Virginia Morell ScienceNow 21 Dec 10;
It would be hard to confuse Africa's forest elephants and savanna elephants. Forest elephants, found in dense West African forests, have longer, straighter tusks and round, not pointed, ears. They're also 1 meter shorter and weigh half as much as the savanna elephants, which range from South to East Africa. Yet for years, scientists have classified the two as the same species, arguing that they were slightly different populations that mingled on the edges of the forest.
A new genetic analysis, however, finds that forest and savanna elephants are as different from each other as modern Asian elephants are from ancient mammoths. The findings, which split the elephants into two species, could improve the conservation of African elephants overall, say researchers.
The study is not the first to analyze the elephants' DNA. In 2001, researchers compared the mitochondrial DNA (mtDNA) of forest and savanna elephants and reached much the same conclusion. (mtDNA is inherited only from the mother and is found in mitochondria, the cell's energy factories.) And a subsequent study of the forest and savanna elephants' nuclear DNA showed that the two had diverged more than 3 million years ago. Both studies concluded that forest and savanna elephants are separate species, but they did not sway all taxonomists, who felt that certain data suggested that some forest and savanna elephants shared a recent maternal ancestor.
Many studies use mtDNA to determine whether a species designation is valid. But mtDNA has its limitations. It represents only a small fraction of an animal's genome (the rest is nuclear DNA), and because it is transmitted only from the mother, it reveals just the genetic history of females.
To resolve the debate, an international team of scientists once again compared the animals' nuclear DNA. But this time, they analyzed large amounts of nuclear DNA sequences from one individual of each of the three existing elephant groups (Asian elephants, African forest elephants, and Africa savanna elephants), and from two elephant species that recently became extinct (a mammoth and a mastodon). It's the first time that scientists have sequenced a mastodon's nuclear genome and the first time that the five species' nuclear DNA has been compared.
"It was a big challenge to extract the DNA sequences from the fossil mammoths and mastodons and then to line these up with DNA from the modern elephants," says Nadin Rohland, an evolutionary geneticist at Harvard Medical School in Boston and the study's lead author.
The results, published online today in PLoS Biology, should finally convince the skeptics, the researchers say. They corroborate the previous nuclear DNA findings and show that savanna and forest elephants separated between 1.9 million and 6.7 million years ago. Asian elephants and wooly mammoths began diverging then, too.
The study also reveals that the species have surprisingly different amounts of genetic diversity. Savanna elephants and wooly mammoths have very low diversity, whereas the genetic diversity of forest elephants is very high; Asian elephants fall in the middle. The differences likely reflect the elephants' social behaviors, says Alfred Roca, a conservation geneticist at the University of Illinois, Urbana-Champaign, and one of the study's authors. "In savanna elephants, the large males dominate the matings. Apparently, based on what we see, the wooly mammoths had a similar type of male competition" for matings.
The team thinks this explains the previous mtDNA results, which suggested that some forest elephants shared a maternal ancestor with savanna elephants as recently as 500,000 years ago. Because the savanna males are larger, they likely outcompete the forest males in the areas where the two groups of elephants overlap, effectively erasing their deeply divergent genetic history.
If the report's conclusions are accepted by the African Specialist Group of the International Union for Conservation Nature (IUCN), the African elephant (Loxodonta africana) may be split into two species: L. africana, for those living on the savanna, and L. cyclotis, for those in the forest. Right now, the two are classified as subspecies: L. africana africana and L. africana cyclotis.
"This is wonderful work and a major step forward in our understanding of the relationships of elephants," says Robert Fleischer, geneticist at the Smithsonian Institution in Washington, D.C. "It's an absolute tour de force, with immediate consequences for the conservation of elephants," adds conservation geneticist Sergios-Orestis Kolokotronis of the American Museum of Natural History in New York City.
That's because poachers are decimating the forest elephants, says Samuel Wasser, a conservation biologist at the University of Washington, Seattle. Although African elephants are listed as an endangered species, with between 500,000 and 600,000 left in the wild, some African countries continue to push for legalizing trade in ivory tusks. If forest elephants, which number approximately 20,000 are recognized as a separate species, they may garner more protection. "[They] might have a fighting chance," he says.
Diane Skinner, a spokesperson for the African Elephant Specialist Group in Nairobi, Kenya, says that the group will review the new study. But for now, the forest elephant's status remains unchanged.
Africa Has Two Species Of Elephants, Not One
Julie Steenhuysen PlanetArk 22 Dec 10;
Instead of one species of elephant, Africa has two, researchers said on Tuesday, confirming suspicions about the two distinctly different looking pachyderms.
Using gene sequencing tools, teams from Harvard, the University of Illinois and the University of York in Britain have shown that instead of being the same species -- as scientists have long believed -- the African savanna elephant and the smaller African forest elephant are distant cousins, having been largely separated for 2 million to 7 million years.
"What our study suggests is forest and savanna elephants are very distantly related to each other and not just subspecies or populations of the same species," said Alfred Roca of the University of Illinois, who worked on the study published in the Public Library of Science journal PLoS Biology.
The teams compared the genetic code of modern elephants from Africa and Asia to DNA taken from two extinct species -- the woolly mammoth and the American mastodon.
"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," David Reich of Harvard Medical School in Boston, who worked on the study, said in a statement.
Africa's forest and savanna elephants are vastly different in size. The savanna elephant is roughly double the weight of the forest elephant at six to seven tons and measures about 11.5 feet tall at the shoulder -- about 3 feet taller than the forest elephant.
Even so, many scientists had thought the two populations of elephants came from the same species, in part because they mated and produced offspring.
Not so, says Professor Michi Hofreiter, an expert in ancient DNA from York.
"The divergence of the two species took place around the time of the divergence of the Asian elephant and woolly mammoths," Hofreiter said in a statement.
"The split between African savanna and forest elephants is almost as old as the split between humans and chimpanzees.
"This result amazed us all."
Roca said comparing the genetic sequence of the mastodon -- a very distant cousin of the other species -- allowed the researchers to see where in evolution the elephants split.
"The forest and savanna elephants proved to be as genetically distinct from each other as the woolly mammoth from the Asian elephant," Roca said in a telephone interview.
On a practical basis, the study means that conservationists will need to think about the two species differently.
"For the last 50 years, all African elephants have been treated as the same species. In fact, they are so different you really have to come up with a different conservation plan for each of the two," Roca said.
(Editing by Mohammad Zargham)
Seeing double: Africa's 2 elephant species
University of Illinois College of Agricultural, Consumer and Environmental Sciences EurekAlert 21 Dec 10;
Contrary to the belief of many scientists (as well as many members of the public), new research confirms that Africa has two—not one—species of elephant. Scientists from Harvard Medical School, the University of Illinois, and the University of York in the United Kingdom used genetic analysis to prove that the African savanna elephant and the smaller African forest elephant have been largely separated for several million years.
The researchers, whose findings appear online in PLoS Biology, 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. Not only is this the first time that anyone has generated sequences for the mastodon nuclear genome, but it is also 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.
"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 the Department of Genetics at 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 the time 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 Professor Michi Hofreiter, who specializes in the study of ancient DNA in the Department of Biology at 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 in the Department 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."
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This research was funded by the Max Planck Society and by a Burroughs Wellcome Career Development Award in Biomedical Science.
'African Elephant' Actually Two Separate Species
Jennifer Welsh livescience.com Yahoo News 22 Dec 10;
Everyone is taught that there are two species of elephants - the African and the Asian - but new research is suggesting this isn't the whole truth. The "African elephant" is actually two species, as evolutionarily different as lions and tigers are from one another.
"It's really a remarkable degree of divergence between the two," said study leader Alfred Roca of the University of Illinois at Urbana-Champaign. "The forest and savanna [elephants] are as different as the Asian elephant and woolly mammoth."
Roca and his collaborators discovered the evolutionary discrepancy by analyzing DNA of the living elephant species and two of their extinct evolutionary cousins, the woolly mammoth and mastodon. The study is published in this week's issue of the journal PLoS Biology, and is the first sequence of these extinct animals' nuclear genomes, which is the DNA that resides in the nuclei of cells and gets passed down to offspring by both parents. (By contrast, mitochondrial DNA hides out in the energy-making structures of cells and is only passed down by females.)
The species, which can be divided by their habitat into the forest elephant and savanna elephant, seem to have separated several million years ago, about the same time that humans diverged from chimps. They probably diverged for the same reason too, Roca said. [Images of forest elephant and savanna elephant]
"The thing that caused them to split was climate change - Africa became drier and the forest retreated," Roca told LiveScience. "These are the same factors that lead to the divergence between humans and chimpanzees."
The forest elephant is smaller, and is sometimes referred to as the "dwarf African elephant," standing at about 8.2 feet (2.5 meters) high compared with the savanna elephant's 11.5 feet (3.5 m), and weighing about half as much. The forest elephant also has straighter tusks and oval-shaped ears.
"It's important to classify the two as different species for the conservation aspects. You would want to develop a separate conservation plan for each one," Roca said. The African elephant is listed as endangered by the U.S. Endangered Species Act, and splitting the population into two different species places the forest elephant in much more dire straits. A little over a fifth of Africa's 500,000 elephants are forest elephants, and their numbers are dwindling quickly as their habitats disappear and poachers kill them for their ivory tusks, Roca said.
The researchers also discovered that the forest elephant is less genetically diverse than the savanna elephant, which Roca thinks is due to the intense competition between males. With male-male fighting, only the strongest would get the gals and so few males would pass along their genes to offspring. The woolly mammoth shows similar low genetic diversity, which may mean they were also competitive, Roca said.
Sergios-Orestis Kolokotronis, a biologist at the Institute for Comparative Genomics at the American Museum of Natural History, who wasn't involved in the study, called it a "tour-de-force in the field of paleogenomics" that convincingly refuted earlier, misleading mitochondrial DNA studies of African elephants.
"The confirmation of an old split between forest and savanna elephants is of great taxonomic and conservation significance, as this can allow for species-specific management decisions," Kolokotronis said.
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