Allozymic heterozygosity and morphological variation in house sparrows

Several reports have shown that greater heterozygosity (both between individuals and between populations) is associated with lower morphological variance and asymmetry. Most previous work concerned poikilothermic organisms (for example, fish, butterflies, lizards, shellfish, salamanders and plants). Reports concerning two homoiotherms gave conflicting results. The report by Handford on a songbird, Zonotrichia capensis, failed to support the relationship, although these results have been questioned in the literature. Handford suggested that the lack of relationship in Zonotrichia could indicate a fundamental difference between homoiotherms and poikilotherms, reflected in their apparent differences in heterozygosity. However, we report here on electrophoretic and morphometric studies on another songbird species (Passer domesticus), in which the relationship appears to be upheld. We find consistently, among four locality samples, that the class of individuals of greatest allozyme heterozygosity nearly always exhibits the lowest multivariate morphological variance, and the class of greatest homozygosity nearly always exhibits the highest.