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.