A test of the good-genes-as-heterozygosity hypothesis using red-winged blackbirds

Abstract

Brown recently proposed that the ‘‘good genes’’ that females pursue when choosing mates may be individual heterozygosity because more heterozygous mates sire offspring with higher fitness. Further, because heterozygosity might enhance developmental stability, males with more heterozygosity are recognized by the reduced fluctuating asymmetry (FA) of their bilaterally paired traits. We used a point sample of 67 male red-winged blackbirds (Agelaius phoeniceus) to test two predictions of this hypothesis: (1) males with more heterozygosity have higher fitness, and (2) males with more heterozygosity have lower FA. We identified 7 polymorphic loci from an initial screening of 16 enzymes; 32 individuals were completely homozygous, and 35 individuals were heterozygous at at least 1 locus. Larger and older males realized higher mating success in this population, but neither size nor age was related to heterozygosity. Heterozygous males were not in better condition than homozygous males, nor were they less infected by hematozoa, lice, or mites. Among 1-year old males, epaulet length did not differ between homozygotes and heterozygotes, but among older males, heterozygotes did have longer epaulets. Homozygotes and heterozygotes did not differ in their mean FA scores for nine individual characters. Although the two groups of males did differ in composite FA, heterozygous males were less symmetrical. Interestingly, this difference was attributable to a single allele at the PGM-3 locus. Combined with previous results showing that FA was generally unrelated to male health, viability, parental care, social dominance, or mating success, the present results indicate that Brown’s hypothesis does not explain mate choice or male quality in this population of red-winged blackbirds.