Photograph by Michael Nichols, National Geographic
Published December 22, 2010
The African elephant is actually two different species, according to a new DNA study that may settle a long-simmering debate.
(See African forest elephant pictures from National Geographic magazine.)
According to the new research, the two major types of African elephants are about as genetically distinct from each other as the Asian elephant is from the extinct woolly mammoth.
And that difference has deep roots in the elephant family tree, the DNA evidence suggests.
The two apparent African elephant species appear to have evolved from a common ancestor between two and a half million and five million years ago—nearly as long ago as the human and chimpanzee lineages diverged, according to some genetic studies.
For Species Designation, Size Doesn't Matter
Traditionally, the forest and savanna elephants have been classified as subspecies of the same species. But numerous distinctions have been noted. For example, forest elephants live in family groups of just a few animals, whereas savanna elephant family groups number about ten and often congregate in groups of 70 or so.
And—perhaps unsurprisingly, given its wide-open habitat—the African savanna elephant (Loxodonta africana) has evolved to be about twice as big as the forest elephant (Loxodonta cyclotis).
The savanna elephant tips the scales at up to seven tons and stands a full meter (3.3 feet) taller at the shoulder than the African forest elephant, which lives in equatorial forests of central and western Africa.
But even plainly visible morphological, or physical, differences don't necessarily indicate that animals are of separate species.
"Animals have an amazing capacity to change in morphology over short periods of time," said Reich, a population geneticist at Harvard Medical School.
Without pressures from predators and competitors, for example, species isolated on islands can shrink in just tens of thousands of years—a blink of the eye in evolutionary time.
Elephants have experienced such transitions before, producing animals like the "pygmy" Asian elephant of Borneo, which isn't considered a separate species, despite its relatively short, round shape.
Interspecies Elephant Sex?
Debate over the species status of African elephants has been simmering for at least a decade.
A 2001 study in the journal Science included the first DNA evidence that the savanna and forest elephants are separate species.
But then other studies showed that at least a small number of savanna elephants shared mitochondrial DNA—genetic information passed down from only mothers—with forest elephants.
This "proved there was some interbreeding within at least the past 500,000 years," Reich explained.
But that limited interbreeding isn't evidence that the two elephant types are from the same species, he said. It's just an example of interspecies hybridization, relatively common in the animal world, ha added.
Mammoth DNA Called Into Play
The key to the new discovery was some "cold case" genetics work on ancient, extinct elephant relatives: the woolly mammoth and the mastodon. The mastodon's nuclear genome, in particular, was sequenced for the first time for the study.
The genomes of five distinct animals—the Asian elephant, African savanna elephant, African forest elephant, woolly mammoth, and American mastodon—were then compared and contrasted.
The results showed that "in fact these [African elephant] populations diverged long ago and are at least as different as Asian elephants and mammoths—and those two are not only different species but entirely different genera," Reich said.
The apparent new species discovery is more than just cocktail party fodder for geneticists—it may have important conservation and management implications.
If Africa's elephants are from two distinct species, then each has a smaller population than previously believed. In this case, forest elephants may be of particular concern, because far less is known about their population status. Their numbers may prove small enough to garner additional protections.
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