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Thursday, Feb. 28, 2002

NATURAL SELECTIONS

Tracing the evolutionary flight of the dodo


A strong contender for the title of most misunderstood animal must be the flightless dodo, the bird universally derided as fat, slow and stupid. To top it all, it's dead.

Formerly inhabiting Mauritius, east of Madagascar in the Indian Ocean, the dodo -- its name derives from the Portuguese doudo, meaning foolish or stupid -- also vies with dinosaurs for the title of most famous extinct animal.

The dodo has also been poorly understood by scientists, who have been scratching their heads over the bird for years. Where did it come from? What did it evolve from?

Now DNA extracted from the preserved dodo in the University of Oxford's Museum of Natural History, thought to have provided the inspiration for Lewis Carroll's Dodo in "Alice's Adventures in Wonderland," has helped shed light on its evolutionary history. Whether it will also help the dodo shed its reputation for being dumb and outdated, however, is another matter.

Carroll, real name Charles Lutwidge Dodgson, was a lecturer in mathematics at Oxford from 1855-81. On seeing the dodo in the museum, and good-naturedly aware of how he, a stutterer, pronounced his own name ("Do-do-dodgson"), Carroll conceived the Dodo character for his stories to the young Alice Liddell.

Fast forward about 150 years. Beth Shapiro and colleagues in the department of zoology at Oxford analyzed DNA from that same dodo and from another extinct flightless island bird, the solitaire, which lived on Rodrigues, an island in the same Mascarene chain as Mauritius. Like many island species, both birds underwent significant evolutionary changes, and from morphology alone it has not been easy to determine which ancestral birds they evolved from.

Flightlessness has evolved many times in different bird groups, always from ancestors able to fly. When birds are isolated from predators on islands, the costs of flying often outweigh the benefits. For the ancestors of the dodo and the solitaire, it was more efficient not to fly (their wings and sternum became vastly reduced and all the energy wasted on growing flight muscles could be used for other things). Freed from the weight restrictions that flying animals have to follow, the ancestors of the two birds evolved large size -- perhaps to increase the range of foods they could eat, or to make them more efficient at fighting each other.

Both bird species had been linked to groups as diverse as the ratites (a large group of flightless birds that includes the ostrich, emu, kiwi and the extinct moa), raptors (birds of prey) and columbids (pigeons and doves). The DNA analysis conducted by Shapiro and colleagues confirms that the dodo and solitaire are sister species and that the closest living common relative is the Nicobar pigeon, native to the Nicobar Islands. The results suggest that the extinct species diverged from their ancestral pigeon stock about 42.6 million years ago, and the dodo and solitaire separated from each other about 25.6 million years ago.

The interesting thing about that date is that Mauritius was formed by volcanic activity around 7 million years ago, whereas Rodrigues only emerged from the ocean 1.5 million years ago. In other words, the two species existed long before the formation of the islands on which they were later discovered. Drilling projects, however, have established that ridges surrounding the islands were above water at that time. The researchers, writing in today's issue of Science, therefore propose that the birds used the ridges as "stepping stones," dispersing across the sea before settling on their respective islands.

The dodo was discovered around 1600 by Portuguese sailors. Eighty years later, it was extinct. Some dodos were killed for food, but most died because of deforestation and the activities of the animals the Portuguese (and later the Dutch) brought with them. Cats, rats and pigs destroyed the nests of the dodo, which, according to contemporary records, approached the sailors like innocent children. Having lived isolated from any predators for millions of years, the dodos had lost the escape response -- and so gained their reputation for stupidity, walking up to the sailors who skewered them for their dinner.

As for the charges of fatness and slowness, Andrew Kitchener, a curator at the Royal Museum of Scotland, discovered that the drawings and paintings of dodos showing them to be fat were made in Europe. While those dodos were being shipped back, they were fattened up on a diet of ship biscuits. Writing in New Scientist, Kitchener says that illustrations made in the wild show a thinner bird. Contemporary reports describe it as being able to run fast. In any case, bird species on Mauritius today put on fat in the summer to burn off in the winter, something that the dodo is also likely to have done.

The Dodo in "Alice in Wonderland" organized the Caucus Race, to dry off Alice and the other animals after they'd become soaked with Alice's tears. After half an hour of random running, the Dodo stops the race. "But who has won?" ask the animals. The Dodo thought hard and declared, "Everybody has won, and all must have prizes."

Carroll's Dodo, at least, wasn't as dumb as the Europeans thought. As for the real dodos, their rapid extinction has been called the first act of ecovandalism.

E-mail Rowan Hooper at rowan@japantimes.co.jp


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