Comparative analysis of the G- and C-banding patterns in four morphologically poorly differentiated Gerbillus species (G. pyramidum, G. perpallidus, G. tarabuli and G. occiduus) was carried out. These gerbils have similar karyotype morphology with 2n and NF equal to 38/76, 40/76, 40/78 and 40/80, respectively. Our study revealed that possibly 70 Robertsonian (Rb) fusions, two pericentric inversions, one tandem translocation and at least 13 non-identified rearrangements have occurred during the karyotypic evolution of these species. The number of chromosomal changes by which any of these species differ from each other ranges from 33 to 49. One Rb fusion was common to two of the species, with only a single autosome-gonosome translocation shared by all four, suggesting a monophyletic origin of these karyotypically highly divergent species. Based on the chromosomal data obtained here, the systematic and geographic implications for these North African species are also discussed.

Chlaida, M., Laurent, V., Kifani, S., Benazzou, T., Jaziri, H., and Planes, S. 2009. Evidence of a genetic cline for Sardina pilchardus along the Northwest African coast. – ICES Journal of Marine Science, 66: 264–271. In all, 700 Sardina pilchardus from 14 locations throughout the Atlantic and Mediterranean Moroccan coastlines were screened for eight enzymatic loci that show polymorphism. Analysis of allelic frequencies showed a genetic break in the area of the Bay of Agadir, segregating two groups of samples, confirmed by analysis of molecular variance; a first consisting of Sidi Ifni (29°12′N) and southern samples down to the southern limit of the species in Mauritania (19°03′N 16°28′W), and a second starting in the Bay of Agadir (30°48′N) and consisting of northern samples that appeared homogeneous with the Mediterranean samples. Specifically, a survey of the SOD* loci demonstrated a genetic cline in allelic frequencies along the coastline. Using a clinal variation model under a state of equilibrium, we estimate a dispersal rate of 189 ± 52 km per generation between Mauritania and Ras Kebdana. This major break towards the south of the Bay of Agadir offers a new perspective on the management of sardine, which ideally ought now to be managed as two stocks along the Moroccan coast. The break is most likely induced by hydrodynamic influences that virtually isolate southern from northern populations.

Natural Hybridisation between two sympatric species of mice Mus musculus domesticus L. and Mus spretus Lataste. Using protein loci and DNA markers, we show by a multilocus genetic analysis that certain populations of the two sympatric mouse species Mus musculus domesticus and Mus spretus show clear signs of partial introgression. Given the sterility of F1 males and the known partial genetic incompatibilities between the genomes of the two species, our finding does not invalidate the biological species complex, but allows to think that very limited genetic exchanges remain possible even long after the divergence of taxa. This may have some consequences on the dynamics of certain kinds of invasive or advantageous DNAs like transposable elements or pathogen resistance genes.

The two monogenean species Metamicrocotyla cephalus and Microcotyle mugilis have specific microhabitats on the gills of Mugil cephalus on which they may or may not coexist. M. cephalus is found in sector 1 of the posterior hemibranch of arch I. M. mugilis is found on the filaments of sector 5 of the posterior hemibranch of arch I. The coexistence of these two monogenean species on the same fish does not induce a change in their respective distribution, except for a marked preference of M. cephalus for the left side and of M. mugilis for the right. This 15-month-long study shows that when the two species of monogeneans coexist the infection prevalence and intensity are higher than in cases of monospecific infection. The specific character of the microhabitat, the apparent absence of interspecific competition, and the existence of positive species interactions are discussed.

The sex chromosomes of 11 species of Gerbillidae (Meriones tristrami, M. crassus, M. libycus, M. persicus, M. unguiculatus, Gerbillus hesperinus, G. nigeriae, G. gerbillus, G. campestris, Gerbillurus tytonis, and Taterillus gracilis) are reported. A very complex evolution of the X chromosome and, to a lesser degree, of the Y chromosome was observed, including several inversions, translocations with autosomes, and an increase in heterochromatin. The role of constitutive heterochromatin, isolating autosome and gonosome segments in translocations (thus preventing any position effect), is discussed. The sequence of rearrangements affecting the sex chromosomes is considered with a view toward establishing the phylogenetic relationship of the species studied. The tendency to accumulate the same rare type of rearrangement, namely, gonosome-autosome translocations, is another demonstration that chromosomal evolution is not random in a given group of species.