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The Green Weaver ants, Oecophylla smaragdina are iconic animals known for their extreme cooperative behaviour where they bridge gaps by linking to each other to build living chains. They are visually oriented animals, build chains towards closer targets, use celestial compass cues for navigation and are visual predators. Here, we describe their visual sensory capacity. The major workers of O. smaragdina have more ommatidia (804) in each eye compared to minor workers (508), but the facet diameters are comparable between both castes. We measured the impulse responses of the compound eye and found their response duration (42 ms) was similar to that seen in other slow-moving ants. We determined the flicker fusion frequency of the compound eye at the brightest light intensity to be 132 Hz, which is relatively fast for a walking insect suggesting the visual system is well suited for a diurnal lifestyle. Using pattern-electroretinography we identified the compound eye has a spatial resolving power of 0.5 cycles deg−1 and reached peak contrast sensitivity of 2.9 (35% Michelson contrast threshold) at 0.05 cycles deg−1. We discuss the relationship of spatial resolution and contrast sensitivity, with number of ommatidia and size of the lens.

Jumping is a rapid locomotory mode widespread in terrestrial organisms. However, it is a rare specialization in ants. Forward jumping has been reported within four distantly related ant genera:Gigantiops,Harpegnathos,Myrmecia, andOdontomachus. The temporal engagement of legs/body parts during jump, however, varies across these genera. It is unknown what morphological adaptations underlie such behaviors, and whether jumping in ants is solely driven directly by muscle contraction or additionally relies on elastic recoil mechanism. We investigate the morphological adaptations for jumping behavior by comparing differences in the locomotory musculature between jumping and non-jumping relatives using x-ray micro- CT and 3D morphometrics. We found that the size-specific volumes of the trochanter depressor muscle (scm6) of the middle and hind legs are 3-5 times larger in jumping ants, and that one coxal remotor muscle (scm2) is reduced in volume in the middle and/or hind legs. Notably, the enlargement in the volume of other muscle groups is directly linked to the legs or body parts engaged during the jump. Furthermore, a direct comparison of the muscle architecture revealed two significant differences between in jumping versus non-jumping ants: First, the relative Physiological Cross-Sectional Area (PCSA) of the trochanter depressor muscles of all three legs were larger in jumping ants, except in the front legs ofO. rixosusandM. nigrocincta; second, the relative muscle fiber length was shorter in jumping ants compared to non-jumping counterparts, except in the front legs ofO. rixosusandM. nigrocincta. This suggests that the difference in relative muscle volume in jumping ants is largely invested in the area (PCSA), and not in fiber length. There was no clear difference in the pennation angle between jumping and non-jumping ants. However, the length of hind legs relative to body length was longer in jumping ants. Based on direct comparison of the observed vs. possible work and power output during jumps, we surmise that direct muscle contractions suffice to explain jumping performance, in two species, but elastic recoil is likely important in one. We suggest that increased investment in jumping-relevant musculature is a primary morphological adaptation that separates jumping from non-jumping ants. These results elucidate the common and idiosyncratic morphological changes underlying this rare adaptation in ants.

Spiders, the most specious taxon of predators, have evolved an astounding range of predatory strategies, including group hunting, specialized silk traps, pheromone-loaded bolas, and aggressive mimicry. Spiders that hunt prey defended with behavioral, mechanical, or chemical means are under additional selection pressure to avoid injury and death. Ants are considered dangerous because they can harm or kill their predators, but some groups of spiders, such as the Theridiidae, have a very high diversification of ant-hunting species and strategies [J. Liu et al.,Mol. Phylogenet. Evol. 94, 658–675 (2016)]. Here, we provide detailed behavioral analyses of the highly acrobatic Australian ant-slayer spider,Euryopis umbilicata(Theridiidae), that captures much larger and defendedCamponotusants on vertical tree trunks. The hunting sequence consists of ritualized steps performed within split seconds, resulting in an exceptionally high prey capture success rate.

The Green Weaver ants, Oecophylla smaragdina are iconic animals known for their extreme cooperative behaviour where they bridge gaps by linking to each other to build living chains. They are visually oriented animals, build chains towards closer targets, use celestial compass cues for navigation and are visual predators. Here, we describe their visual sensory capacity. The major workers of O. smaragdina have more ommatidia (804) in each eye compared to minor workers (508), but the facet diameters are comparable between both castes. We measured the impulse responses of the compound eye and found their response duration (42ms) was similar to that seen in other slow-moving ants. We determined the temporal resolution of the compound eye at the brightest light intensity to be 131.54 Hz, which is relatively fast for a walking insect suggesting the visual system is well suited for a diurnal lifestyle. Using pattern-electroretinography we identified the compound eye has a spatial resolving power of 0.52 cycles deg− 1 and reached peak contrast sensitivity of 2.88 (34.67% Michelson contrast threshold) at 0.05 cycles deg− 1. We discuss the relationship of spatial resolution and contrast sensitivity, with number of ommatidia and size of the lens.

Current global challenges call for a rigorously predictive ecology. Our understanding of ecological strategies, imputed through suites of measurable functional traits, comes from decades of work that largely focussed on plants. However, a key question is whether plant ecological strategies resemble those of other organisms. Among animals, ants have long been recognised to possess similarities with plants: as (largely) central place foragers. For example, individual ant workers play similar foraging roles to plant leaves and roots and are similarly expendable. Frameworks that aim to understand plant ecological strategies through key functional traits, such as the ‘leaf economics spectrum’, offer the potential for significant parallels with ant ecological strategies. Here, we explore these parallels across several proposed ecological strategy dimensions, including an ‘economic spectrum’, propagule size-number trade-offs, apparency-defence trade-offs, resource acquisition trade-offs and stress-tolerance trade-offs. We also highlight where ecological strategies may differ between plants and ants. Furthermore, we consider how these strategies play out among the different modules of eusocial organisms, where selective forces act on the worker and reproductive castes, as well as the colony. Finally, we suggest future directions for ecological strategy research, including highlighting the availability of data and traits that may be more difficult to measure, but should receive more attention in future to better understand the ecological strategies of ants. The unique biology of eusocial organisms provides an unrivalled opportunity to bridge the gap in our understanding of ecological strategies in plants and animals and we hope that this perspective will ignite further interest. Read the free Plain Language Summary for this article on the Journal blog.

Kleptoparasitic spiders live and forage in the webs of other spiders. Using vibratory cues generated by the host spider during prey capture, they leave their resting positions in the upper peripheries of the host web and move towards the centre of the web where they feed along with the host spider or steal small pieces of prey. While the triggers for initiating the foraging raids are known, there is little information about the fine-scale trajectory dynamics in this model system. We mapped the movement of the kleptoparasite Argyrodes elevatus in the web of the host Trichonephila clavipes. We filmed the movement of the kleptoparasite spiders and quantified the trajectory shape, speed, heading directions and path revisitation. Our results show that kleptoparasitic spider movement is spatially structured, with higher levels of speed at the peripheries and slower in the centre of the web. We found a high level of variation in trajectory shapes between individuals. We found that the majority of heading orientations were away from the hub suggesting that detouring or repeated approaches are an essential component of kleptoparasite movement strategies. Our results of the revisitation rate also confirm this pattern, where locations close to the hub were revisited more often than in the periphery. The kleptoparasite–host spider system is a promising model to study fine-scale movement patterns in small bounded spaces.

State-of-the-art algorithms for visual place recognition, and related visual navigation systems, can be broadly split into two categories: computer-science-oriented models including deep learning or image retrieval-based techniques with minimal biological plausibility, and neuroscience-oriented dynamical networks that model temporal properties underlying spatial navigation in the brain. In this letter, we propose a new compact and high-performing place recognition model that bridges this divide for the first time. Our approach comprises two key neural models of these categories: (1) FlyNet, a compact, sparse two-layer neural network inspired by brain architectures of fruit flies, Drosophila melanogaster, and (2) a one-dimensional continuous attractor neural network (CANN). The resulting FlyNet+CANN network incorporates the compact pattern recognition capabilities of our FlyNet model with the powerful temporal filtering capabilities of an equally compact CANN, replicating entirely in a hybrid neural implementation the functionality that yields high performance in algorithmic localization approaches like SeqSLAM. We evaluate our model, and compare it to three state-of-the-art methods, on two benchmark real-world datasets with small viewpoint variations and extreme environmental changes - achieving 87% AUC results under day to night transitions compared to 60% for Multi-Process Fusion, 46% for LoST-X and 1% for SeqSLAM, while being 6.5, 310, and 1.5 times faster, respectively., Preprint version of article published in IEEE Robotics and Automation Letters

Visual animal communication, whether to the same or to other species, is largely conducted through dynamic and colourful signals. For a signal to be effective, the signaller must capture and retain the attention of the receiver. Signal efficacy is also dependent on the sensory limitations of the receiver. However, most signalling studies consider movement and colour separately, resulting in a partial understanding of the signal in question. We explored the structure and function of predator–prey signalling in the jumping spider–tephritid fly system, where the prey performs a wing waving display that deters an attack from the predator. Using a custom-built spider retinal tracker combined with visual modelling, as well as behavioural assays, we studied the effect of fly wing movement and colour on the jumping spider's visual system. We show that jumping spiders track their prey less effectively during wing display and this can be attributed to a series of fluctuations in chromatic and achromatic contrasts arising from the wing movements. These results suggest that displaying flies deter spider attacks by manipulating the movement biases of the spider's visual system. Our results emphasise the importance of receiver attention on the evolution of interspecific communication.

Nocturnal insects likely have evolved distinct physiological adaptations to enhance sensitivity for tasks, such as catching moving prey, where the signal-noise ratio of visual information is typically low. Using electroretinogram recordings, we measured the impulse response and the flicker fusion frequency (FFF) in six congeneric species of

Summary Solitary foraging insects, such as ants, maintain an estimate of the direction and distance to their starting location as they move away from it, in a process known as path integration. This estimate, commonly known as the “home vector,” is updated continuously as the ant moves 1 , 2 , 3 , 4 and is reset as soon as it enters its nest, 5 yet ants prevented from returning to their nest can still use their home vector when released several hours later. 6 , 7 This conjunction of fast update and long persistence of the home vector memory does not directly map to existing accounts of short-, mid-, and long-term memory; 2 , 8 , 9 , 10 , 11 , 12 hence, the substrate of this memory remains unknown. Chill-coma anesthesia 13 , 14 , 15 has previously been shown to affect associative memory retention in fruit flies 14 , 16 and honeybees. 9 , 17 , 18 We investigate the nature of path integration memory by anesthetizing ants after they have accumulated home vector information and testing if the memory persists on recovery. We show that after anesthesia the memory of the distance ants have traveled is degraded, but the memory of the direction is retained. We also show that this is consistent with models of path integration that maintain the memory in a redundant Cartesian coordinate system and with the hypothesis that chill-coma produces a proportional reduction of the memory, rather than a subtractive reduction or increase of noise. The observed effect is not compatible with a memory based on recurrent circuit activity and points toward an activity-dependent molecular process as the basis of path integration memory.

In addition to the compound eyes insects possess simple eyes known as ocelli. Input from the ocelli modulates optomotor responses, flight-time initiation and phototactic responses, behaviours that are predominantly mediated by the compound eyes. In this study, using pattern electroretinography (pERG), we investigated the contribution of the compound eyes to ocellar spatial vision in the diurnal Australian bull ant, Myrmecia tarsata by measuring the contrast sensitivity and spatial resolving power of the ocellar second-order neurons under various occlusion conditions. Furthermore, in four species of Myrmecia ants active at different times of the day and in European honeybee, Apis mellifera, we characterized the ocellar visual properties when both visual systems were available. Among the ants, we found that the time of activity had no significant effect on ocellar spatial vision. Comparing day-active ants and the honeybee we did not find any significant effect of locomotion on ocellar spatial vision. In M. tarsata, when the compound eyes were occluded, the amplitude of the pERG signal from the ocelli reduced by three times compared to conditions when the compound eyes were available. The signals from the compound eyes maintained the maximum contrast sensitivity of the ocelli as 13 (7.7%), and the spatial resolving power as 0.29 cpd. We conclude that ocellar spatial vison improves significantly with input from the compound eyes, with a noticeably larger improvement in contrast sensitivity than in spatial resolving power.

We constructed a large projection device (the Antarium) with 20,000 UV-Blue-Green LEDs that allows us to present tethered ants with views of their natural foraging environment. The ants walk on an air-cushioned trackball, their movements are registered and can be fed back to the visual panorama. Views are generated in a 3D model of the ants' environment so that they experience the changing visual world in the same way as they do when foraging naturally. The Antarium is a biscribed pentakis dodecahedron with 55 facets of identical isosceles triangles. The length of the base of the triangles is 368 mm resulting in a device that is roughly 1 m in diameter. Each triangle contains 361 blue/green LEDs and nine UV LEDs. The 55 triangles of the Antarium have 19,855 Green and Blue pixels and 495 UV pixels, covering 360° azimuth and elevation from -50° below the horizon to +90° above the horizon. The angular resolution is 1.5° for Green and Blue LEDs and 6.7° for UV LEDs, offering 65,536 intensity levels at a flicker frequency of more than 9,000 Hz and a framerate of 190 fps. Also, the direction and degree of polarisation of the UV LEDs can be adjusted through polarisers mounted on the axles of rotary actuators. We build 3D models of the natural foraging environment of ants using purely camera-based methods. We reconstruct panoramic scenes at any point within these models, by projecting panoramic images onto six virtual cameras which capture a cube-map of images to be projected by the LEDs of the Antarium. The Antarium is a unique instrument to investigate visual navigation in ants. In an open loop, it allows us to provide ants with familiar and unfamiliar views, with completely featureless visual scenes, or with scenes that are altered in spatial or spectral composition. In closed-loop, we can study the behavior of ants that are virtually displaced within their natural foraging environment. In the future, the Antarium can also be used to investigate the dynamics of navigational guidance and the neurophysiological basis of ant navigation in natural visual environments.

Kleptoparasitic spiders live and forage in the webs of other spiders. Using vibratory cues generated by the host spider during prey capture, they leave their resting positions in the upper peripheries of the host web and move towards the centre of the web where they feed along with the host spider or steal small pieces of prey. While the triggers for initiating the foraging raids are known, there is little information about the fine-scale trajectory dynamics in this model system. We mapped the movement of the kleptoparasite Argyrodes elevatus in the web of the host Trichonephila clavipes. We filmed the movement of the kleptoparasite spiders and quantified the trajectory shape, speed, heading directions and path revisitation. Our results show that kleptoparasitic spider movement is spatially structured, with higher levels of speed at the peripheries and slower in the centre of the web. We found a high level of variation in trajectory shapes between individuals. We found that the majority of heading orientations were away from the hub suggesting that detouring or repeated approaches are an essential component of kleptoparasite movement strategies. Our results of the revisitation rate also confirm this pattern, where locations close to the hub were revisited more often than in the periphery. The kleptoparasite-host spider system is a promising model to study fine-scale movement patterns in small bounded spaces.

Summary Prior to leaving home, insects acquire visual landmark information through a series of well-choreographed walks or flights of learning [ 1 , 2 , 3 , 4 ]. This information allows them to pinpoint goals both when in their vicinity [ 5 , 6 , 7 ] and from locations they have not previously visited [ 8 , 9 , 10 ]. It is presumed that animals returning home match memorized views to their current view for successful view-based navigation [ 11 ]. While view-based navigation strategies have been incorporated into several navigation models [ 8 , 12 , 13 ], we still know little about how this behavior is performed by the insect brain. Mushroom bodies are essential for visual learning and memory [ 14 , 15 , 16 ], and therefore we investigated their role in view-based navigation in a visually oriented ant, Myrmecia midas. We injected the local anesthetic procaine [ 15 , 17 , 18 ] into the mushroom body vertical lobes (VLs) to selectively inhibit neural activity in this region. We compared the behavior of VL-procaine-treated ants with three groups: untreated control, VL-saline, and off-target (antennal lobe) procaine. Experienced foragers were collected, treated, and released in their familiar environment where we documented their behavior. Animals with procaine-inactivated VLs had tortuous paths and were unable to find their nest, whereas ants from the untreated and off-target procaine groups were well directed and were the most successful at returning home. Untreated animals walked faster when their gaze was directed toward home, and this behavior was eliminated by anesthetizing the VL region. Our data provide neurobiological evidence that the mushroom body vertical lobes are necessary for retrieving visual memories for successful view-based navigation.

International audience; Solitary foraging ants rely on vision when travelling along routes and when pinpointing their nest. We tethered foragers of Myrmecia croslandi on a trackball and recorded their intended movements when the trackball was located on their normal foraging corridor (on-route), above their nest and at a location several metres away where they have never been before (off-route). We found that at on-and off-route locations, most ants walk in the nest or foraging direction and continue to do so for tens of metres in a straight line. In contrast, above the nest, ants walk in random directions and change walking direction frequently. In addition, the walking direction of ants above the nest oscillates on a fine scale, reflecting search movements that are absent from the paths of ants at the other locations. An agent-based simulation shows that the behaviour of ants at all three locations can be explained by the integration of attractive and repellent views directed towards or away from the nest, respectively. Ants are likely to acquire such views via systematic scanning movements during their learning walks. The model predicts that ants placed in a completely unfamiliar environment should behave as if at the nest, which our subsequent experiments confirmed. We conclude first, that the ants' behaviour at release sites is exclusively driven by what they currently see and not by information on expected outcomes of their behaviour; and second, that navigating ants might continuously integrate attractive and repellent visual memories. We discuss the benefits of such a procedure.

For many animals, visual landmarks provide information about their location in space and the direction to a goal. Insects acquire this visual information through a series of well-choreographed walks or flights of learning carried out prior to leaving home. Views acquired during learning walks are sufficient for pinpointing goals both when in their vicinity and when animals are at locations they have not visited previously. It is presumed that animals returning home match the memorised views to their current view for successful view-based navigation. While view-based navigation strategies have been incorporated in a wide variety of navigation models used in robotics, we still know very little about how view-based navigation is performed by the insect brain. We investigated the role of the mushroom bodies in view-based navigation in a visually oriented Australian bull ant Myrmecia midas. We targeted the mushroom body vertical lobes (VL) because they are innervated by the visual input regions of the mushroom body and are known to be involved in learning and memory. To ensure that ants in our experiments could navigate using only visual landmarks, we captured experienced foragers close to their nest when they were returning home. For our treatment group, we selectively inhibited neural activity in the VL of the mushroom bodies using the anesthetic procaine and compared their behaviour with three groups: untreated control, VL saline injected, and off-target (antennal lobe) procaine injected groups. Ants were then released at their familiar foraging tree, their subsequent paths were filmed, and their final destinations were determined. While all groups exhibited similar walking speeds, we found significant differences in their orientation and the ability of ants to successfully return home. Untreated control and off-target procaine injected ants were well directed and the most successful at returning home. Animals with procaine-inactivated VL had tortuous paths with multiple loops and were unable to find their nest. We analysed their walking speed relative to gaze direction and found that untreated animals accelerated when their gaze was directed toward home. This behaviour was eliminated by anaesthetizing the VL. Our data show that a simple and effective view-based navigation strategy – accelerate whenever a homeward view is in the frontal visual field – is mediated by the VL of the ant brain. We therefore provide neurobiological evidence that view-based navigation requires functional mushroom bodies.

Continuously monitoring its position in space relative to a goal is one of the most essential tasks for an animal that moves through its environment. Species as diverse as rats, bees, and crabs achieve this by integrating all changes of direction with the distance covered during their foraging trips, a process called path integration. They generate an estimate of their current position relative to a starting point, enabling a straight-line return, following what is known as a home vector. While in theory path integration always leads the animal precisely back home, in the real world noise limits the usefulness of this strategy when operating in isolation. Noise results from stochastic processes in the nervous system and from unreliable sensory information, particularly when obtaining heading estimates. Path integration, during which angular self-motion provides the sole input for encoding heading (idiothetic path integration), results in accumulating errors that render this strategy useless over long distances. In contrast, when using an external compass this limitation is avoided (allothetic path integration). Many navigating insects indeed rely on external compass cues for estimating body orientation, whereas they obtain distance information by integration of steps or optic-flow-based speed signals. In the insect brain, a region called the central complex plays a key role for path integration. Not only does the central complex house a ring-attractor network that encodes head directions, neurons responding to optic flow also converge with this circuit. A neural substrate for integrating direction and distance into a memorized home vector has therefore been proposed in the central complex. We discuss how behavioral data and the theoretical framework of path integration can be aligned with these neural data. Heinze, Narendra and Cheung discuss the fundamental principles of insect path integration behavior and highlight interactions with other navigational strategies using insights from behavioral data, the theoretical underpinnings, and from recent discoveries illuminating the neural control of path integration. (Less)

Insects are well known to orient using celestial cues. The pattern of polarised skylight is the dominant celestial compass information that insects use, which they detect using a specialised set of ommatidia. The number of ommatidia decreases with body size, and it is unknown how this reduction in the number of ommatidia affects the precision of orienting using celestial cues. We investigated this in eight different ant species that had varying numbers of ommatidia. We captured ants returning home, displaced them to an unfamiliar location and measured their precision in determining heading direction using celestial cues. The heading direction of the ants measured at a fixed distance from the release and also at a distance scaled to their body size was not correlated with the number of ommatidia. However, both the path straightness and walking speed were lower in smaller ants indicating the ability to orient at a finer scale was affected by miniaturisation.

Insects have exquisitely adapted their compound eyes to suit the ambient light intensity in the different temporal niches they occupy. In addition to the compound eye, most flying insects have simple eyes known as ocelli, which assist in flight stabilisation, horizon detection and orientation. Among ants, typically the flying alates have ocelli while the pedestrian workers lack this structure. The Australian ant genus Myrmecia is one of the few ant genera in which both workers and alates have three ocellar lenses. Here, we studied the variation in the ocellar structure in four sympatric species of Myrmecia that are active at different times of the day. In addition, we took advantage of the walking and flying modes of locomotion in workers and males, respectively, to ask whether the type of movement influences the ocellar structure. We found that ants active in dim light had larger ocellar lenses and wider rhabdoms compared with those in bright-light conditions. In the ocellar rhabdoms of workers active in dim-light habitats, typically each retinula cell contributed microvilli in more than one direction, probably destroying polarisation sensitivity. The organisation of the ocellar retina in the day-active workers and the males suggests that in these animals some cells are sensitive to the pattern of polarised skylight. We found that the night-flying males had a tapetum that reflects light back to the rhabdom, increasing their optical sensitivity. We discuss the possible functions of ocelli to suit the different modes of locomotion and the discrete temporal niches that animals occupy.

Visual navigation is a benchmark information processing task that can be used to identify the consequence of being active in dim-light environments. Visual navigational information that animals use during the day includes celestial cues such as the sun or the pattern of polarized skylight and terrestrial cues such as the entire panorama, canopy pattern, or significant salient features in the landscape. At night, some of these navigational cues are either unavailable or are significantly dimmer or less conspicuous than during the day. Even under these circumstances, animals navigate between locations of importance. Ants are a tractable system for studying navigation during day and night because the fine scale movement of individual animals can be recorded in high spatial and temporal detail. Ant species range from being strictly diurnal, crepuscular, and nocturnal. In addition, a number of species have the ability to change from a day- to a night-active lifestyle owing to environmental demands. Ants also offer an opportunity to identify the evolution of sensory structures for discrete temporal niches not only between species but also within a single species. Their unique caste system with an exclusive pedestrian mode of locomotion in workers and an exclusive life on the wing in males allows us to disentangle sensory adaptations that cater for different lifestyles. In this article, we review the visual navigational abilities of nocturnal ants and identify the optical and physiological adaptations they have evolved for being efficient visual navigators in dim-light.

Individual differences in response thresholds to task-related stimuli may be one mechanism driving task allocation among social insect workers. These differences may arise at various stages in the nervous system. We investigate variability in the peripheral nervous system as a simple mechanism that can introduce inter-individual differences in sensory information. In this study we describe size-dependent variation of the compound eyes and the antennae in the ant Temnothorax rugatulus. Head width in T. rugatulus varies between 0.4 and 0.7 mm (2.6-3.8 mm body length). But despite this limited range of worker sizes we find sensory array variability. We find that the number of ommatidia and of some, but not all, antennal sensilla types vary with head width. The antennal array of T. rugatulus displays the full complement of sensillum types observed in other species of ants, although at much lower quantities than other, larger, studied species. In addition, we describe what we believe to be a new type of sensillum in hymenoptera that occurs on the antennae and on all body segments. T. rugatulus has apposition compound eyes with 45-76 facets per eye, depending on head width, with average lens diameters of 16.5 μm, rhabdom diameters of 5.7 μm and inter-ommatidial angles of 16.8°. The optical system of T. rugatulus ommatidia is severely under focussed, but the absolute sensitivity of the eyes is unusually high. We discuss the functional significance of these findings and the extent to which the variability of sensory arrays may correlate with task allocation.

When an insect is intercepted by a spider web, spiders quickly locate the prey, and run towards it. Once they make contact with the prey, they immobilise the prey and retrieve it to the centre of the web or the retreat for consumption. However, in rare circumstances, the spider can also pull the prey towards itself either while running to the prey or from a stationary position, a behaviour termed as ‘reeling’. Reeling is paradoxical since it can lead to web deformation or damage, thereby jeopardising future foraging success. Reeling may lead to increased retention time for heavier prey or for information acquisition with respect to the prey's identity, especially when these prey can cause damage to either the web or the spider itself. We explored the function of reeling behaviour in a neotropical orb web spider Verrucosa arenata. We show that spiders performed reeling behaviour irrespective whether they were approaching heavy or light prey, but they changed their trajectories of approach. Spiders approached heavier prey slower than light prey and they showed significantly higher frequencies of changes in velocities. We discuss these findings in the context of prey capture strategies and prey recognition.

Solitary foraging ants rely on vision when travelling along routes and when pinpointing their nest. We tethered foragers of

Few walking insects possess simple eyes known as the ocelli. The role of the ocelli in walking insects such as ants has been less explored. Physiological and behavioural evidence in the desert ant, Cataglyphis bicolor, indicates that ocellar receptors are polarisation sensitive and are used to derive compass information from the pattern of polarised skylight. The ability to detect polarised skylight can also be inferred from the structure and the organisation of the ocellar retina. However, the functional anatomy of the desert ant ocelli has not been investigated. Here we characterised the anatomical organisation of the ocelli in three species of desert ants. The two congeneric species of Cataglyphis we studied had a fused rhabdom, but differed in their organisation of the retina. In Cataglyphis bicolor, each retinula cell contributed microvilli in one orientation enabling them to compare e-vector intensities. In Cataglyphis fortis, some retinula cells contributed microvilli in more than one orientation, indicating that not all cells are polarisation sensitive. The desert ant Melophorus bagoti had an unusual ocellar retina with a hexagonal or pentagonal rhabdomere arrangement forming an open rhabdom. Each retinula cell contributed microvilli in more than one orientation, making them unlikely to be polarisation detectors.

The eyes of most animals exhibit a trade-off between spatial resolving power and absolute sensitivity, which likely reflects functional adaptations for the animals' visual ecology. When animals operate in dim light conditions, the sensitivity of an eye needs to be increased because the signal-noise ratio of visual information is typically low, even though this potentially compromises spatial resolving power. Here, we investigated the spatial resolving power and contrast sensitivity in two congeneric ant species: the diurnal-crepuscular Myrmecia tarsata and the nocturnal Myrmecia midas using pattern electroretinography (PERG). Both ant species have a specialised zone in the medio-frontal region of the eye that has enlarged facets compared to the rest of the eye. Using the PERG technique, we found that spatial resolving power was 0.60 cycles per degree (cpd) in M. tarsata, while it was 0.57 cpd in M. midas. This variation in spatial resolving power is explained by differences in ommatidial facet diameters, which were significantly larger in the nocturnal M. midas. The contrast sensitivity reached a maximum of 15.5 at 0.1 cpd in M. tarsata and 21.2 at 0.05 cpd in M. midas. The contrast sensitivity functions did not differ significantly between the two species. In the diurnal-crepuscular M. tarsata, the specialised eye region with the largest facets provides both high spatial resolving power and contrast sensitivity making it an “acute zone”. In contrast, in the nocturnal M. midas the specialised eye region with the largest facets improves the eye's sensitivity, making it a “bright zone”. The increased sensitivity would be important under low luminance conditions and/or for discriminating objects of low contrast. We conclude that even closely related species active at different ambient light intensities have evolved different strategies to optimise their visual system to match their respective visual ecologies.

Vision is crucial for animals to find prey, locate conspecifics and navigate within cluttered landscapes. Animals need to discriminate objects against a visually noisy background. However, the ability to detect spatial information is limited by eye size. In insects, as individuals become smaller, the space available for the eyes reduces, which affects the number of ommatidia, the size of the lens and the downstream information-processing capabilities. The evolution of small body size in a lineage, known as miniaturisation, is common in insects. Here, using pattern electroretinography with vertical sinusoidal gratings as stimuli, we studied how miniaturisation affects spatial resolving power and contrast sensitivity in four diurnal ants that live in a similar environment but vary in their body and eye size. We found that ants with fewer and smaller ommatidial facets had lower spatial resolving power and contrast sensitivity. The spatial resolving power was maximum in the largest ant Myrmecia tarsata at 0.60 cycles deg−1 compared with that of the ant with smallest eyes Rhytidoponera inornata at 0.48 cycles deg−1. Maximum contrast sensitivity (minimum contrast threshold) in M. tarsata (2627 facets) was 15.51 (6.4% contrast detection threshold) at 0.1 cycles deg−1, while the smallest ant R. inornata (227 facets) had a maximum contrast sensitivity of 1.34 (74.1% contrast detection threshold) at 0.05 cycles deg−1. Miniaturisation thus dramatically decreases maximum contrast sensitivity and also reduces spatial resolution, which could have implications for visually guided behaviours. This is the first study to physiologically investigate contrast sensitivity in the context of insect allometry.

Fabry disease is an X-linked lysosomal storage disorder caused by pathogenic variants in GLA. It manifests in hemizygous males and in many heterozygous females. Cardiovascular and renal involvement are frequent. Adiponectin is a circulating hormone that has been linked to numerous disease conditions including heart and kidney failure. In the present pilot study, we investigated plasma adiponectin levels in a cohort of 56 individuals with a genetic diagnosis of Fabry disease. Adiponectin levels did not differ between patients and controls. However, in male patients, significantly decreased adiponectin levels were associated with cardiovascular manifestation, while increased levels were associated with renal involvement. Similar trends in female patients did not reach statistical significance. Lyso-Gb3, a metabolite with good diagnostic/screening performance, was not indicative of organ involvement. In combination, adiponectin and Lyso-Gb3 may be of value for identification and stratification of Fabry patients. A potential additional relevance for prognosis and monitoring should be addressed by future studies in larger cohorts.

Animals are active at different times of the day. Each temporal niche offers a unique light environment, which affects the quality of the available visual information. To access reliable visual signals in dim-light environments, insects have evolved several visual adaptations to enhance their optical sensitivity. The extent to which these adaptations reflect on the sensory processing and integration capabilities within the brain of a nocturnal insect is unknown. To address this, we analyzed brain organization in congeneric species of the Australian bull ant, Myrmecia, that rely predominantly on visual information and range from being strictly diurnal to strictly nocturnal. Weighing brains and optic lobes of seven Myrmecia species, showed that after controlling for body mass, the brain mass was not significantly different between diurnal and nocturnal ants. However, the optic lobe mass, after controlling for central brain mass, differed between day- and night-active ants. Detailed volumetric analyses showed that the nocturnal ants invested relatively less in the primary visual processing regions but relatively more in both the primary olfactory processing regions and in the integration centers of visual and olfactory sensory information. We discuss how the temporal niche occupied by each species may affect cognitive demands, thus shaping brain organization among insects active in dim-light conditions.

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Evolution of smaller body size in a given lineage, called miniaturisation, is commonly observed in many animals including ants. It affects various morphological features and is hypothesized to result in inferior behavioural capabilities, possibly owing to smaller sensory organs. To test this hypothesis, we studied whether reduced spatial resolution of compound eyes influences obstacle detection or obstacle avoidance in five different species of ants. We trained all ant species to travel to a sugar feeder. During their return journeys, we placed an obstacle close to the nest entrance. We found that ants with higher spatial resolution exited the corridor, the area covered between either ends of the obstacle, on average 10 cm earlier suggesting they detected the obstacle earlier in their path. Ants with the lowest spatial resolution changed their viewing directions only when they were close to the obstacle. We discuss the effects of miniaturisation on visual navigational competence in ants.