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Males? These Snakes Don’t Need ‘Em

Males? These Snakes Don’t Need ‘Em

By Jennifer Viegas, Discovery Channel

Virgin births among captive animals have sometimes been described as a desperate attempt by females with no access to males to procreate, but a new study documents several cases of birth by wild female snakes that had no help from the males.

The study, published in the latest Royal Society Biology Letters, represents the first time that virgin births have been detected in the wild. It also suggests that absence of males does not always instigate the phenomenon, which occurs among chickens, turkeys, lizards, sharks, insects and many other animals.

NEWS: Boa Constrictor Mom Gives ‘Virgin Birth’

For this latest study, the researchers focused on two closely related species of North American pit viper snakes: the copperhead and the cottonmouth.

“In these populations, males are relatively common, hence females were not restricted from access to males, and therefore isolation from males is not a driving factor for parthenogenic reproduction (virgin births) here,” lead author Warren Booth, an assistant professor of molecular ecology at the University of Tulsa’s Department of Biological Sciences, told Discovery News.

Booth studied field-collected pregnant snakes and worked on the research with colleagues Charles Smith, Pamela Eskridge, Shannon Hoss, Joseph Mendelson III, and Gordon Schuett.

Out of a total of 59 litters from the snakes, the scientists selected two for DNA analysis. These two already showed signs of virgin birthing, since the eggs had multiple yolks and the litters included just a single male offspring.

The genetic analysis supported the suspected lack of paternal DNA contribution. Booth explained that, in each case, the female’s egg cell “fused to a part of itself, and her chromosomes doubled.” The offspring wound up having two copies of her set of chromosomes, and therefore half the genetic materials.

“This means she has very reduced diversity across her genome,” he said. “This is essentially an extreme form of inbreeding.”

Loss of genetic diversity can be a problem, leading to deleterious genes in the population. On the other hand, the process for certain species can sometimes purge out bad genes.

For example, Booth said, “We see extreme inbreeding in many insect species, such as bed bugs and cockroaches, and they thrive. So while inbreeding is never ideal, it is not necessarily bad in all cases.”

So far, the offspring of the studied snakes “are outwardly healthy,” he shared, “and on their way to sexual maturity.”

BLOG: Virgin Shark Birth Pups Living Long, Healthy Lives

Demian Chapman, an assistant professor at Stony Brook University’s School of Marine and Atmospheric Sciences, is a leading shark expert. He has documented virgin births in sharks, such as in a female blacktip that was once housed at the Virginia Aquarium.

At the time, Chapman told Discovery News that such a male-less birth “may just be an occasional mistake that sometimes occurs when eggs are left unfertilized.”

But the latest findings suggest that this form of birth may be far more common among some animals than previously realized. Booth said that, based on his own past research on boa constrictors and cottonmouths, virgin births produce about 2.5 to 5 percent of litters. While those numbers aren’t huge, they indicate that dad-less snakes aren’t just an every-so-often novelty.

It remains a mystery now as to why these births happen, and what triggers them. The copperhead that gave virgin birth was small, Booth said. “If she had never mated, it is possible that she was overlooked by males in favor of larger, more fecund females.”

Another theory is that females produce a single male offspring so that they can later establish a population with their son via inbreeding. Yet another is that bacteria or disease may trigger virgin births.

One thing is certain, at least so far: Mammals, including humans, cannot achieve the feat without significant intervention from scientists. Booth explained that the process seems to require a lack of genomic imprinting (whereby genes of different parental origin must interact). Reproduction among all mammals, save for the platypus and echidna, involves genomic imprinting.



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8:44AM PDT on Mar 16, 2013


12:02PM PDT on Oct 28, 2012

Really a very interesting article! Thanks!

11:01AM PDT on Oct 8, 2012

good read, thanks!

12:43PM PDT on Sep 27, 2012

Slugs do it too.

6:40AM PDT on Sep 26, 2012

This is very interesting , I had a red rat snake for 6months and then i got a yellow rat snake and then got rid of the yellow one and the red rat snake laid eggs and we hatch them out they were all red rat snakes, still by her self she laid eggs again and they were crossed between yellow and red, so i don't know if they can store what they need.

6:23AM PDT on Sep 26, 2012

thanks for sharing :)

12:52PM PDT on Sep 25, 2012

Oh boy, reading this after a huge full grown rattlesnake found under my house and also evidence of thinner slither patterns under there, as well, indicating the birthing of younger snakes occurred there. Did not see the more lethal young snakes in person, but do hope they went to find another place to live and hope the large rattler does too cause I have dogs & need a plumber to do some work to PEX there soon...

3:37AM PDT on Sep 25, 2012

Thanks for sharing!

3:28AM PDT on Sep 25, 2012


3:05AM PDT on Sep 25, 2012

That's very interesting and I hope we get to read more about this in the near future.
I liked the story about the little female copperhead passed over by the males but who was nevertheless able to procreate. I wonder if her offspring were small too.

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Disclaimer: The views expressed above are solely those of the author and may not reflect those of
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