For millions of years, mighty baobabs have stood guard on three different landmasses, asking each other an existential question: who came first?
The huge trees, swollen trunks and stubby foliage, are unmistakable. Baobabs can live for more than 1,000 years and act as the keystone species in dry forest environments in Madagascar, part of continental Africa and northwestern Australia. Known as ‘mother of the forest’ and ‘the tree of life’, almost every part of the tree can be used by humans and animals, meaning they are of enormous value to any ecosystem in which they live.
Their reputation has only been burnished by the mystery of where they came from. Until now, science has had to make do with several conflicting hypotheses – the dominant theory being that they originated in mainland Africa. That is not the case, according to a study published last month in the journal Nature. A team of international academics has successfully sequenced the genomes of each of eight baobab species, examined their relationships with each other and concluded that they originated in Madagascar.
The news comes at a time when trees on the island, home to six baobab species, are suffering a steep decline, with one likely to become extinct by 2080, according to the study, unless major interventions are made.
Biologists have struggled to determine the tree’s origins because no fossils of ancient baobabs or their ancestors have been discovered, Dr. Wan Jun-Nan, one of the study’s authors, a researcher at the Wuhan Botanical Garden in Hubei, China. The genetic data collected from baobabs in previous studies was limited, he continued. But with the first complete genome sequence of any species, “we can tell a good story about evolutionary history,” he argued.
That story begins with the emergence of baobabs in Madagascar, about 21 million years ago, before the genus (scientific name Adansonia) began to diversify, and two species made their way to Africa and Australia about 12 million years ago. This happened long after the separation of the “supercontinent” Gondwana, so the baobab likely spread via seeds carried across the ocean on floating debris caused by flash floods, the researchers said.
The study, a collaboration between the Wuhan Botanical Gardens, China, the Royal Botanic Gardens in Britain, the University of Antananarivo in Madagascar and Queen Mary University of London, was also able to determine the interspecies gene flow of the eight species of baobab trace for the first time. These data, which showed low genetic diversity between two species, and inbreeding of one species with another, more populous species, provide insight into the competition among baobabs today, Dr Wan said, and could help shape the trees of tomorrow to protect.
“We hope that in the future the people of Madagascar can care for baobabs (by) considering them as different species, and not as one whole,” he added.
Only one baobab species is not on the IUCN Red List of Threatened Species: A. figures, which populates mainland Africa. Three species in Madagascar are threatened with extinction, and the study recommended that the IUCN recategorize one: A. suarezensis, from ‘endangered’ to ‘critically endangered’. Climate models indicated that the species could become extinct within fifty years without greater intervention.
That prediction is “plausible” and “highlights the urgent need for action,” said Dr. Seheno Andriantsaralaza, a tropical ecologist working in Madagascar.
Dr. Andriantsaralaza, who was not involved in the research, supported the call to update the IUCN status of certain Malagasy baobabs. While she described the study as “fantastic and meaningful,” providing “valuable” insights into genetic data, she cautioned that it represented “only one piece of the puzzle in understanding the evolutionary history and dispersal mechanisms of these iconic giant trees.”
The study’s modeling concluded that the number of baobab species on the island has been declining for millennia, with human-induced climate change and ongoing deforestation exacerbating the shrinkage and fragmentation of baobab populations in recent decades.
Dr. Andriantsaralaza said: “It is crucial to recognize that amid the challenges there are local success stories and initiatives led by local organizations and local researchers.”
She cited the conservation group Madagasikara Voakajy, which coordinates projects in the north of the island aimed at protecting nature. A. perrieri And A. suarezensis. PEER, a USAID-supported program in which she is involved, also aims to empower local people to contribute to the sustainable management of the ecosystem.
“Madagascar’s baobab forests belong to local communities who rely on natural resources to feed their families,” she added. “They should be part of the solution, not part of the problem.”
Dr. Wan said he hoped the research and media attention would lead to further efforts to conserve the island’s baobabs.
While he welcomed the breakthrough, he acknowledged the study’s limitations – only one individual per species was sequenced – although he hoped future research would expand sampling and answer further outstanding questions about the trees.
The chance that fossil evidence will be found to support the conclusions of the genetic data is small, Dr. Come on. So perhaps these majestic trees retain some of their mystery after all.
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