Causes of Fitness Decline in Hatchery Steelhead from the Hood River

The fitness of hatchery steelhead from the Hood River, Oregon, plummets after only one or two generations through the hatchery.  Yet the cause of this fitness decline remains unknown.  Inadvertent domestication would require very intense selection on highly heritable traits to have such a rapid effect.  Thus, additional explanations such as environmental effects, relaxed natural selection and heritable epigenetic effects have been suggested.  We now have clear evidence from data on individual families that substantial adaptation to captivity, with concomitant tradeoffs in the wild, occurred after a single generation of captive breeding.  That domestication selection explains the fitness decline is good news; if we can identify the traits under selection, it might be possible to modify the captive environment to reduce those selection pressures.  Towards that end we are using Illumina-based RNAseq to quantify genome-wide patterns of gene expression in offspring of wild (W) and first-generation-hatchery (H) steelhead from the Hood River.  The justification is that identifying differentially expressed genes might point us to the traits that were under selection.  Sequencing is currently under way. Pending sufficient progress, we will present results on any loci that appear differentially expressed between fish of different backgrounds, and possible hypotheses about traits involved.