Éditeur(s) : HAL CCSD NRC Research Press
Résumé : Molecular, cytological, and morphological data support the existence of a hybrid population between Schoenus nigricans and Schoenus ferrugineus. This population was found in northeastern Italy, where S. nigricans is central with respect to its natural range and S. ferrugineus is marginal, being most common in the Alps and in central and northern Europe. Molecular marker data show that the putative hybrid population is genetically intermediate between nearby populations of the parent species. Cytological evidence confirmed the hybrid nature of this population, as does the almost complete sterility of plants within the population. Although no seeds were produced by the hybrid population, some possibly fertile pollen grains were produced; this suggests that the possibility of introgression between the two species through the hybrids cannot completely be excluded.
ISSN: 0831-2796

hal-01032047
https://hal.archives-ouvertes.fr/hal-01032047
DOI : 10.1139/G01-138

Éditeur(s) : HAL CCSD BioMed Central
Résumé :  
absent
ISSN: 1471-2148

hal-01032078
https://hal.archives-ouvertes.fr/hal-01032078
DOI : 10.1186/1471-2148-10-202

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
The within-population spatial structure of genetic diversity is shaped by demographic processes, including historical accidents such as forest perturbations. Information drawn from the analysis of the spatial distribution of genetic diversity is therefore inherently linked to demographic-historical processes that ultimately determine the fate of populations. All adult trees and saplings in a 1.4-ha plot within a mixed Norway spruce (Picea abies [L.] Karst) stand were characterised by means of chloroplast (paternally inherited) markers, and a large sub-sample of these were genotyped at mitochondrial (maternally inherited) molecular markers. These data were used to analyse the spatial distribution of genetic variation and to compare the patterns corresponding to the two marker types. The plot presented non-homogeneous local stem density in the younger cohorts, and the indirect effect of this source of variation on the spatial genetic structure was investigated. Results suggest that (i) spatially limited seed dispersal induced patchiness in genotype distribution, while pollen flow had a homogenising effect; (ii) deviations from random spatial structure were stronger in the demographically most stable portions of the stand, while they were weaker where sudden bursts of regeneration occurred; (iii) spatially overlapping adult and sapling cohorts displayed the same spatial genetic structure (stronger on stable areas, weaker in portions of the stand undergoing events of intense regeneration), which was substantiated by the influence of local demographic processes. Regeneration dynamics as modulated by demography thus influences the distribution of genetic diversity within the stand both in the younger life stages and in the adult population.
ISSN: 0378-1127

hal-01032063
https://hal.archives-ouvertes.fr/hal-01032063
DOI : 10.1016/j.foreco.2008.03.023

Éditeur(s) : HAL CCSD Wiley
Résumé : Genetic variation is generally considered a prerequisite for adaptation to new environmental conditions. Thus the discovery of genetically depauperate but geographically widespread species is unexpected. We used 12 paternally inherited chloroplast microsatellites to estimate population genetic variation across the full range of an emblematic circum-Mediterranean conifer, stone pine (Pinus pinea L.). The same chloroplast DNA haplotype is fixed in nearly all of the 34 investigated populations. Such a low level of variation is consistent with a previous report of very low levels of diversity at nuclear loci in this species. Stone pine appears to have passed through a severe and prolonged demographic bottleneck, followed by subsequent natural- and human-mediated dispersal across the Mediterranean Basin. No other abundant and widespread plant species has as little genetic diversity as P. pinea at both chloroplast and nuclear markers. However, the species harbors a nonnegligible amount of variation at adaptive traits. Thus a causal relationship between genetic diversity, as measured by marker loci, and the evolutionary precariousness of a species, cannot be taken for granted
ISSN: 0014-3820

hal-01032062
https://hal.archives-ouvertes.fr/hal-01032062
DOI : 10.1111/j.1558-5646.2007.00294.x

Éditeur(s) : HAL CCSD Wiley
Résumé : [b]Aim[/b][br/] [br/] The phylogeographical history of Neotropical species can be difficult to reconstruct because of superimposed Neogene and Quaternary histories, and because of taxonomic uncertainty. We analysed range-wide genetic diversity in a widespread pioneer tree species, Jacaranda copaia (Aubl.) D. Don, to characterize phylogeographical structure, date the evolutionary relationships among lineages, and evaluate the role of dispersal and vicariance in establishing the present geographical range.[br/] [br/] [br/] [b]Location[/b][br/] [br/] Guiana Shield; central, southern and western Amazon Basin; Chocó region; Central America.[br/] [br/] [br/] [b]Methods[/b][br/] [br/] We analysed nine nuclear simple sequence repeat loci (nuSSR), eight chloroplast SSRs (cpSSR), and two cpDNA intergenic sequences in 341 adult trees. Genetic differentiation at nuSSRs was inferred using Bayesian clustering. Dating of chloroplast lineage divergence was obtained using a range of published mutation rates and Bayesian coalescence analyses. Population divergence dating was performed using an isolation-with-migration model for eight loci (one cp sequence and seven nuSSRs).[br/] [br/] [br/] [b]Results[/b][br/] [br/] Nuclear SSR variation identified three geographically overlapping clusters (nu-1, nu-2, nu-3). Twelve cpDNA haplotypes were clustered into two haplogroups (cp-1, cp-2) with the central Amazon harbouring the highest diversity. Molecular dating analysis suggests that cpDNA haplotype diversification started around the end of the Pliocene (2.61 Ma on average), whereas population divergence was more recent and occurred during the mid-Quaternary (point estimates between 357 and 436 ka).[br/] [br/] [br/] [b]Main conclusions[/b][br/] [br/] The genetic variation of J. copaia in the Neotropics was shaped mainly by Pleistocene events. Chloroplast diversity did not display the expected cis/trans Andean disjunction, indicating recent dispersal. Nuclear variation revealed that separate regions share a recent history, with a centre of diversity in the central Amazon Basin. The geographical pattern of diversity is congruent with the distribution of the two subspecies, J. copaia copaia and J. copaia spectabilis, and evidence of nuSSR admixture between the two taxa supports their classification as subspecies.
ISSN: 0305-0270

hal-01032410
https://hal.archives-ouvertes.fr/hal-01032410
DOI : 10.1111/j.1365-2699.2012.02797.x