Minding the gap: learning and visual scanning behaviour in nocturnal bull ants

Abstract

Insects possess small brains but exhibit sophisticated behaviour, specifically their ability to learn to navigate within complex environments. To understand how they learn to navigate in a cluttered environment, we focused on learning and visual scanning behaviour in the Australian nocturnal bull ant, Myrmecia midas, which are exceptional visual navigators. We tested how individual ants learn to detour via a gap and how they cope with substantial spatial changes over trips. Homing M. midas ants encountered a barrier on their foraging route and had to find a 50-cm gap between symmetrical large black screens, at 1m distance towards the nest direction from the centre of the releasing platform in both familiar (on-route) and semi-familiar (off-route) environments. Foragers were tested for up to 3 learning trips with the changed conditions in both environments. Results showed that on the familiar route, individual foragers learned the gap quickly compared to when they were tested in the semi-familiar environment. When the route was less familiar, and the panorama was changed, foragers were less successful at finding the gap and performed more scans on their way home. Scene familiarity thus played a significant role in visual scanning behaviour. In both on-route and off-route environments, panoramic changes significantly affected learning, initial orientation and scanning behaviour. Nevertheless, over a few trips, success at gap finding increased, visual scans were reduced, the paths became straighter, and individuals took less time to reach the goal.

What view information is most important in the homeward navigation of an Australian bull ant, Myrmecia midas?

“…In the Back Condition, foragers turned around and looked back towards their release point, beyond which the view was blocked. Scanning is interpreted as a response to navigational uncertainty—although we are not saying that the ant explicitly codes uncertainty—and as offering opportunities to learn views (Schwarz et al 2014 ; Wystrach et al 2019 ; Le Moel and Wystrach 2020 ; Murray et al 2020 ; Islam et al 2021a , b ). From these results, we cannot infer to what extent scans are an attempt to lower current uncertainty by increasing information collection, versus learning for the future by storing views that have changed.…”

“…This straight-line orientation behaviour is reminiscent of ball-rolling dung beetles, which often pick a random orientation, and then rely primarily on celestial information, such as the moon and the Milky Way, to maintain that heading (Dacke et al 2013 , 2019 , 2020 ). Since these nocturnal bull ants rely primarily on panoramic view to steer in the correct direction (Freas et al 2017a ; Freas and Cheng 2019 ; Islam et al 2020 , 2021a ), they might be using a distinct navigational strategy similar to that of the dung beetles. When the bull ants have too little panoramic information to orient in the correct direction, they escape in any straight direction.…”

“…Individually foraging ants navigate using the terrestrial panorama and path integration for their visual navigation (Wehner 2009 , 2020 ; Cheng 2012 ; Collett et al 2014 ; Freas and Schultheiss 2018 ). Foragers acquire and retain information from the surrounding terrestrial panorama to navigate between the nest and foraging sites when visual information is available Collett et al 2006 ; Collett 2010 ; Mangan and Webb 2012 ; Freas et al 2017a ; Islam et al 2020 ; Wehner 2020 ; Islam et al 2021 ). A naive ant acquires views of the terrestrial panorama around its nest through a series of learning walks before it begins foraging and uses these learned views for navigation later in life (Zeil 2012 ; Fleischmann et al 2016 , 2017 ; Jayatilaka et al 2018 ; Freas et al 2019 ; Zeil and Fleischmann 2019 ; Deeti and Cheng 2021 ).…”

“…The catchment area depends in good part on how visually cluttered the environment is (Stürzl and Zeil 2007 ; Narendra et al 2013 ; Murray and Zeil 2017 ). The navigational success of foraging ants in an environment depends on the scene similarity between the release-site panorama and previously acquired panoramic information (Freas and Cheng 2019 ; Freas et al 2019 ; Deeti et al 2020 ; Islam et al 2021a ).…”

Oscillators and servomechanisms in orientation and navigation, and sometimes in cognition

“…For example, both meandering and scanning increase if an ant that has almost reached home is picked up by an experimenter and placed back somewhere on the route that it had just traversed, a manipulation called rewinding [29], or when an ant has fallen into a pit trap on the previous trip that took a while to escape from [30]. In bull ants (genus Myrmecia ) as well, unfamiliar visual conditions induce scanning behaviour ( M. croslandi [31]; M. midas [32]). Unlike other cases to come, however, these interruptions do not end with random re-orientation of travel direction.…”