Katherine O’Connor1, Ben Hoffmann2 & Andrew V. Suarez3 Aggressive interactions between invasive yellow crazy ants and five native ants in Northern Australia Katherine O’Connor1, Ben Hoffmann2 & Andrew V. Suarez3 1Department of Animal Sciences, UIUC. katherineoc23@gmail.com 2 CSIRO Darwin, Australia. 3 School of Integrative Biology, UIUC. -Invasive species can alter trophic interactions, change the structure and composition of natural ecosystems, and ultimately displace native species resulting in a homogenization of local faunas. -The yellow crazy ant (Figure 1) has been introduced in many tropical ecosystems throughout the world. It forms dense supercolonies with a high number of workers that can outcompete native ants for resources. Yellow crazy ants are also very aggressive and native species may vary in their sensitivity to their invasion based on individual interactions when their workers meet -The ants were collected from a Eucalyptus woodland in Arnham Land in Australia’s Northern Territory -Five native ants were chosen to reflect variation in biology -Each trial consisted of placing one native worker and one yellow crazy ant worker into a petri dish and then their interactions were filmed for two minutes. -Trials were replicated 20 times for each species for a total of 100 trials -We found significant variation among species in the number of aggressive interactions between native ants and the introduced yellow crazy ant -Aggressive interactions and fighting behaviors were highest in trials with trap-jaw ants and lowest with strobe ants -Future work examining the persistence of native species following invasion (or other disturbances) will allows us to determine if behavioral indicators can be reliable predictors of resilience to disturbances such as biological invasions -Our results suggest that native species can experience different amounts of conflict or aggression from non-native species and behavioral indicators may be useful in helping us predict which species are most vulnerable to invasion EDITS- Introduction The yellow crazy ant (Figure 1) has been introduced in many tropical ecosystems throughout the world. It forms dense supercolonies with a high number of workers that can outcompete native ants for resources. Yellow crazy ants are also very aggressive and native species may vary in their sensitivity to their invasion based on individual interactions when their workers meet. We measured aggressive interactions between yellow crazy ants and five species of native ants to determine if there was variation in the amount of aggression experienced by native species and if yellow crazy ants were more likely to initiate aggressive encounters than their native counterparts. This behavioral information could be useful in predicting which species are most sensitive to invasion of new species. Objectives Quantify patterns of aggression between the Yellow Crazy Ant and five native ant species in Northern Australia to determine which native ants may be mosts sensitive to invasion. Figure 1 Anoplolepis gracilipes the Yellow Crazy Ant Methods All ants were collected from a Eucalyptus woodland in Arnham Land in Australia’s Northern Territory (Figure 2). Five native ants were chosen to reflect variation in biology typical of the Australia fauna including nesting habitat (arboreal versus ground nesting) and taxonomic diversity (Figure 3). Each trial consisted of placing one native worker and one yellow crazy ant worker (order chosen randomly) into a petri dish and then their interactions were filmed for two minutes. We recorded the number of aggressive interactions between the ants and which species initiated each interaction (Figure 4). Trials were replicated at least 20 times for each species . We used an Analysis of Variance (ANOVA) to test for differences among all species. Fisher’s post hoc test was used to examine differences between species pairs. * Figure 2. Map of Australia indicating location of study area (below). Photo of Eucalyptus woodland where ants were collected for trials (left). Iridomyrmex “Meat Ant” Opisthopsis “Strobe Ant” Oecophylla “Weaver Ant” Odontomachus “Trap-jaw Ant” Polyrhachis “Spiny Ant” Figure 3. The five species of native ant used for aggression trials in this study. For each species, the genus and common name are provided. All are abundant in Eucalyptus woodlands in Northern Australia. Figure 4. Still image from one-on-one trials with a trap-jaw ant (left) and a weaver ant (right). Results and Discussion We found variation among species in the number of aggressive interactions (Figure 5). Aggressive interactions and fighting behaviors were highest in trials with trap-jaw ants (genus Odontomachus) and lowest with strobe ants (Opisthopsis). These patterns may reflect overall differences in the tendency of the native ants to engage aggressively with competitors or other threats. Trap-jaw ants are know for their individual fighting ability due to their incredibly fast and powerful jaws. In contrast, strobe ants are known for their ability to move quickly and avoid conflict with other species. When examining initiation of aggressive interactions, we found that yellow crazy ants initiated more interactions with trap-jaw ants than with the other four native species (Figure 6). Collectively, our results suggest that trap-jaw ants may be most sensitive to invasion by non-native species known for their aggressive behaviors. Future work examining the persistence of native species following invasion (or other disturbances) will allows us to determine if behavioral indicators can be reliable predictors of resilience to disturbances such as biological invasions. Our results suggest that native species can experience different amounts of conflict or aggression from non-native species and behavioral indicators may be useful in helping us predict which species are most vulnerable to invasion. # of aggressive interactions/ fights a b c Figure 5. Number of aggressive interactions between yellow crazy ants and five native species. Letters denote species with significant differences in number of aggressive interactions (ANOVA: F-value = 5.304; df = 4, 135; p = 0.0005) Average number of aggressive interactions per trial initiated by yellow crazy ants. Figure 6. Number of aggressive interactions per trail initiated by yellow crazy ants for each native species. Letters denote species with significant differences in number of aggressive interactions (ANOVA: F-value = 5.325; df = 4, 135; p = 0.0006) a b Conclusions Acknowledgments We thank the University of Illinois Office of Undergraduate research and CSIRO Australia for providing opportunities to conduct and present this research. We also thank Elissa Suhr, Adrianna Tienda, Annalise Dunsmore, Emily Feder and Zaira Corral with data collection. Pictures courtesy of Alex Wild and Antweb.ord Finally we thank the Suarez Lab for feedback as well!