Consumption of fire ants, an invasive predator and prey of native lizards, may enhance immune functions needed to combat envenomation

Non-native species invasions are increasing across the globe and are affecting native species in many different ways including through impacts as novel predators or food sources. We sought to understand how eastern fence lizards ( Sceloporus undulatus ) are affected by invasive red imported fire ants ( Solenopsis invicta ), which serve as both predator and prey to the lizards. These ants have been present in the lizards’ range for over 70 years and are associated with altered lizard immune function as compared to lizards from ecologically similar sites not invaded by fire ants. To better assign causation to the correlative field patterns of immune function, we experimentally exposed fire ant-naïve lizards to fire ant venom though ant stings and via consumption of non-stinging dead ants and measured the same immune outcomes. Fire ant consumption increased lizard immune responses relative to lizards stung by fire ants, and two of the four immune differences in the field were also seen in lizards fed fire ants (higher anti-fire ant IgM and basophils). This may indicate that some field-measured immune differences in fire ant invaded populations of lizards are directly due to their exposure to fire ant venom by consuming fire ants rather than through stinging. These results also suggest that consumption of fire ants can bolster immune responses needed to combat envenomation through stinging. This adds to growing evidence that sub-lethal consumption of poisonous/venomous invasive species may reduce deleterious consequences of exposure to these toxins, allowing native species to survive and coexist with otherwise deadly invaders.