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

Abstract

Ecological conditions can influence not only the expression of a phenotype, but also the heritability of a trait. As such, heritable variation for a trait needs to be studied across environments. We have investigated how pathogen challenge affects the expression of MHC genes in embryos of the lake whitefish Coregonus palaea. In order to experimentally separate paternal (i.e. genetic) from maternal and environmental effects, and determine whether and how stress affects the heritable variation for MHC expression, embryos were produced in full-factorial in vitro fertilizations, reared singly, and exposed at 208 degree days (late-eyed stage) to either one of two strains of Pseudomonas fluorescens that differ in their virulence characteristics (one increased mortality, while both delayed hatching time). Gene expression was assessed 48 h postinoculation, and virulence effects of the bacterial infection were monitored until hatching. We found no evidence of MHC class II expression at this stage of development. MHC class I expression was markedly down-regulated in reaction to both pseudomonads. While MHC expression could not be linked to embryo survival, the less the gene was expressed, the earlier the embryos hatched within each treatment group, possibly due to trade-offs between immune function and developmental rate or further factors that affect both hatching timing and MHC expression. We found significant additive genetic variance for MHC class I expression in some treatments. That is, changes in pathogen pressures could induce rapid evolution in MHC class I expression. However, we found no additive genetic variance in reaction norms in our study population.

Declining diversity of egg-associated bacteria during development of naturally spawned whitefish embryos (Coregonus spp.)

“…This decrease suggests a transition of the egg as substrate for bacteria from unselective to more selective throughout the course of embryonic development. Our field study therefore supports conclusions derived from recent laboratory experiments (Clark and Wedekind 2011;Clark et al 2013Clark et al , 2014. Fig.…”

“…Fish embryos seem to complement and specifically increase their immunity through time (Romero and Navarrete 2006). Indeed, towards the end of embryogenesis, important immune genes are expressed (Clark et al 2013) and the immune system can be shown to influence the embryos' resistance to microbial challenges (Ellis 2001;Wedekind et al 2004;Pitcher and Neff 2006). In-vitro fertilized whitefish eggs have been used as models to study genetic and maternal effects during bacterial pathogen incubation (von Siebenthal et al 2009) using full factorial breeding designs ('North Carolina II design', Lynch and Walsh 1998).…”

“…Sensitive life-history responses of the host to changes in its symbiotic microbial community composition have been revealed during specific experimental exposure of whitefish embryos to Pseudomonas fluorescens (von Siebenthal et al 2009;Clark et al 2014) and Saprolegnia ferax (Clark and Wedekind 2011), as well as during non-specific experimental changes of microbial communities on whitefish eggs at varying nutrient broth concentrations . These life-history responses include changes in hatching time (Clark and Wedekind 2011;Clark et al 2013), growth and survival (Clark et al 2014). Some of the effects of host genetics could be linked to the embryo's MHC (major histocompatibility complex), i.e., its allelic diversity (Wedekind et al 2004) and its expression patterns (Clark et al 2013).…”

“…These life-history responses include changes in hatching time (Clark and Wedekind 2011;Clark et al 2013), growth and survival (Clark et al 2014). Some of the effects of host genetics could be linked to the embryo's MHC (major histocompatibility complex), i.e., its allelic diversity (Wedekind et al 2004) and its expression patterns (Clark et al 2013). While maternal effects are important during early developmental stages of the embryo, there is a transition to the importance of paternal effects during later stages of development (Clark et al 2014).…”

Effects of host genetics and environment on egg‐associated microbiotas in brown trout (Salmo trutta)

“…At later developmental stages, the importance of zygotic gene expression becomes crucial for the interaction with associated bacteria (Finn ; Clark et al . , ). Host genetic effects could be revealed for important embryo life‐history traits such as mortality in Oncorhynchus tshawytscha (Aykanat et al .…”