U. ILLINOIS (US) — Forget what you always thought about elephants: There are two—not one—species of African elephant.
Using genetic analysis, scientists have proved that the African savanna elephant and the smaller African forest elephant have been largely separated for several million years.
Researchers compared the DNA of modern elephants from Africa and Asia to DNA that they extracted from two extinct species: the woolly mammoth and the mastodon.
It is the first time that scientists have generated sequences for the mastodon nuclear genome, and the first time that the Asian elephant, African forest elephant, African savanna elephant, the extinct woolly mammoth, and the extinct American mastodon have been looked at together.
The study is published online in PLoS Biology.
“Experimentally, we had a major challenge to extract DNA sequences from two fossils—mammoths and mastodons—and line them up with DNA from modern elephants over hundreds of sections of the genome,” says research scientist Nadin Rohland of Harvard Medical School.
According to David Reich, associate professor in the same department, “The surprising finding is that forest and savanna elephants from Africa—which some have argued are the same species—are as distinct from each other as Asian elephants and mammoths.”
Researchers only had DNA from a single elephant in each species, but had collected enough data from each genome to traverse millions of years of evolution to when elephants first diverged from each other.
“The divergence of the two species took place around the time of the divergence of the Asian elephant and woolly mammoths,” says Michi Hofreiter, professor of biology at the University of York.
“The split between African savanna and forest elephants is almost as old as the split between humans and chimpanzees. This result amazed us all.”
The possibility that the two might be separate species was first raised in 2001, but this is the most compelling scientific evidence so far that they are indeed distinct.
Previously, many naturalists believed that African savanna elephants and African forest elephants were two populations of the same species, despite the significant size differences.
The savanna elephant has an average shoulder height of 3.5 meters whereas the forest elephant has an average shoulder height of 2.5 meters. The savanna elephant weighs between six and seven tons, roughly double the weight of the forest elephant.
DNA analysis revealed a wide range of genetic diversity within each species.
The savanna elephant and woolly mammoth have very low genetic diversity, Asian elephants have medium diversity, and forest elephants have very high diversity. Researchers believe that this is due to varying levels of reproductive competition among males.
“We now have to treat the forest and savanna elephants as two different units for conservation purposes,” says Alfred Roca, assistant professor of animal sciences at the University of Illinois.
“Since 1950, all African elephants have been conserved as one species. Now that we know the forest and savanna elephants are two very distinctive animals, the forest elephant should become a bigger priority for conservation purposes.”
The research was funded by the Max Planck Society and by a Burroughs Wellcome Career Development Award in Biomedical Science.
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