Selection for open-field behaviour in the chicken: The relationship between open-field and social behaviour

Abstract

Two lines of chickens have been divergently selected over seven generations for their open-field activity at 2 days of age. The results show a clear divergence, which is almost symmetrical for most of the behavioural characteristics (latency to move, activity, percentage of birds which peep) at least until the third generation. The calculated and realized heritabilities range between low and medium values. In the active strain, the calculated heritabilities are 0.19 and 0.15 for activity and latency to move, respectively, and 0.32 and 0.35 for the realized heritabilities. In the inactive strain, the calculated heritabilities are 0.12 for both characters and the realized heritabilities are 0.14 for latency and 0.27 for activity. This symmetrical response to selection, coupled with the fact that there is no heterosis for these characters, shows that open-field activity (emotionality) has undergone natural selection for a medium level rather than a low or high one. This is also the case in rats. The only exception to the symmetrical divergence is the percentage of birds which defaecate during the test; there is no change in the active line and a decrease in the inactive one. The active line show less emotionality in the open field. The results of pair contests show that birds with medium levels of neonatal open-field activity, and thus medium emotionality, are most likely to become dominant. Thus, emotionality at two days of age acts as a reliable indicator of dominanceability in adulthood. Thus, we may hypothesize either that heterozygosity at the level of the genes determining open-field activity has a pleiotropic effect on dominance ability, or that very emotional birds may lose the contest because they react fearfully to the opponent, and that the non-emotional birds may also lose be cause they are not psycho-physiologically prepared to fight. FACTORS AFFECTING RESPONSES OF CHICKS TO A NOVEL ENVIRONMENTAL CHANGE D.M. BROOM Department of Zoology, University of Reading, Reading (Gt. Britain)