Early domestication? : Phenotypic alterations of Red Junglefowl selected for divergent fear of humans

Sammanfattning: Domestication is the process through which animals adapt to conditions provided by humans. The domesticated phenotype differs from wild ancestors in a number of traits relating to physiology, morphology and behaviour. One of the most striking differences is the animals’ fear response towards humans, and reduced fear of humans is assumed to have been an early prerequisite for the success of domestication. The early alterations seen in the domesticated phenotype may be traits developed as a correlated selection response due to tameness rather than selected upon one by one.This thesis summarizes a project where Red Junglefowl were selected for divergent fear of humans during six generations. In every generation, fear response to human was assessed in a standardized test and, according to fear score, the animals were bred for either high fear of humans (H) or low fear of humans (L). The animals were, above that of the standardized selection test, behaviourally phenotyped in different tests in each generation mainly focusing on fear, exploration and social behaviour. In addition to behaviour, the animals were phenotyped for body weight, egg weight, metabolism, feed intake, plumage condition, blood plasma corticosterone and peripheral serotonin. After culling, vital organs and brains were harvested and weighed.In paper I, we demonstrated that the selection trait has a significant genetic heritability and is genetically correlated with other behavioural responses associated with fearfulness and exploration. In paper II, we concluded that animals from the L strain had better plumage condition, higher weight, laid larger eggs and also generated larger offspring. Furthermore, when tested in a social dominance test with a limited resource, they received less and performed more aggression regardless of whether the restricted source was edible or not. In paper III, we revealed that animals from the L strain had higher basal metabolic rate as chicks, gained more weight in relation to feed intake and were bolder in a Novel Object test. Furthermore, the L males had higher plasma levels of peripheral serotonin, but the corticosterone after a restraint stress test did not differ. In paper IV and V, we concluded the project by comparing brain and organ weights as well as behaviour of the parental generation (P0) with the fifth selected generation (S5). The absolute brain weight as well as the weight specific brain weight were larger in the animals selected on H than in the L-animals. The relative weight of telencephalon was significantly higher in H whereas relative weight of cerebellum was significantly lower. Heart, liver, spleen and testes were all relatively heavier in H animals than in L. Interestingly, the behaviours assessed in P0 and S5 seemed to be rather resilient to the selection with only small differences in S5.To summarize, the selection on divergent tameness in Red Junglefowl has affected several phenotypic traits associated with the domesticated phenotype. The results of this project indicate that tameness in Red Junglefowl could be an underlying factor driving trait modifications towards the domesticated phenotype.