Relationships among allozyme heterozygosity, morphology and lipid levels in house sparrows during winter

House sparrows (Passer domesticus) were collected during cold (43 individuals) and warm (31 individuals) periods in February 1982 from farms near Lawrence, Kansas. Fat scores (from flank, rump and furcula) and body mass were measured from the carcasses, which were then reduced to skeletons. Heterozygosity was determined by electrophoresis of three polymorphic allozymes. Pectoral lipid content was determined by petroleum ether extraction. Principal component (PC) analysis was conducted on 14 skeletal measurements. Summed fat score, body mass and pectoral lipid content served as dependent variables in three multiple regressions. Sex, period (cold versus warm), number of heterozygous loci (0-3), and scores of PC1, PC2 and PC3 were independent variables. Each of the dependent variables was also included as an independent variable in regressions in which they were not the dependent variable. Pectoral lipid content was significantly related only to the number of heterozygous loci (R2 = 0.18, P = 0.008). Summed fat score differed between sexes and periods (P = 0.012 and 0.001, respectively) when body mass was included in the regression (P < 0.001). Body mass was related to summed fat score as above, and also to body size (PC1, P < 0.0001) and period (P = 0.014). Females exhibited a positive regression between body size and summed fat score (P = 0.007). Body size (PC1) was greater for both sexes in the sample from the warm period (P = 0.022), suggesting that selection for increased body size may have occurred. Increased metabolic efficiency of heterozygous enzymes or individuals is suggested as an explanation for the observed relationship between heterozygosity and intramuscular lipid level.