It is now official. The Cape Floristic Region's beloved Ericas' earliest ancestor originated from the Northern hemisphere and used Africa's highest mountain ranges as stepping stones to reach the Cape about 10 to 15 million years ago.
Once this early ancestor arrived, it found the perfect climatic conditions and topography which allowed it to explode in evolutionary terms. Today there are 860 species worldwide, of which 690 are endemic to the Cape – making Ericas not only the most species rich fynbos family, but also the most successful coloniser of all South African plants.
This is the findings from new research published this week in BMC Evolutionary Biology in an article titled, "The biodiversity hotspot as evolutionary hot-bed: spectacular radiation of Erica in the Cape Floristic Region". The research, conducted by a group of scientists from South Africa and Germany, is based on nuclear and chloroplast DNA sequencing of 606 accessions of 488 species from across the geographic range of the genus, as well as six outgroups. This represents 60% of all Erica species.
Prof. Dirk Bellstedt, an evolutionary biologist in the Department of Biochemistry at Stellenbosch University (SU) and one of the co-authors, says the number of species outside the CFR are lower by an order of magnitude.
"Our research shows conclusively that the diversity of Erica species in the CFR is the result of a single radiation within the last 15 million years. The rate of speciation accelerated across Africa and Madagascar, with a further burst of speciation when it reached the Cape. There are only 170 Erica species in the rest of the world, compared to 690 species endemic to the Cape."
Early botanists originally believed that all Africa's plants originated from Europe. But since the advent of DNA sequencing techniques, it has been shown that migration has taken place in both directions. Proteas also originated in the North, but other fynbos groups, such as Disa and Pentameris, the families Iridaceae and Restionaceae, all migrated from the south to the north.
Prof. Bellstedt says the Cape Ericas' first common ancestor literally arrived "at the right place at the right time".
"When it arrived in the Cape, it coincided with a drying out period, coupled with cooler air from the newly-formed cold Benguela current on the West Coast. With the onset of this aridity, more lush growing vegetation started dying out and that probably opened the space necessary for the medium- and small-sized Erica bushes to expand and form new species at a rampant rate," he explains.
Speciation was also aided by the topography of the Cape, with extremes from very high to low within a short distance: "In some areas of the Kogelberg Nature Reserve you will find once species of Erica endemic to a single spot of 25 square metres. Ericas are extremely localised and therefore appear to occupy specific pockets or niches to which they appear to have adapted perfectly."
But what drives this speciation mechanism in Ericas? Is it inherent to the plant's genetic makeup? Or does it depend on environmental factors?
"That," prof. Bellstedt smiles, "is the million dollar question. We simply do not know.
"We do know that the flowers of the Cape's Ericas are larger than their counterparts in the north. The flowers have evolved to allow sunbirds to pollinate them. But it is very difficult to determine whether the interaction with sunbirds drove this speciation or not.
"We can only stand amazed at this plant's ability to evolve into so many species," he concludes.
- Prof. Bellstedt, Dr Mike Pirie and Dr. Ted Oliver from Stellenbosch University planned and designed the research project. Dr Oliver, regarded as a world expert on Erica taxonomy, identified the different species collected from Europe, Africa, Madagascar, the Indian Ocean islands, the Drakensberg Mountains and the Cape. PhD student Nicolas le Maitre performed the bulk of the DNA sequencing at SU, whilst Dr Mugrabri de Kuppler performed the rest in Germany. Dr M Kandziora, a postdoctoral fellow at the Institüt fur Spezielle Botanik und Botanischer Garten at the Johannes Gütenberg-Universität in Mainz, Germany, used some of the most recently developed analysis methodologies to perform the phylogenetic and speciation rate analyses on the DNA sequence data.
The research was largely funded by the South African National Research Foundation and grants from SU and the Deutsche Forschungs Gemeinschaft.
On the photo above: Prof. Dirk Bellstedt (left), an evolutionary biologist from the Department of Biochemistry at SU, has achieved one of his life ideals by investigating and writing up the evolutionary history of erikas. Because the genus is so large, a team of scientists from South Africa and Germany participated in the project, including Nicholas le Maitre (right), a PhD student in his research group. This photo was taken at the entrance to the SU Botanical Gardens in front of a 20-year-old Erica arborea, one of the few species of erikas that can grow up to 20 metres high and is found over large parts of Africa.
Close-up photo of an Erica arborea taken by Jean-Pol Grandmont, Creative Commons Attribution-Share Alike 3.0 Unported licence
Listen to an interview with Prof. Bellstedt on Radio Today's Sappi Nature Journal.
Contact details:
Prof. Dirk Bellstedt
Department of Biochemistry
T: +27 _21 808 5840
E: dub@sun.ac.za
