40.3 Thursday, Jan. 5 Evolutionary Co-option of Trap-jaw Ant Mandible Strikes: Defensive Interactions with Antlions LARABEE, F. J.*; SUAREZ, A. V.; Univ. of Illinois, Urbana-Champaign; Univ. of Illinois, Urbana-Champaign firstname.lastname@example.org
The co-option of existing traits for novel functions is fundamental to many theories of trait evolution, but few studies have examined evolutionary co-option at a behavioral level. Trap-jaw ants in the genus Odontomachus have a rapid and powerful mandible snap that can be used to catch fast or dangerous prey. In some species this behavior appears to have been co-opted for defense: in threatening situations ants direct their strikes against the substrate and launch themselves into the air. Until now, no actual predators or competitors have been found in the field against which trap-jaw use their ‘escape jumps’. We studied the defensive use of mandible snapping behavior in two trap-jaw species (Odontomachus brunneus and O. relictus) during their interactions with predatory antlions in the genus Myrmeleon, which live in sympatry in the Lake Wales Ridge in central Florida. Using high-speed videography and traditional bioassays, we described how trap-jaw ants can perform escape jumps after falling into antlion pits. Interestingly, while both species use the mandible snap for predation, only O. brunneus used the mandible snap to escape from antlion pits (approximately one third of interactions). A comparison of the kinematic properties of mandible strikes suggested that differences in force generation might contribute to the behavioral differences between these species. Taken together, our results indicate that trap-jaw mandible snaps can be used to escape from natural predators, lending support to the idea that this predatory behavior has been evolutionarily co-opted for defense.