Ephedra pollination and other gnetalean oddities
Humphreys, Aelys M. .
Evolution of ancient lineages: independently evolving higher units in the seed plant order Gnetales.
I will present the research framework of an ongoing project investigating diversification dynamics in ancient lineages, with focus on preliminary results in Gnetales. Recently, Catarina Rydin and co-workers (Rydin et al. 2010) put forward a hypothesis for the diversification history of Ephedra based on analysis of fossils and living species.They hypothesised that extant diversity is the result of a relatively recent re-radiation following extinction of most Cretaceous forms. While it is widely recognised that absence in the fossil record does not necessarily equate to low abundance of living species the hypothesis has support from a small number of morphological features. However, the hypothesis has never been tested numerically against alternative scenarios in a molecular phylogenetic framework. It remains possible therefore that Cretaceous diversity did not dwindle to near extinction but that it is still declining, in a slow decline that has continued throughout the Cenozoic. Alternatively, ephedran diversity may have declined to a new ‘diversity limit’ governed by the new climatic conditions of the Paleogene, at which it may have remained until the present. The use of molecular phylogenies for estimating past extinction has been criticised for a number of reasons, some of which have been overcome by recent improvements to the models used. A remaining difficulty has been defining what clades should be analysed separately, because processes operating in some clades may mask the signature of processes operating in other clades and thus prevent accurate parameter estimation. I will present an approach for delimiting evolutionarily significant units above the species and evidence for (or against) the presence of independently evolving lineages in Gnetales, as a step toward testing alternative hypotheses of extinction in Gnetales.
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1 - Stockholm University, Department of Botany, Botaniska Institutionen, Stockholm, SE-10691, Sweden
Presentation Type: Symposium or Colloquium Presentation
Location: Delaware A/Hyatt
Date: Monday, July 9th, 2012
Time: 10:00 AM