Relationships between sediments and tissue contamination and allozymic patterns in Hediste diversicolor (Polychaeta Nereididae) in the Pialassa lagoons (north Adriatic Sea)

An increasing number of investigations revealed that responses of populations to environmental stressors may be genetically dependent. Occurrence of genetic adaptation to high concentrations of heavy metals in Hediste diversicolor local ecotypes has also been hypothesised. Analyses of allozymic patterns are a promising tool for the genetic monitoring of environmental stressors. The aim of this study was to investigate whether the allozymic patterns of H. diversicolor could be affected by levels of contamination. Five sites were investigated: four in a polluted brackish habitat, the Pialassa lagoons, and a reference site in the Lamone estuary. Total mercury was used as a tracer of the overall level of contamination. Concentrations of mercury were quantified in both sediments and H. diversicolor tissues by means of cold vapour atomic fluorescence spectroscopy. A gradient of mercury concentration in both sediments and H. diversicolor tissues was found. Moreover, significant differences in concentration of mercury were observed among and within sites. Allozyme electrophoresis was used to test the occurrence of genetic differentiation among H. diversicolor samples. A total of 19 putative gene loci were analysed. For six gene loci, significant variability in genotypic and allelic frequencies was detected. Patterns of differentiation, which could be related to the contamination levels, were found at loci LDH, PGI, SDH. Other loci (ALD, FH, HBDH) showed a significant genetic structuring among samples, not related to concentrations of mercury.