Biology subjects

Burt de Perera, T.

Publications and source records attributed to Burt de Perera, T..

9 recordsLinked to original sources

bioRxiv2024

A sensory approach to turbidity: How sources and levels shape aquatic light environments and fish visual ecology

Turbidity is a ubiquitous source of sensory pollution that is likely to impact the appearance of the visual stimuli that animals rely on for survival and reproduction. Understanding how different turbidity sources impact the appearance of the ambient light environment is the foundational first step towards predicting whether and how animals will cope with the global increases in the severity and frequency of high turbidity events caused by anthropogenic disturbance. Here, we measured how four common turbidity sources (algae, bentonite, calcium carbonate, and kaolin), and variable turbidity levels, changed the appearance of the ambient light environment. We measured total number of photons (luminance), hue, chroma, and image contrast, and we evaluated the effect of each turbidity source and level on settling rate, pH, and KH. Both turbidity source and turbidity level impacted the appearance of the ambient light environment. With increasing turbidity level, calcium carbonate and kaolin increased luminance while algae decreased luminance, bentonite caused the greatest change in hue, and algae caused the greatest change in chroma. This demonstrates that the impacts of different turbidity sources on the ambient light environment are not uniform, giving a potential explanation for the discrepancies between studies on the effects of turbidity on fish behaviour. Consideration of the effect of specific turbidity sources on ambient light is crucial for the design of experiments that seek to investigate how changes in turbidity impact the perception of important visual information, which underpins the survival and reproductive success of aquatic organisms around the world. Summary StatementDifferent turbidity sources and levels uniquely affect aquatic light environments and fish visual perception, emphasizing the need for these factors when interpreting fish behaviour and the ecological consequences of turbidity.

animal behavior and cognition↗

bioRxiv2024

Evidence for homing behaviour consistent with path integration in Dascyllus trimaculatus

Path integration is a strategy that allows animals to monitor their movement relative to a starting point using directional and distance cues. It has been observed in a wide range of terrestrial species, but evidence of this behaviour in fish is still lacking. In contrast to most animals shown to navigate via path integration, fish are not surface bound but exist within a three-dimensional medium. This may present additional challenges when monitoring their position relative to a specific point. We developed a novel experimental paradigm to test whether the coral reef-dwelling domino damselfish Dascyllus trimaculatus could use path integration to navigate back to a shelter location. This consisted of a circular pool with a shelter and landmarks near the edge and a trap containing food in the centre. Our results show that these fish follow homing trajectories back to the previous location of the removed shelter without using landmarks after a foraging trip into the central trap. Error in homing trajectory increased with outward path length, consistent with the use of path integration. These results add D. trimaculatus to the growing list of path-integrating species, opening new avenues for investigating the evolution and neural underpinnings of this navigational strategy.

animal behavior and cognition↗

bioRxiv2022

Weakly electric fish use self-generated motion to discriminate object shape

Body movements are known to play an active role in sensing. However, it is not fully understood what information is provided by these movements. The Peters elephantnose fish, Gnathonemus petersii sense their environment through active electrolocation during which they use epidermal electroreceptors to perceive object-induced distortions of a self-produced electric field. The analysis of electric images projected on their skin enables them to discriminate between three-dimensional objects. While we know the electric image parameters used to encode numerous object properties, we dont understand how these images encode object shape. We hypothesise that movement-induced modulations (MIMs) evoked by body movements might be involved in shape discrimination during active electrolocation. To test this, we trained fish to complete a shape discrimination task in a two-alternative forced-choice setup, and then manipulated the space available to individuals for scanning movements to see if this led to a change in their discrimination performance. We found that if enough space was available, fish were very good at discriminating objects of different shapes. However, performance decreased strongly when the space was reduced so that scanning movements were impaired. Our study demonstrates the importance of body movements for gaining complex environmental information such as object shape through active electrolocation. Movement can enhance perception by allowing the extraction of certain kinds of information. Similar observations have been made in other animals using different senses, suggesting that the core principles of sensory-motor integration might be valid for various sensory modalities.

zoology↗

bioRxiv2022

The influence of visual pollution on navigation mechanisms in the damselfish (Chrysiptera cyanea)

Here, we investigate whether visual pollution has an effect on navigation in coral reef damselfish (Chrysiptera cyanea). Turbidity had no significant influence on the individual fishs preference between egocentric and visual cues in a simple navigation task, with all individuals exhibiting a striking egocentric preference across all turbidity levels under testing. However, an alteration of cue preference may have occurred on a fine scale. Turbidity had profound effects on fish movement and decision-making behaviour, which has substantial implications for the behaviour of fishes on the ecological scale of a coral reef.

animal behavior and cognition↗

bioRxiv2022

Decision-making strategies of a coral reef fish given changing visual signal reliability

Making informed decisions is fundamental to intelligent life and is crucial to survival. The problem many organisms face, is how to make optimal decisions in the face of incomplete, unreliable, or conflicting information. In many aquatic environments, fish use visual information to guide key behaviours, but the environment itself can alter or mask the very signals they rely on. Here, we asked how a highly visual species, Rhinecanthus aculeatus, responds to a learned discrimination task as signal reliability decreases, and whether probabilistic information gained during previous experience can be incorporated into their decision strategy. Fish were first trained to select a target (dark grey circle) from three distractors (light grey circles). In the first experiment, the target was more likely to appear in one of four possible stimulus positions. In the second experiment, the target appeared in all positions equally. In a series of trials, the difference in brightness between the target and distractors was reduced until all four stimuli were identical. We found that target selection accuracy decreased with decreasing target and distractor disparity. However, in Experiment 1 where the target was more likely to be in one position, fish increasingly selected stimuli in the biased position as target selection accuracy decreased, but not in Experiment 2. These results demonstrate 1) that fish learned more than a simple select/avoid rule based on stimulus brightness, but also integrated information (stimulus position) that could be considered ancillary to the primary task. 2) Fish can learn probability distributions and apply this knowledge as uncertainty increases, ultimately increasing the overall frequency of correct choices. Our results reveal that probabilistic decision rules can be used by fish when visual information is unreliable, indicating a possible mechanism for decision making given the inherent noise in incoming sensory information.

animal behavior and cognition↗

bioRxiv2022

Distance estimation in the Goldfish (Carassius auratus)

Neurophysiological advances have given us exciting insights into the systems responsible for spatial mapping in mammals. However, we are still lacking information on the evolution of these systems and whether the underlying mechanisms identified are universal across phyla, or specific to the species studied. Here we address these questions by exploring whether a species that is evolutionarily distant from mammals can perform a task central to mammalian spatial mapping - distance estimation. We developed a behavioural paradigm allowing us to test whether goldfish (Carassius auratus) can estimate distance and explored the behavioural mechanisms that underpin this ability. Fish were trained to swim a set distance within a narrow tank covered with striped pattern. After changing the background pattern, we found that goldfish use the spatial frequency of their visual environment to estimate distance; doubling the spatial frequency of optic flow pattern resulted in a large overestimation of the swimming distance. These results provide robust evidence that goldfish can accurately estimate distance, and show that they use optic flow to do so. These results provide a compelling basis to utilise goldfish as a model system to interrogate the evolution of the mechanisms that underpin spatial cognition, from brain to behaviour.

animal behavior and cognition↗

bioRxiv2019

A new method for measuring fish swimming patterns in shallow water and a previously undescribed swimming gait

Hill stream loaches are fish which live their entire lives in close contact with rock. They have elaborate physical adaptations to fast flow, adherence to substrate, and movement in very shallow water. Here we describe a method for observing how they swim in detail. There are many similarly shaped rheophilic fish, insects, and amphibian larvae, which live in fast flowing water, and a method of observing their swimming modes has wide potential application. We measured the deflection of the water surface around a swimming fish by viewing a fixed pattern on the bottom of the tank through the water surface. This is a Schlieren method in which the movement or other physical properties of a medium are derived from the deflection of a pattern viewed through that medium. We used this method to describe a new type of swimming gait which is likely to be common among small rheophiles - pulse swimming mode - in which thrust is produced in a series of discrete impulses. The method of analysis described here is beneficial in that the fish is allowed to swim freely in relatively normal conditions without the use of intrusive equipment such as lasers, dyes, or additives to the water, and the pattern of thrust is viewed directly against the skin of the fish rather than being inferred from the wake pattern behind the fish. The method is also low cost and easily set up.

zoology↗

bioRxiv2019

The structure and function of the sucker systems of hill stream loaches

Hill stream loaches (family Balitoridae and Gastromyzontidae) are thumb-sized fish that effortlessly exploit environments where flow rates are so high that potential competitors would be washed away. To cope with these extreme flow rates hill stream loaches have evolved adaptations to stick to the bottom, equivalent to the downforce generating wings and skirts of F1 racing cars, and scale architecture reminiscent of the drag-reducing riblets of Mako sharks. Hill stream loaches exhibit far more diverse flow-modifying morphological features than fast pelagic predators, suggesting as yet unknown drag reducing systems remain to be discovered. Here we describe the skeletal structure of Sewellia lineolata and Gastromyzon punctulatus and contrast that with other fish that face similar hydrodynamic challenges. We identify a major structural variation within Balitoridae pelvic sucker attachment positions which may explain fundamental constraints on the parallel development of different genera and which has not been described before. We also use high speed video capture, CT scans and Frustrated Total Internal Reflection to image and measure the sucker system in live operation and describe how it functions on a familiar activity for hill stream loaches (climbing waterfalls). We show how they can drag 3 to 4 times their own bodyweight up a vertical glass waterfall. Adaptations to high flow rates are the inspiration for this study, because there are many engineering applications where the ability to deal with high flow rates are important - either by reducing drag, or by generating the forces needed to hold an animal in place.

zoology↗

bioRxiv2019

Teleost fish can accurately estimate distance travelled

Terrestrial animals compute shortcuts through their environment by integrating self-motion vectors containing distance and direction information. The sensory and neural mechanisms underlying this navigational feat have been extensively documented, but their evolutionary origins remain unexplored. Among extant vertebrates, the teleost fish make up one of the most diverse and earliest-branching phylogenetic groups, and provide a powerful system to study the origins of vertebrate spatial processing. However, how freely-swimming teleost fish collect and compute metric spatial information underwater are unknown. Using the Picasso triggerfish, Rhinecanthus aculeatus, we investigate the functional and mechanistic basis of distance estimation in teleost fish for the first time. We show that a fish can learn and remember distance travelled with remarkable accuracy. By analysing swimming trajectories, we form hypotheses about how distance is represented in the teleost brain, and propose that distance may be encoded by dedicated neural structures in a similar way to terrestrial vertebrates. Finally, we begin exploring the sensory mechanisms underlying distance estimation in fish. Many walking animals use a step counter for odometry. By quantifying finbeat use during our distance task, we show that a functionally equivalent finbeat counter is unlikely to provide reliable and precise distance information in an aquatic environment.

animal behavior and cognition↗