Percorrer por autor "Shaw, B."
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- Extant diversity of bryophytes emerged from successive post-Mesozoic diversification burstsPublication . Laenen, B.; Shaw, B.; Schneider, H.; Goffinet, B.; Paradis, E.; Desamore, A.; Heinrichs, J.; Villarreal, J. C.; Gradstein, S. R.; McDaniel, S. F.; Long, D. G.; Forrest, L. L.; Hollingsworth, M. L.; Crandall-Stotler, B.; Davis, E. C.; Engel, J.; Von Konrat, M.; Cooper, E. D.; Patino, J.; Cox, C. J.; Vanderpoorten, A.; Shaw, A. J.Unraveling the macroevolutionary history of bryophytes, which arose soon after the origin of land plants but exhibit substantially lower species richness than the more recently derived angiosperms, has been challenged by the scarce fossil record. Here we demonstrate that overall estimates of net species diversification are approximately half those reported in ferns and similar to 30% those described for angiosperms. Nevertheless, statistical rate analyses on time-calibrated large-scale phylogenies reveal that mosses and liverworts underwent bursts of diversification since the mid-Mesozoic. The diversification rates further increase in specific lineages towards the Cenozoic to reach, in the most recently derived lineages, values that are comparable to those reported in angiosperms. This suggests that low diversification rates do not fully account for current patterns of bryophyte species richness, and we hypothesize that, as in gymnosperms, the low extant bryophyte species richness also results from massive extinctions.
- Newly resolved relationships in an early land plant lineage: Bryophyta class Sphagnopsida (peat mosses)Publication . Shaw, A. J.; Cox, C. J.; Buck, W. R.; Devos, N.; Buchanan, A. M.; Cave, L.; Seppelt, R.; Shaw, B.; Larraín, J.; Andrus, R.; Greilhuber, J.; Temsch, E. M.Premise of the study : The Sphagnopsida, an early-diverging lineage of mosses (phylum Bryophyta), are morphologically and ecologically unique and have profound impacts on global climate. The Sphagnopsida are currently classifi ed in two genera, Sphagnum (peat mosses) with some 350 – 500 species and Ambuchanania with one species. An analysis of phylogenetic relationships among species and genera in the Sphagnopsida were conducted to resolve major lineages and relationships among species within the Sphagnopsida. Methods : Phylogenetic analyses of nucleotide sequences from the nuclear, plastid, and mitochondrial genomes (11 704 nucleotides total) were conducted and analyzed using maximum likelihood and Bayesian inference employing seven different substitution models of varying complexity. Key results : Phylogenetic analyses resolved three lineages within the Sphagnopsida: (1) Sphagnum sericeum , (2) S. inretortum plus Ambuchanania leucobryoides , and (3) all remaining species of Sphagnum . Sister group relationships among these three clades could not be resolved, but the phylogenetic results indicate that the highly divergent morphology of A. leucobryoides is derived within the Sphagnopsida rather than plesiomorphic. A new classifi cation is proposed for class Sphagnopsida, with one order (Sphagnales), three families, and four genera. Conclusions : The Sphagnopsida are an old lineage within the phylum Bryophyta, but the extant species of Sphagnum represent a relatively recent radiation. It is likely that additional species critical to understanding the evolution of peat mosses await discovery, especially in the southern hemisphere.
- Peatmoss (Sphagnum) diversification associated with Miocene Northern Hemisphere climatic cooling?Publication . Shaw, A. J.; Devos, N.; Cox, C. J.; Boles, S. B.; Shaw, B.; Buchanan, A. M.; Cave, L.; Seppelt, R.Global climate changes sometimes spark biological radiations that can feed back to effect significant ecological impacts. Northern Hemisphere peatlands dominated by living and dead peatmosses (Sphagnum) harbor almost 30% of the global soil carbon pool and have functioned as a net carbon sink throughout the Holocene, and probably since the late Tertiary. Before that time, northern latitudes were dominated by tropical and temperate plant groups and ecosystems.