Reconstruction of the refuge theory in tropical Africa in the Marantaceae
Final Report Abstract
Vegetation history of the African rainforest is still largely unknown. One popular hypothesis suggests major speciation events to have happend during Pleistocene climate fluctuations which forced repeated forest retractions into isolated refuge areas. To falsify this hypothesis studies are already underway in several tree species. To extent these tests to herbal species confined to the tropical rainforest understorey sister taxa of different Marantaceae genera representing different life-forms (lianas and herbs), seed sizes, pollinators and breeding systems (autogamy versus allogamy) were submitted to phylogeographic analyses. If the refuge hypothesis was correct we expected equal spatial genetic diversity patterns of rare mutations in all investigated taxa. The analyses included sequencing of nuclear (5S) and chloroplast (trnC-petN1r, psbA-trnH) DNA markers as well as the addition of AFLP markers to achieve a better coverage across the whole nuclear genome. We thereby developed a novel approach to assess band reproducibility and chose reliable bands. In two liana species from the genus Haumania the distribution pattern of genetic diversity strongly indicated allopatric speciation with H. danckelmaniana originating in Gabon/Cameroon and H. liebrechtsiana having expanded into Gabon from Southeastern populations. The suggested localities of origin are concordant with postulated refuge areas. In the area of species overlap morphological and genetic signs (haplotype sharing) of hybridization were documented. In the herbal genus Marantochloa again haplotype-sharing occurred indicating the hybrid origin of M. incertifolia from interbreeding of M. congensis and M. monophylla. This was supported by morphologically intermediate characteristics found in M. incertifolia. Surprisingly, no genetic variability could be found over the entire distribution area of M. congensis from Senegal to eastern DRCongo. This might hint towards an extremely rapid expansion of M. congensis based on the vegetative reproduction through frequently produced bulbils. The herbal species Halopegia azurea showed concordant diversity pattern of locally restricted haplotypes with the other two genera in the topographically rich areas of Mt. Cameroun, Mt. de Cristal and the Chaillu massif. These concordant patterns might hint towards a common evolutionary history in these three genera, however, referring to the Pleistocene refuge hypothesis, the timing of the observed patterns is still unknown. In the future we want to intensify sampling efforts across the Congo Basin, as it plays an important role in the vegetation history of central African rainforests, as shown by the data, try to quantify the extend of hybridization and the influence of different life-history traits (e.g. clonality, pollen and seed dispersal) onto phylogeographic pattern and compare genetic diversity patterns with species range extrapolations based on climate reconstructions of different time slices in the past.
Publications
- 2010. Species delimitation in the Central African herbs Haumania (Marantaceae) using georeferenced nuclear and chloroplastic DNA sequences. Molecular Phylogenetics and Evolution 57: 859–867
Ley, A.C. and O.J. Hardy
