Madagascar is the most plausible center of origin for the iconic baobabs, also known as upside-down trees, or the tree of life, according to new research.
The baobab tree in Senegal. Image credit: Viajesunion2.
The genus Adansonia, better known as the baobabs and ‘mother of the forest’, has captivated botanists, tourists, naturalists and passers-by for centuries.
Probably the earliest record of humans marveling at these amazing trees can be traced back to the Ancient Egyptians, around 2,300 BCE.
With their grotesque appearance, enormous size, reputed longevity and diverse uses, baobabs have become one of the most charismatic species on our planet.
Embedded in folklore and tradition, baobabs have inspired innumerable pieces of art and have been associated with human settlements and cultures over millennia.
Adansonia comprises eight morphologically distinct species: one widespread across Africa, one located in Northwestern Australia, and the other six endemic to Madagascar.
However, owing to the lack of fossil evidence, there has been a long-running debate about where the baobabs originated.
“Our work has uncovered new insights into the patterns of speciation in baobabs and shows how climate change has influenced baobab distribution and speciation patterns over millions of years,” said Dr. Ilia Leitch, a researcher Royal Botanic Garden Kew.
Dr. Leitch and his colleagues conducted genomic analyses of all eight baobab tree species and combined these datasets with ecological analyses.
The analyses indicate that the stem lineage of Adansonia originated around 41 million years ago and diversified around 20 million years ago.
The researchers found that the historical population dynamics of baobabs are closely related to both interspecific competition and geological changes in Madagascar, especially the change in sea level.
Based on data including phylogenetic relationship, gene flow and genetic diversity of different baobab species, they suggest that the hypothesis of Madagascar as the center of origin for baobabs offers the most reasonable explanation of the current data, as opposed to the hypotheses for mainland Africa and Australia.
The findings also enabled the scientists to re-evaluate the conservation strategies and status of baobabs.
For example, they propose that a higher conservation status should be assigned to the two endangered Malagasy baobab species, Adansonia suarezensis and Adansonia grandidieri.
High levels of inbreeding, low genetic diversity and declining population size all suggest that these endangered species are lacking in resilience to ecological perturbations and will potentially be under severe threat from climate change.
“We were delighted to be involved in this project uncovering patterns of baobab speciation in Madagascar followed by the astonishing long-distance dispersal of two species, one to Africa and another to Australia,” said Professor Andrew Leitch, a researcher at Queen Mary University of London.
“This was accompanied by the evolution of some fascinating pollination syndromes involving hawkmoths, lemurs and bats.”
The study was published in the journal Nature.
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JN. Wan et al. The rise of baobab trees in Madagascar. Nature, published online April 19, 2024; doi: 10.1038/s41586-024-07447-4
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