Genetic diversity of the killifish Aphanius fasciatus paralleling the environmental changes of Tarquinia salterns habitat.

The habitat in the Natural Reserve of the Tarquinia salterns, located on the Tyrrhenian coast of central Italy, has undergone dramatic alterations over the last 10 years. After salt production was terminated in 1997 the site was abandoned until 2002, with consequent degradation of habitat quality and stiffening of the environmental conditions. From 2003 to 2006 ecological rehabilitation of the site was carried out, restoring water circulation to its previous equilibrium. The genetic variation in the killifish Aphanius fasciatus inhabiting the salterns was monitored using allozymes from 1998. The results showed that the genetic variability of the killifish strongly reduced through time: a high number of rare alleles were lost and both heterozygosity and allele richness were significantly decreased. The most recent samples, taken after the ecological restoration, showed that to date the genetic erosion of A. fasciatus gene pool has slowed down, since no significant differences have been detected for any genetic variability parameter. Concerning the mechanisms leading to the impoverishment of the genetic variability, the strong loss of rare alleles suggests a role of genetic drift, which accords with the fluctuation of the effective population size recorded over the period of study and with the low gene flow typical of this species. The low levels of gene flow reported for this species imply that once lost, the genetic variability can rarely be restored through immigration from highly variable populations.