Foraging ecology, navigation and the visual systems of the strobe ants, <i>Opisthopsis</i>

<p dir="ltr">The study of solitary foraging ants in visually complex environments offers valuable insights into how ecological pressures shape sensory and behavioural adaptations. Ants of the genus <i>Opisthopsis</i>, notable for their distinctive strobing gait and large eyes, remain poorly studied in terms of their ecology and visual function. In this thesis, I investigate the natural history, visual adaptations, and navigational strategies of two species, <i>O. rufithorax</i> and <i>O. haddoni</i>, using a combination of field observations, morphometric analysis, electrophysiology, and behavioural experiments. Field observations confirmed diurnal activity and solitary foraging in both species, with ground-nesting colonies and foragers that routinely climb trees. These observations, along with literature and citizen science records, show that <i>Opisthopsis </i>species occupy a range of habitats and engage in diverse ecological interactions. Morphometric comparisons revealed that <i>Opisthopsis </i>ants have relatively large eyes located at the back of the head capsule compared to other formicine ants. While both species had similar facet counts and mean facet diameters, <i>O. rufithorax</i> exhibited a broader distribution of larger facets extending into the posterior eye region. Electrophysiological measurements showed that both species possess visual systems adapted to bright-light conditions. However, <i>O. rufithorax</i> exhibited significantly higher temporal resolution, and while spatial resolution and contrast sensitivity did not differ significantly between species, both showed values comparable to larger diurnal ants, suggesting miniaturised but efficient visual systems. Navigation experiments on <i>O. rufithorax</i> revealed strong directional fidelity to terrestrial visual landmarks, with no evidence of celestial compass use. Notably, inbound foragers returning to the nest exhibited an interesting behaviour: rather than climbing down tree trunks, they dropped directly from the canopy. These drops were directionally biased toward the nest-facing side and occurred within a narrow time window. After landing, ants successfully oriented and returned to the nest. This suggests that the dropping behaviour is an integral part of the homing routine, likely serving to reduce predation risk and streamline the inbound journey. Overall, this thesis demonstrates how ecological pressures influence the evolution of visual systems, navigation strategies, and locomotor behaviours in <i>Opisthopsis </i>ants. It contributes to a broader understanding of how insects integrate sensory and locomotory strategies to navigate effectively in complex environments.</p>