Fluctuating Asymmetry in Relation to Stress and Social Status in Inbred Male Lewis Rats

Abstract

Environmental or intrinsic stressors acting on growing animals and humans may be expressed as small, random  deviations from symmetry in otherwise bilaterally symmetrical characters – a phenomenon known as  fluctuating asymmetry (FA), the mechanism behind which is not yet clear. In this study, we investigated the  effects of two known stressors (grid floor and single housing) on the development of FA in young male  Lewis rats compared to housing under normal conditions (bedding) or an enriched environment. It was  found that such environmental factors have an impact on FA in rats. Initially, FA was found to be high in  all rats. In bedding and in enrichment groups, FA decreased throughout the study (P<0.05 in bedding group  and P<0.001 in enrichment group from five to eleven weeks of age). FA in singly housed rats and in rats  on a grid floor did not change significantly throughout the study. FA in these rats was considerably higher  than in rats housed on bedding with or without environmental enrichment (P<0.001). Moreover, the influence  of social status on FA was evaluated. Dominant rats housed in the enriched environment were found  to have a higher FA of combined traits than subordinate rats at eight weeks of age (P<0.01), but except for  this result, no relationship between FA and dominance was found. Singly housed rats showed significantly  higher FA than dominant as well as subordinate rats (P<0.001). In conclusion, FA of selected traits may  hold a potential for measuring stress influences in laboratory animals, which can be of some importance in  welfare research.