Early-life fitness trait variation among divergent European and North American farmed and Newfoundland wild Atlantic salmon populations

It has long been clear that interbreeding between domesticated and wild Atlantic salmon can lead to negative fitness consequences for native populations. Few studies, however, have examined these consequences at critical early life stages, particularly in the context of distinct geographical and ancestral relationships among populations as well domestication selection. In Newfoundland (NF), Canada, while the majority of aquaculture sites use the North American (NA) Saint John River strain, site-specific permission has been granted to farm a strain of European origin (EO). We designed a common-garden experiment to compare fitness-related traits (e.g. development time, survival, size and growth) at different early-life stages (eye development, hatch and yolk absorption) among EO and NA farmed, 2 NF wild and F₁ hybrid groups. Significant differences (p < 0.001) were observed in development time, survival, growth and energy conversion among farmed, F₁ hybrid and wild populations. While pure populations (farmed and wild) differed amongst one another, we found few differences in fitness-related traits between F₁ hybrids and their maternal wild/farmed strains. This suggests that the early-life fitness consequences of F₁ hybridization will be largely manifested through the action of maternal effects. Additionally, significant associations between the maternal effects of egg size and alevin development time, size, survival, growth, condition and energy conversion efficiency were found. These findings suggest that early-life fitness-related trait differences among farmed, wild and their related F₁ hybrids are generated by the geographic and ancestral relationship and maternal effects of egg size and less so by domestication selection.