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The World's Largest Snake Doesn't Need Males to Breed

We talked to the zookeeper in charge of Thelma, the world-famous snake that just had a virgin birth. It may be unsettling to imagine one less barrier in the way of more snakes, but finding new ways of making snakes might just be important.
Screencaps via the Louisville Zoo YouTube channel

In late October, the Louisville Zoo announced that a reticulated python named Thelma had produced the first documented virgin birth for its species, and it wasn't the most pleasant of potential solutions. Sure, it didn't involve the Archangel Gabriel, and it's not quite the same as the plot device in Jurassic Park where some female dinosaurs became male. But the idea of a virgin birth (or parthenogenesis) still sounds creepy as hell, especially if you've ever seen David Cronenberg's The Brood.


I spoke to Bill McMahan, the Louisville Zoo's Curator of Ectotherms, about whether or not this is completely fucked up and whether Thelma's offspring will be able to reproduce.

VICE: How do you feel about the term "virgin birth"? 
​Bill McMahan: If you define virgin as having had sex with another animal ten years ago, you might be able to say it's not a virgin in that respect, [because] we don't know that this snake, Thelma, has never had sex with another snake.

Right. It's not like we can ask it how it lost its virginity. 
​They lay eggs. I guess you could argue over whether something can reproduce through eggs and whether that actually constitutes the word "birth." Ironically, I guess I'd have more problem with the word "birth" than the word "virgin."

So tell me about Thelma.
​Thelma is an 11-year-old reticulated python that we've had here at the zoo for four years. She's 20 feet long and she weighs about 200 pounds. She presented us with a clutch of 61 eggs in June of 2012, and we ended up hatching six of those in September.

Is Thelma a normal snake?
​She's what's known as a morph. She's a pattern that's not found in nature very often, but one that's been perpetuated in captivity because it's different from the normal wild pattern that's routinely observed in reticulated pythons.

Is "virgin birth" something that could be considered helpful for endangered species? I assume it only happens in egg-laying animals.
​It's been done in a laboratory with mice. I think it would be more advantageous to do that for animals that are captive. In the wild, these animals don't have as many genes to deal with if they keep reproducing that way.


And you get a genetic bottleneck?
​Yeah, after a while you're quite limited. You want as many genes as possible potentially in the mix, so that if climatic conditions or other things change, there may be something there that can complement that or fill in for that. If you have such a limited number of genes, the possibilities are greatly reduced.

When people hear stories about things like this, they get a little bit unsettled, and think it's a result of pollution or things that humans are doing to destroy the planet. There's nothing sinister to parthenogenesis, right? 
​I don't think there's anything that would suggest some sort of ecological disturbance, whether that be pollution or climate change. I suspect this has occurred over a myriad of species for millions of years. And recently, people just couldn't get their head around it because they thought the prospects of "virgin birth" or parthenogenesis were so remote that it wasn't even worth looking at.

If Thelma or a snake like her were to exist in the wild, would she be as able to reproduce successfully?
​I think it's possible that these snakes do do this in the wild.

Has that been seen in other species where parthenogenesis occurs?
​The thing that we have the most information about are some turkeys. There's a breed of turkey called a Beltsville Small White, and about a half of one percent of the eggs laid by that particular breed are parthenogens. But in their case, they generally produce a male bird.


I would have assumed that Thelma's offspring would all be clones, or identical sextuplets. 
​They're half-clones, technically. It's a little bit confusing. They have [Thelma's] genetic material, and the other half is homozygous. It's from the genes that are there from the species.

Are there any plans to introduce Thelma to a male to see if they might reproduce?
​There's not a need to do that because this species has such a wide geographic range; it's the most widespread python on earth. These things can survive in relatively populated areas, even on the outskirts of big cities. So there's not a conservation need to do that.

Of Thelma's six babies, did they all survive?
​They did. They occurred in two morphs, interestingly. Thelma is a tiger morph, and all six offspring are female. Three are the wild pattern, like you would see in nature and which Thelma carries the genes for, and three are what's called a "super-tiger" pattern, which is really bizarre by wild standards. They're yellow snakes with black stripes down them, very different from the animal in nature.

Are Thelma's offspring likelier to reproduce in this way? Or are they sterile?
​That's the $64 question. That's not been determined yet, and there's a lot of speculation and interest as to whether these parthenogens can reproduce similarly-or sexually, for that matter.

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