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