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.LinkDoi: 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.LinkDoi: 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.
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, 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.
Rosselló JA, Cosín R, Bacchetta G, Brullo S, Mayol M (2009) Nuclear and chloroplast DNA variation in Cephalaria squamiflora (Dipsacaceae), a disjunct Mediterranean species. Taxon 58: 1242-1253.
Molins A, Mayol M, Rosselló JA (2009) Phylogeographic structure in the coastal species Senecio rodriguezii (Asteraceae), a narrow endemic Mediterranean plant. Journal of Biogeography 36: 1372-1383.
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.
Dubreuil M, Riba M, Mayol M (2009) Cercant els refugis de l'Orella d'ós. UAB DIVULGA 05/2009.
Molins A., Mayol M., Rosselló J.A. (2009) Phylogeographical structure in the coastal species Senecio rodriguezii (Asteraceae), a narrowly distributed endemic Mediterranean plant. Journal of Biogeography. 36: 1372-1383.LinkDoi: 10.1111/j.1365-2699.2009.02108.x
Aim Our goals were (1) to assess the levels of chloroplast DNA variation in a narrowly distributed plant restricted to continental islands, (2) to ascertain whether a phylogeographical structure is present in plants restricted to coastal linear systems, and (3) to interpret the results in the light of the known palaeogeography of these islands. Location The Eastern Balearic Islands (Majorca and Minorca) in the Western Mediterranean Basin. Methods Sampling included 134 individuals from 28 populations of Senecio rodriguezii covering the entire range of the species. Sequences of the chloroplast genome (trnT-trnL spacer) were obtained and parameters of population genetic diversity and substructure were determined (hsht, Gst). The geographical structure of genetic variation was assessed by an analysis of molecular variance (AMOVA). Additionally, a spatial AMOVA (SAMOVA) was used to identify groups of populations that were geographically homogeneous and maximally differentiated from each other. Finally, a pattern of isolation by distance was assessed by testing the correlation between the matrix of pairwise ΦST values and the matrix of geographical distances between pairs of populations using a Mantel test. Results Seven haplotypes were detected in S. rodriguezii. Only two of them were shared between islands; all of the others were restricted to Majorca (two) or Minorca (three). Overall, we found high levels of genetic diversity and significant geographical structuring of cpDNA markers. Most of the variation detected can be attributed to differences among populations (84.6%), but there was also a significant differentiation between the islands. Main conclusions Our results support the view that the Balearic Islands constitute a reservoir of genetic diversity, not only for widespread Mediterranean taxa, but also for endemic ones. The intraspecific genetic structure found in S. rodriguezii suggests that its population history was dominated by both expansion and contraction events. This has resulted in a species that is highly structured genetically, showing very few shared haplotypes between islands, and a high number of haplotypes restricted to small geographical areas within the islands. Changes in habitat availability and dynamic processes of population fragmentation and connectivity due to repeated cycles of sea-level changes during the Quaternary are the possible underlying factors that have shaped the cpDNA pool of this endemic species on a regional scale. © 2009 Blackwell Publishing Ltd.
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.LinkDoi: 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).
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