Parental Influences on Pathogen Resistance in Brown Trout Embryos and Effects of Outcrossing within a River Network

Abstract

Phenotypic plasticity can increase tolerance to heterogeneous environments but the elevations and slopes of reaction norms are often population specific. Disruption of locally adapted reaction norms through outcrossing can lower individual viability. Here, we sampled five genetically distinct populations of brown trout (Salmo trutta) from within a river network, crossed them in a full-factorial design, and challenged the embryos with the opportunistic pathogen Pseudomonas fluorescens. By virtue of our design, we were able to disentangle effects of genetic crossing distance from sire and dam effects on early life-history traits. While pathogen infection did not increase mortality, it was associated with delayed hatching of smaller larvae with reduced yolk sac reserves. We found no evidence of a relationship between genetic distance (W, FST) and the expression of early-life history traits. Moreover, hybrids did not differ in phenotypic means or reaction norms in comparison to offspring from within-population crosses. Heritable variation in early life-history traits was found to remain stable across the control and pathogen environments. Our findings show that outcrossing within a rather narrow geographical scale can have neutral effects on F1 hybrid viability at the embryonic stage, i.e. at a stage when environmental and genetic effects on phenotypes are usually large.

Outbreeding Depression in Atlantic Salmon Revealed by Hypoxic Stress During Embryonic Development

“…Darwish and Hutchings (2009) detected worse performances of hybrids in thermal reaction norms for several developmental and morphological traits but not for survival. In contrast, Clark et al (2013) did not detect any effect of outbreeding in reaction norms to a bacterial challenge in brown trout (Salmo trutta) embryos. The occurrence of outbreeding depression only under stressful conditions may have important consequences for interpopulation hybrids under natural settings.…”

“…Nevertheless, the impact of environmental stress on consequences of outbreeding in wild populations of these taxa has not been comprehensively explored yet (Fraser et al 2008;Darwish and Hutchings 2009;Fraser et al 2010a, b;Debes et al 2012;Solberg et al 2012Solberg et al , 2013. Embryonic development constitutes a critical life stage in salmonids during which mortality can be high in relation to various environmental stressors including high temperature (Ojanguren et al 1999;Haugen and Vollestad 2000;Jensen et al 2008), pathogens (Jacob et al 2010;Clark et al 2013) or low levels of dissolved oxygen (Dumas et al 2007). In addition to high mortality, oxygen stress (i.e.…”

MHC class I expression dependent on bacterial infection and parental factors in whitefish embryos (Salmonidae)

“…) and a ‘low virulence strain’ (‘PF2’) that had been isolated from whitefish gills and had been observed to cause little embryonic mortality, but to delay hatching of smaller larvae in both brown trout (Clark et al . ) and whitefish (E. Clark, unpublished data). PF2 had been collected by swabbing gills with Amies agar gel transport swabs, followed by elution of bacteria into phosphate‐buffered saline.…”

“…; Clark et al . ). If the impact of environmental change on trait heritability is likely dependent on both the stressor and trait at hand, and perhaps even varies among types of genes, evaluation on a case‐by‐case basis seems necessary.…”

“…), and other isolates causing sublethal effects, that is, delayed hatching and reduced growth (Clark et al . ). We assessed whether challenge with both ‘high’ (i.e.…”