Genetic variability and divergence among Italian populations of common ash (Fraxinus excelsior L.)

Abstract

-The level of genetic variation throughout the Italian range of common ash (Fraxinus excelsior L.) was estimated using six microsatellite markers. High levels of allelic diversity was detected. The levels of expected heterozygosity for each of the populations ranged from 0.726 to 0.871, with an average of 0.798, and indicated that populations have a high level of genetic variation. A general and significant homozygote excess was found at most loci in all populations, with an overall mean F IS of 0.284. Possible explanations for such situations are discussed. Only 4.9% of the total diversity was attributable to differentiation among populations. Although divergence among pedo-climatic regions explained only a small part of the variance it was possible to observe some partial clustering of populations belonging to the same regions. The contribution of the results in relation to the definition of the most appropriate strategies to collect forest reproductive material is discussed.genetic variation / microsatellite / population differentiation / seed zone designation / Fraxinus excelsior Résumé -Variabilité génétique et différenciation entre populations italiennes de frêne commun (Fraxinus excelsior L.). Le niveau de variation génétique dans l'aire de distribution naturelle du frêne commun (Fraxinus excelsior L.) en Italie a été estimé à l'aide de six marqueurs microsatellite. Des niveaux élevés de diversité allélique ont été détectés. L'hétérozygotie théorique varie de 0,726 à 0,871, avec une moyenne de 0,798, ce qui indique que les populations ont un niveau élevé de variation génétique. Un excès général et significatif de l'homozygotie a été trouvé pour la plupart des loci dans toutes les populations, avec une moyenne globale F IS de 0,284. Des explications possibles pour de telles situations sont proposées. Seulement 4,9 % de toute la diversité est attribuable à la différenciation entre populations. Bien que la divergence entre régions pédo-climatiques explique une petite partie de la variation, il est possible d'observer des regroupements partiels de populations appartenant aux mêmes régions. La contribution de ces résultats à la définition des stratégies les plus appropriées pour rassembler le matériel forestier de reproduction est discutée. diversité génétique / microsatellite / différenciation entre populations / région de provenance / Fraxinus excelsior

Variation de la résistance au gel au printemps et en automne entre et dans les populations espagnoles sauvages de Castanea sativa

“…Chestnut pollination is mainly entomophilous (Manino et al, 1991;Oliveira et al, 2001), and this species has large, sticky pollen, which may reduce gene flow among populations due to poor ability of pollen to be moved by wind (Ferrazzini et al, 2007). We thus suggest that the presumed low gene flow may lead to reduced genetic variation within populations.…”

“…In the Iberian peninsula, considered by several authors as a possible site of its autochthonous origin (Aira-Rodríguez and Ramil-Rego, 1995;Fineschi et al, 2000;García-Antón et al, 1990;Krebs et al, 2004), it is present as a natural or naturalised tree. The scattered distribution and isolation of populations may have resulted in differentiation among chestnut populations in adaptive traits (Ferrazzini et al, 2007), with drought and frosts being expected to be causal forces of natural selection (Fernández-López et al, 2005a). In fact, several authors have observed differentiation among populations for different adaptive traits, such as vigour, growth initiation and cessation, and drought resistance (Fernández-López et al, 2005a;2005b;Lauteri et al, 2004;Pliura and Eriksson, 2002), and some of these authors have suggested drought as a selective force in natural selection.…”

What sampling is needed for reliable estimations of genetic diversity in Fraxinus excelsior L. (Oleaceae)?

“…At least for the case of the widespread common ash in Europe, genetic diversity results derived from nuclear microsatellite loci Ferrazzini et al, 2007;Gerard et al, 2006;Hebel et al, 2006;Heuertz et al, 2001;Morand et al, 2002) suggest that allelic richness and gene diversity are fairly similar. Yet, more important than the numbers of alleles is the identity of those alleles and genetic conservation should favor the preservation of private alleles (Kalinowski, 2004;2005), a result only possible if several populations are sampled.…”

Paternity analysis of pollen-mediated gene flow for Fraxinus excelsior L. in a chronically fragmented landscape

“…The phylogeography of the species is now well described (Morand et al, 2002;Heuertz et al, 2004;Ferrazzini et al, 2007). F. excelsior displays a complex, polygamous sexual system (FRAXIGEN, 2005) in which individuals may be classified phenotypically across a continuum from purely male to purely female with a whole range of hermaphroditic intermediates.…”