Using DNA extracted from the dung of wild elephants in Africa, biologists at the University of California, San Diego have determined that three different types of elephants exist on the African continent.
Their discovery, detailed in a paper to be published in the October 7 issue of the Proceedings of the Royal Society, Series B, affirms the existence of the well-known savanna elephant and the recently recognized forest elephant of central Africa. But it also suggests that the elephants of west Africa, which live in both the forest and savanna, represent a third, genetically distinct population that has been diverging from the other two groups for some two million years.
Biologists and conservationists now widely accept the designation of two species of elephants: Asian and African. The UCSD discovery could, if confirmed by additional genetic evidence, split the African group into three distinct species or subspecies.
"This discovery is important, because the west African elephants are threatened with extinction as a result of human activities," says David S. Woodruff, a professor of biology and chair of the Ecology, Behavior and Evolution Section of UCSD's Division of Biological Sciences. "If these findings are confirmed, zoologists and conservation managers will need to recognize three different species of African elephants, all of which need protection because their numbers are declining."
"Knowing that forest elephants are very different genetically from savanna elephants means that overpopulation in some southern African savanna parks should not lead to a relaxation of the protection for elephants elsewhere, especially in the forests," says Lori S. Eggert, the first author of the paper and a postdoctoral researcher at the Smithsonian Institution's National Museum of Natural History. "These populations are not exchangeable, either ecologically or genetically."
Eggert traveled to Africa to collect her samples while working as a doctoral student in Woodruff's UCSD laboratory, which specializes in the development of non-invasive techniques to collect and assess genetic information from dangerous or difficult to observe wildlife populations. Wild elephants fit this category since they can kill humans when threatened and are almost impossible to see in the dense vegetation of the forest regions. Because the fibrous vegetation eaten by the elephants continuously scrapes cells from their intestines into their dung, Eggert, Woodruff and Caylor A. Rasner, a research assistant in Woodruff's laboratory, were able to extract their DNA and genotype the dung samples. In a separate study, more intensive genotyping methods are being used to help African wildlife managers more accurately estimate the number of remaining forest elephants to improve conservation planning.
"Since it's difficult to see forest elephants in the dense vegetation, we don't have solid census data from many populations, including some of the largest ones," explains Eggert. "Only a quarter to a third of African elephants are forest elephants, so there are only about 120,000 to 150,000 of them. They live in a habitat that is rapidly being logged and converted to agriculture. Increasingly, forests in Africa are becoming fragmented and elephant populations are being isolated in a sea of farms and villages."
Wildlife managers estimate that 400,000 to 500,000 elephants now live in Africa. The majority of these African elephants, about 250,000 to 350,000, are savanna elephants, while western elephants are estimated to number only about 12,000. Forest elephants are significantly smaller than the savanna forms; have longer, thinner and straighter tusks, smaller and more rounded ears, a flatter forehead region and a larger number of toenail-like structures on their feet. West African elephants, which the UCSD study suggests are genetically and geographically isolated from elephants elsewhere on the continent, have been described as morphologically "indeterminate," or having both forest and savanna forms.
Their geographic isolation may have been caused by the desertification of a region in west Africa called the Dahomey Gap that separated the forests in central Africa from the forests in west Africa. Other potential barriers between the two regions include the Niger River Delta and the volcanic region of southwestern Cameroon. Based on their genetic data, the UCSD biologists believe that the west African populations have been isolated for as long as 2.4 million years.
The UCSD scientists note in their paper that while their genetic analyses of the mitochondrial, or maternally inherited, DNA sequences and nuclear microsatellite loci (short repetitive segments of DNA that show differences among populations and individuals) suggest the existence of "three recognizable taxa of African elephants," their results need to be confirmed before a formal taxonomic revision of the African elephants is proposed. That confirmation would require examination of additional nuclear DNA sequences which are inherited paternally as well as maternally.
"If the level of genetic differentiation between the three taxa identified here is confirmed to reflect several million years of divergence, it will be appropriate to treat them as species in recognition of their long independent evolutionary trajectories," they write in their paper.
Because nearly all of the African elephants in zoos are savanna elephants, the results do not have implications for elephants now in captivity. Zoos do not have forest elephants, largely because they are so elusive, and only three western elephants are now in captivity at the Abidjan Zoo in Côte d'Ivoire. However, the results have widespread implications for the management of all three types of wild African elephants. Although the ivory trade ban has slowed the slaughter of elephants, some countries have appealed for permission to resume the harvest.
"Only the savanna elephant populations of Botswana, Namibia and Zimbabwe in southern Africa have been considered for limited resumption of the ivory trade," says Eggert, "and they have been allowed this only because their management has been so successful that it has resulted in elephant populations that are stable or growing too large."
"If current trends of forest conversion and human-elephant competition for necessities like habitat and water continue, all elephants other than those in the highly managed protected areas of southern Africa will continue to be endangered. Even a limited resumption of the ivory trade could lead to increased hunting of forest elephants for ivory. Thus, while all three genetically distinct types of elephants are threatened, those in west Africa are now highly endangered."
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