Domestication leads to increased predation susceptibility

Abstract

Domestication involves adapting animals to the human-controlled environment. Genetic changes occurring during the domestication process may manifest themselves in phenotypes that render domesticated animals maladaptive for life in the wild. Domesticated Atlantic salmon frequently interbreed with wild conspecifics, and their offspring display reduced survival in the wild. However, the mechanism(s) contributing to their lower survival in the wild remains a subject of conjecture. Here, we document higher susceptibility to predation by brown trout in fast-growing domesticated salmon, as compared to their slow-growing wild conspecifics, demonstrating that directional selection for increased growth comes at a cost of decreased survival when under the risk of predation, as predicted by the growth/predation risk trade-off. Despite earlier documentation of altered risk-taking behavior, this study demonstrates for the first time that domestication of Atlantic salmon has lead to increased predation susceptibility, and that this consitutes a mechanism underpinning the observed survial differences in the wild.

Figure 1

Map. Study area showing the origin of the domesticated (farmed) strain and the location of the wild strain (river Etne, 59°40′N, 5°56′E) from which gametes were collected and brought to Matre Research station (IMR) where the experimental domesticated, wild and F1 hybrid crosses were produced. Eyed eggs were sent to the NINA Research Station at Ims, where the experiment was conducted during the early juvenile stage.

Figure 2

Initial weights of all genetic groups. Observed body mass of wild, F1 hybrid and domesticated Atlantic salmon families prior to the onset of the experiment (yolk-sac fry). Numbers on the x-axis represent the identity of the different families. Colours illustrate the strains (wild = red, F1 hybrid = green or domesticated = blue). Error bars show the 5–95 percentile (total n = 300).

Figure 3

Body mass at termination of all genetic groups. Specific growth rate (SGR) of wild, F1 hybrid and domesticated Atlantic salmon families in the indoor hatchery tanks with surplus of feed (hatchery control), in the outdoor semi-natural stream channels with competition for natural feed (no predation) and in the semi-natural stream channels with competition for natural feed under the risk of trout predation (predation). Numbers on the x-axis represent the identities of the different families. Colours illustrate the strains (wild = red, F1 hybrid = green or domesticated = blue). Error bars show the 5–95 percentile (total n = 512, 368 and 147 in the hatchery controls, the no predation treatment and the predation treatment, respectively).

Figure 4

Observed survival of all genetic groups. Observed survival (%) of wild, F1 hybrid and domesticated Atlantic salmon families in the indoor hatchery tanks with surplus of feed (hatchery control), in the outdoor semi-natural stream channels with competition for natural feed (no predation) and in the semi-natural stream channels with competition for natural feed under the risk of trout predation (predation). Numbers on the x-axis represents the identity of the different families. Coloured lines illustrate the strains (wild = red, F1 hybrid = green or domesticated = blue) average survival in the respective replicate (total n = 512, 368 and 147 in the hatchery controls, the no predation treatment and the predation treatment, respectively).

Figure 5

Probability of survival for all genetic groups. Estimated probability of survival, against initial fry size (centred, mg), of wild, F1 hybrid and domesticated Atlantic salmon in the indoor hatchery tanks with surplus of feed (hatchery control), in the outdoor semi-natural stream channels with competition for natural feed (no predation) and in the semi-natural channels with competition for natural feed under the risk of trout predation (predation). Dotted lines illustrate uncertainty caused by the random effect of family, maternal identity and replicate.