ORCID Profile
0000-0002-4612-1399
Current Organisation
University of Pretoria
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Publisher: Elsevier BV
Date: 10-2009
DOI: 10.1016/J.YMPEV.2009.05.031
Abstract: Crabs of the family Hymenosomatidae are common in coastal and shelf regions throughout much of the southern hemisphere. One of the genera in the family, Hymenosoma, is represented in Africa and the South Pacific (Australia and New Zealand). This distribution can be explained either by vicariance (presence of the genus on the Gondwanan supercontinent and ergence following its break-up) or more recent transoceanic dispersal from one region to the other. We tested these hypotheses by reconstructing phylogenetic relationships among the seven presently-accepted species in the genus, as well as examining their placement among other hymenosomatid crabs, using sequence data from two nuclear markers (Adenine Nucleotide Transporter [ANT] exon 2 and 18S rDNA) and three mitochondrial markers (COI, 12S and 16S rDNA). The five southern African representatives of the genus were recovered as a monophyletic lineage, and another southern African species, Neorhynchoplax bovis, was identified as their sister taxon. The two species of Hymenosoma from the South Pacific neither clustered with their African congeners, nor with each other, and should therefore both be placed into different genera. Molecular dating supports a post-Gondwanan origin of the Hymenosomatidae. While long-distance dispersal cannot be ruled out to explain the presence of the family Hymenosomatidae on the former Gondwanan land-masses and beyond, the evolutionary history of the African species of Hymenosoma indicates that a third means of speciation may be important in this group: gradual along-coast dispersal from tropical towards temperate regions, with range expansions into formerly inhospitable habitat during warm climatic phases, followed by adaptation and speciation during subsequent cooler phases.
Publisher: Elsevier BV
Date: 09-2008
DOI: 10.1016/J.YMPEV.2008.05.030
Abstract: Phylogeny reconstruction is challenging when branch lengths vary and when different genetic loci show conflicting signals. The number of DNA sequence characters required to obtain robust support for all the nodes in a phylogeny becomes greater with denser taxon s ling. We test the usefulness of an approach mixing densely s led, variable non-coding sequences (trnL-F rpl16 atpB-rbcL ITS) with sparsely s led, more conservative protein coding and ribosomal sequences (matK ndhF rbcL 26S), for the grass subfamily Danthonioideae. Previous phylogenetic studies of Danthonioideae revealed extensive generic paraphyly, but were often impeded by insufficient character and taxon s ling and apparent inter-gene conflict. Our variably-s led supermatrix approach allowed us to represent 79% of the species with up to c. 9900 base pairs for taxa representing the major clades. A 'taxon duplication' approach for taxa with conflicting phylogenetic signals allowed us to combine the data whilst representing the differences between chloroplast and nuclear encoded gene trees. This approach efficiently improves resolution and support whilst maximising representation of taxa and their sometimes composite evolutionary histories, resulting in a phylogeny of the Danthonioideae that will be useful both for a wide range of evolutionary studies and to inform forthcoming realignment of generic delimitations in the subfamily.
Publisher: Springer Science and Business Media LLC
Date: 21-06-2011
Publisher: Royal Botanical Gardens and Domain Trust
Date: 13-11-2006
Publisher: Missouri Botanical Garden Press
Date: 10-2010
DOI: 10.3417/2009006
Publisher: Wiley
Date: 21-10-2011
Publisher: JSTOR
Date: 2002
DOI: 10.2307/4115718
Publisher: Springer Science and Business Media LLC
Date: 12-2012
Publisher: Wiley
Date: 30-07-2007
Publisher: Proceedings of the National Academy of Sciences
Date: 06-01-2009
Abstract: Dating the Tree of Life has now become central to relating patterns of bio ersity to key processes in Earth history such as plate tectonics and climate change. Regions with a Mediterranean climate have long been noted for their exceptional species richness and high endemism. How and when these biota assembled can only be answered with a good understanding of the sequence of ergence times for each of their components. A critical aspect of dating by using molecular sequence ergence is the incorporation of multiple suitable age constraints. Here, we show that only rigorous phylogenetic analysis of fossil taxa can lead to solid calibration and, in turn, stable age estimates, regardless of which of 3 relaxed clock-dating methods is used. We find that Proteaceae, a model plant group for the Mediterranean hotspots of the Southern Hemisphere with a very rich pollen fossil record, ersified under higher rates in the Cape Floristic Region and Southwest Australia than in any other area of their total distribution. Our results highlight key differences between Mediterranean hotspots and indicate that Southwest Australian biota are the most phylogenetically erse but include numerous lineages with low ersification rates.
Publisher: Elsevier BV
Date: 04-2009
DOI: 10.1016/J.YMPEV.2008.12.013
Abstract: The angiosperm family Proteaceae is a distinct component of the Cape Floristic Region bio ersity hotspot with 330 endemic species. Phylogenetic analyses of subfamily Proteoideae using sequence data from one nuclear and six plastid loci show that most of this ersity is contained in two distinct Cape floral clades. Molecular dating analyses, using Bayesian and penalized likelihood methods and four phylogenetically supported fossil age constraints, reveal contrasting histories for these two clades. The genus Protea belongs to a lineage that may have been in Africa since the Late Cretaceous but began to ersify in the Cape only 5-18 Myr ago. In contrast, the Leucadendrinae clade presumably arrived in the region no earlier than 46 Myr ago by long-distance dispersal from an Australian ancestor and the extant members of this clade began to ersify in the Cape 22-39 Myr ago. These results join a growing number of case studies that challenge the commonly accepted view that most of the Cape flora radiated synchronously in the Late Miocene and Early Pliocene when a Mediterranean climate settled in the region.
Publisher: Wiley
Date: 30-08-2013
DOI: 10.1111/JBI.12201
No related grants have been discovered for Nigel Barker.