Microsatellite diversity predicts recruitment of sibling great reed warblers

Inbreeding increases the level of homozygosity, which in turn might depress fitness. In addition, individuals having the same inbreeding coefficient ( e.g. siblings) vary in homozygosity. The potential fitness effects of varia tion in homozygosity that is unrelated to the inbreeding coefficient have s eldom been examined. Here, we present evidence from wild birds that genetic variation at five microsatellite loci predicts the recruitment success of siblings. Dyads of full-sibling great reed warblers (Acrocephalus arundinac eus), one individual of which became a recruit to the natal population whil e the other did not return, were selected for the analysis. Each dyad was m atched for sex and size. Local recruitment is strongly lied to fitness in g reat reed warblers as the majority of offspring die before adulthood, philo patry predominates among surviving individuals and emigrants have lower lif etime fitness. Paired tests showed that recruited individuals had higher in dividual heterozygosity and higher genetic diversity, which was measured as the mean squared distance between microsatellite alleles (mean d(2)), than their non-recruited siblings. These relationships suggest that the microsa tellite markers, which are generally assumed to be neutral, cosegregated wi th genes exhibiting genetic variation for fitness.