Sensory systems comprise the frontlines of an organism’s interaction with its environment. These systems are key in resource acquisition, interacting with conspecifics, and avoiding danger. Ants are well known for their sophisticated use of chemical and tactile cues, but the visual apparatus of many species is engaged in behaviors including navigation and prey capture. In tropical rain forest, ant assemblages experience a vertical gradient of light regimes from the bright canopy to the dim understory, which may have consequences for the utility of visually guided behavior over evolutionary time. We examined the role of visual and olfactory cues in the homing behavior of Pseudomyrmex boopis, an understory twig-nesting ant with a canopy-nesting ancestor, which halts foraging at sunset. We collected P. boopis workers from twig nests on Barro Colorado Island, Panama throughout the wet season in 2017-2019. We separated workers into control (senses intact) and sensory manipulation treatments: we painted over workers’ compound eyes and ocelli (blind), only their ocelli (ocelli-occluded), only their compound eyes (CE-occluded), and we ablated antennae at their base (deantennated). We then observed each worker's homing route and measured their success in returning to their nest after displacement.
Results/Conclusions
Pseudomyrmex boopis exhibits visually-guided homing behavior that is most efficient when the antennae, the primary olfactory organs, are intact. Homing success in blind and CE-occluded workers is significantly impaired (5% and 26% success rate, respectively), compared to control, ocelli-occluded, and deantennated workers (75-88% success). Blind workers were predated upon by other ants (Odontomachus bauri or Ectatomma ruidum) in 28% of trials, while predation was observed in 16% of CE-occluded trials. Control and ocelli-occluded workers took less time to return to the nest than deantennated workers, suggesting that the detection of olfactory cues close to the nest entrance is an important component of efficient homing behavior. While input to the compound eyes is essential for long-range homing, input to the ocelli is not necessary for navigation at this scale. Despite living in the dark understory, the activity and success of P. boopis workers is bound by visual information perceived by their compound eyes.