Rhode Island State Council on the Arts (1979-1992): Report 02

.csv file with the outcome data for predatory trials in the restraint experimen

Mandible-Powered Escape Jumps in Trap-Jaw Ants Increase Survival Rates during Predator-Prey Encounters

<div><p>Animals use a variety of escape mechanisms to increase the probability of surviving predatory attacks. Antipredator defenses can be elaborate, making their evolutionary origin unclear. Trap-jaw ants are known for their rapid and powerful predatory mandible strikes, and some species have been observed to direct those strikes at the substrate, thereby launching themselves into the air away from a potential threat. This potential escape mechanism has never been examined in a natural context. We studied the use of mandible-powered jumping in <i>Odontomachus brunneus</i> during their interactions with a common ant predator: pit-building antlions. We observed that while trap-jaw ant workers escaped from antlion pits by running in about half of interactions, in 15% of interactions they escaped by mandible-powered jumping. To test whether escape jumps improved individual survival, we experimentally prevented workers from jumping and measured their escape rate. Workers with unrestrained mandibles escaped from antlion pits significantly more frequently than workers with restrained mandibles. Our results indicate that some trap-jaw ant species can use mandible-powered jumps to escape from common predators. These results also provide a charismatic example of evolutionary co-option, where a trait that evolved for one function (predation) has been co-opted for another (defense).</p></div

Summary

Data summarizing the outcomes of trials between unrestrained trap-jaw ants (Odontomachus brunneus) and pitbuilding antlion

Restrained mandibles.

<p>Trap-jaw ant mandibles were glued shut to prevent ants from snapping.</p

Still images from high-speed video (S2 Video) showing escape jumps of <i>Odontomachus brunneus</i> during interactions with the antlion, <i>Myrmeleon carolinus</i>.

<p>After being attacked by an antlion (location at base of pit marked by black arrows in each frame), the trap-jaw ant (white arrows in each frame) strikes the side or center of the pit with her mandibles and propels herself away from the antlion. Time stamp indicates the time elapsed since first frame (upper left). Scale bar = 1cm.</p

Frequency of escape behavior by trap-jaw ants in restraint experiment.

<p>Frequency of escape by running or jumping was quantified for each interaction. Ants were unmanipulated (Control), had glue applied to the exterior edge of mandible (Mock), or had their mandibles glued shut (Restrained). Each treatment was replicated 76 times.</p