Estimation of heritability for fluctuating asymmetry in chickens by restricted maximum likelihood. Effects of age and sex.

The purposes of the present study were to estimate the heritability of the fluctuating asymmetry in chickens, using the restricted maximum likelihood procedure, and to evaluate the effects of age and sex on the fluctuating asymmetry. Leg, wing, and feather lengths and ear-lobe and wattle areas were measured. In experiment 1, 1,073 birds were used from 2 generations with complete pedigree of the Quail Castellana breed to estimate the heritability for the fluctuating asymmetry at 36 wk of age. The estimated heritability of absolute fluctuating asymmetry was not significantly different from zero for all 5 traits, and similar estimates were obtained for relative fluctuating asymmetry, directional asymmetry, transformed absolute and relative fluctuating asymmetry, and 3 alternative indexes of fluctuating asymmetry. The heritability of the combined absolute or relative fluctuating asymmetry was still very low, indicating that fluctuating asymmetry was determined solely by environmental sources of variation and that fluctuating asymmetry estimates should not be confounded by appreciable additive genetic contributions. The genetic correlation between sides was not significantly different from one, indicating that differences between sides were purely environmental in origin. Different traits rarely showed much correlation in their level of fluctuating asymmetry, indicating that the level of fluctuating asymmetry in all traits did not reflect equally the quality of animals. In experiment 2, fluctuating asymmetry differences among ages and sexes were investigated at 8, 12, 16, 20, 24, 28, 32, 36, and 40 wk in 360 birds from the same breed. Significant variation with age was observed in leg length, wing length, feather length (females), and wattle area (females), which was mainly related to onset of sexual maturity and adult stage. Females showed significantly greater fluctuating asymmetry for ear-lobe area than males. There were significant differences in fluctuating asymmetry for wing length, feather length, and wattle area near the onset of sexual maturity, with males having significantly greater fluctuating asymmetry than females for wing length and the opposite being true for feather length and wattle area.