Genetic structure of bisexual and parthenogenetic populations of Artemia from Italian brackish–hypersaline waters

Eight populations of Artemia displaying different reproduction modalities (amphigonic vs. parthenogenetic) and ploidies (diploid vs. polyploid) have been collected from Italian salt-works or brackish coastal lagoons, and their genetic structure has been investigated using allozyme electrophoresis. The results obtained on genetic differentiation showed that the Tyrrhenian bisexual samples (A. salina) are genetically homogeneous even between populations located in relatively faraway sites (Sardinia–Latium), having a moderate gene flow assisted by migratory waterfowl. The parthenogenetic samples (A. parthenogenetica) are genetically well differentiated both from the bisexual ones and among them, even when characterised by the same ploidy. Each sample presents few genotypes (i.e. few or single clones have been found in each sampling site), well distinguished from all the others. Further results concern the levels of genetic variability recorded. The parthenogenetic populations have an extremely high level of heterozygosity, due to a remarkable number of loci showing fixed heterozygosity, up to 13 out of 18 analysed. The preliminary data presented here show that some strains of A. parthenogenetica have a number of biological features typical of species of hybrid origin: fixed heterozygosity at many loci, parthenogenetic reproduction and genome polyploidisation. While too preliminary to advance a new hypothesis on the origin of A. parthenogenetica, our data suggest that further studies need to be carried out aimed at the research of possible bisexual parental species of A. parthenogenetica suspected hybrid strains.