William Balla – Literature Review
Emadzade, K and Hörandl, E. (2011). “Northern Hemisphere origin, transoceanic dispersal and
diversification of Ranunculeae DC (Ranunculaceae) in the Cenozoic.” Journal of Biogeography. Volume
38, Issue 3. Pages 517-530.
Elvira Hörandl is interested in phylogeny, evolution, and taxonomy of Ranunculus and related genera
and evolution and biogeography of apomictic plants. Department of Systematic and Evolutionary
Botany, University of Vienna, Vienna, Austria.
Khatere Emadzade has an interest in phylogenetic analysis and biogeographical studies. Department of
Systematic and Evolutionary Botany, University of Vienna, Vienna, Austria.
The research problem or question:
To reconstruct divergence dates of Ranunculaceae, determine the geographical origin, and identify
whether the disjunct distribution patterns of the plant are either a result of dispersal or vicariance.
The background knowledge leading up to this study:
Disjunct distributions are widely accepted to be explained by either vicariance events or dispersal across
a barrier. One way to show the most likely method of distribution is to estimate divergence dates and
reconstruct the time period of when and where the evolution of the species began. Ranunculaceae Juss
is a plant family that is both widespread across all continents and species rich, so it makes a good model
to use for reconstructing its evolution.
The methods used by investigators:
Phylogenic analysis of nuclear and chloroplast DNA sequences for 18 genera and 89 species. Estimating
divergence dates using Bayesian uncorrelated rates analysis. Parsimony based methods for dispersal –
vicariance analysis (DIVA and MESQUITE) and maximum likelihood based method (LAGRANGE) used for
reconstructing ancestral areas.
What are the results of the study:
Results suggest that the origin of several clades of Ranunculaceae is most likely in the Northern
Hemisphere. Clade 1 was found by two methods to be most likely originating from Europe or Asia and
Clade 2 was found by all three methods to have originated from North America. The age of the split of
the two main clades most likely date back to the late Eocene around 38 million years ago, around the
same time as the separation of Greenland form Europe and the opening of the North Atlantic. The two
main clades diversified on opposite sides of the Atlantic and at the time of the late Eocene the
continents of North and South America were not connected. The results show that all diversification
likely took place during the Cenozoic when there were oceanic barriers in place between all the major
continents.
What are the weaknesses of the study:
Accuracy can be questioned because of the inability to differentiate accurately between pollen fossils of
closely related species of plants. The node has a bootstrap of less than 50 and results of the
biogeographical conclusion must be taken as tentative.
What we learned new from the research:
The distribution of the species of plant likely occurred when oceanic barriers likely existed between
continents and so dispersal is the probable method for its evolution. Potential is in place for both transoceanic dispersal and migration across land bridges to have occurred. The break-up of Gondwanaland
had been a major theory for the modern distribution of some taxa, but with recent evidence from
molecular DNA and phylogenetic studies on plants there is solid reasoning to reject the former theory in
favor of dispersal and even trans-oceanic dispersal, which had been thought previously to be mostly
unlikely.