Consequences of envenomation: red imported fire ants have delayed effects on survival but not growth of native fence lizards.
Context. Aggressive encounters, including those with venomous species, impose selective pressure on native species. Immediate lethal outcomes of these encounters have been the primary focus of research in this field. However, not all aggressive interactions result in immediate mortality, and indirect consequences of aggressive interactions may be an equally important but under-considered selective force. The red imported fire ant is a globally important venomous invader that imposes novel selective pressure on native communities. Aims. We examined indirect effects of fire ant envenomation on native fence lizard growth rates and subsequent survival. Methods. Fence lizards are subject to fire ant envenomation in the field when they eat fire ants (they are stung inside the mouth) and through fire ant attack (they are stung on the body). We quantified body sizes of adult lizards from fire ant-invaded and uninvaded sites. We then experimentally exposed hatchling fence lizards to the two modes of fire ant envenomation, and quantified their growth and survival over 1 year. Key results. Lizards from fire ant-invaded sites were smaller than those from an uninvaded site, even at similar latitudes. However, in contrast to studies on other native taxa, we found no effect of fire ant venom on growth rates of lizards from naïve or fire ant-invaded populations. Lizards exposed to fire ant venom, through both eating and attack, experienced higher rates of delayed mortality, with 34% of lizards dying 1-11 weeks post-envenomation compared with 12% of lizards in the control treatment. These patterns were true for fire ant naïve populations as well as those exposed to fire ants for ∼35 generations. Conclusions. These results suggest that the smaller body sizes observed in fence lizards from fire ant-invaded sites are not a consequence of exposure to fire ant venom. However, fence lizards from both sites suffer delayed survival costs of fire ant envenomation. Implications. The present study highlights the importance of considering indirect fitness consequences of aggressive encounters if we are to fully understand the ecological and evolutionary consequences of these interactions, and adequately manage and predict the impacts of invasive species.