Genetic monitoring of brackish-water populations: the Mediterranean toothcarpAphanius fasciatus(Cyprinodontidae) as a model

The measurement of genetic variability and assessment of population genetic losses are important components of environmental management programs. Twenty-three natural populations of the Mediterranean brackish-water toothcarpAphanius fasciatuswere investigated using different statistical approaches based on genetic data at 13 polymorphic allozyme loci. In general, no differences between values of within-population genetic variability estimates occurred. The Wilcoxon sign-rank test for heterozygosity excess due to a recent bottleneck was conducted on the array of populations. In addition, a qualitative descriptor of allele frequency distribution was used to infer bottlenecks. Only populations from the Orbetello lagoon and La Salina at Elba Island revealed significant heterozygosity excess under both the infinite allele model (IAM) and stepwise mutation model (SMM). A recent dystrophic crisis may account for the genetic loss detected in the population ofA. fasciatusfrom the Orbetello lagoon, whereas exceptionally high predation pressure and/or the increased mortality rate created by local hydrological conditions could be responsible for the bottleneck in the population at La Salina. Tests for bottlenecks have proved effective tools for genetic monitoring ofA. fasciatuspopulations.