Clonal stability and mutation in the self-fertilizing hermaphroditic fish, Rivulus marmoratus

Previous investigations of natural populations of the hermaphroditic, self-fertilizing fish species Rivulus marmoratus demonstrated a surprising amount of interclonal differentiation among highly polymorphic "DNA fingerprint" loci. The genetic differentiation observed among clones was thought to be the effect of extreme population mixing because of high rates of migration and population extinction. It was demonstrated that mutation rates at hypervariable loci would have to exceed 10(-4) on average to alone account for the observed interclonal differences. The present study reports that, among laboratory lines of this species, mutation rates at the most unstable set of hypervariable loci are not greater than 3.52 x 10(-4), and are probably lower. Mutation rates at several other sets of loci are even lower. A field transplantation study demonstrated complete clonal stability over several generations. These results suggest that the high interclonal differences observed in natural populations of this species is not caused by a generally higher rate of mutation at these specific loci.