VARIABLE NUMBERS OF SIMPLE TANDEM REPEATS MAKE BIRDS OF THE ORDER CICONIIFORMES HETEROPLASMIC IN THEIR MITOCHONDRIAL GENOMES

We have analyzed a variable domain of the mitochondrial DNA control re gion of 18 avian species. Intra-individual length variation was identi fied and characterized in 15 species. The occurrence of heteroplasmy a mong species is phylogenetically consistent with a current classificat ion of birds. Polymerase chain reaction amplifications, direct sequenc ing, and Southern analysis of mitochondrial DNA showed that the hetero plasmy is due to variable numbers of direct repeats in a tandem organi zation, located in the control region close to the tRNA(Phe) gene. The tandem repeats consist of short sequence motifs that vary in size fro m 4 to 32 base pairs between species. Sequence complexity of the repea t motifs was low, with almost exclusively Ts and Gs in the heavy-stran d. Extensive variation in the copy number of the repeats was seen both intra-specifically and within individuals. This is the first report o f mitochondrial heteroplasmy characterized at the sequence level in bi rds.