Predators select against high growth rates and risk–taking behaviour in domestic trout populations

Abstract

Domesticated (farm) salmonid fishes display an increased willingness to accept risk while foraging, and achieve high growth rates not observed in nature. Theory predicts that elevated growth rates in domestic salmonids will result in greater risk-taking to access abundant food, but low survival in the presence of predators. In replicated whole-lake experiments, we observed that domestic trout (selected for high growth rates) took greater risks while foraging and grew faster than a wild strain. However, survival consequences for greater growth rates depended upon the predation environment. Domestic trout experienced greater survival when risk was low, but lower survival when risk was high. This suggests that animals with high intrinsic growth rates are selected against in populations with abundant predators, explaining the absence of such phenotypes in nature. This is, to our knowledge, the first large-scale field experiment to directly test this theory and simultaneously quantify the initial invasibility of domestic salmonid strains that escape into the wild from aquaculture operations, and the ecological conditions affecting their survival.

Behavioural mediation of the costs and benefits of fast growth in a marine fish

“…This is often difficult in behavioural studies, which may account for the relative paucity of data. Although there are few studies, evidence for growth-mortality trade-offs has been documented in a wide variety of taxa including damselflies (Stoks et al 2005), rainbow trout (Biro et al 2004(Biro et al , 2006 and house mice, Mus musculus (Biro & Stamps 2008). However, our study shows that correlations among behavioural and growth traits do not necessarily provide evidence of growth-mortality trade-offs and that spatial and temporal variation in the direction of growth-selective processes might be sufficient to produce both consistent variability in growth patterns among individuals and submaximal growth rates of populations.…”

“…This occurred because fast-growing fish were more likely to use habitats that were more productive in terms of food resources, but placed the fast-growing fish at greater risk of predation than the habitats used by slow-growing individuals (Biro et al 2006). Such trade-offs are thought to explain the evolution of submaximal growth rates in wild populations of fishes (Biro et al 2004(Biro et al , 2006 and other animals (Stoks et al 2005).…”

“…As all animals are prey, at least during their early life history stages, greater foraging effort can increase the visibility of prey to predators with a concomitant increase in the probability of mortality. Evidence for the role of behaviour comes from a variety of sources (reviewed in Stamps 2007;Biro & Stamps 2008), including recent studies in lake systems that have shown that fast-growing rainbow trout, Oncorhynchus mykiss, that had high foraging rates were preferentially removed by predators (Biro et al 2004(Biro et al , 2006. This occurred because fast-growing fish were more likely to use habitats that were more productive in terms of food resources, but placed the fast-growing fish at greater risk of predation than the habitats used by slow-growing individuals (Biro et al 2006).…”

An evolutionary process that assembles phenotypes through space rather than through time

“…For example, some taxa are transported by attaching themselves to other species (e.g., burrs, ticks), or in the digestive tract [e.g., seeds and fruits (32)], or in vehicles [stowaways in cars and boats (33)(34)(35)]. Spatial sorting also may favor bold, risk-taking behaviors (36) or individuals that readily handle the stress of intense physical activity and novel environments. Our first human ancestors to cross the oceans and invade new lands probably were highly nonrandom in dispersal-relevant traits as well as in behavioral flexibility and within-group cooperation (5, 37).…”

Human-induced evolution caused by unnatural selection through harvest of wild animals

“…Some authors have reported differences in angling vulnerability between domestic and wild strains of fish (33,34). Biro and Stamps (35) argued that behaviors such as boldness and activity, which are often correlated with growth rate, are likely to affect productivity and could respond to selective mortality.…”