Two ants, two species, one mother

0:24Welcome back to the Nature Podcast. This week, the bizarre breeding strategy of the Iberian harvester ant. And how to prevent deadly bridge collapses. I'm Lizzie Gibney. And I'm Benjamin Thompson.

0:45First up, reporter Nick Petridge-Howe is here with an unusual insect story. This week on the podcast, I want to tell you about two ant. brothers. Now, these siblings are quite different from one another. For example, one is hairy, while the other is almost hairless. They have different shaped abdomens. Oh, and despite having the same mother, as it turns out, these brothers are actually different species. Which appears completely biologically impossible. This is Jonathan Remigia, one of the authors of a new Nature paper documenting this bizarre phenomenon. He and a team of researchers found that queens of Mesa Ibericus, the Iberian harvester ant, can not only lay eggs of their own species, they can also lay eggs of males that are genetically an entirely different species of ant, called Mesa Structa, a species that diverged evolutionary from the Iberian ants some five or six million years ago.

1:56Not to put too fine a point on it, but these are very different animals. So it's basically something, yeah, human and chimp, basically, this scale. This discovery, which the team says is the first of its kind, was set into motion when they were studying ants on the Italian island of Sicily. What the team found there were hybrid ant workers, ants that were genetically a mix of Meso-Abericus and Mesostructa. Now, some ants do produce such hybrids, but these ones occurring in Sicily were a bit of a puzzle. In Sicily, we found absolutely no traces of the father species. And the fact that Sicily is an island, that Mesostructa are unknown in Italy, means that there is something very, very, very abnormal here.

2:52So we have to find how they're able to produce these hybrid walkers. Now, many ants have odd reproductive strategies, and breeding between species is not uncommon. In some cases, ant queens will go out and mate with another species and store their sperm, something known as sperm parasitism. In fact, for some ants, they need to do this in order to produce workers at all. They can only produce hybrid workers. But in this case, only one of the species, Mesa abiricus, is present on the island. So without the Mesa Structa fathers needed, what were the queens mating with to produce these hybrids? Where did they come from?

3:36Jonathan and the team searched for years to see if they'd missed any Mesa Structa ants, but they found no evidence of messa structure in Sicily, which led them to an unusual conclusion. The only possibility is that the queen is able to lay the two species of males, but I mean, it sounds so impossible that we needed to have a direct evidence. So we needed to have a colony in the lab with a single queen and see the two species of males emerge from these colonies. This was no easy task and the team waited for years to observe a male mesostructor being born in the lab. With the mesostructor males being produced in a lab locked down from any wild males sneaking in, the only explanation left was the Mesa Ibericus queens were able to lay eggs of a different species.

4:35How are they doing it? Well, the evidence points to a strange combination of sperm parasitism and cloning. Now, that may sound a bit strange and conjure images of Dolly the sheep, but it's known now that a few ant species have this ability to clone, to reproduce asexually. Although it's not clear how, queens are able to strip their own genome out of an egg and replace it with the genome of the father. This asexual reproduction is normally done within the same species, but in this case is going on between them, and appears to have been happening for about several million years, according to genetic analysis.

5:19So, long ago, a Meso-Abericus queen will have mated with a Mesostructor male, taken its sperm, then for some as yet unknown reason, just carried on producing these males whenever they needed them. When the new generation of Mesa Ibericus queens are born, they would mate with the cloned Mesa Structa males, allowing them to produce hybrid workers. This bizarre strategy allows them to continue producing hybrid workers without having to rely on wild Mesa Structa males being present. And so being able to produce the males you need for producing workers is an advantage. So probably evolve for that. As advantageous as it is in principle, it's certainly a bizarre observation representing the first time we know of that a species has cloned another species, beating humans cloning sheep by a few million years.

6:16This is the first time I think that, at least in the insects that I'm familiar with or any of the animals that I'm familiar with, we found a species where a mother can produce offspring of two different species. but if it was going to happen in any system, it doesn't surprise me that it happened in ants. This is Jessica Purcell, a social insect geneticist who's been writing a News & Views article on this new paper. She also thought that this was an odd discovery, and one that may have implications for how we think about what a species actually is. I think it does force us to reckon with some of the complications of our favourite species concepts.

6:56So the most widely used is called the biological species concept. And this is probably what most of us learned in school, where a species is defined as groups of individuals that can freely mate with one another and produce viable and fertile offspring. But this case is obviously a big deviation from that. So we have our host species, the Iberian harvester ant or Messor Ibericus, which are now producing males that are genetically more akin to this other species. and yet those males are perfectly integrated or quite integrated into the host species. And so what that means is that maybe these males are actually better described as members of the Iberian harvester ant species even though genetically they're more similar to this mesostructor species.

7:43Jessica wasn't completely convinced that these ants could really be called different species anymore with the cloned Mesostructa so integrated into the life cycle of Mesa Arbericus. So she'd like to see if it would be possible for the cloned Mesostructa males to mate with wild Mesostructa queens. If they were successful in producing offspring that way then they would better meet the criteria of being a species in her eyes. Jonathan thinks that there's no reason why they wouldn't be able to mate in this way but it's not something they've observed yet. By his definition, though, a phylogenetic one that bases what a species is more on the genetics, these are two different species being produced by the same mother.

8:32And while biologists will have to reckon with the already blurry species concepts, for Jonathan, this is just an example of how complex and wonderful biology can be. We know that humans are able to clone other species for their own need. But we realise that ants are also able to clone other species, and actually in a more spectacular way, because they use their own reproductive organs to clone these other species, and they actually need these clones for their own life cycle. So, yeah, basically it shows how complex and fascinating can be ants. That was Jonathan Romigier from the University of Montpellier in France.

9:16You also heard from Jessica Purcell from the University of California Riverside in the US. For more on that story, check out the show notes for some links. Coming up on the show, the surprising ways that bridges resist collapse. Right now, it's time for the research highlights with Dan Fox.

9:36People are living longer lives than ever before. But the 100-year life expectancy is still a way off. Researchers used mortality forecasting methods to project the life expectancy of people born between 1939 and 2000 in 23 wealthy countries. They then compared those results with the life expectancy for generations born from 1900 to 1938. Their results suggest that the pace of life expectancy improvement will drop sharply for generations born after 1938, due mostly to a stagnation in child mortality reductions. The phenomenon is widespread across generations and geographies. As a result, the authors suggest that none of the currently alive generations are likely to achieve an average life expectancy of 100, as would have been predicted if the previous pace of life expectancy growth were to continue.

10:34You can find that research in the Proceedings of the National Academy of Sciences of the United States of America.

10:44Birds in brightly lit cities have been found to sing for an average of 50 minutes longer each day than those in the darkest environments. To investigate how light pollution affects birds, researchers analysed data from acoustic sensors maintained by volunteers in almost 6 ,000 locations around the world. They found that species with large eyes were especially sensitive to light pollution, starting to sing 35 minutes earlier each morning and wrapping up 56 minutes later in the brightest areas than in the darkest. The extra singing time could cut into sleep and rest, but longer days aren't necessarily all bad for these city-dwelling birds.

11:26Prolonged activity has been linked to benefits such as an increase in foraging time and greater success in reproducing and raising chicks. The early bird can catch that research in science.

11:42Next up on the show, researchers have been investigating what makes bridges collapse and how this knowledge could help design ones that stay standing. Reporter Nick Petrich-Howe is back and here with more. Steel truss bridges are a very common kind of bridge. Although they have differing designs, these all use a crisscrossing of metal bars to create a load-bearing structure. You've probably seen a few in your lifetime. The Forth Bridge across the Firth of Forth in Scotland, the Quebec Bridge and the Tokyo Gate Bridge are all examples. You may also remember when a boat collided with the Francis Scott Key Bridge in Baltimore last year, causing it to collapse with the loss of six lives.

12:28That was also a steel truss bridge. And the thing is, bridges like this are vulnerable to collapse. Now, in the case of the Francis Scott Key Bridge, a boat collided with one of its pillars. But many of these bridges around the world were built over 100 years ago and were never designed for the very heavy traffic they now serve. And climate change may be making them more vulnerable. Increasing extreme weather events may lead to more degradation, for example. Together, these pressures are increasing the risk that individual components could rust and break with catastrophic consequences. In 2007, for example, the I-35W bridge in Minneapolis collapsed, killing 13 people.

13:16It's still unclear what exactly happened here, but the initial failure appeared to start due to a plate buckling, resulting in the collapse of the whole bridge. So figuring out how bridges collapse can be life or death. The problem is that data on damaged bridges is scarce and it's not easy to find. This is Juan Camilo Reyes, a structural engineer from the Polytechnic University of Valencia in Spain. Because monitoring a collapsing bridge or a damaged bridge is not so easy. Finding that kind of data is not so easy. Indeed, while a bridge is collapsing, it's not the easiest time to collect data.

13:57and every one would need to be wired with sensors to capture a rare event like this. So Juan and a team of researchers had a different approach. They built their own bridge. So we chose a bridge that is located in the province of Alicante in Valencia as our reference bridge. Why we chose this reference bridge? Because it's a still trust bridge and we knew all the characterisation around this bridge. The team looked at a 21-metre section of bridge in Alicante and used it to build a 6-metre model in the lab. With this, they could essentially test it to destruction to see what drives bridge collapses.

14:38They report their results in this week's Nature. After having done this process, we choose some characteristic damage scenarios that could happen to the bridge. and we chose 10 damage scenarios to analyse what was happening. We stick a lot of sensors into the bridge. It was around 94 sensors that measure deformation and monitor movement. And once we had monitored this structure, we started cutting elements to simulate the disconnection or the initial damage. After cutting various struts and elements of the bridge in different places with a saw, the team simulated heavy loads going across the bridge by pushing down on it from above.

15:25They saw that parts of the bridge would bend and twist with the strain, and information on this deformation was captured using their system of sensors. Wan and his colleagues then used the data from the lab tests to create a computer simulation of the bridge, in which they tested another 222 scenarios. Through this they found that the bridge was actually pretty resilient. When components were damaged other parts of the bridge could bend and move and essentially take up the strain. The bridge was still able to carry heavy loads despite the damage. In fact they found six common mechanisms of how the bridge could resist collapsing.

16:08For example if parts of the side or bottom were damaged, then the whole bridge could twist. Or if parts of the bridge were damaged width ways, other components could bend over the damage to take up the strain. It's the way the bridge compensates the damage. The team were surprised at how resilient the bridge was. That doesn't mean we should relax though. Obviously, a twisted or bent bridge isn't exactly ideal, and further failures could lead to collapse. But this knowledge could represent a way to prevent bridges coming down in the future. For example, what the team found could be used to focus efforts to reinforce existing bridges, as Bela Rivero, a structural engineer and another member of the team, explains.

16:54This can help us to save money during the retrofitting because it can guide or put the focus on those critical elements that need more attention and of course somehow help us to optimise deployment of new sensors for the monitoring, because there are some elements that has a clear, larger impact in other elements or in the structural integrity than others. Now, this study focused on a simply supported bridge, and one with a fairly common truss arrangement. There are, of course, many other kinds of steel truss bridge that this study didn't investigate. Some more work will need to be done to ensure that these resistance mechanisms are relevant.

17:34But the data from this and their study could help build bridges that are more resistant to collapse in the future. The design of bridges is following some rules that have been put into the standards many years ago and this is difficult to change. So our idea now is to develop or to transfer our findings to industry and to code development entities in order to take them into account, not only in the intervention in existing bridges, but to consider then also into the design of new bridges, because we now know that we can even optimize more the design of new structures. That was Belén Rivero from the University of Vigo in Spain.

18:18You also heard from Juan Camilo Reyes from the Polytechnic University of Valencia, also in Spain. For more on that story, check out the show notes for some links. Finally on the show, it's time for the briefing chat. where we discuss a couple of stories that have been featured in the Nature Briefing, which is, of course, Nature's daily roundup email of all the latest science news. Lizzie, why don't you go first this week? What have you got? I've got something fun. So we're looking at the chemistry of beer and how beer drinkers, or people who like beer, kind of fall into two different camps, depending on the kinds of chemicals or the chemical signatures that they prefer in terms of taste in their beer.

18:57So this was a presentation at the American Chemical Society and what they did in this research was they looked at the tastes of 135 people who all professed to being people who enjoyed beers. There were 18 different beers. They were all lagers and they were all similar in terms of their strength and similar levels of bitterness. And they got all of the tasters to evaluate all these different lagers on a bunch of different characteristics, things like sweetness, the intensity of the aroma, things like that. And then they also did the science bit. They use a mass spectrometer to figure out the different chemical compositions of the beers.

19:34Right, because I guess you hear a lot about this one's got floral notes, a little bit like wine, I suppose. This one's quite hoppy. This one you can taste a bit of cherry, that sort of thing, right? Exactly. And there are the equivalent in the beer world. there are people who are expert in distinguishing those different flavours. But in this particular study, they wanted just to figure out what the consumer, what the everyday person like you or I thinks, how they taste, and whether there are some different preferences that they could pick apart. And what they found was interesting, actually, people seem to fall into two distinct factions.

20:05People who like the stronger flavours and people who like the more mellow flavours. So in this particular study, the stronger beers were from Sam Adams, Brooklyn lager, and the more mellow ones were like Budweiser. So they also were able to then tie these different flavors with particular chemistry of those beers. So in the stronger flavored lagers, there was something often called furaniole. And in the more mellow ones, it was ethyl-3-methyl-thiopropionate, often cropped up. So they were actually able to tie these flavours to these different kind of factions of beer lovers. And they pointed out that the stronger flavour ones, that the chemistry in that was often associated with things like strawberry and jam.

20:51And the more mellow flavours were the chemistry of kind of pineapple. That was the example that my colleague Jenna used in the story. And this is maybe an interesting exercise, right? But one can imagine this being used to maybe point people in the direction of something they might enjoy more. Yeah, I think that's it. My other half always complains about certain beers tasting like pineapple. And I wonder if he's like a super beer taster or something because he really hates them. My main gripe, in fact, also with the study is that it was only lagers. So what about ales? What about beers? There might be a whole different kind of spectrum there that we could place people on.

21:24But in this study, they were looking at lagers and they found these two really distinct different types of preference. And the idea is that you can maybe tailor the beers so that they fit with those different, quite distinct consumer groups. And so, yeah, maybe it will lead to some new kinds of lager that are really aimed at those particular preferences. But we also had a point in the story of saying that probably your favourite beer won't be messed with. It's unlikely that, you know, a bit like with Coca-Cola, it's a recipe that's been around for ages. People know the taste. And, you know, even if you might be improving on a taste, if it's changed from what people have come to expect, consumers may not like it.

21:59Well, cheers for bringing that story to us there, Lizzie Gibney. Let's move on to my story this week. Now, we started the show with an animal oddity. I'll say. And I'd like to end with a story that's equally bizarre, but it's very, very different. Now, this is a story about a worm a few centimetres across, and it's been written about in PLOS Biology, and I read about it in Science. Now, Lizzie, let me send you a picture of this worm. Listeners, you'll find a link in the show where you can see it, and I urge you to do so. Right, Lizzie, what do you make of this? It's quite a fantastic looking thing, right?

22:31Okay. Oh, wow. Yeah. Yes, it's got like feathery kind of antennae. Those are its gills. Gills, wow. It's got a bit that looks like a head end that's covered in like some kind of swirly garb. And then these huge feathery looking things, which are apparently gills. So this is a sea worm, right? This is a worm that lives under the sea. And it's bright yellow. It's bright yellow. I wasn't sure, yeah, if this was a false colour for the purpose of the picture. But no, looking at the caption, it is really that incredible kind of really deep, rich yellow colour. And this is quite unusual, I have to say, for animals that live deep in the sea.

23:08You know, they don't usually bother making any pigments because there's no one there to see it because it's totally dark. And so this is quite an unusual thing, this bright, lurid yellow worm. But this colour is actually key to the animal's survival. Now, this creature lives attached to these brutally hot hydrothermal vents. It's in this case in the Okinawa Trench in the Western Pacific Ocean. And understandably, it rather stood out a kilometre below the surface of the ocean. And so what is it about this worm that means it can live at such kind of extreme depths and conditions? Yeah, extreme conditions is right.

23:43And it's a wonder of evolution. So hydrothermal vents, kind of a double-edged sword, it has to be said. They are absolutely teeming with things like microbial life, which can support an intricate food web. But on the other hand, you've got huge pressure, both figuratively and literally. This massive weight of water from above, the superheated water, as I say, and water that's laced with toxic chemicals. And it's this colour that really helps these worms survive these chemicals. So what happened was the researchers behind this work got some tissue from these worms underneath the microscope, and they found these spherical yellow granules in its skin cells.

24:22Now, they initially thought, not unreasonably, that these might be microbes which are helping these worms survive and are making this colour. But no, it turns out this colour is made of a mineral called orpiment, which is arsenic sulphide. Oh, blimey. I mean, you may well have seen this in the real world. Orpiment is a Latin name, which means gold pigment. And it was used by artists for years and years and years and years and years, from antiquity until the 19th century. Now, anything containing arsenic, surprise, is likely to be toxic. And that's why many old paintings have to be looked after very, very carefully because they're really poisonous.

24:59But in this case, for this worm, this mineral is less toxic than its constituent parts. So what is happening is it seems that somehow this worm builds up large amounts of arsenic in its skin, like over 1 % of its body weight is arsenic. but that arsenic what it does is it reacts with the sulfide found in this hydrovent fluid as it sort of comes up from beneath the ground and the two things react together to form clumps of orpiment and the authors describe this as fighting poison with poison that is amazing so the pigment is just a result of this reaction they don't need the pigment for anything it's just the fact that they're mixing the arsenic which is poisonous with something else that's poisonous and they end up being this incredible colour.

25:45And yeah, how it happens, really, really hard to know, right? Obviously, difficult place to study and explore. And it shows that once again, evolution has beaten humans to the punch by millions of years, just like with the ant story. And in this case, making a pigment that is this amazing colour. And incredible to think like, we understand so little about the depths of the ocean and what's going on around these hydrothermal vents. So we've just discovered this one worm, but like what other processes are going on? What other creatures are coming up with incredible strategies to survive down there?

26:18Absolutely right. And when I first saw a picture of this worm, you know, it does look alien, right? And I think it's true. The surface of the moon is better studied than the bottom of the ocean. And yeah, who knows what else there is to find? I mean, we do love a deep ocean story. And it could be that this technique could one day be used to detoxify environmental hazards. But, you know, that's a ways off and kind of speculation. But I think in this case, we should just marvel that this little worm, and I should give its name, Paravanilla hessleri, I've got my Latin correct there, is just a beauty to behold.

26:46Wow. Well, I love it. Right. Well, I think that's all for this week. But if you'd like to stay in touch with us, you can. We are at Nature Podcast on X and on Blue Sky. Or you can email podcast at nature.com. I'm Lizzie Gibney. And I'm Benjamin Thompson. Thanks for listening.