Rattlesnake

No, it's not the immaculate conception.
But, one scientist has found that his female timber rattlesnake, which he has had since it was born in 1981, has given birth. Not a fantastic feat in itself, but the snake has never had contact with a male snake.

"I was more than a little perplexed, " said David Chiszar, an animal behavioural psychologist at the University of Colorado in Boulder, after coming upon a litter of four unfertilized eggs, two stillborn, and one live male baby.

When Chiszar compared the DNA of the baby snake with his mother's DNA, he found that all of the baby's DNA came from his mother, thus wiping out any possibility of an unknown father.

The case is one of four different species of snakes, all described in a study published in Herpetological Natural History, vol. 5, p1. The same thing occurred in three other snakes raised in captivity: a Wandering Garter snake and an Aruba Island rattlesnake at Arizona State University, and a Checkered Garter snake at the Phoenix zoo.


Garter snake

Parthenogenesis or virgin birth is not uncommon in nature, especially among vertebrate animals. In the snake community, the only one known to reproduce through parthenogenesis is the blind snake. It can only reproduce this way. The process is called obligate parthenogenesis.

However, "all of these four species of snake are known to be sexual animals," explains Chiszar. These four cases represent facultative parthenogenesis -- virgin birth among sexual animals.

So what caused these female snakes to all of sudden reproduce on their own?

"We don't think that this is anything new. We believe that this has happened in the past, except that in the past people didn't notice it," says Chiszar. "It's been known for years that females can store sperm for years to use in the future."

Chiszar explains that some female snakes and turtles have been known to store male sperm for years -- up to seven years in a snake as far as Chiszar knows -- to use it in the future to fertilize their eggs. So, many would assume the births were a result of stored sperm. But, this snake has been in isolated captivity since birth -- being one of the offspring of a captured pregnant snake.


What exactly triggered the virgin births among these snakes?

"I don't know... that's one of the big mysteries. We don't understand the mechanisms that underly the females' ability to produce these babies."


The findings raise many more questions than answers, says Chiszar. One thing Chiszar knows is that he will keep a close eye on the live male baby, which will be sexually mature in two years.

If he turns out to be sterile, that would suggest the incidence were simply "a misfiring of a normal reproductive system, " says Chiszar. If the baby is able to mate and lead to a fertile union with a female, it may play a role in evolution.