Microsatellite mutations in litters of the Australian lizard Egernia stokesii

Seven tetranucleotide (AAAG) loci were analysed in a population (including 19 litters) of the Australian lizard Egernia stokesii. In an examination of 76 offspring we observed 13 mutations involving five loci. Two of our loci were highly mutable, with observed mutation rates of 2.7% and 4.2%, representing some of the highest mutations rates reported so far. A high proportion of mutations (46.2%) could not be assigned to changes involving only a single repeat, suggesting that mutations in at least two of the loci follow a multistep model. There was no significant bias of mutations leading to an increase or decrease in allele size; however, all multistep mutations involved a loss of repeats. These results add to increasing evidence casting doubt on microsatellite mutations being primarily single step mutations.