Differential Size Variation of Male and Female Bumblebees

The theory of polygenic inheritance predicts that, due to hapiodiploidy in the Hymenoptera, males should be more variable than females. Variation of radial-cell length (a wing-length measure) in the bumbiebee Bombus rufocinctus was examined in a sample of 787 young queens (from 43 colonies) and 680 males (from 38 colonies). The males (coefficient of variation [C.V.] = 5.75%) were significantly more variable (P < .01) than the females (C.V. = 3.98%). There were also significant (P < .005) intraclass correlations between male ($t^m=0.553$) and young queen ($t^f=0.435$) offspring, indicating a considerable degree of phenotypic resemblance between bees of the same caste within each colony. Heritability, estimated from offspring-parent regression, was 0.20 ± 0.19 for queens and 0.47 ± 0.38 for males, considerably lower than that estimated from intraclass correlations. This suggests that environmental variation is of the same order of magnitude as additive genetic variation.