« From Sea To Shining Sea - The Distance Diminishes | Main | Ele-Facts: Elephant Seal Mating Season »

January 11, 2007

Island Isolation And Dad-Less Dragons

Growing to almost 10 feet long, Komodo Dragons are the largest lizards on earth, nowadays, anyway. Found exclusively in Indonesia, these carnivorous reptiles are endangered. According to Wikipedia, there are approximately 6000 living dragons, but the main concern is that there may be as few as 350 breeding females.

With a population of 6000, why so few breeding females? Some recent behavior in captive dragons at Chester Zoo may shed some light. It's like a story out of Jurassic Park - Nature finds a way...

Flora the Komodo dragon ... has laid fertile eggs despite never having had a mate.

DNA tests confirmed Flora was the sole parent

...

Flora, along with another female Komodo dragon from the London Zoo, represent the first known cases of virgin birth in the world's largest lizard, according to researchers.

The two reptiles are examples of a process called parthenogenesis, in which offspring are produced without fertilization by a male, according to a report in the current issue of the journal Nature.

Single-parent reproduction is hardly ever seen in such complex animals, having been documented in just 0.1 percent of vertebrates, the study team says.

...

The reptiles are native to islands in Indonesia, where female castaways could have need to start new colonies on their own, the researchers say.

"If a female gets swept off her desert island to a new desert island where there are no other dragons, then she can reproduce parthenogenetically," Gibson said.

...

Parthenogenesis has been found in a number of other unexpected animals in recent years, he added.

"It was recorded in a python a couple of years ago," he said. "Turkeys can do it, and it's also happened in fish."

More at: National Geographic: Virgin Birth Expected at Christmas -- By Komodo Dragon

In the process of parthenogenesis, unfertilized eggs develop into embryos using two sets of the female chromosomes instead of one set of the mother's and one of the father's. The resulting baby dragons are always male and once they reach sexual maturity, the mothers can mate normally again. Still, this two-stage inbreeding means that genes from different dragon populations are not mixing and diversifying for at least two generations.

So why so few breeding females in the wild? The Komodo Dragons' numbers have been dwindling for some time. What if they have been reproducing in the wild using parthenogenesis for a generation or so - then one would expect there would be significantly more young males running around. Komodos can live for several decades, and it is somewhat unclear when they reach sexual maturity - one source claims that females mature after 9 years and males after 10 years.

The bad news is that the true breeding population may be much smaller and more fragile than the population numbers reflect. The good news here is that the dwindling dragon population may have a way of recovering itself.

Posted by sorsha at January 11, 2007 3:45 PM