Developmental instability and light regime in chickens (Gallus gallus)

Measures of developmental instability such as fluctuating asymmetry reflect the ability of individuals to cope with stressful conditions during ontogeny, and a very low level of asymmetry is known a priori to be the optimal solution from a functional morphological point of view. Fluctuating asymmetry represents a potentially important tool for assessment of the reaction of animals to their environment and thus for the study of animal welfare. We measured fluctuating asymmetry in three skeletal characters in chickens raised under three different light regimes: (A) a 16:8 light-dark cycle, (B) a changing light regime, and (C) permanent light. Chickens reared under permanent light developed 40% larger relative asymmetry than chickens subjected to changing light and dark conditions. Tonic immobility, a behavioural measure of fearfulness, was positively correlated with fluctuating asymmetry in chickens reared under all three light regimes. Fluctuating asymmetry was also positively related to the severity of a leg pathological condition (tibial dyschondroplasia) and positively related to a measure of impaired walking performance, These results suggest that fluctuating asymmetry may provide a reliable indicator of the reactions of domestic animals to their rearing conditions. (C) 1999 Elsevier Science B.V. All rights reserved.