Genetic variation was investigated in 17 populations of the Italian endemic Apennine yellow-bellied toad using both mitochondrial (598 bp of the cytochrome b gene) and nuclear (21 allozyme loci) markers. Populations from central Calabria (southern Italy) showed the highest levels of intrapopulation genetic variation, whereas samples located north of this region were nearly lacking in variation. This appears to be a typical pattern of 'southern richness and northern purity', usually attributed to the prolonged population stability within southern refugia coupled with the loss of variation during postglacial northward expansion. However, the overall pattern of genetic variation observed has a strong geographical component, suggesting two Calabrian plains, Catanzaro and Crati-Sibari, as historical barriers to dispersal separating three population groups. These findings cannot be explained by the prolonged stability of southern populations alone, and suggest that the southern richness has been at least in part shaped by allopatric differentiation within the refugial range, followed by intermixing of previously differentiated lineages. From a conservation standpoint, Calabria is the major genetic diversity reservoir for this species, thus deserving particular conservation efforts. Furthermore, although the low intrapopulation genetic variation outside Calabria appears to be of clear historical origin, evidence of a current reduction of gene flow suggests that human disturbance has also played a part, particularly in the anthropogenic impacted Volturno river drainage basin.

We investigated the geographical patterns of genetic diversity in the Italian treefrog through sequence analysis of a mitochondrial cytochrome b gene fragment. Three main mitochondrial lineages were identified, distributed in northern, central and southern Italy, respectively. Their divergence appears indicative of a split time largely predating Late Pleistocene climatic oscillations, and syntopy between them was only observed in the geographically intermediate populations. The historical demographic reconstructions suggest that in both northern and central Italy, an expansion occurred during the last major glacial phase, when a vast widening of the lowland habitats followed the glaciation-induced fall of the sea level. Instead, in southern Italy an expansion event likely followed the end of the last glaciation, although the inference of expansion appears less reliable for the southern clade than for the others. Within this geographical area, a sharp phylogeographic discontinuity separated peninsular from Sicilian populations, and the overall pattern of diversity suggests that the latter derived from a recent colonization of the island, probably through a Late Pleistocene land bridge. Phylogenetic, phylogeographic and historical demographic analyses thus concur in delineating a scenario of multiple refugia, with four groups of populations which survived the last glacial-interglacial cycles in at least three distinct refugia arranged along peninsular Italy, and have recently come into contact following range expansions. Therefore, these results support the hypothesis that a plethora of microevolutionary processes, rather than the prolonged stability of populations, were mainly responsible for shaping the patterns of diversity within this major biodiversity hotspot.

No abstract

For most species in the Western Palaearctic region, southern Mediterranean peninsulas have been identified as major Quaternary refugia and hotspots of intraspecific diversity, and thus, as areas of particular relevance for the conservation of the evolutionary potential. We analysed the patterns of geographical variation among 26 populations of the Italian stream frog, using both nuclear (allozymes) and mitochondrial (partial cytochrome b sequences) markers. Phylogenetic, phylogeographical and population genetic analyses suggested that the species survived the last glacial-interglacial cycles in two distinct refugia, one restricted to the tip of the Calabrian peninsula, at the extreme south of the species' range, the other spanning from central Calabria to central Apennines and showing evidences for further population subdivision therein. Historical demographic tests suggested a significant population expansion from the latter, which most likely began around the last pleniglacial. This expansion would have led to the rapid colonization of the northern Apennines to the north, and to a secondary contact and population admixture with the population from the southern refugium in southern central Calabria. A comparison of the evolutionary history inferred for the Italian stream frog with the data emerging for other codistributed species suggests: (i) the generality of a multiple-refugia scenario for the Italian peninsula, (ii) the possible occurrence of at least one suture zone in southern Italy, and (iii) that for most species, this Pleistocene refugium is not only a hotspot, but also a melting pot of intraspecific genetic diversity. Finally, the conservation implications of these results are also briefly highlighted.

This study aimed at assessing the genetic structure and the state of the stocks of the European hake (Merluccius merluccius). To this end, 15 samples were taken from the whole range of the species and analysed using allozymes. Since 11 samples were taken from the poorly studied Mediterranean Sea, the results obtained provided a complete picture of the hake's genetic structure and an initial insight into its relationships with environmental features. Atlantic and Mediterranean hake populations are separated by the Almeria-Oran front. This area has been proved to be the boundary between Atlantic and Mediterranean stocks of many marine organisms, but some doubt exists concerning the efficaciousness of the local gyres as barriers to the gene flow. Our data have evidenced a latitudinal cline at loci Gapdh and Gpi-2 within the Mediterranean Sea, with a further steep change across the Almeria-Oran front. The genetic pattern showed a strong correlation with the values of the salinity both at the surface and at -320 m and of the salinity + temperature at the surface, suggesting a role for these parameters in maintaining the genetic differentiation among the two population groups through selective processes. Finally, the levels of genetic variability were found to be slightly lower in the depleted Atlantic stock than in the Mediterranean one.