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As the number of Asian and African elephants in the wild continues to dwindle, a key to bolstering their survival could be contained within their DNA, according to researchers at the Smithsonian’s National Zoo.
The scientists successfully analyzed part of the complex gene family that helps determine how resistant elephants are to the type of infectious diseases that have been devastating to their species, including tuberculosis and the herpes virus. These genes are crucial to most vertebrates’ ability to fight off pathogens, and the National Zoo’s researchers and collaborators are the first in the world to “characterize,” or interpret and describe, these genes in elephants. The researchers’ findings, which were published this month in the scientific journal Immunogenetics, could provide the building blocks for captive-breeding programs that increase elephants’ resistance to viruses, parasites and bacteria.
“Elephants are not only endangered, but they are also highly charismatic and loved by many people,” said Robert Fleischer, head of the Center for Conservation and Evolutionary Genetics at the National Zoo and one of the paper’s co-authors. “What we learn about the genetics of their immune system may help us to conserve the species and also inform people about how they have evolved and responded to their environment.”
The National Zoo’s three Asian elephants, Shanthi, Kandula and Ambika, were among the elephants included in the research, which focused specifically on the immune-system gene family known as the major histocompatibility complex. Pairs of genes, known as alleles, determine traits such as eye color or, in this case, disease resistance. Proteins made by different alleles in the MHC recognize the proteins in harmful pathogens and attack them, so the more varied the alleles, the stronger the animals’ line of defense against disease.
The National Zoo’s researchers found about 10 alleles in the MHC of African and Asian elephants, compared to 20-50 alleles in other vertebrates and up to 100 in humans. One allele, however, was particularly common in the 30 African and three Asian elephants involved in the study, suggesting that elephants may have evolved genetically in response to a past epidemic.
Fleischer also said that the MHC markers may help researchers understand why elephants appear to recognize their own kin, preventing the type of inbreeding that could genetically weaken the species and affect their long-term viability.
“Elephants not only avoid maternal relatives but also paternal relatives,” said Elizabeth Archie, former postdoctoral fellow at the National Zoo and lead author of the paper. “In other systems, MHC genes have been implicated in kin recognition. Scientists think animals can smell animals that are related to them by products of MHC genes.”
Although Asian and African elephants became two distinct genera at least 6 million years ago, the researchers found that these particular genes have not changed much between the two. This is unusual relative to other genes that have diverged naturally and indicates that the elephants have had to fight off similar diseases over time.
Because of infectious disease, poaching and habitat loss, the Endangered Species Act considers African elephants to be a threatened species and Asian elephants to be endangered. There are only an estimated 575,000 African elephants and 30,000 Asian elephants left in the wild—combined that is less than the human population of El Paso, Texas. Elephants in captivity, meanwhile, have been plagued by elephant endotheliotropic herpesvirus, which is responsible for about half of the deaths of young elephants in zoos. One of the next steps for the Zoo’s researchers is to determine whether the MHC affects susceptibility to this disease.
Elephants belong to the superorder of mammals called Afrotheria, which includes aardvarks, manatees and golden moles. Scientists have never studied the MHC in other members of the group; National Zoo scientists are the first to conduct this research on this unique superorder of animals.
“I find it very exciting and rewarding to be a member of a team of researchers that were the first to look at the genetic diversity of these genes in African and Asian elephants,” said Jesus Maldonado, Zoo research geneticist and paper co-author. “Elephant conservation is a high priority at the National Zoo as exemplified by the work that many scientists, curators and zookeepers conduct here with our captive population and with the research that we conduct with wild, threatened populations.”
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Lindsay Renick Mayer