Tracking Kenya’s Big Game for Bits of DNA : Genetics: Effort is part of project to examine the evolution of many of Africa’s large mammals to determine whether they originated in Africa or Eurasia.

For five hours, the hunters had been bouncing across the Savannah in a battered Land Cruiser, looking for elephants. Now, at last, they sighted the quarry: a group of about 20 females, calves and immature males, huddling under a tree to escape the scorching midday heat.

Pieter W. Kat, the leader of the party, fitted a slender orange arrow onto a black crossbow mounted on a rifle stock. He took aim at a 10-year-old male and squeezed the trigger.

The arrow hit the young bull in the hindquarters a few inches to the right of his tail and promptly bounced out, dropping into the tall grass. The elephant flapped his ears, looked around for the source of the sting and then returned to eating.

Plugging the arrow’s hollow tip was the hunters’ trophy: a grayish patch of tissue no bigger than a fingernail paring, but containing enough DNA to allow Kat and his colleague, Danish geneticist Peter Arctander, to construct a genetic portrait of the animal.

On the plains where Ernest Hemingway and Theodore Roosevelt shot game for sport, Arctander and Kat were on a gene safari. They had come to collect samples from about 20 elephants in Masai Mara to compare them with specimens from elephant populations in other regions of Kenya.

The work is part of a five-year, $1-million project funded by the Danish International Development Agency to examine the genetics and evolution of many of Africa’s large mammals.

This is the first time that the genetics of African wildlife has been probed in detail. The scientists expect the results to help answer longstanding scientific questions, such as whether bovids--the group that includes cows, goats, antelopes and buffalo--originated in Africa or Eurasia, and how Africa’s many antelope species are related to one another.

The work should also reveal the scope of genetic diversity within a single species, such as the African elephant, which will help wildlife managers understand the genetic consequences of moving animals from one population or area to another.

Africa is the only place where this research can be done, according to Kat, a molecular geneticist at the National Museums of Kenya in Nairobi. Elsewhere, animals have been hunted, bred and moved by humans for so many centuries that the genes carried by today’s populations cannot be used to deduce evolutionary history.

Kat’s specimens are immediately frozen in a canister of liquid nitrogen and later taken to laboratories at the Nairobi museum or at the Institute of Population Biology in Copenhagen. There the DNA will be extracted and “amplified” with a genetic engineering technique called polymerase chain reaction.

Using PCR, researchers can select any portion of a gene and use an enzyme to make multiple copies of it, quickly accumulating enough to decipher the gene’s entire sequence. They can then compare sequences from different species or different populations within a single species and draw conclusions about how they have evolved.

The project, which started in Kenya about 18 months ago, began by exploring relationships among Africa’s more than 75 species of bovids. Arctander and Kat have collected DNA specimens from about 30 different species, hoping to answer such questions as: How is a wildebeest related to an eland? How is an eland related to a cow? How is a cow related to an oryx?

“A lot of basic questions are not settled at all,” said Arctander. “It’s not settled whether bovids originated in Africa or Eurasia.”

He added that most evolutionary biologists assume that the common ancestors of today’s cows, goats and antelopes first appeared on one of those land masses, perhaps 20 million years ago, then crossed to the other via a land bridge that existed before the continents drifted apart.

Already, the Danish project’s gene sequences have delivered some surprises.

Take the Grant’s gazelle, a diminutive and elegant antelope found in arid parts of Kenya, Tanzania, Somalia, Ethiopia and the Sudan. Kat and Arctander obtained DNA samples from 44 Grant’s gazelles living in six different areas of Kenya.

They compared the information contained in a portion of a gene found in mitochondria, structures inside cells which contain a handful of genes that are passed from a mother to her offspring.

Arctander said the particular gene they chose, known as the control region or D-loop, is one of the fastest-evolving genes known, making it useful for studying genetic change.

Although Grant’s gazelles from different parts of Kenya looked almost identical, the DNA analysis revealed startling differences. Genetically, they could be sorted into three separate populations: a northern group from Sibiloi and Samburu; a central group in the region of Masai Mara, Nairobi and Amboseli National Parks; and an eastern group in Tsavo East National Park.

The D-loop DNA sequence from the Tsavo East group showed about a 12% difference from the sequences for any other group. Arctander said such a large genetic difference within a single species has never been noted before.

The researchers said such a finding must mean that the Tsavo East gazelles do not breed with the gazelles in nearby Amboseli National Park, although there is no geographic barrier separating the two groups. Grant’s gazelles live all along the 110-mile stretch of land separating the two parks.

Arctander believes the single species is in the process of splitting into more than one. He suggested that perhaps several hundred thousand years ago changing climate patterns may have separated a single population of Grant’s gazelles into two or more groups, driving each group into an arid region that was separated from the others by a wetter, forested zone, where such animals do not live. Now the climate over the entire area is arid; but the groups were isolated for so long they have accumulated genetic differences and will no longer interbreed.

“When they come together, something has happened,” he said. “They don’t like the smell of each other; they don’t like the look of each other; they don’t like the horn shape.”

In the case of another antelope, the waterbuck, the researchers discern an opposite process: two species merging into one. Waterbuck--brown, shaggy, long-horned animals--are classified as two species: the common waterbuck, which has a white ring on its rump; and the Defassa waterbuck, with an all-white rump.

When the scientists compared gene sequences from waterbuck found in Tsavo East and in Masai Mara, they found an interesting paradox. Based on genes found in the cells’ nuclei, the two species did appear different. But based on mitochondrial genes, which more quickly show the effect of interbreeding, they appeared the same.

Arctander said the results suggest that the two “species” are mingling and mating, and that, in time, the remaining genetic differences will disappear.

Tracking Kenya’s Big Game for Bits of DNA

Using DNA sampling techniques, scientists in Kenya discovered that Grant’s gazelle--a species whose members look almost identical--is actually in the process of splitting into two or more distinct species.

Genetic studies show that two distinct species of antelope--the common waterbuck and the Defassa waterbuck, which have distinctively different markings--are in fact merging into a single species.

Source: Grizmek’s Animal Life Encyclopedia