Domestication and responses to stress

Domestication is a process by which animals become adapted to captive life conditions by way of natural and/or artifi cial selection. Genetic drift and inbreeding may also contribute to the evolution (deleterious or not) of numerous traits during domestication. In fi sh, domestication has been shown to infl uence growth, behavior (aggressiveness, dominance, alertness, feeding) and stress responsiveness. With respect to the later, it seems that stress-resistant animals may be selected during domestication as a result of an improved fi tness. In percid species, some studies already investigated the effects of several husbandry stressors (chronic confi nement, repeated water emersion, single and repeated hypoxia) on the physiological and immune responses along domestication process, by comparing Eurasian perch juveniles from distinct generation levels (Filial 1–5). Under chronic confi nement, domestication resulted in a reduction in cellular (HSP70) and physiological (subsequent handling stress) stress response as well as the maintenance of immune status (no decrease in transferrin, complement C3 levels in Filial 4 fi sh). Domestication did not infl uence physiological and immune responses to repeated emersion stressor and repeated hypoxia. Eurasian perch has however been shown to be responsive to hypoxic conditions (hyperglycemia, spleen contractions, high transferrin level) and to potentially develop some acclimation mechanism to the repeated disturbance at the expense of some immune functions. All together, the studies demonstrated that domestication positively infl uenced fi sh tolerance to chronic confi nement but not to hypoxia or water emersion and that this might be linked to the stressor severity. Moreover, F4/F5 fi sh groups displayed a better immune and physiological status than their F1 counterparts. A microsatellite analysis however revealed that these F4/F5 generations display a lower genetic diversity. Thus, loss of genetic diversity did not appear detrimental to the fi sh but will nevertheless limit the possibilities of genetic improvement in upcoming generations.