HOCK, A. D.; KNIGHT, F. M.; Univ. of the Ozarks: Size and growth variance within and among armadillo clones (Dasypus novemcinctus)

Nine-banded armadillos are born in litters of monozygotic quadruplets. Thus, armadillos provide a rare model system for assessing the relationship between genetic homogeneity and phenotypic homogeneity. Obviously, for armadillos we expect that phenotypic variance between litters will be greater than the phenotypic variance between siblings. Phenotypic variance may decrease with age as a result of intrinsic regulatory mechanisms, producing a pattern of convergent growth; or accumulation of extrinsic effects with age may increase variance and produce divergent growth. Previous studies have found different patterns for different traits. We measured weight, head length, and tail length for four litters of wild-conceived, lab-born armadillos housed with their mothers. Early growth rate was estimated with linear regression. We analyzed log-transformed data with Levene�s test and ANOVA. Some consistent results were observed: The within-litter variances in rate of weight gain did not differ significantly among litters. The between-litter variance was greater than within-litter variance for the three measurements at the three ages and for all growth rates. For data pooled by age, the within-age variances differed between ages for each of the three measurements, with variance generally increasing with age. When analyzed by litter, no consistent pattern among within-age variance was observed; however, the between-litter variances generally increased with age. From birth to weaning, each genetically homogeneous litter of armadillos exhibited a high degree of phenotypic homogeneity, and each litter generally diverged from other litters as individuals grew.