Biology subjects

Ioannou, C. C.

Publications and source records attributed to Ioannou, C. C..

At least 19 recordsLinked to original sources

bioRxiv2026

DigiFish: A flexible open-source tool for animating realistic virtual fish and reconstructing visual fields from tracking data

1. For many animals, vision represents the primary sensory modality governing a vast diversity of behaviours. Creating 'virtual twins', or visually realistic digital reconstructions of real individuals interacting within their environments, offers a promising approach for understanding how visual information guides an animal's decisions, behaviours, and interactions. Such systems enable the creation of video scenes from any view, including the viewpoint of the animals themselves. This allows receiver information to then be analysed from the perspective of species-specific visual systems, or for the accurate reconstruction of a real animal's movement to provide social stimuli for behavioural experiments. 2. Despite advances in 3D modelling, photorealistic scene rendering, and animal tracking, efficiently creating realistic digital reconstructions of movement remains challenging for many species. In fishes, a continuously-deforming body due to the absence of discrete joints make it particularly difficult to map tracked body keypoints onto articulated digital models, often resulting in unnatural or erratic animations. 3. Here, we introduce DigiFish, an add-on for the open-source animating software Blender, that generates realistic fish animations from tracking data. By integrating anatomical keypoint tracking with spline-based body curvatures, DigiFish reconstructs biologically-realistic swimming postures and movements of fishes within customisable virtual aquatic environments. The system also supports virtual 'point-of-view' cameras that can be placed arbitrarily within a scene, or dynamically driven by eye-tracking data, enabling unlimited perspectives on how individuals, conspecifics, or landmarks appear against complex backgrounds and how these views change with realistic swimming and eye movements. 4. We provide the Blender add-on and user guide and use DigiFish to reconstruct two different contexts: staged predator-prey interactions in the laboratory and natural schooling of wild fish in the field. Using a further reconstruction of fish swimming in an arena, we also use an Elementary Motion Detector model to show that our virtual reconstructions successfully capture perceptually-realistic movements and postures of individual fish within a digitally reconstructed scene. 5. By integrating photo-realistic scenes with biologically-realistic, simulated motion, DigiFish offers a flexible and accessible platform for investigating visually guided behaviour, perception, and cognition in complex and dynamic environments.

animal behavior and cognition↗

bioRxiv2026

Perceptual constraints of motion shape animal movement strategies

As animals explore their environment, self-generated motion can affect visual perception, while perceptual constraints shape movement decisions. Movement strategies should therefore balance the benefits of exploration against the potential perceptual costs of motion. Here, we test whether the movement strategies animals adopt can enhance information acquisition while accounting for the constraints that motion imposes on visual perception. We first quantified the visual perceptual abilities of freely moving fish in three dimensions by projecting virtual prey around three-spined sticklebacks (Gasterosteus aculeatus), determining how the likelihood of detecting prey varied across the fish's visual field as a function of their movement. Self-induced motion reduced the likelihood prey were detected, with increases in speed non-linearly reducing the perceptual abilities of the fish. Using agent-based simulations based on empirical models of visual perception, we demonstrate that when visual perception degrades non-linearly with speed, the strategy that maximizes prey detection is 'saltatory' locomotion, involving stationary pauses interspersed with movements. Moreover, experiments with freely swimming fish showed they adopted specific durations of stops and movements that improved prey detection given the way motion impacts their perception. Our results reveal that some movement strategies are more effective than others at gathering information during exploration.

animal behavior and cognition↗

bioRxiv2025

Visual lateralisation in female guppies demonstrates social conformity but is reduced when observing a live predator

Living in groups offers individuals a way of reducing their risk of predation. Visual lateralisation, characterised as an asymmetry in eye-use, may offer an additional advantage to group-living animals by enabling them to manage two concurrent visual tasks simultaneously. This could enhance multi-tasking efficiency by facilitating cohesion with group mates while monitoring for threats. In our study, we examined visual lateralisation of Trinidadian guppies (Poecilia reticulata) tested either alone or in groups, in either the presence or absence of a live predator, the blue acara (Andinoacara pulcher). We consistently observed low levels of visual lateralisation across all treatments. Contrary to our expectations, however, guppies exhibited significantly higher absolute lateralisation when tested alone in the absence of the predator compared to the other treatments. Moreover, a significant left-eye bias was observed when the predator was present, and the fish showed a right-eye bias when the predator was absent. Use of a repeated measures design and assessing individual and group ID as random effects provided evidence that both relative and absolute laterality were repeatable at the group level, but there was limited evidence for repeatability at the level of the individuals. This repeatability in lateralisation when tested as a group, but not when individual fish composing these groups were tested alone, suggests social conformity in lateralisation. Our results suggest that social processes may have a significant impact on within-population variation in lateralisation.

animal behavior and cognition↗

bioRxiv2025

Shoal cohesion and polarisation increase in turbid water and improve foraging performance

Group living can make animals more resilient or more susceptible to human-induced rapid environmental change, and whether animals demonstrate plasticity in their collective behaviour to mitigate the effects of environmental change is unknown. Freshwater and coastal habitats are becoming increasingly turbid as a result of human activity, which limits the availability of information and hence responses to critical stimuli such as food and predators. Here, we tested whether the well-documented improvement in foraging performance by larger groups is affected by moderate levels of water turbidity. Fish shoals were faster to attack the food stimulus in larger groups and slower in turbid water, effects which were independent of one another. However, shoals became more cohesive and coordinated (i.e. more polarised in direction) in turbid water, and this corresponded to more cohesive and polarised shoals being faster to attack the food stimulus in turbid water but slower in clear water. Our results demonstrate that fish shoals can increase cohesion and coordination in moderate levels of turbidity, that this plasticity improves their response to ecologically relevant ephemeral stimuli, and that collective behaviour, rather than group size, can mediate the response of groups to environmental change.

animal behavior and cognition↗

bioRxiv2025

Group personality, rather than acoustic noise, causes variation in group decision-making in guppy shoals

Group living has essential fitness benefits for many species. While numerous studies have explored how environmental conditions impact collective movement, their impact on decisions made in a social context--a central component of group-living--is poorly documented. In this study, we assess how acoustic noise impacts group decision-making, cohesion and activity in fish shoals, using Trinidadian guppies (Poecilia reticulata) as a model species. Movements within a radially symmetric five-armed maze were measured using high-resolution trajectory data from video-tracking software. The behaviour of groups with and without continuous acoustic white noise were measured over a four-day testing period in a repeated-measures design. We found no significant change in swimming speed or group cohesion with additional acoustic noise. However, there was evidence for fewer following events (moves into already occupied arms) in the noise treatment compared to the control, but this additional noise had no effect on leadership attempts (moves into empty arms). We found strong evidence for consistent, repeatable differences between groups in all behavioural parameters indicating strong personality variation at the group level. Rather than environmental factors, these results provide evidence that consistent group-level differences dominate variation in collective behaviour, including group decision-making, in fish shoals.

animal behavior and cognition↗

bioRxiv2024

Enhanced conspicuousness of prey in warmer water mitigates the visual constraint of turbidity for predators

O_LIChanges in environmental conditions impact predator-prey interactions by altering behaviour through sensory and non-sensory pathways. Elevated water temperature and turbidity are known to alter activity levels and anti-predator responses in prey fish, and are increasing globally as a result of anthropogenic activities. Less is known about how temperature and turbidity impact predators ability to detect prey directly, or indirectly via changes to prey behaviour. C_LIO_LIWe quantified the detectability of Trinidadian guppies (Poecilia reticulata) free-swimming in a large arena from the perspective of a stationary visual predator (simulated as an underwater camera). We used a fully factorial experimental design testing the independent and combined effects of increased temperature and turbidity. C_LIO_LIWe found that both stressors had a strong influence on the appearance of prey (objectively quantified as the mean magnitude of the optical flow in the videos). As expected, turbidity reduced the frequency of detection between the guppies and the simulated predator, i.e. the magnitude of optical flow exceeded the threshold for a detection event more often in clear water. Events were also shorter in duration in turbid water, reducing the time available for a predator to detect the prey. However, during an event, prey were more detectable in warmer water (i.e. the mean magnitude was greater). C_LIO_LIAlthough we found no evidence of interactive effects of turbidity and temperature on the response variables, their cumulative main effects suggest an antagonistic effect on the overall rate of prey capture. C_LI

animal behavior and cognition↗

bioRxiv2024

Does temperature, light or inter-individual variation explain feeding motivation in a tropical freshwater predator?

Variability in environmental conditions in freshwater ecosystems are increasingly driven by human activity. Increased temperature and light intensity are among the anthropogenic stressors dramatically altering these ecosystems, for example through deforestation that reduces canopy cover of riparian vegetation. Simultaneous exposure to multiple stressors complicates predictions of responses to environmental stressors due to potential interactions, yet the interaction between temperature and light intensity on feeding motivation remains poorly understood. Here, a fully factorial design was employed to investigate the combined effect of increased temperature and light intensity on the feeding motivation of a freshwater predator, the pike cichlid Saxatilia proteus. Strikes toward food items were used to quantify the subjects motivation to feed. We found no effect of temperature or light intensity on feeding motivation, either individually or as an interaction. Our repeated measures design allowed us to test whether the predatory fish showed personality variation, i.e. consistent inter-individual differences, in their motivation to feed. While the time taken to make the first strike was not consistently different between individuals, the number of strikes in 1 minute, 3 minutes and the time taken for the 10th strike (which were strongly correlated to one another), was consistently different between individuals. This variation could not be explained by variation in body length, which had no effect as a main effect. Variation between individuals is likely to be magnified in wild predators that are likely to vary more in experience and genetic background than the captive subjects in our study. Thus, we suggest that anthropogenic effects that alter the composition of individuals in a population of predators, for example selective harvesting, will have a greater ecological effect than direct short-term effects of variability in environmental factors.

ecology↗

bioRxiv2023

Temperature and turbidity interact synergistically to alter anti-predator behaviour in the Trinidadian guppy

Due to climate change, freshwater habitats are facing increasing temperatures and more extreme weather that disrupts water flow. Together with eutrophication and sedimentation from farming, quarrying and urbanisation, freshwaters are becoming more turbid as well as warmer. Predators and prey need to be able to respond to one another adaptively, yet how changes in temperature and turbidity interact to affect predator-prey behaviour remains unexplored. Using a fully factorial design, we tested the combined effects of increased temperature and turbidity on the behaviour of guppy shoals (Poecilia reticulata) in the presence of one of their natural cichlid predators, the blue acara (Andinoacara pulcher). Our results demonstrate that the prey and predator were in closest proximity in warmer, turbid water, with an interaction between these stressors showing a greater than additive effect. There was also an interaction between the stressors in the inter-individual distances between the prey, where shoal cohesion increased with temperature in clear water, but decreased when temperature increased in turbid water. The closer proximity to predators and reduction in shoaling in turbid, warmer water may increase the risk of predation for the guppy, suggesting that the combined effects of elevated temperature and turbidity may favour predators rather than prey.

animal behavior and cognition↗

bioRxiv2022

A novel method for investigating fish social behaviour in the field

Field studies of social behaviour are challenging due to having to observe multiple individuals simultaneously. In aquatic environments, these challenges are often amplified by environmental conditions such as habitat complexity, turbidity or darkness, which are often the conditions of interest in the context of studying anthropogenic impacts. Many fish species rely on social interactions for at least part of their life cycle, and while these interactions are known from laboratory studies to be impacted by environmental factors, approaches to quantify social behaviour under natural conditions are limited. Here, we present a novel method whereby multiple funnel traps are deployed simultaneously within a pond to quantify the aggregation and assortment of wild fish populations, using three-spine sticklebacks (Gasterosteus aculeatus) as a model species. The number of sticklebacks caught decreased in lower temperatures and through the seasons, from May to November. There was some evidence for decreases in fish numbers with reduced light intensity and higher dissolved oxygen levels. No effect of turbidity was found. The only evidence for changes in aggregation was related to the proportion of breeding males caught, where sticklebacks were less aggregated during the breeding season. These trends are expected based on previous work and knowledge about stickleback biology, validating the method. However, in contrast to previous studies, we found little evidence for phenotypic assortment. This study establishes a new cost-effective technique for investigating the social behaviour of wild fish, with some important benefits over existing techniques.

animal behavior and cognition↗

bioRxiv2022

Predatory fish preferentially target virtual prey with Levy motion rather than Brownian motion

Of widespread interest in animal behaviour and ecology is how animals search their environment for resources, and whether these search strategies are optimal. However, movement also affects predation risk through effects on encounter rates, the conspicuousness of prey, and the success of attacks. Here we use predatory fish attacking a simulation of virtual prey to test whether predation risk is associated with movement behaviour. Despite often being demonstrated to be a more efficient strategy for finding resources, we find that prey displaying Levy motion are twice as likely to be targeted by predators than prey utilising Brownian motion. This result emphasises that costs of predation risk need to be considered alongside the foraging benefits when comparing different movement strategies.

animal behavior and cognition↗

bioRxiv2022

Personality variation is eroded by simple social behaviours in collective foragers

The movement of groups can be heavily influenced by leader individuals who differ from the others in some way. A major source of differences between individuals is the repeatability and consistency of their behaviour, commonly considered as their personality, which can influence both position within a group as well as the tendency to lead. However, links between personality and behaviour may also depend upon the immediate social environment of the individual; individuals who behave consistently in one way when alone may not express the same behaviour socially, when they may be conforming with the behaviour of others. Experimental evidence shows that personality differences can be eroded in social situations, but there is currently a lack of theory to identify the conditions where we would expect personality to be suppressed. Here, we develop a simple individual-based framework considering a small group of individuals with differing tendencies to perform risky behaviours when travelling away from a safe home site towards a foraging site, and compare the group behaviours when the individuals follow differing rules for aggregation behaviour determining how much attention they pay to the actions of their fellow group-members. We find that if individuals pay attention to the other members of the group, the group will tend to remain at the safe site for longer, but then travel faster towards the foraging site. This demonstrates that simple social behaviours can result in the repression of consistent inter-individual differences in behaviour, giving the first theoretical consideration of the social mechanisms behind personality suppression.

animal behavior and cognition↗

bioRxiv2021

The measure of spatial position within groups that best predicts predation risk depends on group movement

Both empirical and theoretical studies show that an individuals spatial position within a group can impact the risk of being targeted by predators. Spatial positions can be quantified in numerous ways, but there are no direct comparisons of different spatial measures in predicting the risk of being targeted by real predators. Here we assess these spatial measures in groups of stationary and moving virtual prey being attacked by three-spined sticklebacks (Gasterosteus aculeatus). In stationary groups, the limited domain of danger best predicted the likelihood of attack. In moving groups, the number of near neighbours was the best predictor but only over a limited range of distances within which other prey were counted. Otherwise, measures of proximity to the groups edge outperformed measures of local crowding in moving groups. There was no evidence that predators preferentially attacked the front or back of the moving groups. Domains of danger without any limit, as originally used in the selfish herd model, were also a poor predictor of risk. These findings reveal that the collective properties of prey can influence how spatial position affects predation risk, via effects on predators targeting, hence selection may act differently on prey positioning behaviour depending on group movement.

animal behavior and cognition↗

bioRxiv2021

Responsive robotic prey reveal how predators adapt to predictability in escape tactics

To increase their chances of survival, prey often respond to predators by being unpredictable when escaping, but the response of predators to such tactics is unknown. We programmed interactive robot-controlled prey to flee from an approaching blue acara predator (Andinoacara pulcher), allowing us to manipulate the predictability of the preys initial escape direction. When repeatedly exposed to predictable prey, the predators adjusted their behaviour before the prey even began to escape: prey programmed to escape directly away were approached more rapidly than prey escaping at an acute angle. These faster approach speeds compensated for a longer time needed to capture such prey during the subsequent pursuit phase, and predators showed greater acceleration when pursuing unpredictable prey. Collectively, these behaviours resulted in the preys predictability having no net effect on the time to capture prey. Rather than minimising capture times, predators adjust their behaviour to maintain an adequate level of performance.

animal behavior and cognition↗

bioRxiv2021

Emergence of variation between groups through time in fish shoal collective motion

Despite extensive interest in the dynamic interactions between individuals that drive collective motion in animal groups, the dynamics of collective motion over longer time frames are understudied. Using three-spined sticklebacks, Gasterosteus aculateus, randomly assigned to twelve shoals of eight fish, we tested how six key traits of collective motion changed over shorter (within trials) and longer (between days) timescales under controlled laboratory conditions. Over both timescales, groups became less social with reduced cohesion, polarisation, group speed and information transfer. There was consistent inter-group variation (i.e. collective personality variation) for all collective motion parameters, but groups also differed in how their collective motion changed over days in their cohesion, polarisation, group speed and information transfer. This magnified differences between groups, suggesting that over time the typical collective motion cannot be easily characterised. The minimal sample size of independent groups and their divergence over time need to be considered in future studies.

animal behavior and cognition↗

bioRxiv2020

Fish avoid visually noisy environments that reduce their perceptual abilities

The environment contains different forms of ecological noise that can reduce the ability of animals to detect information. Here we ask whether animals can adapt their behaviour to either exploit or avoid areas of their environment with increased dynamic visual noise. By immersing three-spined sticklebacks (Gasterosteus aculeatus) into environments with a simulated form of naturally occurring visual noise - light bands created by the refraction of light from surface waves termed caustic networks - we tested how such visual noise affected the movements, habitat use, and perceptual abilities of these fish. Fish avoided areas of higher visual noise, and achieved this by increasing their activity as a function of the locally perceived noise level, resulting in individuals moving away from noisier areas. By projecting virtual prey into the environment with different levels of visual noise, we found that the fishs ability to visually detect prey decreased as visual noise increased. We found no evidence that fish increased their exploration (and decreased their refuge use) in environments with increased visual noise, which would have been predicted if they were exploiting increased visual noise to reduce their own likelihood of being detected. Our results indicate that animals can use simple behavioural strategies to mitigate the impacts of dynamic visual noise on their perceptual abilities, thereby improving their likelihood of gathering information in dynamically changing and noisy environments.

animal behavior and cognition↗

bioRxiv2020

Accurate and interpretable prediction of poor health in small ruminants with accelerometers and machine learning

Assessment of the health status of individual animals is a key step in the timely and targeted treatment of infections, which is critical in the fight against anthelmintic and antimicrobial resistance. The FAMACHA scoring system has been used successfully to detect anaemia caused by infection with the parasitic nematode Haemonchus contortus in small ruminants and is an effective way to identify individuals in need of treatment. However, assessing FAMACHA is labour-intensive and costly as individuals must be manually examined at frequent intervals. Here, we used accelerometers to measure the individual activity of extensively grazing small ruminants (sheep and goats) exposed to natural Haemonchus contortus worm infection in southern Africa over long time scales (13+ months). When combined with machine learning, this activity data can predict poorer health (increases in FAMACHA score), as well as those individuals that respond to treatment, all with precision up to 83%. We demonstrate that these classifiers remain robust over time. Interpretation of trained classifiers reveals that poorer health significantly affects the night-time activity levels in the sheep. Our study thus reveals behavioural patterns across two small ruminant species, which lowcost biologgers can exploit to detect subtle changes in animal health and enable timely and targeted intervention. This has real potential to improve economic outcomes and animal welfare as well as limit the use of anthelmintic drugs and diminish pressures on anthelmintic resistance in both commercial and resource-poor communal farming.

animal behavior and cognition↗

bioRxiv2020

The impact of turbidity on foraging and risk taking in the invasive Nile tilapia (Oreochromis niloticus) and a threatened native cichlid (Oreochromis amphimelas)

Anthropogenic activity can increase water turbidity, changing fish behaviour by reducing visibility. The spread of invasive species is also facilitated by human activity, further increasing the pressure on native species. In two experiments we measured the foraging efficiency, risk perception and inter-individual consistency of risk-taking (personality variation in boldness) of an invasive species, the Nile tilapia (Oreochromis niloticus), and a threatened tilapia, the Manyara tilapia (Oreochromis amphimelas), in clear and turbid water. In experiment one, O. niloticus was faster to initiate feeding, encountered more food items, and consumed more than O. amphimelas. The latency to start foraging by O. niloticus decreased in turbid water. Turbidity did not affect the latency to start foraging in O. amphimelas but the number of food items they encountered was highest at the intermediate turbidity. There was however no significant effect of turbidity in either species on the total food consumed. In contrast to this foraging context, in experiment two with a refuge and no food available, risk taking behaviour was similar in both species and they both responded with similarly reduced risk taking in turbid water. Evidence of personality variation was weak, being observed only in O. amphimelas when first leaving the shelter in turbid water. Overall, species differences were greater in the foraging context but turbidity was more important in the risk-taking context. O. amphimelas is more sensitive to turbidity during foraging, and O. niloticus is likely to have a competitive advantage in foraging situations, especially in degraded turbid habitats. Significance StatementUnder human-induced environmental change, native species are often exposed to multiple stressors. Here we tested the responses of two cichlid fish to increasing turbidity. The Nile tilapia (Oreochromis niloticus), which is invasive throughout the tropics, and the Manyara tilapia (Oreochromis amphimelas), a threatened species, indigenous to Tanzania. We found that turbidity was beneficial to the foraging of O. niloticus, which in both clear and turbid water consumed and encountered more food than O. amphimelas. In contrast, without food present, both species displayed similar responses of increased risk perception in turbid water with little evidence of personality variation between individuals in either species. Our results suggest that invasive species tolerant of degraded habitats may outcompete less well adapted native species for food.

animal behavior and cognition↗

bioRxiv2020

State-behavior feedbacks suppress personality variation in boldness during foraging in sticklebacks

Consistent inter-individual variation within a population, widely referred to as personality variation, can be affected by environmental context. Feedbacks between an individuals personality and state can strengthen (positive feedback) or weaken (negative feedback) individual differences when experiences such as predator encounters or winning contests are dependent on personality type. We examined the influence of foraging on individual-level consistency in refuge use (a measure of risk-taking, i.e. boldness) in three-spined sticklebacks, Gasterosteus aculeatus, and particularly whether changes in refuge use depended on boldness measured under control conditions. In the control treatment trials with no food, individuals were repeatable in refuge use across repeated trials, and this behavioral consistency did not differ between the start and end of these trials. In contrast, when food was available, individuals showed a higher degree of consistency in refuge use at the start of the trials versus controls but this consistency significantly reduced by the end of the trials. The effect of the opportunity to forage was dependent on personality, with bolder fish varying more in their refuge use between the start and the end of the feeding trials than shyer fish. This suggests a state-behavior feedback, but there was no overall trend in how individuals changed their behavior, with some individuals spending more, and others less, time in the refuge area at the end than at the start of the trials. Our study shows that personality variation can be suppressed in foraging contexts and a potential but unpredictable role of feedbacks between state and behavior.

animal behavior and cognition↗