Eating fire ants could prepare lizards for future fire ant attacks

Eating fire ants could prime a lizard’s immune system to be stung by the ants, according to a new study by Penn State researchers. The study comprehensively assessed how the immune system responds to lizards being eaten and stung by these ants and could help researchers understand how other native species respond to and adapt to the invasive insects.

Fire ants are an invasive pest species in the southeastern United States that will expand their range as the climate warms. When they sting, they inject venom that triggers an immune response in a variety of species from humans to livestock to lizards. For eastern sand lizards — also found throughout the region — repeated stinging can cause paralysis and even death. Despite this, lizards often eat fire ants, along with other ant species.

“We know that lizards from areas with fire ants have different immune profiles than lizards from areas without fire ants,” said Tracy Langkilde, a professor of biology at Penn State and leader of the research team. “Because the immune system is so vital to survival, we wanted to find out if these differences in immune profiles are a direct result of lizards being frequently stung by fire ants, eating fire ants, or something else.”

The researchers examined six immune responses to lizards being either fed dead fire ants or stung by fire ants three times a week for three weeks.

“We conducted a comprehensive assessment of most branches of the immune system, including measurements of the innate immune system – resources a person is born with – and the adaptive immune system, which develops immune resources after exposure to a foreign substance such as an infection or vaccine” said Catherine Tylan, a graduate student at Penn State who led the research, “This allowed us to see how different immune resources are allocated in response to exposure to fire ants.”

The researchers present their results in Biological invasions.

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

“All three of these immune aspects are designed to help lizards survive a fire ant attack,” Tylan said. “For example, the fire ant-specific antibodies and complement could help bind venom so it can no longer negatively affect the body. So consuming fire ants may help lizards prepare for future venom exposure from stings.”

The researchers said these findings may also help explain immune patterns they’re observing in lizards in the field.

“Lizards captured from areas with fire ants have more anti-fire ant antibodies and basophils than lizards from areas without fire ants,” Tylan said. “This study showed the same immune responses when lizards were fed fire ants, suggesting that the difference between these two immune responses in the field could be due to lizards eating fire ants.”

However, other results did not agree with all patterns observed in the field. The researchers suggest that other immune patterns observed in the field may be due to the stress of fire ant encounters, which are known to impair immune function, rather than a direct effect of being eaten or stung by fire ants, or something else entirely.

“Taken together, these results help us to understand the potential health consequences of exposure to invasive species,” Langkilde said. “Interestingly, our results suggest that native animals may be able to counterbalance the immunological consequences of venom exposure by consuming the same species.”