regressions lines are shown for illustration).</p

The effects of treatment, time point of infection/sampling and their interaction on (a) proportional changes in astaxanthin, (b) lutein and (c) zeaxanthin tested with a multivariate analysis of variance (MANOVA).

<p>Proportional changes are the difference between carotenoid contents in eggs and embryos divided by the carotenoid content in eggs.</p

Spearman’s rank correlation (<i>rho</i>) between carotenoid measurements in the sham-treated controls and in <i>Pseudomonas fluorescens</i> (PF) treated embryos.

<p>Spearman’s rank correlation (<i>rho</i>) between carotenoid measurements in the sham-treated controls and in <i>Pseudomonas fluorescens</i> (PF) treated embryos.</p

Consumption of carotenoids not increased by bacterial infection in brown trout embryos (<i>Salmo trutta</i>) - Table 3

<p>The effects of treatment, proportional change in carotenoid contents on (a) hatching time, (b) hatchling length, (c) yolk sac volume at hatching, and (d) larval growth.</p

R-script_Oecologia_Wilkins_et_al_2017

R script that was used for all analyses and figures

Parents_sheet_230616

Input data for statistical analyses with all parental characteristics (e.g., skin colouration, carotenoid measures in unfertilized eggs, egg sizes)

data12_carotenoids_230616

Embryo characteristics for statistical analysis after individual embryos were transferred from 24-well to 12-well plates (e.g., this includes only survivors and their size and growth measures)

data24_carotenoids_230616

Embryo characteristics for statistical analysis before individual embryos were transferred from 24-well to 12-well plates (e.g., survival, origin, plate position and ID)