A new study shows that there has been a larger gene flow than previously thought among elephant species, both living and extinct. In addition, it points out that African savannah elephants and forest elephants should be seen as two different species.

2018-03-05

The elephant - the largest mortal mammal - began to land on the earth 5-10 million years ago in Africa. Today, there are less than 500,000 live elephants left, making this group of animals to protected species, especially in Africa where ivory trade continues to threaten them. The shrinking elephant population thus constitutes an "isolated branch" in development, with only three living species: the Asian elephant, the African savannah elephant and the African forest elephant.

About 50,000 elephants are killed every year by poaching, which threatens many populations. Mastodonts and mammoths, who were close relatives, have disappeared. Knowledge of the genetic heritage of the elephant can play a valuable role in future conservation work to prevent these animals from being eradicated.

An international consortium, using senior researchers from the Broad Institute of MIT and Harvard, Harvard Medical School, Uppsala University, University of Potsdam and McMaster University, has used advanced sequencing technology to explore the legacy of living and extinct elephant species. In the article, which is now published in PNAS, the authors report a comprehensive genetic record for now-living elephant species, as well as mammals, extinct elephants with straight bites and the American mastodont, an extinct relative to the elephant family. The article shows that the gene flow (genetic mix) between elephant species was common in their history, unlike previous studies, which presented their family as simple trees.

"Over the years, there has been a debate about whether African savannah and jungle elephants are two different species," says Kerstin Lindblad-Toh, working at Broad Institute and Professor of Comparative Genomics at IMBIM, Uppsala University, one of the key organizers of Elephant Genome Project (EGP), when it started in 2008. Our data show that these two species have been isolated for long periods of time, and therefore both should be preserved.

The article confirms that African savannah elephants and forest elephants are two different species, thus forming an argument for protecting both species.

The researchers took the tag for all now living elephant species and a high quality genome for an extinct 120,000-year-old elephant with straight grazing, as well as generating common genomes from several ancient mastodont and mammoth genes.

"The combined analysis of common genomes of all these ancient elephants and mastodonts has given us knowledge of the history of the elephant population, and revealed a complexity that we were previously completely unaware about," says Kerstin Lindblad-Toh.

The extinct elephants with straight grazing have traditionally been grouped with today's Asian elephant due to morphological similarities in skulls and teeth. However, an article published last year by a group led by Michael Hofreiter showed that elephants with straight grazing on average were closer to African forest elephants than with Asian elephants.

"We were confused by the difference between morphological and genetic results, but our analyzes show that the straight-elephant elephants were very complex, and included three different components," said Eleftheria Palkopoulou, the article's first author.

The article reveals that the extinct elephant derives from a mixture of ancient African elephant, wicked mammoth and today's forest elephant.

"The results were extremely surprising," said Palkopoulou. The relationship of the elephant population could not be explained by simple divisions that gave clues to understand the
In fact, her analysis revealed several cases of crossings between different ancient species, emphasizing that mixing between divergent species is a fundamental feature of the elephant's development, and it raises the question of how widespread blends are in other species.

The article is published today in the scientific journal PNAS:
Paper cited: Palkopoulou E, et al. A comprehensive genomic history of extinct and living elephants. PNAS. Online February 26, 2018. DOI: 10.1073

Anneli Waara

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