Laboratory of Plant Systematics

Evolution of Spermacoceae on Madagascar

The tribe Spermacoceae is the largest herbaceous group within Rubiaceae. This first part of my postdoc project focuses on the evolution, origin and biogeography of Spermacoceae on Madagascar. An ongoing taxonomical revision of Spermacoceae on Madagascar demonstrates that the tribe is represented on the island by about 17 genera and more than 40 species. At least six genera and 20 species are endemic to Madagascar; the remaining taxa are also present in other tropical regions.

A molecular phylogenetic study based on atpB-rbcL, petD, rps16 and trnL-trnF sequences supports the hypothesis that the current diversity of Spermacoceae on Madagascar is the result of at least twelve independent colonisation events, most likely long-distance dispersals from the African continent. Dating analyses are currently carried out to estimate divergence times of the Madagascan Spermacoceae. Furthermore, we are planning to reconstruct the historical biogeography of Spermacoceae on the island. The final goal is to get insights into the mechanisms that have driven the radiation of Spermacoceae on Madagascar. By comparing our results with those of Dr. James Tosh, who works on woody Malagasy Ixoreae, we will be able to formulate general hypotheses on island speciation.

 

 

 

Molecular evolution and phylogenetic performance of non-coding chloroplast DNA: a case study in Rubiaceae

The application of non-coding DNA in plant molecular systematics has been steadily increasing over the last decade, and has proven useful at different taxonomic levels. Microstructural mutations (insertions, deletions and inversions) present in non-coding sequences are a valuable source of information for phylogenetic studies. Unfortunately, little is known on the exact evolution of these microstructural mutations, which is crucial for a correct use of non-coding DNA in phylogenetic studies. Using the family Rubiaceae as a model, the general objective of this part of the project is to produce new insights into the evolution of non-coding chloroplast DNA, and to explore its potential for phylogenetic reconstruction. Patterns of evolution in microstructural mutations will be characterized in a selection of chloroplast introns and spacers. A general methodology for phylogenetic inference based on non-coding chloroplast DNA will be proposed to increase the effective application of non- coding sequences in phylogenetic studies on flowering plants.

 

Evolution of corolla slits within Rubiaceae

In general, Rubiaceae are characterized by tubular sympetalous corollas. However, some Rubiaceae are exceptional in having openings or slits at the base or in the middle of their corolla tube, e.g. Pentas, Sacosperma, Pentodon, Paederia, and Mussaenda. Our molecular phylogenetic hypothesis suggests that these corolla slits have evolved several times independently during the evolution of Rubiaceae. An on-going floral ontogenetic homology assessment of corolla slits in Rubiaceae will determine which types of corolla slits are homologous.