Fluctuating asymmetry in male secondary sexual traits:: association with indicators of stress in chickens

Bilateral asymmetry of several secondary sexual traits (wattle, ear-lobe, and wing-bay areas), heterophil to lymphocyte ratio, and tonic immobility duration were studied in cocks from two Spanish breeds (Black-red Andaluza and Red Villafranquina) and a tester line (e(y)). Directional asymmetry occurred together with fluctuating asymmetry or antisymmetry for the same trait in the three analysed populations. There was no significant difference in relative asymmetry among breeds for either analysed trait. The degree of relative asymmetry found for wattle, ear-lobe and wing-bay areas was elevated. Mean relative asymmetry varied significantly among traits and populations. There were significant differences among breeds for heterophil to lymphocyte ratio and tonic immobility duration. Although there was no significant association between relative asymmetry and leukocyte ratio, the duration of tonic immobility was negatively associated with the relative asymmetry of wattle area in cocks from the Villafranquina breed (r = -0.32**), but this finding was not consistent across the different breeds or traits. These results suggest that relative asymmetry measures of secondary sexual traits did not provide a tool to assess stress or fear susceptibility in chickens.