Nest excavators' learning walks in the Australian desert ant Melophorus bagoti.

The Australian red honey ant, Melophorus bagoti, stands out as the most thermophilic ant in Australia, engaging in all outdoor activities during the hottest periods of the day during summer months. This species of desert ants often navigates by means of path integration and learning landmark cues around the nest. In our study, we observed the outdoor activities of M. bagoti workers engaged in nest excavation, the maintenance of the nest structure, primarily by taking excess sand out of the nest. Before undertaking nest excavation, the ants conducted a single exploratory walk. Following their initial learning expedition, these ants then engaged in nest excavation activities. Consistent with previous findings on pre-foraging learning walks, after just one learning walk, the desert ants in our study demonstrated the ability to return home from locations 2 m away from the nest, although not from locations 4 m away. These findings indicate that even for activities like dumping excavated sand within a range of 5-10 cm outside the nest, these ants learn and utilize the visual landmark panorama around the nest.

Scanning behaviour in ants: an interplay between random-rate processes and oscillators.

At the start of a journey home or to a foraging site, ants often stop, interrupting their forward movement, turn on the spot a number of times, and fixate in different directions. These scanning bouts are thought to provide visual information for choosing a path to travel. The temporal organization of such scanning bouts has implications about the neural organisation of navigational behaviour. We examined (1) the temporal distribution of the start of such scanning bouts and (2) the dynamics of saccadic body turns and fixations that compose a scanning bout in Australian desert ants, Melophorus bagoti, as they came out of a walled channel onto open field at the start of their homeward journey. Ants were caught when they neared their nest and displaced to different locations to start their journey home again. The observed parameters were mostly similar across familiar and unfamiliar locations. The turning angles of saccadic body turning to the right or left showed some stereotypy, with a peak just under 45°. The direction of such saccades appears to be determined by a slow oscillatory process as described in other insect species. In timing, however, both the distribution of inter-scanning-bout intervals and individual fixation durations showed exponential characteristics, the signature for a random-rate or Poisson process. Neurobiologically, therefore, there must be some process that switches behaviour (starting a scanning bout or ending a fixation) with equal probability at every moment in time. We discuss how chance events in the ant brain that occasionally reach a threshold for triggering such behaviours can generate the results.

Resolving conflict between aversive and appetitive learning of views: how ants shift to a new route during navigation.

Ants store and recall views associated with foraging success, facilitating future foraging journeys. Negative views are also learned, but instead prompt avoidance behaviors such as turning away. However, little is known about the aversive view's role in navigation, the effect of cue conflict, or the contextual relationship between learning and recalling. In this study, we tested Myrmecia midas' capacity for aversive learning of views either independently of or in conflict with appetitive events. We either captured and released foragers when reaching a location or let them pass unhindered. After a few journeys, captured foragers exhibited aversive learning by circumventing the capture location and increasing both meandering and scanning. Ants that experienced foraging-appetitive and homing-aversive events on their journeys exhibited lower rates of avoidance behavior and scans than those experiencing aversive events in both outbound and homebound journeys. The foraging-aversive and homing-aversive ants exhibited similar levels of avoidance and scanning as those that experienced the foraging-aversive and homing-appetitive. We found that foragers showed evidence of context specificity in their scanning behavior, but not in other measures of aversive learning. The foragers did not increase their meandering and scans while approaching the views associated with aversive events. In addition to shedding light on the role of aversive views in navigation, our finding has important implications for understanding the learning mechanisms triggered by handling animals.

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

Many insects orient by comparing current panoramic views of their environment to memorised views. We tested the navigational abilities of night-active Myrmecia midas foragers while we blocked segments of their visual panorama. Foragers failed to orient homewards when the front view, lower elevations, entire terrestrial surround, or the full panorama was blocked. Initial scanning increased whenever the visual panorama was blocked but scanning only increased along the rest of the route when the front, back, higher, or lower elevations were blocked. Ants meandered more when the front, the back, or the higher elevations were obscured. When everything except the canopy was blocked, the ants were quick and direct, but moved in random directions, as if to escape. We conclude that a clear front view, or a clear lower panorama is necessary for initial homeward headings. Furthermore, the canopy is neither necessary nor sufficient for homeward initial heading, and the back and upper segments of views, while not necessary, do make finding home easier. Discrepancies between image analysis and ant behaviour when the upper and lower views were blocked suggests that ants are selective in what portions of the scene they attend to or learn.

Learning walks in an Australian desert ant, Melophorus bagoti.

The central Australian ant Melophorus bagoti is the most thermophilic ant in Australia and forages solitarily in the summer months during the hottest period of the day. For successful navigation, desert ants of many species are known to integrate a path and learn landmark cues around the nest. Ants perform a series of exploratory walks around the nest before their first foraging trip, during which they are presumed to learn about their landmark panorama. Here, we studied 15 naive M. bagoti ants transitioning from indoor work to foraging outside the nest. In 3-4 consecutive days, they performed 3-7 exploratory walks before heading off to forage. Naive ants increased the area of exploration around the nest and the duration of trips over successive learning walks. In their first foraging walk, the majority of the ants followed a direction explored on their last learning walk. During learning walks, the ants stopped and performed stereotypical orientation behaviours called pirouettes. They performed complete body rotations with stopping phases as well as small circular walks without stops known as voltes. After just one learning walk, these desert ants could head in the home direction from locations 2 m from the nest, although not from locations 4 m from the nest. These results suggest gradual learning of the visual landmark panorama around the foragers' nest. Our observations show that M. bagoti exhibit similar characteristics in their learning walks to other desert ants of the genera Ocymyrmex and Cataglyphis.

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

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 1 m 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. The results showed that on the familiar route, individual foragers learned the gap quickly compared with 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.

The effect of spatially restricted experience on extrapolating learned views in desert ants, Melophorus bagoti.

Desert ants are known for learning walks at the beginning of their foraging life, during which they learn terrestrial cues of the panorama and surrounding landmarks around their nest. Foragers retain memories of the visual cues of the nest panorama learned during the pre-foraging trials. When away from the nest, they can compare these stored views with their current vision to return to their nest. In this study we investigated whether spatially restricted foraging ants can extrapolate their memory of visual cues to unexperienced sites. We carried out two conditions to examine whether desert ants extrapolate learned views. In the first condition, naïve ants of Melophorus bagoti were restricted to a nest arena 1 m in radius with a 10 cm high wall (wall condition) for 3 days, then released at distant locations on the fourth day and focal individuals return trips were recorded. In the second condition, a 10 cm sunken metallic barrier was constructed around the nest (moat condition) and the restricted foragers that viewed the unrestricted visual panorama around the 1 m-radius nest arena were then displaced away from the nest as in the wall condition. In the wall condition, most of the ants were unable to orient in the correct heading towards the home direction. In the moat condition ants were able to correctly orient to the nest from displacement sites up to 8 m from the nest. We conclude that while travelling to unfamiliar sites, M. bagoti ants can extrapolate views learned from foraging in a restricted area when given unrestricted views.

Inter-turn intervals in Paramecium caudatum display an exponential distribution.

In navigating to a better location, mobile organisms in diverse taxa change directions of travel occasionally, including bacteria, archaea, single-celled eukaryotes, and small nematode worms such as Caenorhabditis elegans. In perhaps the most common form of goal-orientated movement, the rate of such turns is adjusted in all these taxa to ascend (or descend) a chemical gradient. Basically, the rate of turns is reduced when the movement results in better conditions. In the bacterium Escherichia coli and in C. elegans, the turns are generated by random-rate processes, in which the probability of a turn occurring is constant at every moment. This is evidenced by a distribution of inter-turn intervals that has an exponential distribution. For the first time, we examined the distribution of inter-turn intervals in the single-celled eukaryote, Paramecium caudatum, in a class exercise for first-year university students. We found clear evidence for an exponential distribution of inter-turn intervals, implying a random-rate process in generating turns in Paramecium. The exercise also shows that university laboratory classes can be used to generate scientific data to address research questions whose answers are as yet unknown.

Intricacies of running a route without success in night-active bull ants (Myrmecia midas).

How do ants resolve conflicts between different sets of navigational cues during navigation? When two cue sets point to diametrically opposite directions, theories predict that animals should pick one set of cues or the other. Here we tested how nocturnal bull ants Myrmecia midas adjust their paths along established routes if route following does not lead to their entry into their nest. During testing, foragers were repeatedly placed back along their homeward route up to nine times, a procedure called rewinding. This procedure produced an accumulating path integrator, or vector, in diametric opposition to the learned landmark views of the route. Repeated rewinding made some individuals head initially in the nest-to-feeder vector direction, but all ants ended up using the visual scene for homing, demonstrating the importance of view-based homing in this species. Repeated rewinding, however, led to path deteriorations; with increased path meander and scanning, results also found in desert ants. After nine rewinding trips, ants were displaced off their route in further manipulations, to a site near the nest, an unfamiliar site, or with the terrestrial surround entirely covered. The results show that a change in visual conditions diminished the weight accorded to path integration: the off-route ants no longer headed off in the vector direction as they did on the immediately preceding trial. They relied on celestial compass cues in other ways for homing. Experiment 2 showed the effects of rewinding in the unaltered natural habitat were not view-specific in these bull ants. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Detouring while foraging up a tree: What bull ants (Myrmecia midas) learn and their reactions to novel sensory cues.

Many animals navigate in a structurally complex environment, which requires them to detour around the physical barriers that they encounter. Although many studies in animal cognition suggest that they are able to adeptly avoid obstacles, it is unclear whether a new route is learned to navigate around these barriers and, if so, what sensory information may be used to do so. We investigated detour learning in traveling up a tree in the Australian bull ant, Myrmecia midas, which primarily uses visual landmarks. We first placed a barrier on the ants' upward path. Initially, 46% of foragers were unsuccessful in detouring the obstacle. On subsequent trips, the ants became more successful and established a new route. We observed up to eight successful foraging trips detouring around the barrier. We then tested the same foragers in a series of manipulations, including changing the position of the barrier, making a new gap in the middle of the obstacle, or removing the barrier altogether. The ants mostly showed the same learned motor routine, detouring with a similar path as in the initial trials, suggesting that foragers were not relying on barrier cues and therefore learned a new route around the obstacle. When foragers encountered new olfactory or tactile cues, or the visual environment was blocked; however, their navigation was profoundly disrupted. These results suggest that changing sensory information drastically affects the foragers' navigational performance. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

A Brain-Derived Neurotrophic Factor Mimetic Is Sufficient to Restore Cone Photoreceptor Visual Function in an Inherited Blindness Model.

Controversially, histone deacetylase inhibitors (HDACi) are in clinical trial for the treatment of inherited retinal degeneration. Utilizing the zebrafish dye ucd6 model, we determined if treatment with HDACi can rescue cone photoreceptor-mediated visual function. dye exhibit defective visual behaviour and retinal morphology including ciliary marginal zone (CMZ) cell death and decreased photoreceptor outer segment (OS) length, as well as gross morphological defects including hypopigmentation and pericardial oedema. HDACi treatment of dye results in significantly improved optokinetic (OKR) (~43 fold, p < 0.001) and visualmotor (VMR) (~3 fold, p < 0.05) responses. HDACi treatment rescued gross morphological defects and reduced CMZ cell death by 80%. Proteomic analysis of dye eye extracts suggested BDNF-TrkB and Akt signaling as mediators of HDACi rescue in our dataset. Co-treatment with the TrkB antagonist ANA-12 blocked HDACi rescue of visual function and associated Akt phosphorylation. Notably, sole treatment with a BDNF mimetic, 7,8-dihydroxyflavone hydrate, significantly rescued dye visual function (~58 fold increase in OKR, p < 0.001, ~3 fold increase in VMR, p < 0.05). In summary, HDACi and a BDNF mimetic are sufficient to rescue retinal cell death and visual function in a vertebrate model of inherited blindness.

Early safety assessment of human oculotoxic drugs using the zebrafish visualmotor response.

INTRODUCTION: Many prescribed drugs can adversely affect the eye by causing damage to the function of visual pathways or toxicity to the retina. Zebrafish have the potential to efficiently predict drugs with adverse ocular effects at pre-clinical stages of development. In this study, we explore the potential of using a semi-automated visual behaviour assay to predict drug-induced ocular toxicity in wild-type zebrafish larvae. METHODS: 3 dpf larvae were treated with six known oculotoxic drugs and five control drugs in embryo medium containing 0.1% DMSO. After 48 h, larvae were assessed using the visualmotor response (VMR), an assay which quantifies locomotor responses to light changes; the optokinetic response (OKR), a behavioural assay that quantifies saccadic eye responses to rotating stimuli; and the touch response, a locomotor response to tactile stimuli. RESULTS: 9 of 10 negative control drugs had no effect on zebrafish visual behaviour. 5 of the 6 known oculotoxic drugs (digoxin, gentamicin, ibuprofen, minoxidil and quinine) showed adverse effects on zebrafish visual behaviour assessed by OKR or the more automated VMR. No gross morphological changes were observed in treated larvae. The general locomotor activity of treated larvae, tested using the touch response assay, showed no differences with respect to controls. Overall the VMR assay had a sensitivity of 83%, a specificity of 100% and a positive predictive value of 100%. DISCUSSION: This study confirms the suitability of the VMR assay as an efficient and predictive pre-clinical approach to evaluate adverse ocular effects of drugs on visual function in vivo.

Inhibition of the Pim1 oncogene results in diminished visual function.

Our objective was to profile genetic pathways whose differential expression correlates with maturation of visual function in zebrafish. Bioinformatic analysis of transcriptomic data revealed Jak-Stat signalling as the pathway most enriched in the eye, as visual function develops. Real-time PCR, western blotting, immunohistochemistry and in situ hybridization data confirm that multiple Jak-Stat pathway genes are up-regulated in the zebrafish eye between 3-5 days post-fertilisation, times associated with significant maturation of vision. One of the most up-regulated Jak-Stat genes is the proto-oncogene Pim1 kinase, previously associated with haematological malignancies and cancer. Loss of function experiments using Pim1 morpholinos or Pim1 inhibitors result in significant diminishment of visual behaviour and function. In summary, we have identified that enhanced expression of Jak-Stat pathway genes correlates with maturation of visual function and that the Pim1 oncogene is required for normal visual function.