February 25, 2010
Elephants are beloved but threatened animals. African elephants number fewer than 575,000, and Asian elephants, which number only 30,000 and are considered endangered. A recent study of elephant DNA at the Smithsonian National Zoo may bring researchers one step closer to saving them.
Scientists at the zoo and their colleagues were the first group ever to analyze diversity in the elephant genes that detect and fight diseases. It also analyzed how these genes have an effect on the animals’ mating and social behavior.
We spoke with Jesus Maldonado, a member of the research team, about why these creatures seem to have high rates of disease both in captivity and in the wild, and how this study can help future generations of elephants.
Why are Asian and African elephants struggling to survive in the wild?
African and Asian elephants have been under a lot of pressure from humans hunting them in the wild. Elephants are highly prized because of their tusks—people have commercialized the value of them. So they’ve been hunted down almost to the levels of extinction. But there’s also a lot of problems they face with small population sizes, like inbreeding and disease.
Your study was the first to characterize patterns of genetic diversity and natural selection in the elephant. Why?
They’re not an easy organism to study because obtaining samples from an elephant is actually not an easy thing (laughs). Darting an elephant and taking a piece of tissue is very difficult. Imagine the logistics of taking a blood sample from an elephant. Those are intense things. So studying the genetics of elephants in the wild has posed a big problem. One way to get around that is to look at poop samples, and we did some of that within this study. But the thing that allowed us to actually be able to study them was all the connections we had with zoo and captive animals. Having captive animals and obtaining a fresh blood sample that was required for some of this analysis was key. The blood has to be taken almost immediately from the vet and it has to be sent to our lab and preserved in a special buffer so the DNA doesn’t degrade.
Your research focused specifically on the immune-system gene, known as MHC.
For mammals in particular, the MHC gene system is really a functional gene that helps animals fight disease and recognize the various diseases that come into the animals’ system. So the more diverse the MHC genes are, the more capable they are of identify different kinds of diseases. And the more MHC genes an animal has, the better they can fight off those diseases.
What did the DNA tell you about their ability to fight disease? What else did you find?
When we compared the patterns of MHC diversity in elephants we found that they had a relatively lower number of MHC genes than that of other mammals that have been recently surveyed. We also found that one of those genes was especially common and was found in over half of our samples. We think that this gene became so common because it may have been advantageous to individuals in resisting a disease that was or is still highly prevalent. We have not identified the disease. But we know, for instance, that elephants in captivity have been plagued by an endotheliotropic herpesvirus, which is responsible for about half of the deaths of young elephants in zoos, and one of our next steps will be to try to determine whether the MHC affects susceptibility to this disease.
MHC genes have also been implicated in the ability of other mammals to recognize individuals that are close kin. So we are also very interested in studying how elephants choose individuals they want to mate with, or how they recognize their own siblings and so avoid inbreeding.
How does this help protect elephants?
If we have knowledge of the levels of MHC variation in both captive and wild elephants, then we can make predictions about what kind of threat they’re in. Not only will our new findings help us predict how elephants may be able to cope if there is an epidemic, but they may soon help us understand if elephants use this same mechanism to avoid mating with close relatives and consequently decrease inbreeding. With their wild populations dwindling at an alarming rate, not only from disease but from hunting and illegal poaching, we can make a case to politicians and government agencies that we need stronger measures against hunting and over-harvesting of these animals. If we have a better understanding of their mating systems, we can also make recommendations about the minimum number of unrelated versus related individuals that need to be in a group, in order to avoid inbreeding. We can use this information for better management strategies of wild elephant populations.
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