Sonntag, 15. November 2009

The mystery of Darwin's wolf

During the voyage of the Beagle, (just) one (other) of the puzzling observations by Charles Darwin was the presence of a large canid on the remote Falkland Islands - as only native mammal species. On the two islands, Darwin recognized differences between the East Falkland and West Falkland wolves (Dusicyon australis), a further clue for Darwin that species are not fixed entities.

Illustration of Dusicyon culpaeus from Zoology of the Voyage of H.M.S. Beagle (source wikipedia).

Ever since the Falklands wolf was described by Darwin, the biological origin of this now-extinct endemic canid, and how the animal reached the island, 480 kilometres distant from the South American continent, remained a mystery. Possible hypothesis about the ancestry of this enigmatic canid suggested that the Falkland wolf was related to domestic dogs, North American coyotes, or South American foxes, and was brought on the islands by human colonists.


A new study, published in "Current Biology", compared the DNA sequence of preserved museum specimens with modern canids, and helped to solve some of the riddles of this animal.
The analysed DNA sequences show that the closest living relative is actually the maned wolf-, Chrysocyon brachyurus, an unusually long-legged, fox-like South American canid - from the physical appearance very different to the wolf. The researchers also found that the four Falkla
nds wolf samples that they examined shared a common ancestor at least 70,000 years ago, which suggests that they arrived on the islands before the end of the last ice age and appearance of humans on the American continent. This fact seam's to rule out the prevailing theory that Native Americans brought the first animals on the Falkland's.
A possible remaining explanation for the wolves' presence on the islands, which have never been connected directly to the South American mainland, is the dispersal of individuals by ice or swimming logs.

During ice ages the sea level was up to 200m lower than today. Even if this is not enough to form connecting land bridges between the mainland and the islands, the resulting sea passages were much closer, maybe facilitating significantly the surviving of animals on their "travel" to uncolonized habitats.

Topography of the South American continet and bathygraphy, note the -200m area (data source)

Kommentare:

Aldo Piombino hat gesagt…

David, I have a lack in my knowlege: I don't understand who were the top - predator in South America (as Carnivora in Eurasia, Africa and North America). Before the great exchange there were marsupial meat-eatings and the terror birds. And after? How many wolves there were in tha andean region or in Patagonia? And in the rainforest of Amazonas there were only caymans, felides and snakes?

David Bressan hat gesagt…

That´s a good question, I found this first infos:
PROTHERO (2006): After the Dinosaurs - The AGe of Mammals

“The carnivores of the “Great American Interchange” comprise cats (including sabertoothed cats), dogs, bears, racoons and weasel from the Uquian mammal age”
“South America had many endemic canids that radiated from the Pliocene forms. “

The study of SLATER et al mention also that the split from the maned wolf appears to have occurred 6.7 million years ago — some four million years before wolves are known to have lived in South America. At that time, maned wolves lived in North America, and it seems that all of South America’s canids originated in the north.

I will engross the theme in the weekend, it´s worth a post, but first I have to do some research…

Aldo Piombino hat gesagt…

very thanks
Aldo