Genetic diversity and environmental stress in Italian populations of the cyprinodont fish Aphanius fasciatus

Allozyme electrophoresis has been used to analyse the genetic structure of ten populations of the killifish, Aphanius fasciatus, sampled from Italian coastal brackish lagoons or salterns. The goal of the study was to compare the genetic structure of samples obtained from habitats characterised by environmental stress of different kinds, with the aim of gaining a better understanding of the relationships between the genetic variation of natural populations and environmental disturbance, either natural or man-made. Therefore, the sampling scheme has been planned to provide samples from both brackish habitats, characterised by natural stress with seasonal marked fluctuations of chemical and physical parameters, and from coastal lagoons suffering from a high human impact due to fishing, pollution, aquaculture, etc. Many sample pairs from the two sets were also geographically very close, allowing a better comparison of the genetic variation of populations tolerating different kinds of environmental stress (i.e., natural vs. anthropogenic). The obtained data evidence three main genetically distinct population groups, including samples from: (1) central-northern Tyrrhenian and northern Sardinian coasts; (2) southern Tyrrhenian and southern Sardinian coasts; (3) Adriatic Sea. Within the two Tyrrhenian groups, a general trend indicates a lower genetic variability for the samples obtained from highly human disturbed brackish waters. In particular, samples characterised by well documented pollution and dystrophic crises (i.e., Orbetello and Cagliari–Santa Gilla lagoons) have a lower genetic variability with respect to nearby scarcely disturbed populations (Tarquinia saltern and Sant'Antioco lagoon). The Adriatic populations exhibit a low level of genetic variation, which may be due to the persistent hypoxic condition of the sea basin combined with the paleogeographic history of the area.