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- 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.
- A new species of Leskeodon (Daltoniaceae) from EcuadorPublication . Buck, W. R.; Shaw, A. J.; Cox, C. J.Leskeodon caducifolius is described from recent collections made at a single site in a cloud forest in southern Ecuador. The species is distinctive in its small, caducous leaves and elongate, porose exothecial cells.
- Evolution of multiple paralogous adenosine kinase genes in the moss genus Hygroamblystegium: phylogenetic implicationsPublication . Vanderpoorten, A.; Shaw, A. J.; Cox, C. J.Maximum likelihood analyses of DNA sequences from two chloroplast regions, trnL–trnF and atpB–rbcL, and the internal transcribed spacers of 18S–5.8S–26S rRNA gene array, were performed to resolve species relationships within the moss genus Hygroamblystegium. Constraining morphospecies to monophyly resulted in significantly less likely trees for H. tenax, but not for the other species. The lack of support for most clades and the partial incongruence among topologies necessitated the use of another independent, more variable region, namely the adenosine kinase gene (adk). Sequences for adk were polymorphic but were present as multiple copies within individuals, making parology a problem for phylogenetic analyses. Adk evolution was reconstructed using a reconciled gene tree approach in which duplications and losses were minimized in the context of an estimate of the species tree derived from the analysis of the cp and nrDNA sequence data. Additional resolution of the species tree was then obtained by searching for reconstructions that further reduced adk duplications and losses. All the traditionally recognized morphospecies appeared to be polyphyletic in the resulting tree. Together with previous data from different molecular markers, the results support the interpretation that Hygroamblystegium represents a recent radiation in which molecular and morphological evolution have been uncoupled.
- Polarity of peatmoss (Sphagnum) evolution: who says bryophytes have no roots?Publication . Shaw, A. J.; Cox, C. J.; Boles, S. B.The class Sphagnopsida (Bryophyta) includes two genera: Ambuchanania and Sphagnum. Ambuchanania contains just one rare species known from two Tasmanian localities, but Sphagnum comprises a speciose clade of mosses that dominates many wetland ecosystems, especially in the boreal zone of the Northern Hemisphere. Recent phylogenetic analyses have resolved well-supported clades within Sphagnum, but polarizing Sphagnum evolution has been problematic because the genus is so isolated that it is difficult to determine homologies between morphological and/or molecular traits within Sphagnum with those of any potential outgroup. DNA sequences from 16 genomic regions representing the mitochondrial, chloroplast, and nuclear genomes (ca. 16 kilobases) were obtained from 24 species of Sphagnum plus one species each from Takakia and Andreaea in order to resolve a rooted phylogeny. Two tropical species, S. sericeum and S. lapazense, were resolved as sister to the rest of the genus and are extremely divergent from all other sphagna. The main Sphagnum lineage consists of two clades; one includes the sections Sphagnum, Rigida, and Cuspidata, and the other includes Subsecunda, Acutifolia, and Squarrosa. The placement of section Subsecunda is weakly supported, but other nodes are strongly supported by maximum parsimony, maximum likelihood, and Bayesian analyses. In addition to homogeneous Bayesian analyses, heterogeneous models were employed to account for different patterns of nucleotide substitution among genomic regions.
- Global patterns of moss diversity: taxonomic and molecular inferencesPublication . Shaw, A. J.; Cox, C. J.; Goffinet, B.Taxonomic and molecular data were utilized to test the hypothesis that moss diversity is greatest near the equator. Species richness estimates from 86 taxonomic checklists representing global moss diversity do not support the hypothesis that, in general, mosses are more species-rich in the tropics than at higher latitudes.
- Phylogenetic relationships among the diplolepideous-alternate mosses (Bryidae) inferred from nuclear and chloroplast DNA sequencesPublication . Cox, C. J.; Goffinet, B.; Newton, Alice; Shaw, A. J.; Hedderson, T. A. J.The diplolepideous-alternate peristome, when most highly developed, has endostome segments attached to a basal membrane and positioned alternate to the outer exostome teeth, with cilia often present between the segments. This peristome type defines the Bryidae (sensu Vitt et al. 1998), which includes four orders: the Bryales, Leucodontales, Hypnales, and Hookeriales, of which the latter three are mainly pleurocarpous in their growth form. Chloroplast (rbcL, rps4, and trnL-trnF) and nuclear (18S rRNA) gene sequences have been analyzed using the parsimony optimality criterion to elucidate relationships among the Bryidae. The analyses strongly support the paraphyly of the Bryidae, with the Splachnidae, and possibly the Orthotrichidae, having arisen from ancestors within the Bryidae. The Leucodontales, Hypnales, and Hookeriales form a monophyletic group, as do the pleurocarpous members of the Bryidae. However, the two pleurocarpous clades are not resolved as sister groups, although their non-monophyly is not supported by the bootstrap. The phylogenetic hypothesis provides a context in which to infer evolutionary transitions in some key morphological characters relating to the peristome and the transition from the acrocarpous to pleurocarpous growth forms.
- 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.
- Phylogenetic significance of the rpoA loss in the chloroplast genome of mossesPublication . Goffinet, B.; Wickett, N. J.; Shaw, A. J.; Cox, C. J.A recent survey of arthrodontous mosses revealed that their chloroplast genome lacks the gene encoding the alpha subunit of the RNA polymerase (i.e., rpoA), and that at least in Physcomitrella patens the gene has been transferred to the nuclear genome. Subsequently the gene was recorded from the cytoplasmic genome in Takakia and Sphagnum. Here we extend the survey to representatives of all major lineages of mosses to determine when in the evolutionary history of the Bryophyta the loss took place. Amplifications using primers annealing to the flanking regions of the rpoA gene yield a product that contains the gene in Takakia, Sphagnum, Andreaea, Oedipodium, Polytrichaceae, and Buxbaumia. The gene is lacking in all arthrodontous mosses, including Diphyscium but also in both species of Tetraphis. Reconstruction of the transfer on the phylogeny of mosses suggests (a) that the rpoA gene was lost twice and (b) that the gene was lost after the divergence of Buxbaumiidae and prior to the divergence of Diphyscium from the remaining Bryopsida.
- Variation in “biodiversity value” of peatmoss species in Sphagnum section Acutifolia (Sphagnaceae)Publication . Shaw, A. J.; Cox, C. J.Species are the most common currency by which biodiversity is measured, but species are not equivalent in ‘‘biodiversity value’’ because of differences in phylogenetic history and current population processes. Morphologically defined species in Sphagnum section Acutifolia (Bryophyta) were compared with regard to how phylogenetically distinct each is from its sister species and how much nucleotide variation each encompasses. Comparisons were based on sequence variation at seven nuclear and chloroplast loci. Assignment of collections to morphospecies accounted for about 57–75% of the overall nucleotide variation at the seven loci, but morphospecies differed greatly in how much nucleotide diversity they encompass. In addition, morphospecies varied widely in their genetic distinctiveness, estimated as the length of the stem branch from the most recent common ancestor and numbers of differentially fixed and shared polymorphic nucleotides among taxa. Levels of molecular diversity within morphospecies were not correlated with their degree of isolation. Factors that affected the biodiversity value of species include age, mode of origin, demographic history, and reproductive biology.
- Phylogeny, species delimitation, and recombination in Sphagnum section AcutifoliaPublication . Shaw, A. J.; Cox, C. J.; Boles, S. B.Nucleotide sequences for six nuclear loci and one chloroplast region were used to reconstruct phylogenetic relationships in Sphagnum section Acutifolia. The combined data matrix, which includes 136 accessions (129 ingroup taxa and seven outgroups) and 5126 nucleotide sites, was analyzed using Bayesian inference. Most of the individual morphospecies commonly recognized in the section were represented by multiple populations, in some cases by up to 16 accessions from throughout the Northern Hemisphere. Results of the combined seven-locus analysis resolved many of the species as monophyletic, but the deeper nodes were generally without support. Separate analyses of single-locus data sets revealed significant conflicts, indicating gene flow among both closely and more distantly related species within the section. The sequence data allowed likely parentage to be identified for several species of hybrid origin, and identified individual accessions that appear to be genetic admixtures. Taxonomic conclusions that can be made from the analyses include: 1. Sphagnum wulfianum and S. aongstroemii should both be included in section Acutifolia, 2. S. subtile cannot be separated from S. capillifolium, and the two should be synonymized, 3. S. capillifolium and S. rubellum each contain a monophyletic core of populations and should be retained as separate species, but 4. S. rubellum cannot be separated from S. andersonianum and S. bartlettianum and the three should be merged, 5. S. tenerum is highly differentiated from S. capillifolium and should be treated as a separate species, 6. interspecific mixed ancestry is demonstrated for S. russowii (a likely allopolyploid), S. skyense, S. arcticum, and S. olafii. Interspecific recombination appears to be rather common in section Acutifolia, yet species, for the most part, maintain cohesiveness.
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