Cleaner fish recognize self in a mirror via self-face recognition like humans

The influence of sleep disruption on learning and memory in fish

Sleep is a ubiquitous process that has been conserved in animals. Yet, our understanding of the functions of sleep largely derives from a few species. Sleep is considered to play an important role in mental processes, including learning and memory consolidation, but how widespread this relationship is across taxa remains unclear. Here, we test the impact of sleep disruption on the ability of the cleaner fish (Labroides dimidiatus) to both learn and remember a novel cognitive task. Sleep was disrupted by exposing a subset of fish to light at set intervals during the night. We found a significant negative relationship between sleep disruption and the ability to learn a novel task. Specifically, we found that fish in the light-disturbed sleep treatment took significantly longer and made more incorrect decisions to find a food reward, compared with the undisturbed sleep treatment. All fish were then allowed a normal sleep schedule and retested several days later to assess their ability to remember the task. In contrast to the learning phase, we observed no significant differences between the two treatment groups in remembering the food reward several days later. Our results demonstrate a negative impact of sleep disruption on performance in a cognitive challenging task that appeared to have the strongest effect when fish were first exposed to the challenge. Importantly, we show that the association between sleep and mental processes, such as learning, may be widespread across vertebrate taxa and potentially have an early origin in the evolutionary history of vertebrate animals.

Client reef fish prefer more blue-saturated cleaner wrasses Labroides dimidiatus

In interspecific signalling, vivid colours have been interpreted to enable species recognition and maximise signal detection. Recently, it has been shown that vivid colours can also convey information on individual fitness, which could be advantageous for receivers. In the marine cleaning mutualism between the Indo-Pacific bluestreak cleaner wrasse (Labroides dimidiatus) and their reef fish visitors (known as clients), the colour of cleaners may provide behavioural cues, which clients could use to make decisions, as higher blue saturations are associated with better cleaning services. Here, we asked whether clients perceived differences in blue saturation when evaluating individual cleaners, and whether they used this information to choose them. To do this, we introduced the client threadfin butterflyfish (Chaetodon auriga) to three differently saturated video sequences of cleaners (minimum saturation, control and maximum saturation). We found that clients actively preferred video sequences of more saturated cleaners when played against lower saturations (i.e. spending more time in the preference area, facing more frequently and for longer periods, and entering the preference areas near the more saturated monitors more frequently), which provided more evidence that the blue colouration of cleaners may be a true signal of individual quality. By being able to distinguish these saturations, it is likely that in the wild, clients use this signal to make decisions and select the cleaners that provide a better cleaning service.

Evaluating animal consciousness

An emerging field shows how animal feelings can be studied scientifically.

Self-face processing in relation to self-referential tasks in 24-month-old infants: A study through eye movements and pupillometry measures

The aim of the current study was to investigate visual scan patterns for the self-face in infants with the ability to recognize themselves with a photograph. 24-month-old infants (N = 32) were presented with faces including the self-face in the upright or inverted orientation. We also measured infants' ability to recognize oneself in a mirror and with a photograph. Results showed that only in trials with the self-face was pupil dilation greater in the upright orientation than in the inverted orientation, and that eye movements and pupil dilation were not associated with PSR tasks. Our findings suggest that the processing of the self-face was processed in a manner similar to that of others, with longer and more fixations on eyes and nose, but infants allocated more attentional resources to processing upright self-face. Self-face processing in infancy may be independent of the understanding of the self beyond the here and now.

The ability of teleost fishes to recognize individual faces suggests an early evolutionary origin in vertebrates

The face is the most important area on the human body for visually differentiating between individuals. When encountering another person, humans initially gaze at and perceive the face holistically, utilizing first-order relational information and specific neural systems. Information such as identity and emotional state are then obtained from the face by distinguishing between small inter-individual differences, i.e., second-order relational information. Similar patterns and mechanisms underlying individual face recognition have been documented in primates, other social mammals, birds, and more recently in some fishes. Like humans, fish are capable of rapidly (<0.5 s) and accurately recognizing multiple familiar conspecifics by individual-specific variation in the face. Fish can also recognize faces from various distances and angles, providing evidence for mental representation of faces in this large and diverse vertebrate group. One species, the cleaner fish, has even demonstrated mirror self-recognition (MSR) via self-face recognition, strengthening the claim that non-human animals are capable of having mental images and concepts of faces. Here, we review the evidence for individual face recognition in fishes and speculate that face identification neural networks are both similar and widespread across vertebrates. Furthermore, we hypothesize that first-and second-order face recognition in vertebrates originated in bony fishes in the Paleozoic era ~450 Mya, when social systems first evolved, increasing the importance of individual recognition.

Using an Automated Operant Conditioning Procedure to Test Colour Discrimination in Two Juvenile Piranhas, Pygocentrus nattereri: A Lesson on Failures and Pitfalls and How to Avoid Them

Most studies on the cognitive abilities of fish have focused on model organisms adopted in behavioural neuroscience. To date, little attention has been devoted to characiformes fish and we record a lack of cognitive investigation on the piranha. In this study, we conducted a preliminary set of experiments to assess whether red-bellied piranhas (Pygocentrus nattereri) can solve an automated operant conditioning task, specifically, a reversal learning task. In Experiment 1, the fish were required to discriminate between red and green, while in Experiment 2, they had to discriminate between white and yellow. In either case, we found no evidence of learning capacities with our protocol after extensive training exceeding one thousand trials overall. In Experiment 3, we simplified the learning task by using achromatic stimuli (black and white discrimination) and always presenting the reinforced stimulus on the same side of the tank (a combination of response learning and place learning). Subjects did learn how to discriminate between the colours, although no subject was able to reach the criterion in the subsequent reversal learning task, suggesting that piranhas may be limited in their cognitive flexibility. However, our training procedure may have been inefficient in addressing this issue. We outline some potential limitations of the current methodology to help to establish a more effective approach for investigating operant conditioning in this species.

Cleaner fish with mirror self-recognition capacity precisely realize their body size based on their mental image

Animals exhibiting mirror self-recognition (MSR) are considered self-aware; however, studies on their level of self-awareness remain inconclusive. Recent research has indicated the potential for cleaner fish (Labroides dimidiatus) to possess a sophisticated level of private self-awareness. However, as this study revealed only an aspect of private self-awareness, further investigation into other elements is essential to substantiate this hypothesis. Here, we show that cleaner fish, having attained MSR, construct a mental image of their bodies by investigating their ability to recall body size. A size-based hierarchy governs the outcomes of their confrontations. The mirror-naïve fish behaved aggressively when presented with photographs of two unfamiliar conspecifics that were 10% larger and 10% smaller than their body sizes. After passing the MSR test, they refrained from aggression toward the larger photographs but still behaved aggressively toward the smaller ones without re-examining their mirror images. These findings suggest that cleaner fish accurately recognize their body size based on mental images of their bodies formed through MSR. Additionally, mirror-experienced fish frequently revisited the mirror when presented with an intimidating larger photograph, implying the potential use of mirrors for assessing body size. Our study established cleaner fish as the first non-human animal to be demonstrated to possess private self-awareness.

Minimizing the time to evaluate pheromone-mediated reduction of aggressive behavior in Mozambique tilapia (Oreochromis mossambicus)

Some cichlid fishes release urine-containing chemical cues that lower aggression in their opponents. Bioassays to identify the aggression-modulating pheromone include assessing the effect of urine fractions on the behavior towards a mirror image or in interactions with another male. However, many of these methods can be time-consuming and require many fish. The objective of the present study was to assess the behavior of male Mozambique tilapia (Oreochromis mossambicus) towards male urine using two methods with the intent of simplifying the bioassays: aggression towards a mirror image (mirror assay) and real opponents in which the urogenital papilla was tied using surgical silk to prevent urination. The results confirm the aggression-reducing effect of dominant male urine in both experimental approaches. Ten minutes of biting or 15 min of tail-beating behaviors in the mirror assay, or 5 min of opercular expansion or 15 min of lateral display in interactions with real opponents were necessary to detect a statistically significant reduction in aggressive behavior towards dominant male urine. We also found that males with subordinate status had lower latency to initiate aggressive behaviors towards the mirror than dominants in the same condition, even though fish had been isolated for 1 week. However, no such differences in latency were found in the real opponent assay. We conclude that 5 min of opercular expansion behavior in real opponent fights or 10 min of biting behavior in the mirror assay are the shortest times necessary to test aggressive behavior in urine fractions in bioassay-guided identification of pheromones.

Ghost crab (Ocypode quadrata) modify their behavior during mirror exposure

Recently, ghost crabs (Ocypode quadrata) were shown to exhibit behavior consistent with passing the mark test, which implies the capacity for self-recognition. Considering this, it seems reasonable to suggest these animals can also distinguish their mirror image from different social stimuli, such as live conspecifics. In the current research, ghost crabs were placed in an experimental tank bisected by a mirror, clear partition separating a conspecific, and non-reflective partition on separate trials. Aggressive threat displays, time spent near partitions, eye cleaning, and partition contact were recorded during each condition. Results showed more aggression in trials with a conspecific present (i.e. clear partition), though this effect was only marginally significant. In addition, eye cleaning was significantly lower in the clear, compared to mirror and non-reflective treatments. Significantly more contact occurred with non-reflective partitions and time near each barrier was similar. These findings might suggest the capacity to distinguish mirror reflections from conspecifics, and mirror self-recognition could promote such ability. This, and other alternatives, are discussed as potential explanations for the observed effects.

Correlation between bioluminescent blinks and swimming behavior in the splitfin flashlight fish Anomalops katoptron

BACKGROUND

The light organs of the splitfin flashlight fish Anomalops katoptron are necessary for schooling behavior, to determine nearest neighbor distance, and to feed on zooplankton under dim light conditions. Each behavior is coupled to context-dependent blink frequencies and can be regulated via mechanical occlusion of light organs. During shoaling in the laboratory individuals show moderate blink frequencies around 100 blinks per minute. In this study, we correlated bioluminescent blinks with the spatio-temporal dynamics of swimming profiles in three dimensions, using a stereoscopic, infrared camera system.

RESULTS

Groups of flashlight fish showed intermediate levels of polarization and distances to the group centroid. Individuals showed higher swimming speeds and curved swimming profiles during light organ occlusion. The largest changes in swimming direction occurred when darkening the light organs. Before A. katoptron exposed light organs again, they adapted a nearly straight movement direction.

CONCLUSIONS

We conclude that a change in movement direction coupled to light organ occlusion in A. katoptron is an important behavioral trait in shoaling of flashlight fish.

Beyond the mark: Signatures of self-recognition in fish

A new study with cleaner fish demonstrates the need to expand cognitive testing of animals beyond success testing (a simple pass or fail criteria), and instead investigate the signatures of how animals solve tasks. By tailoring traditional cognitive tests to the focal species' natural behaviour, researchers can provide animals with a better chance for demonstrating their cognitive abilities, offering a more comprehensive understanding of the evolution of cognition.

Evolution of Consciousness

The natural evolution of consciousness in different animal species mandates that conscious experiences are causally potent in order to confer any advantage in the struggle for survival. Any endeavor to construct a physical theory of consciousness based on emergence within the framework of classical physics, however, leads to causally impotent conscious experiences in direct contradiction to evolutionary theory since epiphenomenal consciousness cannot evolve through natural selection. Here, we review recent theoretical advances in describing sentience and free will as fundamental aspects of reality granted by quantum physical laws. Modern quantum information theory considers quantum states as a physical resource that endows quantum systems with the capacity to perform physical tasks that are classically impossible. Reductive identification of conscious experiences with the quantum information comprised in quantum brain states allows for causally potent consciousness that is capable of performing genuine choices for future courses of physical action. The consequent evolution of brain cortical networks contributes to increased computational power, memory capacity, and cognitive intelligence of the living organisms.

Roosters do not warn the bird in the mirror: The cognitive ecology of mirror self-recognition

Touching a mark on the own body when seeing this mark in a mirror is regarded as a correlate of self-awareness and seems confined to great apes and a few further species. However, this paradigm often produces false-negative results and possibly dichotomizes a gradual evolutionary transition of self-recognition. We hypothesized that this ability is more widespread if ecologically tested and developed such a procedure for a most unlikely candidate: chickens (Gallus gallus domesticus). Roosters warn conspecifics when seeing an aerial predator, but not when alone. Exploiting this natural behavior, we tested individual roosters alone, with another male, or with a mirror while a hawk's silhouette flew above them. Roosters mainly emitted alarm calls in the presence of another individual but not when alone or seeing themselves in the mirror. In contrast, our birds failed the classic mirror test. Thus, chickens possibly recognize their reflection as their own, strikingly showing how much cognition is ecologically embedded.

Gene losses, parallel evolution and heightened expression confer adaptations to dedicated cleaning behaviour

BACKGROUND

Cleaning symbioses are captivating interspecific interactions in which a cleaner fish removes ectoparasites from its client, contributing to the health and diversity of natural fish communities and aquaculture systems. However, the genetic signatures underlying this specialized behaviour remain poorly explored. To shed light on this, we generated a high-quality chromosome-scale genome of the bluestreak cleaner wrasse Labroides dimidiatus, a dedicated cleaner with cleaning as primary feeding mechanism throughout its life.

RESULTS

Compared with facultative and non-cleaner wrasses, L. dimidiatus was found with notable contractions in olfactory receptors implying their limited importance in dedicated cleaning. Instead, given its distinct tactile pre-conflict strategies, L. dimidiatus may rely more heavily on touch sensory perception, with heightened gene expression in the brain in anticipation of cleaning. Additionally, a reduction in NLR family CARD domain-containing protein 3 might enhance innate immunity of L. dimidiatus, probably assisting to reduce the impacts from parasite infections. In addition, convergent substitutions for a taste receptor and bone development genes across cleaners (L. dimidiatus and facultative cleaners) may provide them with evolved food discrimination abilities and jaw morphology that differentiate them from non-cleaners. Moreover, L. dimidiatus may exhibit specialized neural signal transductions for cleaning, as evidenced by positive selection in genes related to the glutamatergic synapse pathway. Interestingly, numerous glutamate receptors also demonstrated significantly higher expression in L. dimidiatus not engaged in cleaning, as compared to those involved in cleaning. Besides, apparent contractions in L. dimidiatus for protocadherins, which are responsible for neuronal development, may further promote specialized neural signal transductions in this species.

CONCLUSIONS

This study reveals that L. dimidiatus harbours substantial losses in specific gene families, convergent evolutions across cleaners and a large-scale high gene expression in preparation for cleaning, allowing for adaptation to the dedicated cleaning behaviour.

The Self Course: Lessons Learned from Students' Weekly Questions

In this paper, I tentatively answer 50 questions sampled from a pool of over 10,000 weekly questions formulated by students in a course entitled "The Self". The questions pertain to various key topics related to self-processes, such as self-awareness, self-knowledge, self-regulation, self-talk, self-esteem, and self-regulation. The students' weekly questions and their answers highlight what is currently known about the self. Answers to the student questions also allow for the identification of some recurrent lessons about the self. Some of these lessons include: all self-processes are interconnected (e.g., prospection depends on autobiography), self-terms must be properly defined (e.g., self-rumination and worry are not the same), inner speech plays an important role in self-processes, controversies are numerous (are animals self-aware?), measurement issues abound (e.g., self-recognition as an operationalization of self-awareness), deficits in some self-processes can have devastating effects (e.g., self-regulatory deficits may lead to financial problems), and there are lots of unknowns about the self (e.g., gender differences in Theory-of-Mind).

African jewel fish (Hemichromis bimaculatus) distinguish individual faces based on their unique iridophore patterns

Previous research has shown that African jewel fish (Hemichromis bimaculatus) recognize pair-bonded mates during their exchanges of egg-guarding duties. The current research examined the perceptual cues for face recognition by comparing two face models displaying anatomically realistic arrangements of blue iridophores derived from discriminant function analysis of distinct sibling groups. Four groups each consisting of 9 subadults were examined using a narrow compartment restraining lateral movement where face models were presented at eye level for eight trials. Because respiratory movement of the operculum can mechanically displace the eye thereby shifting the retinal image, jewel fish reduce their respiration rate during increased attention. When two experimental groups were presented with the same face models on four trials following initial model presentations, both groups exhibited stable respiration rates indicative of model habituation. When the habituated face models were switched to novel face models on the fifth trial, the rates of respiration decreased as measured by reliable increases in the elapsed times of opercular beats. Switching the models back to the habituated models on the sixth trial caused reliable decreases in the elapsed times of opercular beats, resembling the earlier trials for the habituated models. Switching the face models again to the formerly novel models on the seventh trial produced respiration rates that resembled those of the habituated models. The two control groups viewing the same models for all eight trials exhibited no substantial change in respiration rates. Together, these findings indicate that jewel fish can learn to recognize novel faces displaying unique arrangements of iridorphores after one trial of exposure.

Male Guppies Recognize Familiar Conspecific Males by Their Face

Individual recognition is a necessary cognitive ability for the maintenance of stable social relationships. Recent studies have shown that like primates, some fish species can distinguish familiar fish from unfamiliar strangers via face-recognition. However, the taxa of the studied fish species are restricted (within Perciformes) and the visual signal used for the recognition of fish remains unclear. Here, we investigated the visual signal for individual-recognition in males of a sexually dichromatic guppy (Poecilia reticulata, Cyprinodontiformes). Using guppy males, we examined the hypothesis that fish distinguish between familiar individuals and unknown strangers by their faces rather than by body coloration. We randomly presented focal fish with four types of composite photo-models: familiar (familiar-face and familiar-body = F/F), stranger (stranger-face and stranger-body = S/S), familiar face combined with stranger body (F/S) and stranger face combined with familiar body (S/F). Focal males infrequently attacked familiar-face models but frequently attacked stranger-face models, regardless of body types. These behavioral reactions indicate that guppy males discriminate between familiar and stranger males by their face, not body coloration with wide variation. Importantly, male faces contain clear individual-variation in white/metallic colored patches on the operculum visible for humans. Considering the photo-model, our results suggest that these patches might be an important visual stimulus for face-recognition in guppy males, like some cichlids. Comparative examination among males of different guppy variants, including wild type phenotype, suggests that the face color-patch is stable regardless of variation in body color, with a different genetic mechanism potentially underlying face and body colors.