Where did the first baobab trees appear? Published Wednesday May 15 in the journal Nature, the resolution of this enigma leads to Madagascar, according to the results of a large genomic study carried out by an international team led by scientists from the Wuhan Botanical Garden (China) and Queen Mary University from London.
To reach this conclusion, the researchers, who do not hide their fascination for this tree “with its grotesque shape, gigantic size and legendary longevity”, sequenced the genome of the eight known species, all grouped in the genus Adansonia , named after the French botanist Michel Adanson, who first described the tree in Senegal in the mid-18th century. Six of these species are found in Madagascar, another populates the African savannahs, and the last nests in northwest Australia.
The analysis of the genes of these different species allowed scientists to trace back to a stem species which appeared in Madagascar 41 million years ago, before it diversified through hybridization 20 million years ago. years later. It was only later that one of these species (Adansonia digitata) left the Big Island to conquer the African continent, while Adansonia gregorii migrated towards Australia.
According to the researchers, only the scenario of the Malagasy origin of the baobabs makes it possible to understand the gene flow observed between the different species. While defending the solidity of their work, they nevertheless recognize that the subject cannot be considered definitively settled. This will require “fossil materials or other relevant historical information.”
Vulnerability
The study of the genetic characteristics of species endemic to Madagascar also leads researchers to point out the vulnerability of two of them: Adansonia grandidieri, which makes up, among others, the famous “baobab alley” located on the west coast, near of Morondava, and Adansonia suarezensis, whose populations are concentrated in the north of the island.
Their low genetic diversity and the narrow ecological niches to which they are adapted limit their capacity to adapt to habitat fragmentation and climate change, they explain, pleading for the strengthening of the protection of the two species, now listed on the International Union for Conservation of Nature (IUCN) Red List of Endangered Species.
Previous work had already warned of the consequences of global warming for the emblematic tree of Madagascar. According to a study published in 2021 in the journal Global Change Biology by a team led by scientists from the Center for International Cooperation in Agricultural Research for Development (CIRAD), the increase in temperature differences could be fatal to trees dependent on a environment until now characterized by very low thermal amplitudes.
With this gap increasing by up to 1°C by the end of the century, as predicted by the Intergovernmental Panel on Climate Change (IPCC) scenarios, many species will have to migrate towards the north, where temperature variations are the lowest. But due to terrestrial limits, not all will be able to do so, the study explained. Adansonia suarezensis could thus completely disappear from its distribution area by the end of the century.
