The introduction of non-native species poses a growing threat to global biodiversity. Native species can respond to environmental change at previously unimagined rates. It is critical that we incorporate evolutionary perspectives if we are to understand fundamental processes affecting community structure as well as assess the resilience of native populations to global change. Invasive fire ants and native lizards provide an excellent model for such research. Following fire ant invasion, the lizards develop novel defensive behavior that permits them to survive attack by these globally invasive ants. Ecological and evolutionary approaches will be employed in the field and laboratory to quantify the relative contributions of additive genetic variation and phenotypic plasticity to the development of this adaptive defensive behavior, and shed light on the role of evolutionary processes in the assembly and dynamics of natural communities.
This research investigates how native communities respond to rapid environmental change, and provides critical information on the long-term impact of fire ants, an invasive species of global concern. The study will provide training opportunities for graduate and minority undergraduate students, and will directly involve K-12 students from minority-serving institutions. The local community will be engaged through displays and presentations of the results of this research.
The role that past interactions (e.g. predation) play in shaping existing animal communities is strongly debated, with little experimental support. This is largely due to our inability to observe how populations change across evolutionary history. The well-documented spread of invasive fire ants across the USA provides a natural experiment to test how interactions between this novel antagonist and native species change across co-existence time. We used a combination of ecological and evolutionary approaches in the field and laboratory to gain important insight into the ability of native species to respond to novel selective pressures imposed by fire ants, an invasive species of global importance. The introduction of non-native species poses one of the most serious and growing threats to global biodiversity. We desperately need to adopt a long- term approach to understanding the impact of these changes on native species. The research conducted under this award addressed this critical goal by assessing the consequences of invasion by fire ants on native lizards. This work sheds light on the strength of the impact of fire ants on native lizards, ?and the importance of lifetime exposure to fire ants for triggering behavior that allows lizards to survive this novel threat. We determined that fire ants incur a two-pronged impact on native species; they are novel predators on all life stages (from eggs to adults) and also act as novel toxic prey, killing lizards that eat them. Lizards have developed novel behavior and morphology following the invasion of fire ants. Naïve lizards from uninvaded sites freeze when they encounter predators, relying on their camouflage. This is very effective against native visually-hunting predators, such as birds and snakes. It is ineffective, however, against fire ants which quickly swarm unresponsive lizards and inject venom into the soft tissue under their scales, paralyzing and killing them. Lizards from fire ant invaded sites twitch off attacking ants and flee from the source of attack, avoiding recruitment of additional ants and reducing the amount of venom they receive. They also have relatively longer hind limbs that increase the effectiveness of this behavior by allowing them to perform more vigorous twitches. Our work reveals that this behavior is shaped both by cross-generational exposure to fire ants, suggesting these lizards have evolved to deal with fire ants, and by lifetime exposure to these novel threats, suggesting that these lizards can also learn to deal with these predators. This ‘new’ behavior and morphology are beneficial in the presence of fire ants, allowing the lizards to survive and grow. However, these adaptations are costly in the absence of this invasive threat; lizards that exhibit this behavior and morphology have lower survival, likely because the behavioral response to contact with ants makes them more obvious to visually-hunting native predators. These changes following fire ant invasion reverse the natural latitudinal trends in these traits. Lizards are generally less behaviorally responsive to ants and have shorter legs the further south you go (from PA to TN), suggesting that natural pressures favor unresponsive short-legged lizards in the southeastern USA. However, as you continue to move south, from TN to FL, entering fire ant territory, these lizards become more responsive and longer-legged. This further suggests that these reponses carry costs, shedding light on constraints on adaptation and potentially explaining why animals aren’t perfectly adapted to their environments. Lizards have also evolved to survive this novel venomous ant prey. Though we found that lizards can’t learn to avoid eating fire ants, juvenile lizards from fire ant invaded sites innately avoid eating these toxic invaders (from birth). Large adults that are less susceptible to the effects of fire ant venom can, however, learn to take advantage of this new and abundant food resource. By providing urgently needed insight into the long-term consequences of introduced fire ants, our research facilitates better management and prediction of the global impact of this highly-invasive ant and other invaders, and aids our understanding of how animals are able to coexist within natural communities. Several personnel were trained under this award; the work involved 1 postdoctoral fellow, 1 technician, 3 graduate students, 19 undergraduate students, and 10 low-socioeconomic status minority high-school students. The public’s fascination with fire ants allowed us to use this research as a tool to engage citizens in scientific research that is relevant to their daily lives. We organized summer camp activities for school aged children in Alabama and Pennsylvania, ran workshops for Girl Scouts, and directly involved inner-city high-school students in this research. The results of this work have been reported in 10 scientific publications, 23 talks at universities and scientific meetings, and in the media through outlets including National Geographic, Los Angeles Times, and the Christian Science Monitor. We post weekly blog articles about this and related research on our Lab Blog: http://thelizardlog.wordpress.com/, which attracts hundreds of viewers.
