It's a mystery that stumped even Charles Darwin. How did a reddish, stocky wolf arrive on the Falkland Islands? This small archipelago nearly 500 kilometers off the coast of Argentina has no other endemic terrestrial mammals, not even rodents. Any hope of an answer seemed to die with the last Falklands Island Wolf, shot by a hunter in 1876. But now a research team has used DNA from museum specimens, including one that Darwin collected, to solve the puzzle.
The coyote-sized Falklands Island Wolf (Dusicyon australis) was strikingly different from smaller canids on the South American mainland, Darwin noted during his 1837 voyage on the Beagle. Since then, biologists have argued about whether the wolves were actually foxes (which is what Darwin called them) or, like the Australian dingo, descended from dogs that people had brought to the islands (Science, 30 September 1977, p. 1340 ).
To determine the wolf's ancestral lineage, Graham Slater, an evolutionary biologist at the University of California, Los Angeles, and colleagues compared DNA sequences from five museum specimens with those of living South American canids, including a group of foxlike animals that had been previously suggested as their most likely relatives. The team found that the Falklands wolves proved most similar to the maned wolf (Chrysocyon brachyurus), which hails from the South American savannas.
"That was a big surprise," says Slater, because of the pronounced difference between the two creatures. The maned wolf has much longer legs than the Falklands wolf and long jaws suited for catching rats and mice; the island wolf has shorter, Labrador retriever-like jaws designed for grabbing and shaking large prey, such as seals and penguins.
The study, published online tomorrow in Current Biology, points to a North American origin for all South American canids. The Falklands Island Wolf and the maned wolf diverged 6.7 million years ago, probably in North America given that the oldest fossils of canids in South America date back 2.5 million years, says Slater.
The findings rule out the idea that people played any role in the wolves' arrival on the islands. Instead, an analysis of the museum specimens' mitochondrial DNA shows that they shared a last common ancestor at least 70,000 years ago, suggesting that they reached the Falklands prior to the end of the last ice age; humans only set foot in the New World about 20,000 years ago.
Because the islands were never connected to the mainland, the Falklands wolf must have crossed the sea from South America by clinging to logs or an ice floe, the researchers conclude. "Their incredible journey shows the extraordinary adaptability and tenacity of canids," says David Macdonald, a conservation zoologist at the University of Oxford in the United Kingdom.
"It is a riveting paper and a fitting birthday present to Darwin," says Macdonald, because "the weirdly leggy maned wolf" that became the "somewhat doggy Falklands Island Wolf" shows how mutable species can be.
Darwin predicted that the wolves would soon go extinct because they were being heavily hunted for the North American fur trade. (Indeed, another biologist named and described the species based on pelts found in a New York City fur store.) Its extirpation, says Macdonald, "should stiffen the world's resolve not to let today's rarest canids, the Ethiopian wolf and African wild dog, follow the Falklands wolf to extinction."