Reduced microsatellite heterozygosity in island endemics supports the role of long-term effective population size in avian microsatellite diversity

Because of the high mutation rate of microsatellites, polymorphism at microsatellite loci might be predicted to reflect the effective population size over a time span of about 10,000 years and thus to be associated with biogeographic factors impacting species on that time frame. This prediction was tested by comparing heterozygosity at microsatellite loci from 294 bird species, including 58 species endemic to oceanic islands. Controlling statistically for phylogenetic effects, mean heterozygosity was significantly reduced in oceanic island endemics compared to other species. There was also an effect of current endangerment, statistically independent of the effect of island endemicity. These results support the hypothesis that long-term effective population size can be an important causative factor behind differences among species with respect to microsatellite heterozygosity.