Dubreuil M., Riba M., González-Martínez S.C., Vendramin G.G., Sebastiani F., Mayol M. (2010) Genetic effects of chronic habitat fragmentation revisited: Strong genetic structure in a temperate tree, Taxus baccata (Taxaceae), with great dispersal capability. American Journal of Botany. 97: 303-310.EnllaçDoi: 10.3732/ajb.0900148
Tree species are thought to be relatively resistant to habitat fragmentation because of their longevity and their aptitude for extensive gene flow, although recent empirical studies have reported negative genetic consequences, in particular after long-term habitat fragmentation in European temperate regions. Yet the response of each species to habitat loss may differ greatly depending on their biological attributes, in particular seed dispersal ability. In this study, we used demographic and molecular data to investigate the genetic consequences of chronic habitat fragmentation in remnant populations of Taxus baccata in the Montseny Mountains, northeast Spain. The age structure of populations revealed demographic bottlenecks and recruitment events associated with exploitation and management practices. We found a strong genetic structure, both at the landscape and within-population levels. We also detected high levels of inbreeding for a strictly outcrossing species. Chronic forest fragmentation resulting from long-term exploitation in the Montseny Mountains seems the most plausible explanation for the strong genetic structure observed. Our results support the view that, contrary to some predictions, tree species are not buffered from the adverse effects of habitat fragmentation, even in the case of species with a high dispersal potential.
González-Martínez S.C., Dubreuil M., Riba M., Vendramin G.G., Sebastiani F., Mayol M. (2010) Spatial genetic structure of Taxus baccata L. in the western Mediterranean Basin: Past and present limits to gene movement over a broad geographic scale. Molecular Phylogenetics and Evolution. 55: 805-815.EnllaçDoi: 10.1016/j.ympev.2010.03.001
English yew (Taxus baccata L., Taxaceae), a Tertiary relict, provides a seminal example of a widespread albeit locally endangered (often close to extinction) tree species. In order to gain detailed insights into the evolutionary dynamics of the species on a broad geographical scale, over 1000 trees from 91 populations of English yew in the western Mediterranean were analyzed using seven nuclear microsatellite markers. Our results revealed contrasting patterns of genetic structure at different spatial scales: genetic variation was highly structured at the local scale, while only a low proportion of the observed variation was attributed to regional differences. We also found a geographic gradient of decreasing diversity and increasing population divergence from northwest (central Europe and northern Iberian Peninsula) to southeast (Mediterranean Iberia and North Africa). The patterns revealed in this study probably reflect the combined effects of Quaternary climatic changes and recent impact of human activities, and potentially also more ancient events dating back to the Tertiary. Both climatic and anthropogenic factors seem to have conducted to a long history of population isolation, which may have contributed significantly to enhance population divergence through restricted gene flow and genetic drift. © 2010 Elsevier Inc. All rights reserved.
Dubreuil M, Riba M, González-Martínez SC, Vendramin GG, Sebastiani F, Mayol M (2010) Genetic effects of chronic habitat fragmentation revisited: Strong genetic structure in a temperate tree, Taxus baccata L. (Taxaceae), with great dispersal capability. American Journal of Botany 97: 303-310.
González-Martínez SC, Dubreuil M, Riba M, Vendramin GG, Sebastiani F, Mayol M (2010) Spatial genetic structure of Taxus baccata L. in the western Mediterranean Basin: Past and present limits to gene movement over a broad geographic scale. Molecular Phylogenetics and Evolution 55: 805-815.
Dubreuil M, Riba M, Mayol M (2009) Cercant els refugis de l'Orella d'ós. UAB DIVULGA 05/2009.
Riba M, Mayol M, Giles BE, Ronce O, Imbert E, Van der Velde M, Chauvet S, Ericson I, Bijlsma R, Vosman B, Smulders MJM, Olivieri O (2009) Darwin's wind hypothesis: does it work for plant dispersal in fragmented habitats?. New Phytologist 183: 667-677.
Riba M., Mayol M., Giles B.E., Ronce O., Imbert E., Van Der Velde M., Chauvet S., Ericson L., Bijlsma R., Vosman B., Smulders M.J.M., Olivieri I. (2009) Darwin's wind hypothesis: Does it work for plant dispersal in fragmented habitats?. New Phytologist. 183: 667-677.EnllaçDoi: 10.1111/j.1469-8137.2009.02948.x
Using the wind-dispersed plant Mycelis muralis, we examined how landscape fragmentation affects variation in seed traits contributing to dispersal. • Inverse terminal velocity () of field-collected achenes was used as a proxy for individual seed dispersal ability. We related this measure to different metrics of landscape connectivity, at two spatial scales: in a detailed analysis of eight landscapes in Spain and along a latitudinal gradient using 29 landscapes across three European regions. • In the highly patchy Spanish landscapes, seed increased significantly with increasing connectivity. A common garden experiment suggested that differences in may be in part genetically based. The was also found to increase with landscape occupancy, a coarser measure of connectivity, on a much broader (European) scale. Finally, was found to increase along a south-north latitudinal gradient. • Our results for M. muralis are consistent with 'Darwin's wind dispersal hypothesis' that high cost of dispersal may select for lower dispersal ability in fragmented landscapes, as well as with the 'leading edge hypothesis' that most recently colonized populations harbour more dispersive phenotypes. © New Phytologist (2009).
Dubreuil M., Riba M., Mayol M. (2008) Genetic structure and diversity in Ramonda myconi (Gesneriaceae): Effects of historical climate change on a preglacial relict species. American Journal of Botany. 95: 577-587.EnllaçDoi: 10.3732/ajb.2007320
The importance of the Mediterranean Basin as a long-term reservoir of biological diversity has been widely recognized, although much less effort has been devoted to understanding processes that allow species to persist in this area. Ramonda myconi (Gesneriaceae) is a Tertiary relict plant species restricted to the NE Iberian Peninsula. We used RAPD and chloroplast markers to assess the patterns of genetic structure in eight mountain regions covering almost the full species range, to identify the main historical processes that have shaped its current distribution and to infer the number and location of putative glacial refugia. While no cpDNA variation was detected, the species had relatively high levels of RAPD variation. Maximum levels of diversity were found within populations (71%), but there was also a significant differentiation between geographical regions (20%) and among populations within regions (9%). A spatial AMOVA identified three main groups of populations, corresponding to previously recognized centers of endemism and species richness. In addition, we found a marked geographical pattern of decreasing genetic diversity and increasing population differentiation from west to east. Our results support a complex phylogeographic scenario in the Iberian Peninsula of "refugia-within-refugia" and suggest that the higher diversity observed in western regions might be associated with prolonged and more stable climatic conditions in this area during the Quaternary.
Dubreuil M., Sebastiani F., Mayol M., González-Martínez S.C., Riba M., Vendramin G.G. (2008) Isolation and characterization of polymorphic nuclear microsatellite loci in Taxus baccata L.. Conservation Genetics. 9: 1665-1668.EnllaçDoi: 10.1007/s10592-008-9515-3
Seven polymorphic nuclear microsatellite markers for Taxus baccata L. (English yew) were developed using an enriched-library method. An additional polymorphic SSR was obtained by testing eight primer pairs from the congeneric species Taxus sumatrana. Mendelian inheritance for the seven Taxus baccata SSRs was proved by genotyping 17 individuals and 124 megagametophytes (conifer seed haploid tissue). A total of 96 individuals from 5 different populations (10-26 samples per population) were used to estimate genetic diversity parameters. High levels of genetic diversity, with values ranging from 0.533 to 0.929 (6-28 alleles per SSR) were found. No linkage disequilibrium between pairs of loci was detected. All loci but one showed significant departures from Hardy-Weinberg equilibrium. Excess of homozygosity was probably due to high inbreeding in English yew populations, an outcome of low effective population size and/or fragmented distribution. Highly polymorphic SSRs will be used to conduct population genetic studies at different geographical scales and to monitor gene flow. © 2008 Springer Science+Business Media B.V.
Colas B, Kirchner F, Riba M, Olivieri I, Mignot A, Imbert E, Beltrame C, Carbonell D, Fréville H (2008) Restoration demography: a 10-year demographic comparison between introduced and natural populations of endemic Centaurea corymbosa (Asteraceae). Journal of Applied Ecology 45: 1468-1476.
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