Maternal and paternal effects on fitness correlates in outbred and inbred Atlantic salmon (Salmo salar)

Small populations are at risk of fitness reductions due to inbreeding depression and the loss of within-population genetic diversity. Although this risk can be mitigated by interpopulation outbreeding, any increases in genetic variability may be offset by reductions in fitness attributable to outbreeding depression. Here, we evaluate the risks of inbreeding and outbreeding by quantifying changes in survival and seven other fitness-related traits expressed in early life (e.g., specific growth rate, development time), using three small and neighbouring populations of Atlantic salmon (Salmo salar) reared under a common-garden experimental protocol. After accounting for parental (maternal and paternal) effects on several traits (which differed between pure and F₁ outbred parents), we detected no significant cross type-level differences between inbred and pure (non-inbred, within-population) cross types, outbred and pure cross types, or inbred and outbred cross types. The extent to which parental effects on fitness-related traits might be considered beneficial or detrimental cannot be reliably determined in the absence of information on the adaptive significance of the trait values in the local environment.