Flies with shorter eye-stalks act aggressively because females are less attracted to them
In the stalk-eyed fly world, it's the males with longer eyestalks that get the females. Not only do the females prefer males with longer antennae dotted eye-stalks, but other males are also less likely to fight with these more well-endowed flies.
However, some males will always have short eyestalks due to a copy of the X chromosome that causes the eyestalks to be smaller. While investigating why this genetic mutation hasn't disappeared–despite generations of sexual selection–a team of scientists found that the flies might be compensating for their shorter eyestalks with more aggression. The findings are detailed in a study published October 21 in the journal Frontiers in Ethology.
'These driving X chromosomes are pretty interesting because they are an example of how parts of our genetic code aren't necessarily working together, but have their own selfish interests,' study co-author and State University of New York–Geneseo biologist Josephine Reinhardt said in a statement. 'This is an extreme example, but simply carrying one of these selfish chromosomes impacts so many parts of these animals' biology, even their behavior.'
Gene drives and dueling flies
Stalk-eyed flies is a catchall term for the insects in the fly family Diopsidae and order Diptera. They are typically found among low-lying vegetation in humid areas, generally near rivers and streams. They are only about a centimeter long and feed on decaying animals and plants.
Two types of X chromones are present in stalk-eyed flies. The one carrying the mutation for short eyestalks is a driving X chromosome, or more specifically, a meiotic driver. This means that it carries alleles which are over-represented in a male's sperm, so it is much more likely to be passed on to the next generation.
'The driving X chromosome has a huge natural advantage because it passes itself on more than the fair 50-50 'coin flip' rule of genetics that most of us learned in high school biology,' said Reinhardt. 'Up to 100% of a male's offspring end up inheriting the X and therefore are female. Because of this, we might assume the X will keep increasing in the population and even cause extinction. Since that hasn't happened, we're interested in understanding what other traits could counteract that advantage.'
To defend their access to mates, male stalk-eyed flies generally use intimidating physical displays and fighting. They will also display more aggression against other flies with similarly-sized eyestalks
As a way to test whether the flies carrying the driving X are more aggressive, the team on this study used populations of flies carrying either type of X chromosome–the one that always results in flies with shorter eye stalks and the one that does not. They also matched up competitors with similar eyestalks, recorded their contests, and analyzed their behavior.
The fighting behaviors were more common when the two flies had more closely matched eyestalk sizes. These aggressive actions were also seen more often in male flies with the driving X. The males that deployed more of these fighting behaviors were also more likely to win in these contests. Males with the driving X chromosome were also more likely to come out victorious when they engaged in more fighting than displaying.
'When fighters are mismatched, fights tend to end quickly, with the smaller male retreating,' Reinhardt said. 'When a male with the driving X chromosome is fighting a male with similar-sized eyestalks, he is more aggressive. But because driving X males are on average smaller, it is likely still a disadvantage.'
Mating opportunities
According to the team, this feisty behavior might explain why the flies with short eyestalks were able to mate. Since longer eyestalks signal a larger body size and potentially more dangerous foe, the flies with shorter eyestalks will typically retreat from contests with these bigger flies.
However, if males with the driving X chromosome are more aggressive or fail to accurately assess the threat from other males, they might choose to compete with males with longer eyestalks. This then brings them into contact with the females that are initially attracted to their opponent.
While this extra aggression is potentially dangerous, it may also give the flies access to mating opportunities that they otherwise wouldn't. Still, this can't fully counterbalance sexual selection. The team's modeling of the spread of the driving X suggests it might explain why the shorter eyestalks haven't taken over. The females still prefer males with longer eyestalks, keeping the variant's frequency low.
'I would say that this study is an initial finding,' said Reinhardt. 'A larger study might be done in which we specifically test for the increase in high-intensity behavior that we saw here in a larger sample. In addition, this is a laboratory study, so it is not totally clear how well it would apply to field behavior.'
The study also didn't test female flies. If the driving X chromosome is what directly increases aggression, it might impact females. However, if it's an indirect effect to do with the eyestalk size, the driving X chromosome might not affect the females.
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Yeah, this is the latest in a long line of multimedia objects that I've spent a foolish amount of time and energy curating that have something to do with fungi or mycology. I think I might be the only person alive or dead to curate such a collection or such a large collection. From the very moment I saw the trailer, it met all the important criteria for a show that I would pay attention to. Having had a lot of other mycological media to judge it by, there were some tropes that I was kind of expecting. What kind of tropes? I'd say first and foremost, that mushrooms are reducible to poisons, pizza toppings and party drugs. And a kind of characterization of mushrooms, mycology, people associated with either as being wacky, wild, weird ... not occupying, or perhaps [not] deserving to occupy the mainstream. Like an inherent eccentricity, I guess. And, I mean, there's some ways in which the show kind of invokes some of that, but so far, I think it's doing a really excellent job… And I'm interested to see where it goes. You spent 10 years in Ecuador, what did you learn there? My first involvement in Ecuador [was in 2013] with a group that called itself the Amazon Mycorenewal project. That was a group of mostly Californian volunteers with several Ecuadorian counterparts seeking to find and develop low-tech, easily replicable, inexpensive ways of achieving mycoremediation of the abundant oil contamination in the northeastern corner of the country and what's been called the Chernobyl of the Amazon. And specifically using oyster mushrooms and techniques that were not created by, but were sort of popularized by, Paul Stamets, and a study of his that was really super popularized by his TED Talk, "Six ways mushrooms can save the world." And we most definitely found fungi growing in amongst that contamination. Is that the only thing you would see in these pits, the only life? No, there was other life there. The aggressiveness of life in the Amazon is hard to put down, even when something as catastrophic as oil [is involved]. Oil and toxic formation waters are everywhere. Like it's unequivocal that damage has been done by that contamination. But we did find fungi, we found plants, we found [animals.] We did have some documented successes, including having piles of soil and substrate that had once been, as Paul Stamets would say, dead, dark and stinky, then having plants and seeds and sprouts and worms and bugs and eggs, and having no detectable odor, or consistency between the fingers, of petroleum. Replicating that at scale for the 800+ Olympic swimming pool sized unlined pits was another matter. That fungi growing in proximity to, if not being directly reliant upon, contaminated environments in the Andes, you know that was definitely a very close parallel [with Common Side Effects.] And then you went up to the cloud forest? It would be a couple few years later that I met Dr. Roo Vandergrift, who was doing his PhD work in the cloud forest, a place called Reserva los Cedros. The way that I could be useful to Roo then and now was photography and taxonomy. Those are sort of my areas of interest and of ability. In my time I'd spent, oh seven or so years, you know, mycologizing, both in the US, but also taking every opportunity I had to return to Latin America. People on the expedition had experiences being around nature that I think had not become evolutionarily accustomed to the threat that is our species. Our collecting really didn't happen very much outside of about a 100 meter radius of our base camp. We've 100% found new species. Before "Richer than Gold," there had never been a paper to summarize, or a project to summarize, all of those fungi. [Psilocybe stametsii, which was found by a different group, is] one of surely thousands, if not tens of thousands, of new species that are waiting to be described from Los Cedros. It's part of the Chaco bioregion, which is a forest type that only exists in remnant plots. We're down to 2 or 3% left of the total cover that the Chaco would have had historically. It has been beset on all sides by threats of one kind or another, since, really colonial times, but most recently, that threat has come in the form of mining. Can you tell me about the court case in Ecuador, which was a challenge based on the constitutional rights guaranteed in the country's 2008 Constitution? Specifically, it included "the right of nature to have its existence respected holistically, and to the maintenance and regeneration of its vital cycles, structure, functions, and evolutionary processes," and provides broad legal standing for the launching of judicial claims by "all individuals, communities, peoples and nations" to enforce the rights of nature. It was three, four years ago, because the man who founded [the Los Cedros reserve], a piss-and-vinegar draft dodger and conservation hero named Joseph DeCoux, who recently passed away, and a consortium of Los Cedros supporters, community organizers, and board members brought a case against this Canadian mining company and the Ecuadorian national mining company, and I think by extension, the Ecuadorian Ministry of Mining, claiming the unconstitutionality of this mining concession that covered two-thirds of Los Cedros being given to these companies or this ministry. This court case went from municipal to provincial to constitutional with the Ecuador Supreme Court. And we won, which was a David and Goliath upset, but one that I still can't wrap my head around. I think most of us can't. Not only was that tremendously lucky, also the result of a lot of hard work, but in the initial analyzes that were done illegally by the mining companies, they did not find enough indication of what they were looking for. Perhaps they would have been even more aggressive about turning Los Cedros into a pit mine, if they had found stronger indication [of the copper and gold for which they were prospecting]. [Note: The case was launched as a protective action to stop the initial exploration phase of the Río Magdalena mining project in the Los Cedros protected area. It was ultimately selected by the Constitutional Court to help determine binding jurisprudence on how the Rights of Nature should be applied to endangered ecosystems and species. The court ruled that mining in the protected forest would be a violation of the constitutional rights of nature, but also that the application of these rights applies not just to protected areas, but, because it's a constitutional right, to the entire territory of Ecuador.] I don't want to say they found nothing. In 2019, we went to the exact spot where these technicians from the mining company had illegally entered the property to set up a sort of makeshift base camp to do this soil and water analysis to test for trace amounts and minerals. And that was when the project took on the sort of moniker, "richer than gold." That's how we titled our National Geographic Foundation Explorer grant application. We applied in the area of the category of urgent concern and conservation, citing that this was very likely headed in the direction of becoming a mine very soon, and we wanted to go to exactly that base camp where they had set up shop. And just so if we collect in 100 meter radius from right here, nowhere else, this is all of the biodiversity that will be impacted, and hopefully be able to use that information to argue against the opening of the mine, if it came to that. It was a far, far more remote location prior to these mining company employees coming in during the dry season, being able to drive along a road that would normally be sort of mudded out and then hiking in a relatively short distance. We were coming in the wet season, and had to hike around nine, nine and a half hours in, sometimes thigh-high mud in sometimes 45 degree incline, the hardest hike of everyone's life who participated in that. But our group and this mining company that came in to set up the base camp very likely could have been the first human beings to set foot in this area. The terrain is difficult enough and inaccessible enough that it likely would not have been utilized even by pre-Columbian peoples, certainly not in a permanent way. And the resulting research? Our paper from 2023 is a big, big summary of the fungi found through these opportunistic sampling events over an 11 year period. But [Los Cedros] is just one sort of piece of the larger puzzle. Because these mining activities are replete throughout the country. This kind of rises to the top on account of being the sort of poster child for putting constitutional ideas [about the Rights of Nature] to the test in a way that would ultimately affect the rest of the country. Your , so beautiful. And to someone who hasn't spent that much time looking at fungi they're mind-blowing. I mean, you hear about the diversity of it, but to actually see such gorgeous things is just amazing. Why do you take these wonderful photos? So I hope it doesn't come across as smug to say that's kind of the point. In my first trips to the neotropics, I was seeing these extraordinarily beautiful things that many of which had only ever been written about in a very cryptic, inaccessible Latin or science-speak in 100-year-old tombs collecting dust in the basements of university libraries that, like, you would have to paint a picture in your mind to be able to get an idea of what it looks like. If you can take good pictures of something, you can convey a lot of these characteristics that formerly would have just been illustrated or more often described using taxonomic terminology. There's a section of our paper called "simulated access", where we kind of make this case. The work that we did in Los Cedros, and the work that I try to do everywhere I go, is intended to be a kind of taxonomic brochure. So to not just have the data in a neat package tied with a bow to hand to the specialist, but to also have really captivating and feature-rich images so that they can see the thing. Instead of saying, 'Well, I think we may have found this species that was first described 125 years ago by a German botanist who came on a mission to a remote part of Brazil,' here's a picture of the thing so you can see it. And also have that picture be aesthetically pleasing enough that it appeals to all kinds of people, from a conservational standpoint, trying to galvanize public interest and capital W wonder to really see how extraordinary these things are. Because if we're after public funding or even private funding, the public and the private, I suppose, has to be compelled, has to see that there's something really, really captivating and beautiful there. So that's a big part of why. I just wanted to ask, what is a parataxonomist? I think if that were a Jeopardy question posed to the total world population, you might get 500 people who could answer it correctly. In 1991 an entomologist named Daniel Janzen wrote a paper called 'How to save tropical biodiversity,' and he correctly pointed out that there was this extraordinary amount of tropical biodiversity that at the current or historical rates of species description would take several thousands of years to fully describe. Given the obstacles faced by taxonomic research and researchers and to the planet, we didn't have that long left. And so he devised a division of labor system, which he called parataxonomy. He envisioned local people being trained up in doing essentially the first 90 yards of 100 yard sprint in order to maximize the time of the specialists, the PhD biodiversity researchers, who, up until this point, had been tasked with doing the entire 100 yards themselves, but really their expertise and time and resources were best applied to answering the questions that only they could answer. And you know, he also correctly pointed out that most of these specialists, historically, contemporarily, were coming from somewhere else. They were coming largely from the West to the Global South to do this work, and they could be there for maybe a few days to a few weeks, to, if you were lucky, a month or more. But that from a phenological perspective of what occurs at what times of year, that also is posing a limit that doesn't need to be there. Why not partner with people who are there all the time? Okay, could you tell me about the particular psychedelic mushroom you mentioned, ? So that one was one that had been found during expeditions prior to my involvement. The people who had collected it knew that it was a new species of psilocybin and had expressed an interest in publishing it then going out and collecting fresh material to serve as the type collection for that species that would happen later. They mounted their own separate expedition trip to Los Cedros and got new material to serve as the type for that, describing it and naming it after Paul Stamets. I talked about it a little bit, when I lectured on our work, that I think it was a curious choice to pick the white male straight CEO of a Fortune 500 company in North America to name the first new species of fungus described from Los Cedros after when there were a lot of other, maybe 'better alternatives' lying around. But I am much happier that we live in a mycological world with Paul Stamets in it, as opposed to one without him in it. If it ends up bringing more conservational attention to the reserve, that's positive. What's happened with descriptions of other fungi that you've found that were also never previously described? So those wheels have always moved extraordinarily slowly, and I wish that revelations like Dan Janzen's back in the early '90s would have really changed that in a permanent way, in a global way, but they haven't. We've got very, very few people who are still carrying out the very important and dramatically underfunded work of biodiversity and now, equally, conservation research at a time when every day it's needed more than the day before, and that is, I think, largely a funding problem. You could put the starting point of that as far back as the 1970s, the starting point that I pick in that article is the National Science Foundation coming out and declaring that they were essentially henceforth and forthwith [only] in the business of funding what they call transformative research, which is a little bit oxymoronic. It's like rewarding hips for being taller than feet. The only way you get transformative research is by having something to transform in the first place. So they want cake without having to pay for the flour, eggs and sugar. And this is like these are the vegetables that organismal biological science has to eat that may not have immediate, honestly, won't have immediate, sexy results. It's in the pure or unapplied kind of realm of the sciences that is just exploratory. Then the applied side comes later, people looking at what compounds exist in these things, what applications they might have. We're just in the interest of finding out who else is here on the spinning ball of juice in the sky, you know, whizzing through the galaxy at millions of miles an hour. And I think that that's beautiful and interesting enough in its own right. We don't have to be looking at nature in the form that I think far too many people do, that what can they do for us? I think there's a reverential approach that is just as, if not more, valuable.
