Behavioural variation among divergent European and North American farmed and wild Atlantic salmon (Salmo salar) populations

Abstract

Animals often display consistent differences in behaviours across situations and contexts. However, little is known about how behavioural traits might vary in a context-dependent manner, with selection favouring correlated sets of behaviours in particular types of environments. Comparative studies of behavioural trait differences and associations among different populations can provide valuable insights into how this might operate. For example, farmed Atlantic salmon (Salmo salar) often escape into the wild and may produce hybrid and feral offspring that interact with wild conspecifics. Interactions between these offspring types may be mediated by differences in behaviour reflective of their different selective histories, which may in turn affect their relative fitness. In Newfoundland, Canada, site-specific permission has been granted to farm a strain of European origin (EO) salmon in addition to the current North American (NA) Saint John River strain. However, because these two farmed strains are genetically divergent, there is concern that behavioural trait differences will exist that affect interactions with native wild populations. We thus designed a common-garden experiment to compare the behaviour of individual fish from NA and EO farm strains in four different contexts (exploration, response to a novel object, boldness under predation risk and aggression) relative to that of wild fish and hybrid conspecifics. NA and EO farm fish did not differ in their behaviour (P > 0.05), but both were more explorative (P < 0.001 in 2016; P < 0.05 in 2017), responsive to a novel object (P < 0.05, both years), bold (P < 0.05, both years), and aggressive (P < 0.001, both years) than wild fish and related hybrids. We found the presence of behavioural correlations in some circumstances suggesting that behavioural syndromes covary consistently with aspects of the selective environment. Overall, these results suggest that the variation in the behavioural traits studied among divergent EO and NA farmed and NA wild populations largely reflect domestication selection, and less so the geographic and ancestral relationships.