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The formation of the Amazon Basin influenced the distribution of manatees

Publicado em 10 maio 2021

All three species of manatee now present on Earth share a common ancestor from which they split some 6.5 million years ago, when a huge lake in Amazonia, then linked to the Caribbean, was cut off from the sea. The African manatee Trichechus senegalensis is not as genetically close to the West Indian manatee T. manatus as was thought, and adaptation to this complex environment by the Amazonian manatee T. inunguis has left at least one mark in its genetic code.

These are key findings of a study supported by FAPESP and published in Scientific Reports, with hitherto unknown details of the evolutionary history of these aquatic mammals. The authors are an international group of scientists led by researchers at the University of Campinas (UNICAMP) in the state of São Paulo, Brazil. They achieved the first sequencing of the mitochondrial DNA of all three manatee species.

"About 20 million years ago, Amazonia was connected to the Caribbean by Lake Pebas, a mega-wetland that has since disappeared. Manatees inhabited both Amazonia and the Caribbean—not the extant species but a common ancestor. Some 9 million years ago, the sea level fell, and Pebas shrank and became disconnected from the Caribbean. The manatees in Amazonia became semi-isolated. There was a sea inlet into the lake, but between 6 million and 5 million years ago Amazonia was totally cut off from the Caribbean. The populations became separate and began specializing in either a river or marine environment," said Mariana Freitas Nery, principal investigator for the study. Nery is a professor at UNICAMP's Institute of Biology and has a Young Investigator Grant from FAPESP.

There are few fossil records of manatees, but the researchers were able to reconstruct the evolutionary history of Trichechus by cross-referencing the existing information with geological and genetic data. Tissue samples were obtained via collaboration with researchers at the Mamirauá Institute of Sustainable Development in Amazonas, the Federal University of Minas Gerais (UFMG), and institutions in Belgium and the United States.

Mitochondrial DNA (inherited from the mother) contains fewer genes than nuclear DNA but is easier to…

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