These invasive ants have bizarre genomes that defy biology

Yellow crazy ants (Anoplolepis gracilipes) are, to put it simply, one of the more well known aggressive ‘jerks’ of the ant world. And that’s saying a lot for any of the countless number of invasive ant species that typically don’t have too many fans to begin with.

Outside of Indonesia, A. gracilipes ants have little to no natural predators in the wild. That gives the little bugs an invasive advantage, allowing them to spread to Florida and the American Gulf states, in addition to parts of Australia, New Zealand, Papua New Guinea, Mauritius and throughout Southeast Asia.

Also known as long-legged ants or Maldive ants, these tiny insects don’t have mental illness. Instead, their strange name comes from their infamous frenetic zig-zag scurrying that, to the untrained eye, seems frankly terrifying, especially if you’re squeamish about bugs.

But these ants do have extremely bizarre genetics, according to a recent study in the journal Evolutionary Biology which revealed that all male yellow crazy male ants have both maternal and paternal genomes in different cells of their body, making the ants chimeras, which is somewhat different than the lion-goat-serpent combo from Greek myth. A genetic chimera is simply an organism or tissue that contains at least two different sets of DNA. In this case, the ants have haploid cells from two divergent lineages: R and W. Humans, for example, have X and Y haploid cells.

Male yellow crazy male ants have both maternal and paternal genomes in different cells of their body, making the ants chimeras

Previously, scientists thought that this kind of reproduction happened very rarely and only by accident. But as the study notes, A. gracilipes ants showing “obligate chimerism” via this unique fertilization and reproduction appears to give advantage to their W genome.

“Chimerism appears to provide two related fitness advantages to the W genome which persists in the population despite its association with female sterility,” the study notes. 

“If you study the biology of the yellow crazy ant, they are fascinating,” said Dr. Hugo Darras, an assistant professor at the Johannes Gutenberg University Mainz, and one of the lead co-authors of this new study, told Salon. Darras explained their years-long research confirmed their hunch that A. gracilipes males don’t reproduce the normal way.

Reproduction that breaks all the rules

Ants in the wild live in colonies, typically with one queen ant and many worker ants. All worker ants are female, but the queen ant is the only one that can lay eggs, the most common form of their reproduction. Drones, the male version of ants, have one function only: to mate.

The male yellow crazy ants had essentially cloned themselves, something that was highly unusual

But when it comes to A. gracilipes, particularly males, all of the basic ant reproductive norms are turned on their head.

“The male usually only has one copy of the genome. The way the ants reproduce is one copy of the genome usually comes from the mother, and another from the father in the case of female ants,” Darras explained.

But in this study, the researchers found that the male yellow crazy ants had essentially cloned themselves, something that was highly unusual, Darras said. He quipped that male ants are usually pretty useless when it comes to reproduction, since the queen ant and the female workers often bear the majority of the reproductive-work burden.

The average male lifespan is typically only a few days. In contrast, female worker ants may live a few weeks to a few months on average. Female queen ants live longest, up to a few years in the wild. In lab settings, an ant’s  lifespan can be extended significantly. There are reports of queen ants living for decades in labs, while the average worker ant may live several years in a lab setting.

Darras notes that yellow crazy ants are polygynous, meaning they have multiple queens — in some cases their reproductive capabilities are essentially limitless. While reproduction in these colonies does happen the regular way, crazy ant males simultaneously exhibit these strange reproductive capabilities as well, making them chimeras.

Darras points out another factor that helps yellow crazy ants’ reproductive capabilities is they often cooperate well with other A. gracilipes ants that are not in their native colony — again a very highly unusual trait among these insects. Most ants can be highly territorial and even go to war or enslave other ants.

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Yellow crazy ants have an appetite for everything from nectar, fruit, insects, spiders, all the way to frogs, crabs, nesting birds and other small invertebrates. They will eat whatever is available dead or alive — even other ants on occasion. While the most common form of A. gracilipes ants generally do not bite humans nor do they have stingers, these invasive ants often will swarm in houses, crawl spaces, basements or even electrical units.

A. gracilipes ants generally do not bite humans nor do they have stingers, but often will swarm in houses, crawl spaces, basements or even electrical units

Yellow crazy ants can be incredibly aggressive and successful at competing for resources in their new adopted habitats, Darras said. Naturally, ant colonies with hundreds of thousands of ants (up to an estimated million ants per colony) mean that the high numbers of ants take up a lot of resources in their habitat.

Throughout this multi-year study, researchers observed 30 colonies, each with more than 1,000 workers in European lab settings, while also analyzing the ants’ cellular and genetic makeup. Normally, A. gracilipes ant cells contain identical genetic material. But in the case of the male ant, they possess a unique genetic composition.

“If you would ever see two different copies of the genome, usually it would happen by accident. But in the case of yellow crazy male ants, this was actually happening all of the time. It was kind of strange and remained a mystery for many years,” Darras said. “Before, we didn’t understand the ‘why’ behind it.”

“We suspected this was the case, but only more recently with our research were we able to definitively prove it,” Darras noted the lab team did granular cellular genetic analysis on the ants to definitively confirm their findings.

“There are so many unanswered questions when it comes to chimera studies, involving the influence of paternal genomes,” Darras said. “Sometimes the eggs are fertilized and you get a normal diploid offspring. We have no idea why during the egg stage when it doesn’t fertilize as expected, how does this happen?”

“There are so many unanswered questions when it comes to chimera studies.”

Do these male reproductive capabilities have anything to do with the significant increase seen within the yellow crazy ant population? Perhaps not. But when it comes to better understanding ant reproduction capabilities, these ants certainly are covering all of their bases.

The power of one ant vs. a colony

An ant isn’t necessarily intelligent from an individual perspective and cannot accomplish much on their own, according to ant expert Dr. Andrew Suarez, who is an entomology professor at the University of Illinois at Urbana-Champaign. Ants use very simple decision-making rules, such as where they need to go and forage.

“But when you put ants together, the colony as a whole is doing things that you might not have ever predicted,” Suarez, who was not part of the chimera research, explained to Salon. “The colony is dividing labor in ways that are amazing. There is a lot we can learn from ants, ant colonies and invasive species of ants from how they work together and the things they accomplish. Computer programming, efficiency, architecture, you name it. We are just at the tip of the iceberg.”

Can we slow the global spread of this pest?

For obvious reasons, most humans aren’t so crazy about yellow crazy ants. They don’t just impact native ant populations, but they disrupt bird habitats and breeding areas. They are considered so dangerous and disruptive, they’ve earned a spot in the top 100 of the Global Invasive Species Database’s invasive species list. 

“I don’t know that there is any advantage to having the crazy yellow ant in the United States,” Suarez said. Many experts are not exactly sure where A. gracilipes ants come from originally. “My best guess is they are from Southeast Asia … but we don’t really know where they originate from. But at some point hundreds of years ago they spread to Asia, part of Africa, and then Australia and New Zealand, the United States and elsewhere.”

One A. gracilipes eradication initiative is to introduce hump-backed Phorid flies from South America

But when it comes to their adopted homelands, many believe yellow crazy ants have long overstayed their welcome. Going even further, many humans fear their presence spells ecological disaster. There are some early stage government-sponsored A. gracilipes eradication initiatives that could be brilliant — or completely crazy.

One such initiative, out of the University of Texas, Austin, aims to introduce hump-backed Phorid flies from South America. The idea is the flies will only attack specific species of ants, like A. gracilipes. In lab settings, the experiments have promise, according to emerging research, but there could be off-target effects. If deployed in the wild and things do not go as planned, the fix could be worse than the original problem.

The bottom line is, humans have no idea how to stop invasive A. gracilipes ants from overpopulating any habitat they move to. Many entomologists believe that some ant colonies could be naturally susceptible to viruses and even colony collapse, as is the case with certain bees, but the truth of the matter is this hardy invasive ant species are most likely not going anywhere anytime soon.

Still there are many lessons we can learn from A. gracilipes  ants, no matter how unpopular they may be. Since yellow crazy ants consistently outcompete other kinds of ants and other animals for food and other ecological resources, it’s possible there are many lessons humans could benefit from, such as social cooperation and how to handle competition.

Some scientists hope chimera-specific research could potentially have real-life value for humans. While there are ethical concerns to consider, potential real-life scientific research breakthroughs involving stem cell research, including perhaps a better understanding of cell response to disease growth, are among the benefits down the road.

At any rate, given the widespread problem these strange, crazy ants pose, it would be worthwhile to invest in research into their truly unique reproductive strategies. Yellow crazy ants have much to teach us.

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