Short Wave - No sperm? No problem.

Episode Date: December 2, 2021

Scientists have discovered that some female condors don't need males to reproduce. This phenomenon is known as parthenogenesis, and it's been observed in other animals too. The Atlantic's Sarah Zhang explains how it was found in California condors and its implications for these endangered birds. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Ola Shortwavers, Maria Godoy here, and today on the show, we're going to get a little PG-13. Yep, let's talk about sex, baby. Condor sex, to be exact, or the lack thereof. Scientists have discovered that some female California condors don't need males to reproduce at all. It's a phenomenon known as parthenogenesis or more colloquially as virgin birth. So these were two females who each had a son where there was no father. Without any sperm, wow, that's like amazing.

Sarah Zang is a science writer with the Atlantic, and she says this phenomenon is known as parthenogenesis, or more colloquially as virgin birth. And it's been observed in other animals, too. It seems to happen in a pretty wide range of animals. And by animals, I mean vertebrates, so things with a spinal cord. It happens in sharks. It happens in snakes. It's probably pretty rare occurrence.

But it's not something that is unique to any one species. It seems to be pretty widespread in the animal kingdom. Today on the show, Parthenogenesis and California Condors, how it was found, why it may happen, and the implications for the birds. You're listening to Shortwave, the Daily Science Podcast from NPR. Sarah, we're talking about the sex lives of California Condors because it's a subject that's been closely scrutinized for decades. Their mating lives are even documented in something called a stud book,

which I admit is a name I pretty much love. Yeah, I love the name's Tedbook too. So California condors are really, really endangered. And back in the 80s, there were literally only 22 of them left in the world. And that's when biologists actually went and captured all of the condors that were still living and brought them into captivity and started breeding them. And this was a really interesting. intensive process. This is a case where zookeepers are literally helping chicks out of their

eggshells or feeding them, hand-feeding them with puppets that look like condors. Because the problem is you don't want these condors that are raised in captivity to think that humans are going to be feeding them. So they had to wear these little hand puppets that looked like the face of an actual bird and fed those chicks with them. Another thing they even did is that to kind of double the number of babies that they would get, if you take the first egg away from a pair of condor parents, they'll actually lay a second one, and then you can give that first pair to a pair of foster parents. So over the course of, you know, over 30 years, the California condor population, thanks to this captive breeding program, has recovered to about over 500. So it's been quite a

success, but it's a really human-intensive endeavor. And one of the things that's involved in this breeding program is tracking exactly who's mating with who, right? And how many offspring they had and when that offspring was released into the wild. Exactly. It all goes into the stud book. So this is like, you know, usually you think this is a pretty easy process because what you do is that you, you house a female with a male. And, you know, how is the female going to meet with anyone else? She can't do that. So she obviously had to meet with the male. And that's what they thought happened. Sarah, what is virgin birth or parthenogenesis? How does it happen? So what happens in Parthagin, genesis is that the egg essentially fertilizes itself, right? So like, where is that other half

coming from? How is it replacing the sperm? But what seems to be happening is that when an egg cell is created, you know, it's actually being created as like one cell divides in half and it creates two cells. One becomes the egg and one becomes something that is known as the polar body. And usually the polar body just kind of disintegrates and goes away on its own. But it seems like in really unusual cases, this polar body is actually able to act kind of like as the sperm. But essentially it is an egg fertilizing itself. Interesting, interesting. The California condors we're talking about were the product of a very careful breeding program.

How did scientists discover that two condors had this puzzling origin? Yeah, yeah, as you're saying, this is very careful. We thought we knew who everyone was, who everyone's parents were, whoever's mothers and fathers were. And so what happened is that several years ago, scientists working with the breeding program decided to just do a DNA survey of all of the condor samples that they had lying around. At this point, this was like hundreds of samples. And part of it is they were interested in just like making sure every condor is who they thought they were.

But the other thing is that they just wanted to like, you know, cross-check everything that they knew about these condors. Maybe they'll even figure out something new because all the ones that exist are all pretty inbred, right? There isn't that much genetic diversity. So scientists wanted to make sure that they're not reading condors that are too really. related to each other, and there's sometimes there are genetic diseases that they're trying to avoid. Okay, so that's the preamble of why they were doing this. But what they found was really unexpected, which is there were two birds that didn't have fathers. They only had DNA from their mothers.

That's really fascinating. So these tests weren't meant to be like paternity tests. They just turned out to reveal a shocker. Yeah, no, nobody expected this to happen. It just was something that happened, and here we go. One thing that's sort of interesting is that all of the parthenotes in birds are males. And this has to do with the way their chromosomes work. So they don't have X, Y, or X, X, X, chromosomes.

They have ZZ and ZW chromosomes. And ZZs are males, and ZWs are females. And since Prathor notes need, like, two copies of the same thing, you can only make zZs, which are males. So all birds who are parthenotes are males. Now the two birds in question died before the scientists conducted these DNA tests and found out that they were genetically unique. So they didn't get a chance to study how their unusual parentage may have affected them.

But you write that both birds had documented health issues when they were alive. What kind of problems? Yeah, that's right. These birds are known by their stud book numbers. So one of them is called SB 260. And he had actually died when he was only two years old. Condors can usually live decades. And he was always a little bit small.

and once he was released into the wild, he just didn't really integrate well with the other birds, and he died in the wild. The other one called SB 517, when he was born, he just had a curved spine. You know, just immediately there was something that looked a little bit wrong, and so he had trouble walking, and he was never released into the wild.

He died in captivity at age eight after some complications after a foe got infected. So it's really hard to say exactly that these exact things were caused by, the fact that there are parthenotes. But given what we know about other things and other animals where parthogenesis happens, this is not that unusual. So it may be related. Interesting. So like what kind of other health problems have we seen in other animals besides condors that were the product of parthenogenesis? Yeah. So one of the scientists I talked to,

his name is Warren Both. He told me he was literally dissecting little pit vipers that were parthenotes like the few days before he was talking to me. He's like they had the exact same spinal problems where their spines are kind of curved or maybe a little bit malformed and their skulls are a little bit different. It's also pretty typical for the birds to just not grow very well. So in turkeys, for example, where parthogenesis has been studied. And amazingly, there are lineages of turkeys where prathogenesis happens in like 16% of the eggs. But even when it becomes really common, the birds that are parthinotes, they tend to be a little bit small. and the males, they don't have very good, like, semen quality, so they can't really produce

on their own. There's other species where pathogenesis happens, but the chicks just never really hatch from their eggs. So it's pretty typical for them to, you know, have some issues associated with it. Is it always a bad thing, though? I mean, you're talking about these sort of health issues that happen to animals that are parthenotes. That's a great new word I just learned. But could it possibly have some adaptive benefit? That is such a good question. And maybe, maybe B question to study about prathogenesis. So it seems like in birds, you know, if these Prathnotes are a dead end, if they're unable to reproduce, then like maybe that's like, you know, we can say it was not a great thing for that particular individual, right? But there's

other species where it seems like it's possible for the partha notes to reproduce, for example, in snakes. And there's suggestions that maybe like this is an adaptive strategy. For example, if your population gets really, really tiny, maybe you just like have a couple of snakes that are stranded on island, this is a way to maybe repopulate an area without having to do, having to find a mate, essentially. There's also this idea that, you know, Parthogenesis allows really small populations to purge lethal mutations. And the way this works is that, you know, as we were saying, a Partha note basically gets two copies of the same DNA from its mother. So if it gets like a gene that is lethal, and it gets two copies that lethal gene, that parthenot is like never going to

survive. So the ones that survive, maybe they still do have some health issues, but they don't have the worst genes. Interesting. And do we know why some females of different species go through parthenogenesis? So it's not clear exactly what triggers it. We do know, based on studies in poultry again, that there are some things that maybe do trigger, you know, there's maybe some genetic component to it. Certain breeds are a lot more common than others. It seems like maybe raising those animals in the higher temperature seems to make pathogenesis more likely. Sometimes infection with a virus when the hen is laying an egg might also call it. So it seems like there might be a bunch of different things that might trigger. It's not one thing. Interesting. Okay. I did not know that.

Sarah, we started out talking about virgin births in the endangered California condor. It sounds like in some species, it's a short-term reaction to stress, but is it possible that this remarkable form of reproduction could help the condor recover in numbers over a longer term? That is such a good question. So on one hand, we've talked a little bit theoretically about how this might happen in, for example, snakes, which we've seen partha notes been able to reproduce. We don't really have any evidence that partha notes and birds are capable of reproducing it. If they were, I would say then perhaps this can help condors repopulate. If they just end up being kind of a dead end, but maybe this is more just like a really

interesting and curious thing that happened that tells us a little bit about what's possible, but maybe it won't help us recover condor populations. Sarah, thank you so much for your time. Oh, thank you. It was a pleasure to talk to you. This episode was produced by Eva Tesfai, edited by Giselle Grayson and fact-checked by Margaret Serino. The audio engineer was Neil Rouch. I'm Maria Godoy. Thanks for listening to Shortwave.

Adios for now.