Divergent immunity and energetic programs in the gills of migratory and resident Oncorhynchus mykiss

Abstract

Divergent life history strategies occur in steelhead or rainbow trout Oncorhynchus mykiss, and many populations produce both migrant (anadromous fish that move to the ocean after rearing) and resident (do not migrate and remain in fresh water) individuals. Mechanisms leading to each type are only partially understood; while the general tendency of a population is heritable, individual tendency may be plastic, influenced by local environment. Steelhead hatchery programmes aim to mitigate losses in wild stocks by producing trout that will migrate to the ocean and not compete with wild trout for limited freshwater resources. To increase our understanding of gill function in these migratory or resident phenotypes, here we compare gill transcriptome profiles of hatchery-released fish either at the release site (residents) or five river kilometres downstream while still in full fresh water (migrants). To test whether any of these genes can be used as predictive markers for smoltification, we compared these genes between migrant-like and undifferentiated trout while still in the hatchery in a common environment (prerelease). Results confirmed the gradual process of smoltification, and the importance of energetics, gill remodelling and ion transport capacity for migrants. Additionally, residents overexpressed transcripts involved in antiviral defences, potentially for immune surveillance via dendritic cells in the gills. The best smoltification marker candidate was protein s100a4, expression of which was highly correlated with Na(+) , K(+) ATPase (NKA) activity and smolt-like morphology in pre- and postrelease trout gills.

Capture severity, infectious disease processes and sex influence post-release mortality of sockeye salmon bycatch

“…Despite the comprehensiveness of our screening approach, an unknown viral agent may have been present within these fish. Alternatively, expression patterns may be a relic of cleared, latent, or anticipated viral infection: freshwater-resident Oncorhychus mykiss have shown overexpression of antiviral transcripts relative to out-migrating smolts, suggesting a modulation of immune defences towards viral pathogens in freshwater (Altizer et al ., 2011; Sutherland et al ., 2014). Enhanced expression of immune transcripts, including both cellular and humoral responses, have been documented in sockeye salmon during the spawning migration, corresponding to shifts in environmental and biotic factors (Evans et al ., 2011).…”

Ontogenetic changes in embryonic and brain gene expression in progeny produced from migratory and residentOncorhynchus mykiss

“…; Sutherland et al . ); however, the influence of differential expression on the brain is unknown. Genomic regions of interest include chromosomes OMY12 and OMY14, which appear to be hot spots for migration‐related QTL in this population (Hecht et al .…”

“…; Robertson & McCormick ; Sutherland et al . ) and gene network analysis (Filteau et al . ) have demonstrated differential gene expression between fish with different life histories.…”

Unintentional selection, unanticipated insights: introductions, stocking and the evolutionary ecology of fishes

“…mykiss . Sutherland et al () compared gene expression in the gills of migrating and non‐migrating hatchery‐reared individuals. They found that migrants (presumably in preparation for smoltification) overexpressed gene transcripts related to energy generation (oxygen‐transport proteins and mitochondrion components) and ion transport.…”

“…Fish and Wildlife Service, has contributed significantly to recent work on the genomic underpinning of differences in gill function between migratory and non-migratory O. mykiss. Sutherland et al (2014) compared gene expression in the gills of migrating and non-migrating hatchery-reared individuals. They found that migrants (presumably in preparation for smoltification) overexpressed gene transcripts related to energy generation (oxygen-transport proteins and mitochondrion components) and ion transport.…”