November 13, 2009
Funny, You Don’t Look Related
UCLA biologists, colleagues solve mystery contemplated by Charles Darwin
When Charles Darwin visited the Falkland Islands during the voyage of the Beagle in 1835, he saw a wolf-like species, wrote about it in his diaries and correctly commented that it was being hunted in such large numbers that it would soon become extinct.Darwin was baffled by how this animal got on the islands, and it figured heavily in the formation of his ideas on evolution by natural selection.
Now, UCLA biologists and colleagues have analyzed DNA from museum specimens, including one collected by Darwin, and have solved the puzzle. Their results surprised them.
"It was the only terrestrial mammal on the island," said Robert Wayne, UCLA professor of ecology and evolutionary biology and co-author of the research paper, published Nov. 3 in the journal Current Biology. "How can something the size of a Labrador retriever end up on an island in sufficient numbers that a new population emerges and evolves into a new species? The presence of this large canid, the Falkland Islands wolf, has always been a puzzle, since the early 1800s."
Was it brought to the Falklands, less than 300 miles from the mainland of South America, by humans or did it somehow get there by itself?
"Our analysis rules out humans," said Graham Slater, a postdoctoral scholar in the UCLA Department of Ecology and Evolutionary Biology and lead author of the paper.
Slater, Wayne and colleagues analyzed DNA samples from five Falkland Islands wolves and calculated how long ago those five wolves shared a common ancestor.
"It was at least 70,000 years ago "” well before humans came to the New World," Slater said. "The Falkland Islands wolf clearly precedes any possible human occupation of the New World, which dates back some 12,000 to 13,000 years."
Darwin hypothesized that the Falkland Islands wolf, which became extinct in 1876, may have come to the islands on icebergs. Wayne and Slater think Darwin may be right.
"A large, wolf-size animal could perhaps live on a large iceberg with penguins and sea birds and maybe seals "” enough prey to survive the voyage "” where a vegetarian could not do that very well," Wayne said. "There is a possibility that a pack of wolf-like animals (which are members of the biological family of mammals that includes wolves, foxes, coyotes, jackals and domestic dogs) could be marooned on an iceberg that would eventually land at the shores of the Falkland Islands, then live off the sea birds and marine mammals there and give rise to a new population that over time would turn into a dramatically different species."
"If you look at Darwin's notebooks, the first time he ever raised the idea that species are not fixed entities was after he considered birds from the Galapagos Islands," Slater said. "He is talking about how they are different from island to island, and he says, 'The only other example I can think of is the wolves of the Falkland Islands.' Then, the next sentence is the first time he ever said, 'This leads me to believe that species are not fixed entities and change over time.' When Darwin first was thinking that species evolve, he had the Falkland Islands wolf in mind."
The closest relative to the Falkland Islands wolf, the biologists report, is an odd South American dog species called the maned wolf, which looks nothing like the Falklands species.
"The closet living relative of the maned wolf is the bush dog, which is even more different," Slater said. "These three are a strange group."
"That was a shock to us," Wayne said. "You wouldn't have guessed by looking at them that that the maned wolf and the bush dog could give rise to something like a Falkland Islands wolf, but we have verified it."
"No one has ever suggested that before," Slater said.
The maned wolf, which lives on the grassy plains of Brazil and parts of Argentina, has long, thin legs and is often called the "fox on stilts." The bush dog, which lives in South American rain forests, is tiny, "like a toaster with legs on it," Wayne said. The bush dog hunts large rodents and animals that are much larger than itself, Slater said.
"Our findings firmly align the Falkland Islands wolf with the maned wolf, even though the divergence was fairly ancient, more than 6 million years," Wayne said. "They both probably evolved more than 6 million years ago in North America."
The research was federally funded by the National Science Foundation.
Wayne and Slater collected and analyzed DNA from five Falkland Islands wolves from the British Museum and museums in Philadelphia, Liverpool and New Zealand.
"We sequenced some regions of the mitochondrial genome," Wayne said. The mitochondria are the tiny powerhouses of the cell, whose generators burn food and produce most of a cell's energy. "We also analyzed gene sequences of the nucleus of the cell."
They sequenced sites in the genome of the cell nucleus that are found only in certain groups of related canids, such as South American foxes, the maned wolf and the bush dog; these species have a unique nucleotide DNA sequence.
Previously, some scientists thought the Falkland Islands wolf may have been a domesticated animal from the South American mainland that was brought over by native South Americans and was marooned on the islands.
"The problem is, as far as we know, there were never any permanent settlements on the Falkland Islands before European explorers arrived," Wayne said. "There has been no evidence to my mind of any kind of prehistoric occupation of the Falkland Islands; they are too remote, cold and not very hospitable."
Co-authors on the paper include Olaf Thalmann, a UCLA postdoctoral scholar in Wayne's laboratory; Jennifer Leonard, who earned her Ph.D. from UCLA and is now on the faculty of Sweden's Uppsala University; Rena Schweizer, a UCLA graduate student in Wayne's laboratory; Klaus-Peter Koepfli, a UCLA postdoctoral scholar in Wayne's laboratory; John Pollinger, Wayne's laboratory manager; Nicolas J. Rawlence; Jeremy J. Austin; and Alan Cooper.
In previous research, Wayne and colleagues used molecular genetic techniques to determine that dogs have ancient origins and that the first Americans to arrive in the New World more than 12,000 years ago brought domesticated dogs with them. They have also found that dogs have been living in close association with humans much longer than any other domestic animal, have confirmed that dogs evolved from wolves and have confirmed that today's domestic horse resulted from the interbreeding of many lines of wild horses in multiple locations and was not confined to a small area or a single culture. They also showed that nearly half of North American wolves have black coats as the result of historical matings between black dogs and wild gray wolves.
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