Pelvic Girdle Fluctuating Asymmetry in the Domestic Cat (Felis catus): Associations with Age, Sex, and Body Mass

Fluctuating asymmetry (FA) is commonly used as a phenotypic indicator related to developmental stability, reflecting variation in an organism’s ability to maintain bilateral correspondence during development. Although pelvic morphology has been extensively investigated in the domestic cat (Felis catus), little is known about fluctuating asymmetry of the pelvic girdle and its associations with biological variables such as age, sex, and body mass. This study quantitatively evaluated fluctuating asymmetry of the pelvic girdle in 45 domestic cats using 14 bilateral osteometric traits. Measurement repeatability was assessed using the technical error of measurement (TEM), and traits exhibiting significant directional asymmetry were excluded prior to FA analysis. An individual FA_index was subsequently calculated from the remaining traits and examined in relation to age, sex, and body mass. Six traits exhibited significant directional asymmetry and were therefore excluded from further analyses. Measurement error was low (%TEM: 0.34% to 2.20%) and consistently lower than the corresponding FA values, indicating that the observed asymmetry was greater than the estimated measurement error and was therefore unlikely to be explained primarily by measurement imprecision. The mean FA_index was 0.041 ± 0.032 and showed a positively skewed distribution. Adult cats displayed significantly higher FA_index values than subadults (p = 0.007, effect size: r = 0.40), whereas males also exhibited significantly higher FA_index values than females (p = 0.009, effect size: r = 0.39). No significant association was detected between FA_index and body mass (R2 = 0.014, p = 0.432). These findings demonstrate measurable fluctuating asymmetry of the pelvic girdle and indicate that its magnitude varies according to age group and sex within the studied population. The observed difference between subadult and adult cats is consistent with the use of FA as a phenotypic indicator related to developmental stability but does not demonstrate a decline in developmental stability with age. The observed asymmetry may also reflect cumulative functional and biomechanical influences acting on the pelvic skeleton throughout life.