A new study from the Canadian Journal of Zoology has found that young fence lizards are surprisingly consuming venomous invasive fire ants. The paper reveals new insights on how local species can interact and evolve when presented with an invasive species.
“One of the things that always confused me is when do native species fight back against invasive species,” said Cameron Venable, a study co-author from Pennsylvania State University. Venable’s new paper examines how the fence lizard’s consumption of native versus invasive ants changes over its lifetime.
Fire ants are now a major pest in the southern United States.
Fire ants were first introduced to the United States from South America during the 1930s. They quickly spread to much of the southern United States and are a common household nuisance accruing an estimated US$5 billion on medical treatment, damage, and control each year.
Fence lizards are ant specialists, particularly as juveniles. Invasive fire ants pose a lethal risk to lizards that eat them, especially when the lizards are young. While the exact cause of lizard mortality from fire ants is unknown, Venable said the lizards either die from stings as they eat the ants or from the venom in the ants as the lizards digest them. “It’s ingestion versus injection,” said Venable.
For the study, researchers presented 2- to 3-week-old lizards with a choice of either native or invasive species of ants and then repeated the experiment with adults. They predicted that the juveniles would avoid fire ants and since adults are larger, they would eat both native and invasive ants.
“But it didn’t go the way we expected at all,” said Venable. Instead, the study found that juveniles eat both types of ants in similar numbers and adults consume nearly three times as many native ants as fire ants. “That’s the cool part about science. It’s like a cool TV show, if you can predict everything that can happen, what’s the fun in that?” said Venable.
Up to 80% of a juvenile lizard’s diet is ants. By contrast, adults have a more diverse diet with ants comprising 50% of the diet. The lizards also consume beetles, caterpillars, and fruit.
Venable said this study is important because it provides an avenue to see real-time interactions between invasive and local species. For example, when an invasive species comes into a new area it can destroy habitat and (or) become a predator, and local species can either consume the invasive species or learn to avoid it.
“I think a lot of times, when we think of ecosystems, we think of them in this little bubble of not being able to fix themselves,” he said. “But I feel like nature has its own mechanisms to stabilize itself overtime.”
The paper describes several possible explanations for why lizards are consuming fire ants. It’s possible that the ants are easier to capture or are more nutritious. Or, strangely enough, the lizards may consume the ants as an anti-predator defense, sequestering the venom and using it for itself—a strategy shared with Texas horned lizards. Venable said it’s possible that the lizards, which are not poisonous, may be using the venom to evolve. “Fire ants have been here for 90 years. In evolution, that’s a blink of an eye. But it isn’t impossible,” he said.
Venable also said that in areas with fire ants, lizards have more scars. The scars could mean the lizards escaped predation. “Now why is that? Is it because they ran away or are they distasteful now?” he asked.
Questions that still need to be answered are at what point do juveniles learn to avoid fire ants and how do fence lizards distinguish between ant species? This study looked at the individual level of when native species fight back against invasive species. The next step would be to look at how it cascades through the ecosystem and impacts other species at different trophic levels.
“Studying an invasive species is like watching rapid evolution because the species that survives the presence of invasive species are the ones that multiply,” said Venable.
Read the full study: Lizards display an ontogenetic shift in relative consumption of native and invasive prey in the Canadian Journal of Zoology.
