On May 15, 2024, led by the Wuhan Botanical Garden of the Chinese Academy of Sciences/ Sino-African Joint Research Center (referred to as the "Sino-African Center"), in collaboration with Queen Mary University of London, Royal Botanic Gardens, Kew, BGI Group, University of Antananarivo in Madagascar, National Museums of Kenya, Shanghai Chenshan Botanical Garden, and other research institutions, a research paper titled "The rise of baobab trees in Madagascar" was published in the journal Nature. The study systematically elucidated the evolutionary history of the endangered plant genus Baobab, drawing global attention. It proposed Madagascar as the center of origin and diversification for this genus. Through comprehensive analysis of genetic, ecological, and geographical data, the research highlighted the driving factors behind the historical population dynamics of Baobab trees in Madagascar and put forward scientific and effective conservation strategies and recommendations for their future protection.
Madagascar, the fourth largest island in the world, is renowned for its highly diverse and unique biodiversity, making it one of the most important biodiversity hotspots globally and a "natural laboratory" for studying biological evolution and conservation. Baobab trees (Adansonia), belonging to the mallow family, are deciduous trees found in the subfamily Bombacoideae. There are only eight species of Baobab trees globally, with six endemic to Madagascar, and the remaining two species found in mainland Africa and Australia. Baobab trees can live for over a thousand years, their fruits are edible, their trunks store water, and their bark is used for handicrafts and construction materials. In arid conditions, they provide water, food, and shelter for various animals, earning them the title of "Tree of Life." In Madagascar, they are also known as the "Mother of the Forest," holding significant scientific, economic, ecological, and cultural value. Additionally, their enormous size and unique morphology have created stunning natural landscapes, attracting countless global travelers annually.
Figure 1. Global Distribution Patterns and IUCN Endangered Protection Levels of Baobab Plants
In recent years, the conservation of baobab plant diversity has become a hot topic of discussion in academia and among the general public due to the impacts of global changes and habitat destruction. Particularly in Madagascar, the population sizes and suitable habitats of some baobab species have drastically decreased. Three baobab species have already been listed as endangered or critically endangered species on the IUCN Red List. Meanwhile, there is still significant controversy surrounding the center of origin and the formation history of the geographical distribution patterns of baobab plants. Therefore, it is urgent to clarify the process of baobab plant diversity patterns formation as soon as possible. This will guide the development of more effective conservation strategies through systematic scientific research.
The Avenue of Baobabs in Morondava, Madagascar (Photo: Sino-African Center)
Researchers analyzed the genetic information of wild individuals from eight baobab tree species in Madagascar, Senegal, and Australia, reconstructing the evolutionary history of the baobab genus. They found that the diversification of baobab species began approximately 21 million years ago, much later than the separation of the African and Australian plates and the formation of the island of Madagascar (about 160 million years ago). Furthermore, comprehensive data analysis revealed instances of interspecific hybridization in baobab tree species, including those with intercontinental isolation or island co-distribution in history, leading to inconsistencies in the phylogenetic signals at the whole-genome level within the genus (see Figure 3). Based on the historical sympatric hybridization patterns and the potential for transoceanic dispersal revealed by the study, it is proposed that Madagascar should be considered the center of origin and diversification for the extant baobab genus.
Moreover, by integrating genetic diversity calculated from whole genomes, historical population sizes, and ecological data analysis, the study unveiled the ecological niche competition among the six extant baobab tree species in Madagascar. It was discovered that changes in island area due to historical fluctuations in global sea levels, geological factors such as island uplift and volcanic eruptions, collectively drive the dynamic changes in population size and distribution of baobab tree species on the island (see Figure 4). The rich microhabitat heterogeneity generated by geological evolution and the potential for interspecific hybridization have contributed to the diversity of baobab tree species on the island, providing an important research case for understanding the formation of species evolution and distribution patterns, especially the mechanisms behind the unique biodiversity in Madagascar.
Figure 3. Phylogenetic Relationships and Interspecific Hybridization History of 8 Species in the Baobab Genus
Figure 4. Historical population changes of baobab trees in Madagascar and their impacts from geological events, sea level changes, etc.
Furthermore, the study also found that the IUCN may underestimate the real endangered status of baobab tree species in Madagascar. By assessing interspecific competition and hybridization effects within the genus and integrating genomic and ecological research results, new conservation recommendations and strategies have been proposed for specific baobab tree species in Madagascar, providing a new scientific perspective and important reference for effectively protecting the overall biodiversity of the island.
Concurrently, researchers published a research briefing titled "The evolutionary history of baobabs and implications for their conservation" in the journal Nature.
Dr. Wang Qingfeng and Dr. Wan Tao from the Wuhan Botanical Garden of the Chinese Academy of Sciences are the corresponding authors of the paper. Dr. Wan Junnan, Dr. Wang Shengwei, Professor Andrew R. Leitch from Queen Mary University of London, Professor Ilia J. Leitch from the Royal Botanic Gardens, Kew, and Dr. Jianbo Jian from BGI Group are the co-first authors. This research was supported by the Sino-Africa Center, the National Natural Science Foundation of China, and other projects. This achievement is a phased summary of the Wuhan Botanical Garden/Sino-Africa Center's long-term close collaboration with research institutions in Africa, Europe, and other regions to carry out research and conservation of African biodiversity. The team has previously published a series of related research papers in journals including Nature Plants (2018), and Nature Communications (2021).
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