A test of the hypothesis of mate choice based on heterozygosity in the spotless starling

The hypothesis of mate choice based on heterozygosity predicts that sexual traits will reach their extreme expression in males with the greatest average heterozygosity, and that both a male’s ornament expression and his mating success will correlate positively with degree of individual heterozygosity. In agreement with the first prediction, we found a negative correlation between degree of homozygosity and length of the throat feathers (a secondary sexual trait) in male spotless starlings, Sturnus unicolor. However, we found a quadratic relationship between degree of homozygosity and both mating success and mean number of young sired per year. Hence, males of intermediate heterozygosity were more successful in mating and reproduction than either more homozygous or more heterozygous males. These results do not support the hypothesis of mate choice based on heterozygosity.This study was supported by the project DGICYT (PB 97-1249). P.J.C. and J.M.A. were supported by a postdoctoral contract of the Ministerio de Educacion y Cultura.Peer reviewe