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Email : guia.giovannelli(at)inra.fr

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Doctorante à l'Unité de Recherche  Écologie des Forêts Méditerranéennes rattachée au Département Ecologie des Forêts, Prairies et milieux Aquatiques (EFPA).

Encadrant : Bruno FADY, Directeur de recherche

Title : Evolutionary history and range-wide adaptive diversity in the European black pine, Pinus nigra Arn.

The European black pine (Pinus nigra Arn.) is an ecologically and economically important conifer discontinuously and often patchily distributed across different ecological environments and climatic conditions in Europe and around the Mediterranean Basin. Many studies aiming at understanding the evolutionary history of the species have been carried out, particularly in the hope of resolving the taxonomy of this collective species where many subspecies have been described. Several studies focused on the relationships between radial growth and climate variability were also carried out, in particular to evaluate P. nigra’s growth potential under climate change.

We firstly explored the genetic diversity of several natural populations of P. nigra covering the maximum geographic extend of the species and reviewed the phylogenetic relationships characterizing them using four DNA barcoding regions, three on the chloroplast and one on mitochondrial genomes, and 12 candidate genes. Phylogenetic relationships characterizing P. nigra and its four closest conspecific relatives were also examined. The genetic variability of the European black pine was investigated with the particular aim of providing new insights on population differentiation and for clarifying the taxonomy of the species. Three different but complementary molecular markers were used for this purpose: chloroplast and nuclear microsatellites and Single Nucleotide Polymorphisms at candidate genes. 9 out of the 14 nuclear microsatellites were specifically developed for P. nigra during the thesis. P. nigra differentiation was also investigated for a fitness related trait, radial growth, with the aim of understanding whether phenotypic plasticity or genetic diversity was mainly responsible for the patterns observed. Four common garden trials established in France and 16 different provenances encompassing the maximum diversity of the species through its native range were selected. Dendrochronology was then used to examine the reaction of P. nigra to climate variation. Ring-width x climate relationships were investigated at individual, provenance and subspecies levels. Finally, 23 provenances planted in five common gardens, four located in France and one in Tunisia approximately 40 years ago, were selected in order to understand which response variable: circumference, total height, mean ring width or diameter, would best describe the species capacity to adjust to climate change and if this capacity was spatially variable. Using niche modelling tools, differences in radial growth between provenances were also used to understand how P. nigra might adapt to future climates.

Phylogenetic analysis results grouped P. nigra with the Old World pine species P. sylvestris, P. uncinata, P. densiflora and P. resinosa and showed a complete homogeneity among the different P. nigra subspecies and provenances. Despite the wide but discontinuous geographic distribution of the species, high genetic diversity within populations and low genetic differentiation among P. nigra populations were observed, revealing the existence of substantial gene flow among the different populations. However, seven different lineages could be identified, possibly linked with the Quaternary history of the species which suggest that the taxonomy of P. nigra could be best resolved by identifying seven subspecies.

There were no major differences among subspecies for the relationship between climate and radial growth except for P. nigra salzmanii. The provenance variance component for radial growth was significant but low. The differences in radial growth among individuals and among sites is likely due to phenotypic plasticity rather than strong genetic differences. Finally, although the climatic niche of each P. nigra subspecies could be modeled, additional sites expanding the species transfer distance range are necessary to achieve a deeper