Evolution of microsatellites in Arabis petraea and Arabis lyrata, outcrossing relatives of Arabidopsis thaliana

We examined microsatellite variation in two diploid, outcrossing relativesof Arabidopsis thaliana, Arabis petraea and Arabis lyrata. The primersequences were derived from A. thaliana. About 50% (14 loci) of the A.thaliana primers could successfully amplify microsatellites in the relatedspecies. Analysis of microsatellite structure in the related species showedthat there had been large changes in the microsatellites: there were largedifferences in repeat numbers and many of the A. thaliana simple repeatswere shorter in the related species. For the loci we compared, the relatedspecies had a much lower level of variability at the microsatellites thanJapanese wild populations of A. thaliana. This is presumably related to thedifferent microsatellite structures, because allozyme data showed that theoutcrossing relatives were highly polymorphic compared to other outcrossingherbaceous species. Use of microsatellites in assessing variability orphylogenetic relationships between different species requires caution,because changes in microsatellite structure may alter evolutionary rates.