When eight-year-old Hugo Deans spotted a handful of BB-sized objects lying near an anthill under tree trunks in his backyard, he thought they were some kind of seed. But his father, Andrew Deans, a professor of entomology at Penn State, knew right away what they were, the beams of oak, or the growth of plants caused by insects. What he didn’t immediately realize was that tannins were part of an elaborate relationship between ants, wasps, and oaks, and their discovery would have turned a century of knowledge about insect and plant interactions upside down.
Looking back, Hugo, now 10, says he “thought it was seeds, and got excited because I didn’t know ants collect seeds. I always thought ants would eat leftovers and stuff around the house. Then I got more excited when [my dad] He told me they were symptoms, because [my dad] He was very excited. I was surprised that the ants would collect tannins, so why would they do that? “
According to Andrew Deans, who is also director of the Frost Museum of Insects in Pennsylvania, many interactions between insects and plants are well documented. For example, most species of “cynipid” wasps have long been known to induce oak trees to produce protective galls — or growths — around their larvae to ensure the safety of their developing offspring. In addition, some plants—including blood roots (Sanguinaria canadensis), a wildflower native to North America—produce edible appendages, called elaiosomes, on their seeds to attract ants, which then disperse the seeds by transporting them to their nests. This last example is referred to as “myrmecochory” – or the dispersal of seeds by ants.
“In Myrmecochory, the ants get very little nutrition when they eat the iliosomes, and they scatter plant seeds in a place free of enemies,” explains Deans. “This phenomenon was first documented over 100 years ago, and is usually taught to biology students as an example of plant-insect interaction.”
The team’s new research—initiated by Hugo’s discovery of crests located near an anthill—has revealed a much more complex species of myrrh fly, one that combines the interaction of wasps and oak gall with that of edible ants.
“First, we noticed that although these balls typically had a fleshy, pale pink ‘cap’, ants near the anthill did not have these caps, suggesting that the ants might have eaten them,” says Deans. “Ultimately, this led us to discover that wasp wasps manipulate oak trees to produce mites, and then take another step and manipulate the ants to restore the mites to their nests, where wasp larvae can be protected from predators or receive other benefits. This multi-layered interaction is astonishing; It’s almost hard to get around it.”
The team’s results were published in the journal American naturalist.
To better understand the interaction, the researchers conducted a series of field and laboratory experiments. First, to determine if oak gall caps — which the researchers have dubbed kapéllos (Greek for “cap”) — are actually edible and attractive to ants, the team first observed oak scales in ant colonies in the wild in Western Neo. York and Central Pennsylvania. Additionally, they set up video cameras to capture additional animal/gallbladder interactions. At both sites, they saw ants transfer moths to their nests. Inside the nests, all edible coverings were removed, while the goblins themselves remained intact.
In a second set of experiments to determine if kapéllos act similarly to elaiosomes, researchers investigated the ants’ preference for acorns versus blood root seeds. They set up seed/bitter bait stations and observed that the ants removed the same number of seeds and mites, indicating no difference in ants preference.
Next, the scientists conducted a laboratory experiment to document whether the ants collected the ants due to the feeding capyllus. They set up three Petri-dish treats—with whole balls, gallbladder bodies with kapéllos removed or kapéllos with gallbladder bodies removed—along with a control dish containing a different type of gallbladder with no edible accessory. They introduced the ants to the Petri dishes. They found that interest in ants did not differ between control balls and capello-free treatment sessions, both of which lack edible ingredients. By contrast, interest in ants was greater for squash with intact kapéllos and kapéllos alone than for control ants.
“We showed that imps with hats were more attractive to ants than those without hats, and that the hats per se were also attractive to ants,” says John Tucker, professor of entomology. “This suggests that hats must have evolved as a way to lure ants.”
Finally, the team asked, “What makes them in kapéllos so attractive to ants?” According to Tucker, the chemistry of iliosomes has been well studied and is known to contain nutritious fatty acids. Therefore, the team compared the chemical structures of kapéllos with elaiosomes and found that kapéllos also contain healthy fatty acids.
“It appears that the fatty acids abundantly present in the gallbladder and lysosomes mimic dead insects,” says Tucker. “Ants are scavengers trying to find anything suitable to bring it back to their colony and take it over, so it’s no coincidence that both gall caps and lysosomes have fatty acids typical of dead insects.”
who came first?
The last, and according to the researchers, the most intriguing question that the team pursued was, “Which came first in evolutionary time? The elaiosome interaction or the gallbladder interaction?”
Says Robert C. Professor of Biology, Buffalo State University of New York.
One reason, he explained, is that pest plants, such as blood roots, make up only a very small percentage of all plant species and, therefore, may not contribute enough food resources to drive natural selection in ants. However, oak beams are widely abundant. In fact, Warren says, these animals were once so plentiful that they were regularly used to fatten livestock.
“If these orcs were so abundant and developed this tactic of growing such cover thousands of years ago, it could be a powerful driver of natural selection in ants,” Warren says. “The ants could have long ago been accustomed to capturing the goblins with lids, and then when the spring wildflowers started producing seeds that happened to have an edible supplement, the ants were already ready to pick up the stuff with a fatty acid supplement.”
Deans noted that the team recently won a grant to conduct genetics work to further investigate which of these interactions came first in evolutionary time.
“Understanding how these interactions evolve and how they work helps untangle a little more of the complexity of life on Earth,” he says.
About what it felt like to contribute to such an important discovery, Hugo says “I bet other kids have made similar discoveries but never knew how important they were. I feel really happy and proud to have been part of such an important scientific discovery. It’s strange to think that just some ants who collect what I thought were seeds was actually a significant scientific achievement.”
When asked if he wants to be an entomologist like his father when he grows up, since he’s already made his first scientific discovery, Hugo said “Not really. I want to be different…unique…when I grow up.”
The Crypt-Keeper wasp has been found parasitizing multiple species of gall wasp
Robert J. American nature (2022). doi: 10.1086/720283
Provided by Penn State University
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