Native eastern fence lizards changed their bodies and behavior in response to invasive red imported fire ants

These lizards, especially when they are young, eat a lot of ants of various types. Eating a fire ant, though, can mean getting stung inside the mouth, which can make this a lethal meal. Baby lizards quickly learn to avoid eating fire ants, but this leads to their also avoiding their native ant diet, the consequences of which are unknown.

Adult lizards, on the other hand, are less vulnerable to succumbing to consumed fire ants and take advantage of this new food source. So there’s an upside to these troublesome insect invaders for fence lizards.

Lethal outcomes are the most striking consequence of interactions between fire ants and fence lizards, but that’s not the full story.

As you might imagine – or even have experienced – being stung by fire ants is stressful for lizards, as indicated by an increase in a stress-relevant glucocorticoid hormone following attack, just as you would experience after getting a scare.

We find that lizards that frequently experience fire ant attacks have a different “stress profile.” They have higher concentrations of this stress hormone even while at rest. They show greater increases in glucocorticoids in response to a stressor and have different behavioral and immune responses to glucocorticoid exposure. While stress gets a bad rap, these hormones play an important role and in this case can trigger survival-enhancing behavioral responses to fire ants.

Lizards living with fire ants show changes to their immune systems. They have elevated levels of IgM antibodies that respond to fire ants and higher levels of a type of white blood cell that can help neutralize venom toxins. They also have decreased levels of other immune system components. Together, these immune differences may allow lizards to better coexist with fire ants, with the elevated immune measures being particularly useful when dealing with stings. Tailoring the immune system to survive fire ant attacks may, however, leave lizards more vulnerable to other immune challenges, such as viruses.

Getting stung over a period of time stimulates lizards’ skin immunity, which could guard against effects of skin damage. Additionally, feeding on fire ants that we’ve rendered in the lab incapable of stinging increases some immune measures in the lizards above what we see in lizards that were stung by fire ants. This bolstered immunity may then help lizards survive future stings. We think the elevated immunity we see in wild lizards in fire ant-invaded places may be caused by consumption of fire ants.

The effects of invasive fire ant and eastern fence lizard interactions demonstrate how species can adapt to survive the presence of invasive predators. Behavioral shifts can allow animals to avoid or escape attack, and changes in morphology can make these strategies more effective. And eating venomous prey may provide immune protection against subsequent attack.

However, this research also illustrates that adaptations are not a panacea. While adapting to a changing world is clearly critical for survival, by its very nature this changes animals, pushing them off their original evolutionary trajectory and leaving them vulnerable to new threats. Getting a full picture of the consequences of the presence of a new threatening species, and of the changes that animals may need to make to survive them, is critical if scientists are going to be able to predict and manage the impact of invasive species on native communities.

This article is republished from The Conversation, an independent nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Catherine Tylan, Penn State and Tracy Langkilde, Penn State. The Conversation has a variety of fascinating free newsletters.