Effects of domestication related genes on behaviour, physiology and gene expression in chickens

Sammanfattning: Domestication, the process when animals adapt to captivity, tends to modify a whole array of traits towards what has been termed “the domesticated phenotype”, where the domesticated animal differs from its wild ancestor in morphology, physiology, development and behaviour. Physiological traits and behaviours are controlled by genes. One single gene can control several different traits (pleiotropy), be linked to a neighbouring gene on the chromosome, or interact with another gene that in turn controls another trait. This is the explanation why one can select for high egg production and at the same time get a change in the colour of the plumage. The aim of this thesis was to evaluate the effect of a mutation in two particular genes (PMEL17 and TSHR) related to domestication on behaviour, gene expression and other physiologial traits. The animals investigated were chickens from a cross between the ancestral Red Junglefowl (RJF) and the domesticated White Leghorn (WL) selected for high egg production traits. PMEL17 is a gene affecting plumage colour. A mutation in the gene causes a non-pigmented white plumage and has been shown to protect against feather pecking. Our studies showed that a mutation in the PMEL17 gene affects social, explorative and aggressive behaviour in chickens, but not visual ability. The thyroid stimulating hormone receptor (TSHR) plays an important role in the signal transduction of the hypothalamus-pituitary-thyroid axis that has general effects on development, behaviour and reproduction. A mutation in the TSHR gene affects incubation time, domestication related behaviours such as fear and aggression, gene expression, thyroid hormone levels and photoperiodic reproduction responses in chicken. The results from this thesis suggest that a mutation in the PMEL17 and TSHR genes have pleiotropic effects on behaviour and traits related to domestication, and it is therefore likely that both genes have been important for the domestication of the chicken.