Scientists extracted and sequenced the DNA from seven different extinct and living species from the elephant family. This included the wooly mammoth but also a straight-tusked elephant which lived 120,000 years ago. The genome-wide analysis showed that the modern elephant family tree is more branched out than previously thought. What’s more, African elephants can be split into two different species: those that live in forests and those that roam the savannas. This means that there actually are three species of elephants alive today, the third being the Asian elephant (Elephas maximus).
“Elephants and their ancient relatives like the woolly mammoths and mastodons have long fascinated people the world over. But until now there has been no comprehensive assessment of their evolutionary relationships,” said Professor David Adelson, Director of the University of Adelaide’s Bioinformatics Hub.
For centuries, people have known elephants come in only two varieties, either African or Asian. The two are easily set apart by differences in size and whether females have tusks or not.
African elephants have large ears, shaped much like the continent of Africa itself. The larger surface area of their ears helps to keep African elephants cool in the blazing African sun. Asian elephants have less to worry about heat-wise, as they tend to live in cool jungle areas, so their ears are smaller. What’s more, African elephants have fuller, more rounded heads, and the top of their head is a single dome. Asian elephants can also be recognized by their twin-domed head with an indent in the middle.
Two close cousins
For some time, biologists have suspected that there are, in fact, two species of elephants in Africa, living in the forest (Loxodonta cyclotis) and savannah (Loxodonta africana) elephant. There is no official consensus on the matter, and most often the two are treated as subspecies.
The distinction is very important to make, however, because the difference could mean extinction for one of the two. Forest elephants are far more threatened than their savannah relatives. By being recognized as a different species, forest elephants could receive more attention as conservation efforts get directed more towards them.
Between 2010 and 2014 alone, scientists estimate 100,000 African elephants were killed by poachers for their ivory. At this rate, African elephants could disappear from the wild within a generation.
The most comprehensive elephant genome study to date supports the notion that there are two species of elephant in Africa. First, the Australian researchers completed 14 genome sequences: two from each of the three living species (African savannah, African forest, and Asian elephants) and extinct species: one straight-tusked elephant, four woolly mammoths, one Columbian mammoth and two American mastodons.
The data suggests that African savannah and forest elephants have been genetically isolated for about 500,000 years, despite their geographical proximity — compelling evidence that the two should be treated as separate species. Furthermore, there is no evidence that L. cyclotis and L. africana interbred in the last half a million years. Previously, a 2017 study found L. cyclotis is more closely related to the extinct straight-tusked elephant (Palaeoloxodon antiquus) than to L. africana. Another 2010 study found that African savanna and forest elephants are about as distinct from each other as the Asian elephant is from the extinct woolly mammoth: quite a remarkable difference.
“The most surprising result was the degree of interbreeding between species. We didn’t really expect there would be gene flow between the mammoths and mastodons and the ancestors of modern elephants, but our results showed frequent interbreeding,” said Adelson.
“There’s been a simmering debate in the conservation communities about whether African savannah and forest elephants are two different species,” said David Reich, another co-senior author at the Broad Institute who is also a professor at the Department of Genetics at Harvard Medical School (HMS) and a Howard Hughes Medical Institute Investigator. “Our data show that these two species have been isolated for long periods of time – making each worthy of independent conservation status.”
Using DNA marker techniques, the team of researchers also found new evidence of gene flow between ancient species. For instance, the gene sequences show interbreeding among the Columbian and woolly mammoths, despite the two species are quite dissimilar in terms of size and habitat. Interbreeding among closely related mammals is quite common, for example between brown and polar bears, Sumatran and Bornean orangutans, and the Eurasian gold jackal and grey wolves.
Next, the researchers plan on exploring whether or not the introduction of new genetic lineages into elephant population played a role in their evolution, and how.
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