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In this study we analyzed patterns of sequence divergence in about 1kb of mitochondrial DNA coding for two genes (16S rRNA and Cytochrome Oxidase I, COI) in 15 populations and 61 individuals of the halophilic fairy shrimp Phallocryptus spinosa (Milne-Edwards, 1840). Populations were sampled in saline and hypersaline water bodies from Spain, France, Italy, Greece, Turkey, Ukraine, Iran, Uzbekistan, Cyprus, Algeria, Morocco and Botswana. Our genetic findings suggest complex phylogeographic relationships and pronounced genetic differentiation among populations. Multiple phylogenetic methods and nested clade analysis revealed the existence of four highly divergent maternal lineages with strong phylogeographic patterns and signatures of either allopatric fragmentation or restricted gene flow with isolation by distance. These results are further supported by the hierarchical analysis of molecular variance (AMOVA) and pairwise F ST values, which indicate that most of detected genetic heterogeneity is apportioned among populations. Genetic relationships among haplotypes fit geographical hypotheses in most cases but one. Indeed, one haplotype is shared among French, Iranian and Uzbekistan populations. We hypothesize that this peculiar occurrence might be due to an avian-mediated long distance passive dispersal event.

Allozymic variation at 21-23 loci was studied in 28 populations of Talitrus saltator, 23 populations of Orchestia montagui, 13 populations of O. stephenseni, and five populations of Platorchestia platensis from the Mediterranean Basin. Different levels of gene flow (Nmtheta) were detected within each species at the scale of the whole Mediterranean: O. montagui and P. platensis had low population structure, with levels of Nmtheta > or = 1, whereas the T. saltator and 0. stephenseni populations have values of Nmtheta < 1. The relationship between Nmtheta and geographic distance was analyzed to test for the presence of an isolation by distance pattern in the spatial genetic variation within each species. A model of isolation by distance is useful to describe the pattern of genetic structuring of study species at the scale of the whole Mediterranean: geographic distance explained from 28% to 70% of the variation in gene flow. In the Aegean area all species showed an island model of genetic structuring regardless of the levels of gene flow.

Genetic variability was assessed in eight populations belonging to the Leuciscus souffla complex and in nine populations of Leuciscus cephalus, sampled in France, Italy and Greece and in one population of Leuciscus lucumonis, endemic to Italy. Twenty-six enzymatic loci were analysed in order to clarify the genetic relationships, the patterns of colonisation of peri-Mediterranean area and the taxonomic positions. Results indicate a more ancient penetration of the Leuciscus souffia complex in southern Europe (possibly during the Messinian 'Lago Mare' phase of the Mediterranean), whereas L. cephalus and L. lucumonis seem to have quite recently reached these regions (about 1Myr). These evidences are discussed in relation to the two main proposed models of primary freshwater fishes colonisation of peri-Mediterranean area. In addition, the genetic distance suggests a generic separation between the two complexes. The genus Telestes Bonaparte, is rehabilitated to include members of the Leuciscus souffia complex which is represented by endemic taxa from southern France, Italy and westem Balkans.