New Study Reveals Hidden Pattern in Genetics of Indian Elephant Populations
CERC provides scientific basis for endangered species conservation strategies
The first population genetic study of free-ranging Asian elephant populations has unexpectedly revealed that elephants in Southern India evolved into two genetically distinct groups thousands of years ago. The discovery has important implications for elephant conservation strategies in India.
The research, directed by Professor Don Melnick, Executive Director of the Center for Environmental Research and Conservation (CERC), a part of the Earth Institute, was published this month in the journal Heredity. An abstract and link to the full text can be found at http://www.nature.com/nature/view/041007.html.
The genetically distinct Asian elephant populations are separated by only a 40-km-wide stretch across a gap in the Western Ghats mountain range. The Palghat Gap has been recognized by biologists as a line dividing various animal and plant populations, but prior to this study biologists thought that the divisions were caused by relatively recent, human-related disturbances. Analysis of the elephants’ DNA revealed that the division was actually thousands of years old, perhaps caused by a catastrophic natural event such as an ancient drought.
For conservationists, the implication of the research is that conservation strategies should be aimed at preserving the two distinct populations separately.
“We want to re-establish the flow of genes between fragments of each group of elephants,” Professor Melnick says, “but we do not want to re-open gene flow between elephant populations that have been separated for thousands of years,” That is because the separated populations have probably evolved “co-adapted gene complexes,” groups of genes that work together to help each group of elephants adapt to its local conditions.
The new paper’s lead author T. N. C. Vidya, Project Associate at the Centre for Ecological Sciences at the Indian Institute of Science in Bangalore, explained the results of the study in greater detail. The investigators were surprised by two results, Vidya says. First, that the Nilgiri population north of the Palghat Gap, which is the largest population of Asian elephants in the world, showed no mitochondrial DNA diversity (although it showed apparently normal nuclear diversity), and second that there was marked genetic differentiation at mitochondrial and nuclear microsatellite markers on either side of the Palghat Gap.”
The lack of diversity in the Nilgiri population “may be a result of either an ancient population bottleneck or due to some sort of ‘selective sweep’ facilitated by the maternal inheritance of mitochondrial DNA and the matriarchal social organization of elephants, making it possible for dominant family groups and hence their mitochondrial variants to out compete others,” Vidya explains. The Palghat Gap differentiation, she adds, “could be indicative of the gap having been a biogeographic barrier in the past.” If patterns of genetic differentiation in other species on either side of the gap match those observed with the elephants, it will confirm this hypothesis.
The new study is important because it is the first study of population genetic structure of the Asian elephant in southern India, which holds about one fifth of the world's wild Asian elephant population and is considered crucial for the conservation of the species.
The research was conducted by analyzing mitochondrial DNA and nuclear microsatellite DNA differentiation across several elephant reserves in Southern India. The DNA was extracted from elephant dung, using a non-invasive technique pioneered over the past few years by Professor Melnick and his colleague Dr. Prithiviraj Fernando, who was also a co-author of the new research. For more information on the DNA from dung technique, which facilitates research on elusive, rare, or aggressive species, see http://www.earth.columbia.edu/news/2003/story04-09-03.html.
The elephant population study was conducted in collaboration with the India Institute of Science, and funded by the U.S. Fish and Wildlife Service. The India Institute of Science is also responsible for helping the national government of India to develop conservation strategies. Dr. T.N.C. Vidya, a member of the Centre for Ecological Sciences of the India Institute of Science, was the first author of the study, which was titled Population differentiation within and among Asian elephant (Elephas maximus) populations in southern India and published in the journal Heredity, and she was also the lead coordinator in the field.
Center for Environmental Research and Conservation
A consortium of five leading science and education institutions Columbia University, the American Museum of Natural History, The New York Botanical Garden, the Wildlife Conservation Society, and Wildlife Trustthe Center for Environmental Research and Conservation employs a wide array of resources to train the next generation of environmental leaders charged with conserving Earth’s biological diversity.
The Earth Institute at Columbia University
The Earth Institute at Columbia University is the world’s leading academic center for the integrated study of Earth, its environment and society. The Earth Institute builds upon excellence in the core disciplines earth sciences, biological sciences, engineering sciences, social sciences and health sciences and stresses cross-disciplinary approaches to complex problems. Through research, training and global partnerships, it mobilizes science and technology to advance sustainable development, while placing special emphasis on the needs of the world’s poor.