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Curious boy upends a century of science regarding insects and plants

[July 3, 2023: Staff Writer, The Brighter Side of News]

An ant holds an oak gall containing wasp larvae. Researchers discovered an elaborate relationship among ants, wasps and oak trees. (CREDIT: Andrew Deans, Penn State)

Penn State scientists, thanks to 8-year old Hugo Dean's curiousity, have discovered a new level of complexity in plant-insect interactions through a groundbreaking study that has turned a century of knowledge about the relationship on its head.

The team was investigating ants' attraction to oak galls when they discovered an elaborate relationship between ants, wasps, and oak trees. The researchers found that oak gall wasps are manipulating oaks to produce galls and then manipulating ants to retrieve the galls to their nests, where the wasp larvae may be protected from gall predators or receive other benefits. The discovery is so mind-blowing that it has made it almost hard to wrap one's mind around it.


Looking back, Hugo, now 10, says that he "thought they were seeds, and I felt excited because I didn't know ants collected seeds. I always thought ants would eat food scraps and stuff around the house. Then I got more excited when [my dad] told me they were galls, because [my dad] was so excited. I was surprised that ants would collect galls because why would they do that?" Hugo's father is Andrew Deans, professor of entomology at Penn State.

This discovery led Andrew Dean's team to find a new, multi-layered type of myrmecochory, one that combined the wasp-oak gall interaction with the edible appendage-ant interaction.


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In traditional myrmecochory, certain plants produce edible appendages, called elaiosomes, on their seeds to attract ants, which then disperse the seeds by carrying them back to their nests. The phenomenon was first documented over 100 years ago and is commonly taught to biology students as an example of a plant-insect interaction.

However, the Penn State team's new research has revealed a much more complex type of myrmecochory that combines the wasp-oak gall interaction with the edible appendage-ant interaction.


The team's new findings have been published in the journal American Naturalist, where it details the researchers' field and laboratory experiments to better understand the interaction. The first experiment conducted by the team was to determine if the oak gall caps, which the researchers named kapéllos, were edible and attractive to ants, similar to eliaosomes.

They directly observed oak galls in ant colonies in the wild in Western New York and central Pennsylvania and set up video cameras to capture additional animal/gall interactions. In both locations, they saw ants transporting galls to their nests. Within the nests, all the edible caps were removed, while the galls themselves remained intact.

In a second set of experiments, the team investigated ant preference for oak galls vs. bloodroot seeds to determine if kapéllos functioned similarly to elaiosomes. They set up seed/gall bait stations and observed that ants removed the same number of seeds and galls, suggesting no difference in ant preference.


The scientists then conducted a laboratory experiment to document whether ants collected galls because of their nutritious kapéllos. They set up three petri-dish treatments, containing entire galls, gall bodies with kapéllos removed, kapéllos with gall bodies removed, along with a control dish containing a different type of gall that did not have an edible appendage.

They introduced ants to the petri dishes and found that ant interest did not differ between the control galls and the kapéllo-free treatment galls, both of which lacked edible components. By contrast, ant interest was greater for galls with intact kapéllos and for kapéllos alone than for control galls.

The researchers showed that galls with caps were far more attractive to ants than galls without caps and that the caps by themselves were also attractive to the ants. John Tooker, professor of entomology, said, “This suggested that the caps must have evolved as a way to entice ants.”


Finally, the team asked, "What’s in kapéllos that makes them so attractive to ants?" According to Tooker, the chemistry of elaiosomes is well studied and known to contain nutritious fatty acids. Therefore, the team compared the chemical compositions of kapéllos to elaiosomes and found that kapéllos, too, contained healthful fatty acids.

An ant holds an oak gall containing wasp larvae. Researchers discovered an elaborate relationship among ants, wasps and oak trees. (CREDIT: Andrew Deans, Penn State)

“The fatty acids that are abundant in gall caps and elaiosomes seem to be mimicking dead insects,” said Tooker. “Ants are scavengers that are out trying to find and grab anything that’s suitable to bring back to their colony, so it’s not an accident that the gall caps and the elaiosomes both have fatty acids typical of dead insects.”


Which Came First?

The last, and according to the researchers, most intriguing, question was: which came first, the gall or the ant? Did the wasp begin manipulating oaks to create galls, and then eventually begin manipulating ants to collect them? Or did the ants first begin collecting the galls, and then the wasps learn to manipulate oaks to make them more attractive to the ants?

Ants disperse oak galls of some cynipid wasp species similarly to how they disperse seeds with elaiosomes. (CREDIT: The American Naturalist)

To answer this question, the researchers took a closer look at the evolution of gall wasps and their relationships with oak trees. They found that gall wasps have been inducing oak galls for millions of years, and that some modern-day gall wasps are known to manipulate ants to protect their larvae. Therefore, it seems likely that the wasps began manipulating ants after they had already been inducing galls in oaks for millions of years.

“This finding is really exciting because it suggests that we are only scratching the surface of what we know about plant-insect interactions,” said Deans. “We have been studying these relationships for over 100 years, but there is still so much we don’t know.”


Implications for Ecology and Conservation

The researchers believe that their findings have important implications for ecology and conservation. For example, they suggest that the manipulation of ants by gall wasps could be a more widespread phenomenon than previously thought. Additionally, they point out that the loss of oak trees, which are already threatened by habitat loss and other factors, could have significant impacts on the entire oak gall-ant-wasp ecosystem.

Researchers conducted manipulative experiments in which we removed the putative ant-attracting appendages (“kapéllos”) from galls and found that ants are specifically attracted to kapéllos. (CREDIT: The American Naturalist)

“This research really highlights the interconnectedness of different species in an ecosystem,” said Deans. “It also highlights the importance of protecting biodiversity and the many relationships that exist between different organisms.”

Looking to the future, the researchers hope to continue investigating the complex relationships between plants and insects. They suggest that there may be many more multi-layered interactions waiting to be discovered.


“We are only beginning to understand the complexity of plant-insect interactions,” said Deans. “There is still so much more to learn.”

When asked if he wants to be an entomologist like his dad when he grows up, given that he's already made his first scientific discovery, Hugo says "not really. I want to be different ... unique ... when I grow up."

For more science news stories check out our New Discoveries section at The Brighter Side of News.


Note: Materials provided above by the The Brighter Side of News. Content may be edited for style and length.


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