Goulard, R. | bioRxiv Science

bioRxiv2020

Transfer of orientation memories in untethered wood ants (Formica rufa) from walking in an arena to walking on a motion compensation treadmill

The scale of natural insect navigation during foraging makes it challenging to study, in a controlled way, the navigation processes that an insect brain can support. Virtual Reality and trackball setups have offered experimental control over visual environments while studying tethered insects, but potential limitations and confounds introduced by tethering motivates the development of alternative untethered solutions. In this paper we validate the use of a motion compensator (or treadmill) to study visually-driven behaviour of freely moving wood ants (Formica rufa). We show how this setup allows naturalistic walking behaviour and motivation over long timeframes. Furthermore, we show that ants are able to transfer associative and navigational memories from classical maze and arena contexts to our treadmill. Thus, we demonstrate the possibility to study navigational behaviour over ecologically relevant durations (and virtual distances) in precisely controlled environments, bridging the gap between natural and highly controlled laboratory experiments. 1 Summary statementWe have developed and validated a motion compensating treadmill for wood ants which opens new perspectives to study insect navigation behaviour in a fully controlled manner over ecologically relevant durations.

animal behavior and cognition↗

bioRxiv2020

Mushroom bodies are required for accurate visual navigation in ants

Visual navigation in ants has long been a focus of experimental study [1-3], but only recently have explicit hypotheses about the underlying neural circuitry been proposed [4]. Indirect evidence suggests the mushroom bodies (MB), a known site of olfactory learning [5-10], may also be the substrate for visual memory in navigation tasks [11-14]. Computational modelling shows that MB neural architecture could support this function [15, 16], though there is no direct evidence that ants require MBs for visual navigation. Here we show that lesions of MB calyces impair ants visual navigation to a remembered food location whilst leaving their innate responses to visual cues unaffected. Ants are innately attracted to a large visual cue but we trained them to locate a food source at a specific angle to this visual cue. Subsequent bilateral or unilateral lesioning (through procaine hydrochloride injection) of the MB calyces, caused ants to revert to their innate cue attraction whilst control (saline) injected ants still approached the feeder. The ants path straightness and walking speed were unaffected by lesions. Reversion towards the cue direction occurred irrespective of whether it was ipsi-or contralateral to the lesion site, showing this is not due simply to an induced motor bias. Monocular occlusion did not diminish ants ability to locate the feeder, suggesting the lesion is not merely interrupting visual input to the calyx. The demonstrated dissociation between innate and learnt visual responses provides direct evidence for a specific role of the MB in navigational memory.

animal behavior and cognition↗