Giovanni Zecca

Allopatric divergence and secondary contacts in Euphorbia spinosa L: Influence of climatic changes on the split of the species

Euphorbia spinosa, a perennial xerophilous shrub naturally distributed across the Italian peninsula, was selected for examination of the role of the Ligurian Alps and Apennines in glacial survival. The Italian Peninsula is considered to be one of the principal glacial refugia in Europe, but few plant population genetic and phylogeography studies have been undertaken in this region. The combined analysis of chloroplast and nuclear loci (ITS, cpSSR and ISSR) enabled us to detect extensive DNA variation and proved to be a very powerful tool for the reconstruction of the phylogeography. Molecular data support the hypothesis of a long-term separation of the Northwestern (Maritime Alps, Sardinia, Corsica, Northern Apennines) and Southeastern (Southern Apennines and Balkan area) lineages in glacial refugia. The existence of allopatrically fragmented lineages is most probably the result of isolation in different glacial refugia, possibly due to the Last Glacial Maximum cooling and the topographic complexity of the Italian peninsula. The most plausible hypothesis assumes the formation of two migration paths during more recent periods: the first one starting with southward migration and the second one moving northwards. The Central Apennines should be considered the confluence of migration routes radiating from separate refugia according to this hypothesis.

RPB2 gene reveals a phylodemographic signal in wild and domesticated grapevine (Vitis vinifera)

Polymorphism at the single copy RPB2 locus was investigated to define the relationship between wild and domesticated grapevines. Two different forms still coexist in Eurasia, the cultivated (Vitis vinifera L. ssp. vinifera) and the wild (Vitis vinifera L. ssp. sylvestris (Gmelin) Hegi), referred to as separate subspecies. Using the observed number of mutations at the RPB2 locus, as well as archaeological data, to define an approximate age of domestication, we have estimated a high nucleotide substitution rate (4.25 × 10−7) in the domesticated group. Moreover, the dynamics of population size in the RPB2 gene were estimated using Bayesian coalescent inference. The Bayesian skyline plot offered interesting information on the past dynamics of RPB2 for both wild and domesticated groups. The signal of exponential growth observed in grapevine accessions can be viewed as a consequence of human breeding activity during the domestication of the species. However, a recent and drastic decline of population size has been observed in the Mediterranean wild lineages. This event mirrors the demographic decline of wild grape, probably explained by anthropogenic pressure on its natural habitats and by the introduction of pathogens from North America in recent centuries.

Phylogeographic Insights into a Peripheral Refugium: The Importance of Cumulative Effect of Glaciation on the Genetic Structure of Two Endemic Plants

Quaternary glaciations and mostly last glacial maximum have shaped the contemporary distribution of many species in the Alps. However, in the Maritime and Ligurian Alps a more complex picture is suggested by the presence of many Tertiary paleoendemisms and by the divergence time between lineages in one endemic species predating the Late Pleistocene glaciation. The low number of endemic species studied limits the understanding of the processes that took place within this region. We used species distribution models and phylogeographical methods to infer glacial refugia and to reconstruct the phylogeographical pattern of Silene cordifolia All. and Viola argenteria Moraldo & Forneris. The predicted suitable area for last glacial maximum roughly fitted current known distribution. Our results suggest that separation of the major clades predates the last glacial maximum and the following repeated glacial and interglacial periods probably drove differentiations. The complex phylogeographical pattern observed in the study species suggests that both populations and genotypes extinction was minimal during the last glacial maximum, probably due to the low impact of glaciations and to topographic complexity in this area. This study underlines the importance of cumulative effect of previous glacial cycles in shaping the genetic structure of plant species in Maritime and Ligurian Alps, as expected for a Mediterranean mountain region more than for an Alpine region.

Black Woodpecker Dryocopus martius habitat selection in the Italian Alps: implications for conservation in Natura 2000 network

The Black Woodpecker Dryocopus martius is the largest woodpecker of the Palearctic Region and it has been recognised as a keystone species whose presence provides critical resources to secondary cavity-users in European forest ecosystems. Here we investigate cavity tree and foraging-habitat selection of Black Woodpecker in three natural parks located in the central and eastern Italian Alps and included in the Natura 2000 network. A total of 94 cavity trees were identified, showing a minimum diameter of 35 cm and a mean diameter of 51 cm. We counted 30 active nests, but only 40% were newly excavated. Silver fir Abies alba and larch Larix decidua were preferred as cavity trees, with silver fir also associated with habitat surrounding the cavity trees. Norway spruce Picea abies and Silver fir were found to be positively associated with the surroundings of feeding sites. Logistic regression models identified the average diameter at breast height and the average tree crown height as significant predictors, positively associated with both cavity trees (AUC: 0.988) and cavity tree plots (AUC: 0.866). Also, the total volume of dead logs and the percentage of understorey cover turned out to be significant predictors of feeding sites, showing a positive and a negative association, respectively (AUC: 0.708). Cross validation of logistic regression models indicated that only cavity tree models can be considered useful tools in conservation practice. Overall, our results indicated that the Black Woodpecker behaves like an opportunist when choosing feeding sites. On the other hand, our results also indicate that the Black Woodpecker clearly behaves as a demanding species when it selects cavity trees, showing a hierarchical pattern in habitat selection and a marked preference for large trees with high crown height. We discuss the implications of our results for the conservation of the Black Woodpecker in Natura 2000 alpine sites.

Are the responses of plant species to Quaternary climatic changes idiosyncratic? A demographic perspective from the Western Alps

Background: Previous studies have indicated that several plant species had shown remarkable resistance to Pleistocene climate changes and survived the Last Glacial Maximum in scattered ice-free refugia within the European Alps and peripheral areas nearby. The ‘Expansion–Contraction’ model has been proposed to describe the responses of organisms to Pleistocene climate change. Nevertheless, the timing and extent to which species were affected by Quaternary glaciations remain uncertain. Aims: To test whether the ‘Expansion–Contraction’ model appropriately describes plant distribution responses to Pleistocene climate change in the Western Alps. Methods: We employed two Bayesian coalescent-based methods on plastid DNA sequences to infer the demographic histories of Ranunculus kuepferi, R. glacialis, Biscutella laevigata, Saxifraga oppositifolia, Primula allionii, P. marginata, Silene cordifolia and Viola argenteria. Results: R. kuepferi conformed to the ‘Expansion–Contraction’ model, while other species did not. For example, P. allionii showed an alarming population decline during the Middle-Late Pleistocene. Conclusions: The application of Bayesian coalescent-based methods to plastid DNA data offers useful insights into plant demography as a function of palaeoclimatic events. Our findings favour an idiosyncratic response of plant species in the Western Alps to Pleistocene climate change.