Biology subjects

Freas, C. A.

Publications and source records attributed to Freas, C. A..

6 recordsLinked to original sources

bioRxiv2026

Online extinction and novelty-triggered recovery of life-long visual memories in navigating ants

Insects exhibit flexible memory processes, yet current models often confine these modulations to discrete, reinforced events. During navigation, animals can learn to associate locations with resources or aversive events. However, such events occur sporadically within an otherwise continuous behavioral process involving latent learning. This raises a fundamental question for insect cognition: can insects continuously update visual memories during navigation? We show that navigating ants (Myrmecia midas) dynamically revalue visual memories en-route, even in the absence of any motivational change or external reinforcement. Using a trackball system that prevented visual progress, we found that nest-view attraction declined over time, reflecting a gradual, online extinction of these otherwise life-long attractive visual memories. These memory updates were view-specific, independent of path integrator state, and persisted after 24-hours, indicating the involvement of long-term memory processes. However, brief exposure to a novel visual scene was sufficient to partially restore nest-views attraction, showing that extinction is labile, and the original memories are preserved. Unlike classic paradigms, visual memory extinction operates here as a continuous, time-dependent process without reward-omission or prediction error; whereas memory reinstatement is triggered by discrete visual changes. We propose that these dynamics are mediated by opponent-processes in the insect mushroom bodies, where temporal estimates of view exposure drive extinction and novel view detection gates memory recovery.

ecology↗

bioRxiv2025

Scanning and active sampling behaviours emerge from conserved insect neural circuits

Navigating insects often pause and rotate to sample their surroundings, behaviours termed scanning. These and other active sampling behaviours embody navigational uncertainty, and are key for spatial learning, yet their neural basis remains unclear and existing models impose scanning behaviours rather than explaining its emergence. Here, we show that desert ants scanning dynamics can emerge spontaneously from the same conserved neural circuits used for goal-directed navigation, without requiring a specialized scanning module. We built a biologically grounded model combining central complex (CX) steering and lateral accessory lobe (LAL) oscillators, and added a downstream stochastic inhibition of forward speed. This minimal system produced diverse, realistic scan dynamics; saccades, fixations and reversals, whose features were qualitatively compared to high-speed video recordings of Melophorus bagoti scanning. Detailed analysis of these natural scans confirmed model predictions, including how scan structure depends on oscillator phase, goal-heading deviation, and navigational uncertainty. Furthermore, the model reveals that simple modulation of forward speed unifies a broad range of behaviours across ant species, from dashes to smooth oscillatory trajectories to pirouettes and voltes. Crucially, this model suggests a distributed control principle where forward speed acts as a single adjustable parameter, for both individuals and through evolution, to regulate the balance between goal-driven exploitation and information-seeking exploration.

animal behavior and cognition↗

bioRxiv2025

Nocturnal Navigation via a Time-Compensated Lunar Compass in Bull Ants

Diurnal navigators are well known to orient via the sun, compensating for its movement over time by linking solar position and speed with terrestrial reference points (Beetz & el Jundi, 2018; Dingle, 2014; Dyer, 1987; Mouritsen & Frost, 2002; Stalleicken et al., 2005; Wehner & Lanfranconi, 1981; Wehner & Muller, 1993). In contrast to the sun, the moon is not only dimmer, but its presence is also highly variable, both temporally and in its illuminance, making it a more complex cue to predict. Yet nocturnal animals employ a celestial compass to orient at night (i.e. the moon and stars; (Dacke et al., 2003, 2013; Dreyer et al., 2025), but navigation via a time-compensated lunar compass has yet to be demonstrated. Nocturnal bull ants (Myrmecia midas) navigate home overnight under the dimmest of visual conditions, relying in part on a nocturnal path-integration system informed by lunar cues (Freas et al., 2024). Here, we show the first evidence of a time-compensated lunar compass in a homing animal, with path-integrating ants adjusting path headings by predicting the lunar azimuthal position throughout the night. Ants predict the moons future position based upon a generalised internal estimate of the lunar ephemeris. Rather than detailed knowledge of the moons nightly schedule, these ants form a lunar path representation via a speed-step function, reflecting the moons accelerating then decelerating arc. However, these ants also predictably under- or overestimate the shape of this arc based on individual experience, suggesting a level of temporal uncertainty regarding when the moon rapidly shifts from the eastern to western sky. Additionally, updating this lunar compass relies on the presence of a directionally informative skyline, which allows occasional cross-referencing of lunar movement with external fixed compass cues near the horizon.

ecology↗

bioRxiv2025

Diurnal Bull Ants Navigating by Moonlight: Polarised Light Homing in Myrmecia tarsata

We present evidence that the faint polarised moonlight pattern of the sky can be detected and used for navigation in the diurnal bull ant Myrmecia tarsata, despite this species lacking the highly refined low-light visual specialisations of the nocturnal bull ant, Myrmecia midas. The position of celestial bodies such as the sun and moon can provide navigating animals directional information, yet direct observation can often be occluded. Animals can estimate positional information of solar and lunar cues via their polarised light pattern, present across the sky. The suns polarisation pattern is widely used in animals and a similar, yet much fainter pattern is produced by the moon, yet it is unknown how widespread moonlights use is in navigating animals. Here, we demonstrate that the bull ant Myrmecia tarsata, which forages throughout the day, returning home at sunset, can use both solar and lunar polarised light patterns to navigate. We compare these findings to the closely related M. midas navigating under identical light conditions, as this nocturnal bull ant is known to rely on these polarised light patterns as part of their celestial compass. While M. midas and M. tarsata can clearly use both the solar and lunar polarised light patterns to navigate, M. tarsata showed degraded performance under polarised moonlight as a function of lunar phase, decreasing performance as illumination decreased. M. midas in contrast, exhibited impressive attendance to the overhead lunar polarisation pattern throughout the lunar month, illustrating the highly specialised low-light-detection adaptations of bull ants.

animal behavior and cognition↗

bioRxiv2023

Moonlight Polarisation Pattern Guides Nocturnal Bull Ants Home

For the first time in any animal, we show that nocturnal bull ants use the exceedingly dim polarisation pattern produced by the moon for overnight navigation. The sun or moon can provide directional information via their position; however, they can often be obstructed by clouds, canopy or the horizon. Despite being hidden, these bodies can still provide compass information through the polarised light pattern they produce/reflect. Sunlight produces polarised light patterns across the overhead sky as it enters the atmosphere, and solar polarised light is a well-known compass cue for navigating animals. Moonlight produces an analogous pattern, albeit a million times dimmer than sunlight. Here we show evidence that polarised moonlight forms part of the celestial compass of navigating nocturnal ants. Nocturnal bull ants leave their nest at twilight and rely heavily on the overhead solar polarisation pattern to navigate. Yet many foragers return home overnight when the sun cannot guide them. We demonstrate that these bull ants use polarised moonlight to navigate home during the night, by rotating the overhead polarisation pattern above homing ants, who alter their headings in response. Furthermore, these ants can detect this cue throughout the lunar month, even under crescent moons, when polarised light levels are at their lowest. Finally, we show long-term incorporation of this moonlight pattern into the ants path integration system throughout the night for homing, as polarised sunlight is incorporated throughout the day.

animal behavior and cognition↗

bioRxiv2021

Aversive View Memory and Navigational Risk Sensitivity in the Desert Ant, Cataglyphis Velox

Many ants establish foraging routes through learning views of the visual panorama. Route models have focused primarily on attractive view use, which experienced foragers orient towards to return to known sites. However, aversive views have recently been uncovered as a key component of route learning. Here, Cataglyphis velox rapidly learned aversive views, when associated with a negative outcome, a period of captivity in brush, triggering an increase in hesitation behavior. These memories were based on the accumulation of experiences over multiple trips with each new experience regulating foragers hesitancy. Foragers were also sensitive to captivity time differences, suggesting they possess some mechanism to quantify duration. Finally, we analyzed foragers perception of risky (i.e. variable) versus stable aversive outcomes by associating two sites along the route with distinct captivity schedules, a fixed or variable duration, with the same mean across training. Foragers exhibited significantly less hesitation to the risky outcome compared to the fixed, indicating they perceived risky outcomes as less severe. Results align with a logarithmic relationship between captivity duration and hesitations, suggesting that aversive stimulus perception is a logarithm of its actual value. We conclude by characterizing how these behaviors can be executed within the mushroom bodies neural circuitry.

animal behavior and cognition↗