Genetic similarity and hatching success in birds.

The ecological correlates of fitness costs of genetic similarity in free-living, large populations of organisms are poorly understood. Using a dataset of genetic similarity as reflected by band-sharing coefficients of minisatellites, we show that bird species with higher genetic similarity experience elevated hatching failure of eggs, increasing by a factor of six across 99 species. Island distributions and cooperative breeding systems in particular were associated with elevated genetic similarity. These findings provide comparative evidence of detrimental fitness consequences of high genetic similarity across a wide range of species, and help to identify ecological factors potentially associated with increased risk of extinction.