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Research published this month in
Science by a team from Oxford University and the Natural History Museum, London,
has shed new light on the genetic origins of the Dodo as well as offering
solutions to how the species bird came to be isolated on the island of
Mauritius.
Despite being the emblem of
extinction, the evolutionary history of the Dodo is poorly understood. The
extreme evolutionary changes it has undergone (e.g. gigantism, flightlessness)
on the island of Mauritius have even concealed its closest relatives within the
birds - and it has been linked with everything from parrots, pigeons, and
shorebirds, to birds of prey.
Dr Alan Cooper and Dr Beth
Shapiro from Oxford's Henry Wellcome Ancient Biomolecules Centre, Dr Dean
Sibthorpe, Andrew Rambaut, Dr Graham Wragg, Dr Olaf Bininda-Emonds and Dr
Patricia Lee from Oxford's Department of Zoology, and Dr Jeremy Austin from the
Natural History Museum, London, carried out the research, by retrieving tiny
fragments of Dodo DNA. The samples were taken from the only surviving Dodo
specimen with soft tissues remaining - the 300 year old 'Alice in Wonderland'
specimen in the Oxford University Museum of Natural History - so called because
it was the inspiration for the character in the Lewis Carroll book.
The Dodo DNA (taken from small
pieces of skin and leg bone) was compared to 1400 base pairs (units of DNA
length) of gene sequences from the Solitaire, an extinct Dodo-like bird from
neighbouring Rodrigues Island, and 35 species of pigeon and doves, as well as
other bird groups. The DNA showed that the closest living relative to the Dodo
and Solitaire was the Nicobar pigeon, from southeast Asia - and that the next
nearest relatives were the crowned pigeons of New Guinea, and the unusual
tooth-billed pigeon of Samoa.
Dr Alan Cooper, Director of the
Henry Wellcome Ancient Biomolecules Centre, described how the species became
distinct from each other, saying: 'The genetic differences suggest that the
ancestor of the Dodo and Solitaire separated from the Southeast Asian relatives
around 40 million years ago, and sometime after this point flew across the
Indian Ocean to the Mascarene Islands. The data suggest that the Dodo and
Solitaire speciated from each other around 26 million years ago, about the same
time that geologists think the first (now submerged) Mascarene Islands emerged.
However, Mauritius and Rodrigues islands are much younger (8 and 1.5 million
years respectively), implying that the Dodo and Solitaire used the now sunken
island chain as stepping-stones. Furthermore, the isolation of Rodrigues Island
suggests that the Solitaire, at least, may have still been able to fly as
recently as 1.5 million years ago.'
Specimen:
The 'Alice in Wonderland Dodo' is held at the Oxford University Museum of
Natural History. It consists of a head (with skin) and a leg and foot (also with
skin) - and represents the only known surviving soft tissues of a Dodo. The
entire specimen is thought to be one of the birds brought to Europe for
exhibition in the mid-late 1600s, and was almost thrown away in a museum
clean-up of tatty specimens in the 1700s. Fortunately, a curator grabbed the
leg/foot and head (reputedly from the fire used to dispose the rejects). The
museum kindly gave permission to sample a piece of bone from the leg and a small
section of flesh from the head. Relatively few well-preserved specimens of the
Dodo exist - although a number of bones have been retrieved from the large
swamps in Mauritius. Unfortunately the swamp environment has not allowed the
preservation of DNA. Researchers also examined bone from the Solitaire, a large
Dodo-like bird from Rodrigues island, which lies some distance to the East of
Mauritius. Jeremy Austin, the London based co-author, collected the Solitaire
bones from limestone caves on Rodrigues as part of his research on giant
tortoises. The cave preserved material was in much better condition even than
the 'Alice' specimen - probably because the latter has been on display off and
on for over 150 years (under lights and in warm conditions).
Evolutionary background:
The Dodo was first encountered in the late 1500s or early 1600s and was probably
extinct by the mid 1600s - as a result of human hunting, and especially the
introduction of rats and pigs. The early accounts suggest that like other
'evolutionarily island'
species, the animals did not recognise humans as a predator - and were easy to
hunt. The Dodo and Solitaire were so heavily modified for their island habitats
(eg large, flightless) that it is very difficult to determine their evolutionary
history by looking at their morphology (shape, e.g. bones). In fact early
scientists had considered their closest relatives lay amongst parrots, birds of
prey, shorebirds or pigeons - although by the 1800s the general view was that
they were probably pigeons, or at least somewhat related to them. If they were
pigeons, then the most likely explanation would be that they represented the
descendants of migratory African pigeons that had lost their way and colonised
the islands. The Dodo and Solitaire were different enough morphologically that
it was thought that they represented independent colonisation events - from
differing African pigeons. Interestingly, recent work by Andrew Kitchener of the
Royal Museums of Scotland, has showed that the Dodo was probably not as fat as
generally depicted in the paintings of the time. Most of these were copies, or
not based on original observations - and many may have been based on birds in
captivity in Europe - where they may well have been overfed by people not
familiar with their ecology.
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