A WIDE-RANGE SURVEY OF CROSS-SPECIES MICROSATELLITE AMPLIFICATION IN BIRDS

The possibility to perform cross-species microsatellite amplification in birds was surveyed by analysing sets of primers developed from the swallow and the pied flycatcher genomes on a panel of 48 different bir d species. In total, 162 cases (species/marker combinations) of hetero logous amplification were recorded. Ten amplification products were se quenced and all were found to be true homologues of the original loci. There was a significant and negative relationship between microsatell ite performance and evolutionary distance between the original species and the tested species. As a rough indicator of expected cross-specie s microsatellite performance we estimate that 50% of markers will reve al polymorphism in a species with a DNA-DNA hybridization Delta TmH va lue of 5 separating it from the original species. This corresponds to a divergence time of approximate to 11 million years before present fo r passerine birds. The established relationship between performance an d evolutionary distance agrees very well with data obtained from some mammalian species. The proportion of polymorphic loci among those mark ers that amplified decreased with increasing genetic distance, suggest ing that few long repeats are preserved during evolution. One of the s wallow markers, HrU2, amplified a specific product in all species anal ysed and will thus allow access to nuclear sequence data over a broad range of species. The only predictor of cross-species performance was the amount of nonspecific amplification seen in the original species. An analysis of 10 species from within the family Hirundinidae with the swallow primers consistently revealed extensive polymorphism with ave rage probabilities of identical genotypes ranging from 6 x 10(-4) to 6 x 10(-7). There were distinct allele frequency differences between th e Hirundinidae species and we envisage that microsatellite cross-speci es amplification will be a useful tool in phylogeny construction and i n species identification.