Comparative pattern of genetic structure in two Mediterranean killifishes Aphanius fasciatus and Aphanius iberus inferred from both mitochondrial and nuclear data.

In this study, genetic variation was assessed in Aphanius fasciatus and Aphanius iberus characterized by similar ecological traits but with very different distribution ranges in the Mediterranean area. Five populations of A. iberus and five of A. fasciatus were analysed using five polymorphic microsatellite loci and partial mitochondrial control region (D-loop) sequences. Congruent results were found with both nuclear and mitochondrial molecular markers. The results showed that similar levels of genetic divergence, based on mitochondrial control region sequences, are present among populations of A. iberus and among populations of A. fasciatus despite the very different geographic distance existing among the examined populations of the two species (low geographic distance in A. iberus and high in A. fasciatus). A possible explanation could be that the populations of A. iberus were isolated for a longer time than the populations of A. fasciatus supporting the hypothesis that the split in the lineage leading to A. iberus is older than the split in the lineage leading to A. fasciatus. The possibility that the wide circum-Mediterranean distribution of A. fasciatus ensures the high connectivity of its populations, preventing, in some cases, local differentiation, however, cannot be ruled out.

Morphological analysis of the pharyngeal jaws in two populations of Lebias fasciata Valenciennes, 1821 (Teleostei: Cyprinodontidae).

The study of the pharyngeal jaws in two geographically isolated Italian populations of Lebias fasciata indicated the presence of two phenotypes: the Adriatic phenotype with a large ceratobranchial V and upper and lower pharyngeal jaws bearing few large teeth and the Sicilian phenotype with a smaller ceratobranchial V and pharyngeal jaws with smaller and more numerous teeth. The morphological variations of pharyngeal jaws should be interpreted as a result of the geographical isolation of these two populations.

Chromosomal mapping and molecular characterization of ribosomal RNA genes in Lebias fasciata (Teleostei, Cyprinodontidae).

Chromosome location of major (18S, 5.8S and 28S) and 5S ribosomal RNA genes (rDNAs) was examined in Lebias fasciata collected from different Italian blackish-waters, using silver (Ag)- and chromomycin A3 (CMA3)-staining and/or fluorescence in situ hybridization (FISH). Both 18S and 5S rDNA probes for FISH were obtained with polymerase chain reaction-directed cloning from genomic DNA of the examined species. Nucleolar organizer regions (NORs) containing the major rDNAs showed intraspecific polymorphism in number as detected by Ag-and CMA3-staining and FISH with the 18S rDNA probe. On the other hand, 5S rDNA loci constantly occurred on one chromosome pair and co-localized with a pair of the major rDNA loci as evidenced by two-color FISH using the 5S and 18S rDNA probes. Sequential CMA3- and Ag-NOR staining and FISH revealed apparent inactivation of some NORs. The cloned 5S rDNA was found to contain some TATA-like sequences that might play an important role in the regulation of gene expression.