Eating fire ants might prepare a lizard’s immune system to be stung by the ants, according to a new study.

The study comprehensively assessed how the immune system responds to lizards eating and being stung by these ants and might help researchers understand how other native species respond and adapt to the invasive insects.

“…native animals may be able to offset immune consequences of venom exposure by consuming these same species.”

Fire ants are an invasive pest species in the southeastern United States that are expanding their range as the climate warms. When they sting, they inject venom that triggers an immune response in a wide variety of species, from humans to livestock to lizards. In eastern fence lizards—which also occur throughout the region—repeated stinging can cause paralysis and even death. Nonetheless, lizards often eat these ants, in addition to other ant species.

“We know that lizards from areas with fire ants have different immune profiles than lizards in areas without them,” says Tracy Langkilde, professor of biology at Penn State and leader of the research team. “Because the immune system is so critical for survival, we wanted to determine if these differences in immune profiles can be directly attributed to lizards frequently being stung by fire ants, eating fire ants, or something else.”

The researchers investigated six immune measures in response to three weeks of lizards either being fed dead fire ants or being stung by the ants three times per week.

“We conducted a comprehensive assessment of most branches of the immune system, including measures of the innate immune system—resources that an individual is born with—and the adaptive immune system, which develops immune resources after exposure to a foreign substance like an infection or vaccine,” says Catherine Tylan, graduate student at Penn State who led the research. “This allowed us to see how different immune resources are allocated in response to fire ant exposure.”

When the researchers fed lizards the ants, three immune measures were enhanced in comparison to lizards that were stung. The researchers observed an elevation in a type of white blood cells called basophils; an increase in complement activity, which helps or “complements” antibodies and other aspects of the immune system; and an increase in a type of immunoglobulin antibody (IgM) known to be reactive to fire ant venom.

“All three of these immune aspects are expected to help lizards survive a fire ant attack,” says Tylan. “For example, the fire ant-specific antibodies and complement could help bind up venom so it can no longer negatively impact the body. It’s possible that exposure to fire ant venom from the consumed fire ants stimulates an increased immune response, acting somewhat like a vaccine. So, eating fire ants may incidentally help lizards prepare for future venom exposure from stings.”

The researchers say that these results can also help explain immune patterns they observe in lizards in the field.

“Lizards caught from areas with fire ants have higher anti-fire ant antibodies and basophils than lizards from areas without fire ants,” says Tylan. “This study showed these same immune responses when lizards were fed fire ants, suggesting that the difference in these two immune measures in the field may be a result of lizards eating fire ants.”

Other results, however, did not match all patterns observed in the field. The researchers suggest that rather than a direct effect of eating or being stung by the ants, other immune patterns observed in the field might be due to the stress of fire ant encounters—which are known to affect immune function—or something else entirely.

“Together, these results help us understand the potential health-relevant consequences of exposure to invasive species,” says Langkilde. “Interestingly, our results suggest that native animals may be able to offset immune consequences of venom exposure by consuming these same species.”

The research appears in the journal Biological Invasions.

This research was funded in part by the National Science Foundation.

Source: Penn State

Related

Lizards get twitchy to survive fire ant invasion

Watch: Fire ants climb each other to build moving tower

Stress gets weird for lizards exposed to fire ants

Fire ants use their bodies to build tower-like structures —all without a plan, a leader, or coordinated effort, new research suggests.

Each ant, researchers say, wanders around aimlessly, adhering to a certain set of rules, until it unknowingly participates in the construction of a tower several inches tall.

“If you watched ants for 30 seconds, you could have no idea that something miraculous would be created in 20 minutes,” says coauthor David Hu, a professor in the Georgia Institute of Technology’s George W. Woodruff School of Mechanical Engineering. “With no planning, and using trial-and-error, they create a bell-shaped structure that helps them survive.”

The tower study is a follow-up to the group’s 2014 ant raft research, which examined how the insects link their bodies in order to build waterproof structures that stay afloat for months. The ants march along until they come to an open space—the edge of the raft—then settle in to become a building block of the raft.

They do the same thing for the towers, searching for an empty spot like a car in a crowded parking lot. Once an individual ant finds one, typically at the top of the tower, she stops and braces for more ants to climb on top and go vertical.

They build these towers when they run into a tall obstruction while looking for food or escaping to new areas.

But vertical is a relative term. The ants don’t position themselves straight up and down like a skyscraper. Instead, the tower gets wider as it grows taller, gradually becoming the same shape as Paris’ iconic landmark. The weight of the tower is supported by a wider cross-section at its base, which allows the ants to better distribute their weight.

“The tower is constantly rebuilding and replacing its surface.”

“We found that ants can withstand 750 times their body weight without injury, but they seem to be most comfortable supporting three ants on their backs,” says Craig Tovey, a coauthor of the study and professor in the Stewart School of Industrial & Systems Engineering. “Any more than three and they’ll simply give up, break their holds, and walk away.”

Even though the ants evenly distribute their weight as a group, the tower is in constant motion. The column sinks as the insects work, as if the bottom is being melted like butter. The ants slide down, then exit out of tunnels buried in the base. The tower’s movement is similar to a slow-motion chocolate fountain in reverse.

The sinking towers were discovered by accident. The researchers planned to record ants building for two hours, but the camera rolled for three.

“We didn’t expect to see anything interesting in that extra hour, so we sped up the video to 10 times real speed,” says Tovey. “We were amazed at how different the ant movements appeared.”

Ants wear smells like a uniform

In real time, they saw ants busily moving on the surface of a tower of apparently stationary ants. At high speed, however, the surface ant movements appeared as a blur and the entire tower slipped downward.

“The tower sinking was too slow to see at real speed,” says Tovey.

The sinking was confirmed by X-ray videography. The researchers fed some of the ants radioactive food, then threw the colony in an X-ray machine across campus in Dan Goldman’s physics lab. Cameras again recorded the critters building a tower. Using time-lapse photography, they watched the radioactive insects walk up the sides, gradually sink to the tower’s depths, leave the pile, then continually repeat the process for hours.

“Ant towers are like human skin,” says Hu, who is also a faculty member in the School of Biological Sciences. “The tower is constantly rebuilding and replacing its surface.”

The findings could have implications for modular robots, which currently aren’t very effective at building tall towers.

Tovey, who is also a biologist, has a different reason for studying ant behavior.

Teeming ants act like both a liquid and a solid

“Ninety-nine percent of all the species that have ever lived on Earth are extinct,” Tovey says. “The rest of us have developed very effective techniques to survive. Why wouldn’t we study these processes? Engineers and scientists don’t always know what our findings will lead to, but bioinspired design can be a powerful tool to make our world more efficient.”

The paper appears in the journal Royal Society Open Science.

Source: Georgia Institute of Technology

Related

Listen: What can we do about ant invasions?

How ants tell friends from foes

Food waste fix gets flies to turn waste into useful stuff