Developmental instability in Japanese quail genetically selected for contrasting adrenocortical responsiveness

Differences in developmental instability were assessed with Japanese quail of two lines that had been genetically selected over several generations fo r reduced (low stress, LS) or exaggerated thigh stress, I-IS) plasma cortic osterone response to brief mechanical restraint. At 32 wk of age, three bil ateral traits were selected for study in each quail line. The characteristi cs chosen were length of the metatarsus (shank length, SHL), diameter of th e shank (SHD) perpendicular to the spur, and distance between the auditory canal and the nares (face length, FL). Significantly greater bilateral trai t size variances were associated with the measurement of SHL (P < 0.0088) a nd FL (P < 0.0016) in the HS line than in the LS line. SHD variances did no t differ (P = 0.22) in quail of the HS and LS lines. These findings suggest that developmental instability (i.e., fluctuating asymmetry, FA) is more p ronounced in HS quail than in LS quail. Previous studies have shown that no t only do quail of the HS line show greater adrenocortical responsiveness t o a wide range of stressors but that they are also more easily frightened t han LS birds. Therefore, the line differences in FA found here may reflect the birds' differential responsiveness to chronic social and physical envir onmental stressors. The present findings also support previous suggestions that measuring asymmetries in bilateral traits could be an additional and v alid method of assessing stress and of comparing phenotypic stability in se lected populations.