Abstract
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 F1hybrid groups. Significant differences (p < 0.001) were observed in development time, survival, growth and energy conversion among farmed, F1hybrid and wild populations. While pure populations (farmed and wild) differed amongst one another, we found few differences in fitness-related traits between F1hybrids and their maternal wild/farmed strains. This suggests that the early-life fitness consequences of F1hybridization 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 F1hybrids are generated by the geographic and ancestral relationship and maternal effects of egg size and less so by domestication selection.
Highlights
It is increasingly clear that interactions between domesticated and wild organisms have the potential to lead to negative effects on wild populations, and as such, are of concern (Rhymer & Simberloff 1996, Fleming & Petersson 2001, Ellstrand 2003, Laikre et al 2010, Frankham et al 2011, Glover et al 2017)
Farm (EO) females were longer than Farm (NA) females in both years, while both farm types were longer than both wild (Wild [NAEO] and Wild [not differ from Farm (NA)]) types
Despite Farm (EO) females of both cohorts being of similar sizes, egg size of Farm15 (EO) was smaller than that of Farm16 (EO) and did not differ from Farm (NA)
Summary
It is increasingly clear that interactions between domesticated and wild organisms have the potential to lead to negative effects on wild populations, and as such, are of concern (Rhymer & Simberloff 1996, Fleming & Petersson 2001, Ellstrand 2003, Laikre et al 2010, Frankham et al 2011, Glover et al 2017). Directed selection for economically important traits (e.g. faster growth, delayed maturation, disease resistance) in combination with unintentional and relaxed selection on nontarget traits (e.g. aggression, risk aversion, feeding behaviour) can lead to rapid genetic changes in farm strains (Einum & Fleming 1997, Fleming & Einum 1997, Huntingford & Adams 2005, Houde et al 2010a,b, Debes & Hutchings 2014, Perry et al 2019, Solberg et al 2020) This has, for example, resulted in farmed salmon displaying a growth rate that is over 2- to 3-fold higher than that of wild conspecifics reared under identical culture environments (Glover et al 2018). Likewise, offspring of escaped farmed and hybrid fish may compete with wild salmon for food, habitat and other resources, thereby potentially altering the genetics and depressing the numbers and productivity of wild salmon (Fleming et al 2000, McGinnity et al 2003, Sundt-Hansen et al 2015, Robertsen et al 2019, Bradbury et al 2020)
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