Effects of domestication on parr maturity, growth, and vulnerability to predation in Atlantic salmon

Abstract

Domestication can change fitness-related traits. We investigated domestication-induced changes in fitness-related traits in Atlantic salmon (Salmo salar) under naturally enriched laboratory conditions with and without threat of predation. Selection in two strains for rapid growth for three and five generations resulted in two and three times larger sizes of underyearling parr relative to their wild ancestor. An initially larger size and ability to outgrow prey size more rapidly resulted in lower size-selective predation mortality for domesticated individuals. Growth under threat of predation was only reduced for wild individuals, suggesting that domestication co-selects for predator-related stress resistance. Size-adjusted male parr maturation probability was 34% in the wild strain, but significantly reduced to 10% and 7% after three and five generations of domestication, respectively. Together, freshwater-stage-specific survival for individuals with a domesticated background relative to individuals with a wild genetic background might be higher in the presence of gape-limited predators preferring small individuals, but male reproductive success might be lower for domesticated individuals as their reproduction potential during the freshwater phase is reduced.Résumé : La domestication peut modifier des caractères associés à l'aptitude. Nous avons étudié les modifications de caractères associés à l'aptitude provoquées par la domestication chez le saumon atlantique (Salmo salar) dans des conditions de laboratoire enrichies naturellement avec et sans menace de prédation. La sélection associée à une croissance rapide sur trois et cinq générations dans deux lignées s'est traduite par des tailles de deux à trois fois plus grandes des tacons de moins d'un an par rapport à celles de leurs ancêtres sauvages. Une taille initialement plus grande et la capacité de dépasser la taille de proie plus rapidement se sont traduites par une mortalité par prédation selon la taille plus faible pour les individus domestiqués. La croissance en présence d'une menace de prédation n'était réduite que pour les individus sauvages, ce qui donne à penser qu'il y a cosélection par la domestication d'une résistance au stress associé aux prédateurs. La probabilité de maturation des tacons mâles ajustée selon la taille était de 34 % dans la lignée sauvage, mais significativement réduite à 10 % et 7 %, respectivement, après trois et cinq générations de domestication. Collectivement, la survie durant le stade de vie en eau douce pourrait être plus grande pour les individus d'ascendance domestiquée que pour les individus d'ascendance génétique sauvage en présence de prédateurs dont la commissure des mâchoires est limitée, qui préfèrent de plus petits individus; en revanche, le succès de reproduction des mâles pourrait être plus faible pour les individus domestiqués, leur potentiel de reproduction durant l'étape en eau douce étant réduit. [Traduit par la Rédaction]

Rapid, broad‐scale gene expression evolution in experimentally harvested fish populations

“…In fact, we showed that maturation‐ and reproduction‐related genes were up‐regulated among the random‐harvested fish (from F 5 to F 11 ), and we have shown earlier that the random‐harvested fish have a higher age‐specific maturation probability than large‐harvested fish (Uusi‐Heikkilä et al., ). This is in agreement with other studies showing that fish held in captivity tend to mature later than their wild conspecifics (Debes & Hutchings, ). Thus, it is possible that in captivity, traits under selection are related to body condition (body fat content), growth, and potentially maturation.…”

Half a century of genetic interaction between farmed and wild Atlantic salmon: Status of knowledge and unanswered questions

“…One way to circumvent this challenge is to use a farmed strain that is known to be based on a single or low number of wild populations, either from the onset of domestication (Debes & Hutchings, ; Solberg et al., ), or by altered strain contributions through the first generations of domestication (Einum & Fleming, ). An alternative is to include multiple farmed strains and/or wild populations to identify evidence of parallel evolution.…”

“…Indeed, triploid escapees, which are sterile, may enter freshwater albeit at a considerably reduced frequency compared to diploid escapees (Glover et al., , ). In addition, not all male juveniles escaping to freshwater will become sexually mature as parr, especially because the tendency for parr maturation in farmed strains is lower than in wild populations (Debes & Hutchings, ; Einum & Fleming, ; Morris, Fraser, Eddington, & Hutchings, ; Yates, Debes, Fraser, & Hutchings, ). Therefore, not all escapees found in rivers will reproduce and hybridize with native fish.…”

Plasticity in response to feed availability: Does feeding regime influence the relative growth performance of domesticated, wild and hybrid Atlantic salmon Salmo salar parr?

“…The hatchery environment is typically characterised by high densities, a lack of predation and continuous feed availability. Farmed S. salar have exhibited changes in behavioural traits such as increased aggression, higher stress resistance and decreased predator awareness that are attributed to inadvertent selection resulting from the artificial hatchery environment (Einum & Fleming, ; Fleming & Einum, ; Houde et al , 2010 a , b ; Solberg et al , 2013 a ; Debes & Hutchings, ). Thus, direct and indirect selection has resulted in domesticated fish that are adapted to their captive environment and that typically display traits which may be maladaptive in the wild relative to their wild counterparts.…”