A low mutation rate for chloroplast microsatellites

We used chloroplast simple sequence repeats (cpSSRs) to examine whether the re is any variation present in the chloroplast genome of Pinus torreyana (P arry ex Carriere) that may previously not have been detected using RFLPs. A nalysis of 17 cpSSR loci showed no variation, which is consistent with prev ious cpRFLP work and confirms that the species is descended from an origina l, highly monomorphic population following a bottleneck. This lack of biolo gical variation in the chloroplast genome of P. torreyana allowed us to est imate the mutation rates at cpSSR loci as between 3.2 x 10(-5) and 7.9 x 10 (-5). This estimate is lower than published mutation rates at nuclear SSR l oci but higher than substitution rates elsewhere in the chloroplast genome.