Image: Virgin snake birth
Charles Smith / Pam Eskridge
A female copperhead snake (Agkistrodon contortrix) and her offspring born via parthenogenesis, also called virgin birth, are described in a study published by Biology Letters.
By Contributor
updated 9/11/2012 8:43:55 PM ET 2012-09-12T00:43:55

Wild female pit vipers can reproduce without a male, suggesting that virgin births may take place in nature far more than before thought.

Asexual reproduction is common among invertebrates — that is, animals without backbones. It occurs rarely in vertebrates, but examples of it are increasingly being discovered. For instance, the Komodo dragon, the world's largest living lizard, has given birth via parthenogenesis, in which an unfertilized egg develops to maturity.

Such virgin births have also been seen in sharks at least twice; in birds such as chickens and turkeys; and in snakes such as pit vipers and boa constrictors.

Although virgin birth has been observed in vertebrates in captivity, scientists had not yet seen it happen in the wild. This raised the possibility that such asexual reproduction might just be a rare curiosity outside the mainstream of vertebrate evolution.

"Until this discovery, facultative parthenogenesis — asexual reproduction by a normally sexual species — has been considered a captive syndrome," said researcher Warren Booth, a molecular ecologist at the University of Tulsa in Oklahoma. [7 Shocking Snake Stories]

Now, genetic analysis reveals examples of virgin birth in two closely related species of pit viper snakes — the copperhead (Agkistrodon contortrix) and cottonmouth (Agkistrodon piscivorus).

Mama's offspring
The researchers collected genetic samples from long-term studies of the snakes — copperheads from Connecticut, and cottonmouths from Georgia. They gathered specimens from 22 litters of copperheads and 37 litters of cottonmouths, both the mothers and their offspring. DNA analysis confirmed that in one litter from each species, the offspring were solely the product of the mother, with no genetic contributions from a father.

The researchers were able to analyze the large amount of data due to collaborations with Charles Smith and Pam Eskridge of the Copperhead Institute and Wofford College in South Carolina; and Shannon Hoss, a graduate student at San Diego State University.

"We just sat there stunned at the discovery," Booth told LiveScience. "This is something that we always believed existed, but in order to investigate it, it would take a massive amount of work in the field. … To detect it in both species in our first attempt was astounding.

"I think the frequency is what really shocked us," Booth added. "In the copperhead population, we detected one instance in 22 litters, whereas in the cottonmouths, it was one in 37 litters. Essentially, somewhere between 2.5 and 5 percent of litters produced in these populations may be resulting from parthenogenesis. That's quite remarkable for something that has been considered an evolutionary novelty, even by me up until this finding."

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Pit vipers and many other creatures carry out meiosis, in which cells divide to form sex cells, each of which only possess half the material needed to make offspring. In the female pit vipers, pairs of their sex cells likely fused to generate embryos. The results were progeny that included only the mother's genetic material. However, these offspring weren't clones of the mother since they were not made using identical halves of her genome.

What limits virgin births?
How prevalent, then, is virgin birth? And could it possibly extend to humans?

"In terms of other species, it is evident now that reptiles are a group that appear predisposed to parthenogenesis, whether facultative, as we address here, or obligate, where the primary reproductive mode is parthenogenesis and few or no males are known within the species," Booth said.

Obligate parthenogenesis may have arisen from ancestral interbreeding between species, though scientists aren't sure why some animals seem to randomly give birth without help from the male (the facultative type).

"What is common to those that reproduce facultatively is the lack of genomic imprinting — by that, I mean a process in which a specific set of genes are provided by the mother, and a second set from the father," Booth said. "These genes of different parental origin must interact in a process called genomic imprinting in order for the development of an embryo. This, as far as we are aware, occurs in all mammals with the exception of the monotremes — platypus and echidnas — and therefore explains why we cannot have facultative parthenogenesis in mammalian species without significant intervention by scientists." [The 10 Wackiest Animal Discoveries]

Originally, Booth and his colleagues thought such virgin births might happen if potential mates were not present, but over the years, they have seen six captive female boa constrictors give birth via parthenogenesis even when males were around during their breeding cycles. The number of times virgin births have occurred with different females also seem to rule out a freak accident causing it to occur, Booth and colleagues said.

They are now investigating other possible causes for these virgin births — "these include genetics, viruses, tumors and bacteria," Booth said.

In the future, the researchers also hope to investigate other species for virgin births, such as water snakes in Oklahoma. In addition, they plan to see how well the offspring of virgin births survive and reproduce. It may be that virgin mothers can establish whole area populations of snakes by themselves. "We will know if this is possible in the next two to three years," Booth said.

The scientists detail their findings online in the journal Biology Letters.

© 2012 LiveScience.com. All rights reserved.

Explainer: The 2012 Weird Science Awards

  • Our annual Weird Science Awards pay tribute to the strangest scientific tales of the past year, and you just know the 2012 edition had to be a doozy. While we're waiting for the Maya apocalypse — and we may be waiting a long, long time — let's count down the top 10 Weird Science stories, as determined by an ironically unscientific Live Poll.

    No. 10 is the discovery that having a painful need to urinate can impair your judgment. "When people reach a point when they are in so much pain they just can't stand it anymore, it was like being drunk," says Brown University neurologist Peter Snyder. "The ability to hold information was really impaired." To say nothing of the ability to hold water.

    The research won Snyder and his colleagues a share in one of 2011's Ig Nobel Prizes, which honor science that makes you laugh, and then makes you think. Watch Snyder explain the study in this YouTube video, then click the "Next" button for more laugh-provoking science — or scroll quickly all the way down to the bottom if you have a painful need to go.

    — Alan Boyle, msnbc.com science editor

  • 9. Flies hooked on meth ... and sugar

    Image: Fruit fly
    Botaurus via Univ. of Illinois
    Researchers have found that the fruit fly is a useful model organism for studying the whole-body effects of methamphetamine exposure.

    When researchers noticed that meth addicts often take in large amounts of sugary drinks, they decided to do a little experiment: First, they got fruit flies hooked on methamphetamine. Then the scientists fed some of the flies a diet heavy on trehalose, an insect blood sugar. They found that the sugar-gobbling flies outlived the flies who didn't get the sweet stuff. Maybe sugar metabolism plays a role in meth's toxic effects. "Hopefully, some of these insights might lead to opportunities to deal with the problems associated with the drug," says University of Illinois toxicologist Barry Pittendrigh. But more research is required to trace the effects on mammals. In the meantime, watch out for those meth-head fruit flies.

  • 8. Monster pictures make a splash

    Courtesy of Discovery News
    A photo from a video that claims to show Alaska's own version of a sea monster.

    2011 saw a double-header (so to speak) in the marine-monster category. The most popular Loch Ness monster-like picture came from Alaska, where Andy Hillstrand of the "Deadliest Catch" TV show captured the footage for the Discovery Channel. Some might suggest that the creature is an eel, or a fish, or even a trick of light on the water. Not Hillstrand. "I've never seen anything like it," he told Discovery News. He suspects that the picture shows a Cadborosaurus, a legendary beast that has long been said to frequent Alaska's waters. Meanwhile, another picture purporting to show a creature that's been nicknamed "Bownessie" made waves in England.

  • 7. Glowing dog has an on-off switch

    Image: Glow-in-the-dark paw
    Lee et al. / Genesis
    Photos demonstrate the inducible glow-in-the-dark effect in a genetically modified dog: The left images shows the dog's paw in normal light (upper left) and under ultraviolet light (lower left) after doxycycline is added to the dog's food. The right-hand images show the dog's paw in normal and ultraviolet light after scientists stopped administering the drug.

    In past years, our Weird Science Award winners have included glow-in-the-dark kitties and glow-in-the-dark puppies. How could scientists possibly top that? Would you believe a dog with a gene that turns the fluorescence under UV light on or off, depending on whether a particular drug is added to its food? That's exactly the kind of dog that South Korean scientists produced in 2011. Why, you ask? Well, the ultimate aim of these glow-in-the-dark exercises is to splice in genes that can help treat diseases — and having an on-off switch would give physicians more control over the treatment. That feat would make other researchers turn green ... with envy.

  • 6. Just this once, Samoa skips a Friday

    Image: (FILE PHOTO) Samoa Cancels December 30th As Islands Skip Over The International Dateline
    Hannah Johnston  /  Getty Images
    Samoa and New Zealand-administered Tokelau skip a day as they jump over the international date line in an attempt to improve trade and tourism.

    For more than a century, Samoa was on one side of the International Date Line, and Australia and New Zealand were on the other. When the Samoans were at Sunday church, the Aussies were starting their business week on Monday. And when Samoa was trying to finish up its own business week, the Kiwis were settling into the weekend. To remedy that, the Samoans switched over to the Australia-New Zealand side in 2011, going directly from Thursday, Dec. 29, to Saturday, Dec. 31. To top it all off, workers were paid for the non-existent Friday. If only we could all get to the weekend that quickly ... and spend it on a tropical island.

  • 5. Pole shift forces airport makeover

    Might as well face reality: Shift happens. Earth's shifting magnetic poles are not a sign of the apocalypse. They're just a fact of life on our dynamic planet. We do have to cope to the shift that life throws at us, though. For example, in early 2011, Tampa's airport had to repaint the numbers on its runways to reflect their shifting orientation with respect to magnetic north. The good news is that even dramatic changes in the poles' position would have no effect on life on Earth, despite what the doomsday prophets say.

  • 4. Corpse-dissolving machine invented

    "Build a better mousetrap and the world will beat a path to your door." Does that old saying apply to building a better corpse-dissolving machine as well? Resomation Ltd. hopes so. The Scottish company installed its machine in a St. Petersburg, Fla., funeral home and hopes the system will be legalized in other jurisdictions. The alkaline hydrolysis unit liquefies a body's soft tissues and flushes the sterile liquid into the municipal water system. The bones and other hard parts are left behind to be crushed. Company founder Sandy Sullivan says the machine lets people express their environmental concerns "in a very positive and I think personal way." Sounds good, as long as they don't put a Soylent Green factory next door.

  • 3. Preacher gets doomsday wrong ... twice!

    First, figure out exactly when Noah's Ark was floated by the Flood, and exactly when Jesus was crucified. Then come up with an arcane biblical numerology to add 7,000 years to the former, and 722,500 days to the latter. That was California preacher Harold Camping's formula for determining that May 21 was the date for the beginning of an apocalyptic Rapture. When May 21 didn't work out, he said Oct. 21 was the fallback date for the end of the world. And when that didn't work out ... well, now Camping says he's rethinking this whole doomsday business. But what about the 2012 apocalypse? That's too kooky, even for Camping. "Mr. Camping does not believe the Mayan calendar holds any significance at all," a spokeswoman says. Camping's mathematical acumen earned him a share in one of 2011's Ig Nobel Prizes.

  • 2. 'Aflockalypse' is for the birds

    Image: A dead blackbird on the ground in Beebe, Arkansas,
    Warren Watkins/The Daily Citizen  /  EPA
    A dead blackbird on the ground in Beebe, Arkansas.

    The year 2011 was rung in with a series of reports about mass die-offs, involving blackbirds (the so-called "Aflockalypse" in Arkansas), fish, crabs and other creatures. Some wondered whether a global environmental crisis was in the offing, but experts said the Aflockalypse was simply a case of people connecting the dots between unrelated events, facilitated by global communication systems. Die-offs can happen for a variety of reasons. The Arkansas blackbird deaths, for example, took place after the birds were spooked by New Year's Eve fireworks. And wouldn't you know it? The Aflockalypse happened again to kick off 2012.

  • 1. Fungus turns ants into zombies

    David P. Hughes
    A dead ant, after being zombified by a species of parasitic fungus. The brain-controlling fungus turns ants into zombies that do the parasite's bidding before it kills them.

    If books like "Pride and Prejudice and Zombies" and video games like "Resident Evil" can generate billions of dollars in sales, it shouldn't be surprising that the top Weird Science honors go to a story about zombie ants being taken over by a brain-controlling fungus. The fungus apparently uses temperature cues to decide when to have the ant clamp down on a cool leaf with a death grip. Pennsylvania State University's David Hughes speculates that the fungus does its thing to ensure it "has a long cool night ahead of it, during which time it can literally burst out of the ant's head to begin the growth of the spore-releasing stalk." It's the perfect plot for a horror movie directed by one mean mother: Mother Nature.

  • Honorable (?) mention

    Other weird tales that almost made the top 10:

    Does 13th zodiac sign mean your horoscope is wrong?
    Was the Shroud of Turin created in a blinding flash?
    Science reveals how to win at 'Rock, Paper, Scissors'

    Previous Weird Science winners:

    Cricket testicles and 2011's other Weirdies
    Kinky fruit bats and other Weirdies from 2010
    2,700-year-old marijuana and other 2009 Weirdies
    Glow-in-the-dark kitties and other Weirdies from 2008

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