Lateralized predatory responses in the ornate dragon lizard (Ctenophorus ornatus)

The effect of androgen exposure on cerebral lateralization in the American alligator (Alligator mississippiensis)

The division of the brain manifests in lateralized physical behaviors, where specific tasks originate from one side of the body. Previous studies have shown that birds and reptiles mediate aggression in their right hemisphere and focus on opponents with their left eye. Degree of lateralization varies between sexes, likely due to androgen inhibition of lateralization in mammals, birds, and fish, but remains untested in herpetofauna. In this experiment, we investigated the effect of androgen exposure on cerebral lateralization in the American Alligator, Alligator mississippiensis. Alligator eggs were collected and incubated at female producing temperature with a subset dosed with methyltestosterone in ovo. Dosed hatchlings were randomly paired with control individuals and their interactions were recorded. The number of bites initiated by focus from each eye and the number of times an animal was bitten on each side of the body was recorded for each individual to elucidate cerebral lateralization in aggression. Control alligators had a significant bias towards left-eye bite initiation whereas androgen exposed alligators used both eyes indiscriminately. No significance was found in injury patterns. This study suggests that androgen exposure inhibits cerebral lateralization in alligator brains and corroborates right-hemisphere mediation of aggression, something previously unstudied in crocodilians.

Repeatability of lateralisation in mosquitofish Gambusia holbrooki despite evidence for turn alternation in detour tests

Akin to handedness in humans, some animals show a preference for moving to the left or right. This is often attributed to lateralised cognitive functions and eye dominance, which, in turn, influences their behaviour. In fishes, behavioural lateralisation has been tested using detour mazes for over 20 years. Studies report that certain individuals are more likely to approach predators or potential mates from one direction. These findings imply that the lateralisation behaviour of individuals is repeatable, but this is rarely confirmed through multiple testing of each individual over time. Here we quantify the repeatability of turning behaviour by female mosquitofish (Gambusia holbrooki) in a double sided T-maze. Each female was tested three times in each of six treatments: when approaching other females, males, or an empty space; and when able to swim freely or when forced to choose by being herded from behind with a net. Although there was no turning bias based on the mean population response, we detected significant repeatability of lateralisation in five of the six treatments (R = 0.251-0.625). This is noteworthy as we also found that individuals tended to alternate between left and right turns, meaning that they tend to move back and forth along one wall of the double-sided T-maze. Furthermore, we found evidence for this wall following when re-analysing data from a previous study. We discuss potential explanations for this phenomenon, and its implications for study design.

Asymmetric Behavior in Ptyodactylus guttatus: Can a Digit Ratio Reflect Brain Laterality?

The digit ratio, an indicator of brain laterality, is the ratio of the second and fourth digits on the left (L24) or right foot (R24). Much of the research on the digit ratio and brain laterality focuses on primates, rather than other species such as reptiles. We tested whether the digit ratio in the gecko Ptyodactylus guttatus was associated with behaviors attributed to brain laterality. We examined risk-taking behavior (time spent under cover), foot preference (which foot was the first to start moving) and the side from which geckos bypassed an obstacle, in relation to the digit ratio. Geckos with longer fourth digits on their left hind foot (higher digit ratio) spent more time under cover. Geckos starting to move with their left leg were much more likely to bypass obstacles from the right side, and vice versa. This is the first evidence of laterality being associated with the digit ratio in reptiles. Comparisons among vertebrates are needed in order to decipher the evolutionary origin of the commonalities and peculiarities of brain asymmetry and disentangle the patterns and drivers of our evolutionary tree.

Footedness predicts escape performance in a passerine bird

Behavioral lateralization, which is associated with the functional lateralization of the two brain hemispheres, commonly exists in animals and can provide an individual with benefits such as enhanced cognition and dual tasking. Lateral bias in limb use, as a type of behavioral lateralization, occur in many species, but the reasons for the coexistence of left- and right-biased individuals in a population remain poorly understood. We examined the footedness of male yellow-bellied tits (Pardaliparus venustulus) when they used feet to clamp mealworms against a perch, and tested its association with other fitness-related behavioral traits (i.e., feeding efficiency, exploration tendency, and escape performance). We expected differently footed individuals to have respective advantages in these behaviors and thereby coexist ("respective advantage" hypothesis). We found their footedness repeatable, and there was no population-level bias. While no associations of feeding efficiency and exploration tendency with footedness were detected, the right-footed individuals were found to be harder to catch than the other individuals. Future studies need to investigate the reasons for the right-footed individuals' superior escape performance. Moreover, the escape advantage for being right-footed and the lack of population-level bias in footedness in male yellow-bellied tits suggest that the benefits related to left footedness also remain to be explored.

Dogs can sense weak thermal radiation

The dog rhinarium (naked and often moist skin on the nose-tip) is prominent and richly innervated, suggesting a sensory function. Compared to nose-tips of herbivorous artio- and perissodactyla, carnivoran rhinaria are considerably colder. We hypothesized that this coldness makes the dog rhinarium particularly sensitive to radiating heat. We trained three dogs to distinguish between two distant objects based on radiating heat; the neutral object was about ambient temperature, the warm object was about the same surface temperature as a furry mammal. In addition, we employed functional magnetic resonance imaging on 13 awake dogs, comparing the responses to heat stimuli of about the same temperatures as in the behavioural experiment. The warm stimulus elicited increased neural response in the left somatosensory association cortex. Our results demonstrate a hitherto undiscovered sensory modality in a carnivoran species.

Dynamics of electroencephalogram oscillations underlie right-eye preferences in predatory behavior of the music frog

Visual lateralization is a typical characteristic of many vertebrates; however, its underlying dynamic neural mechanism is unclear. In this study, predatory responses and dynamic brain activities were evaluated in the Emei music frog (Nidirana daunchina) to assess the potential eye preferences and their underlying dynamic neural mechanism, using behavioral and electrophysiological experiments, respectively. To do this, when the prey stimulus (live cricket and leaf as control) was moved around the frogs in both clockwise and anticlockwise directions at constant velocity, the number of predatory responses were counted and electroencephalogram (EEG) absolute power spectra for each band were measured for the telencephalon, diencephalon and mesencephalon. The results showed that: (1) no significant differences in the number of predatory responses could be found for the control (leaf), but the number of predatory responses for the right visual field (RVF) was significantly greater than that for the left visual field (LVF) when the live cricket was moved into the RVF clockwise; (2) compared with no stimulus in the visual field and stimulus in the LVF, the power spectra of each EEG band were greater when the prey stimulus was moved into the RVF clockwise; and (3) the power spectra of the theta, alpha and beta bands in the left diencephalon were significantly greater than those of the right counterpart for the clockwise direction, but similar significant differences presented for the delta, theta and alpha bands in the anticlockwise direction. Together, the results suggested that right-eye preferences for predatory behaviors exist in music frogs, and that the dynamics of EEG oscillations might underlie this right eye/left hemisphere advantage.

The Alpha Hypothesis: Did Lateralized Cattle-Human Interactions Change the Script for Western Culture?

Domestic cattle possess lateralized cognitive processing of human handlers. This has been recently demonstrated in the preference for large groups of cattle to view a human closely within the predominantly left visual field. By contrast, the same stimulus viewed predominantly within the right visual field promotes a significantly greater frequency of dispersal from a standing position, including flight responses. The respective sets of behaviours correspond with the traditional terms of "near side" for the left side of cattle and horses, and the "off" or "far side" for the right side. These traditional terms of over 300 years usage in the literature communicate functional practicalities for handling livestock and the recognition of lateralized cognitive processing. In this review, the possibility of even earlier recognition and the significance of laterality in cattle-human interaction was argued, from the earliest representations of the letter "A", originally illustrated from nearly 4000 years before the present time as the head of an ox as viewed not from the front or from the right, but from the left (near) side. By extension, this knowledge of lateralization in cattle may represent the earliest written example of applied ethology-the study of the behaviour of animals under human management.

Lateralization in accuracy, reaction time and behavioral processes in a visual discrimination task in an Indo-Pacific bottlenose dolphin (Tursiops aduncus)

Perceptual and behavioral asymmetry has been observed in a wide range of vertebrate and invertebrate species with its origin estimated to go back over 500 million years. Previously, hemispheric lateralization in marine mammals has been recorded during foraging, parental care, preferred swimming direction as well as when solving cognitive challenges. Visual laterality has been demonstrated in preferred eye use and performance accuracy. A female Indo-Pacific bottlenose dolphin was trained to associate eight pairs of non-identical visual stimuli. Her performance was tested and compared under binocular and monocular conditions. No significant difference was found in accuracy, while a clear left eye advantage was demonstrated in reaction time. In addition, behavioral asymmetry was observed in movement pattern preference during the stimulus discrimination.

Context-specific response inhibition and differential impact of a learning bias in a lizard

Response inhibition (inhibiting prepotent responses) is needed for reaching a more favourable goal in situations where reacting automatically would be detrimental. Inhibiting prepotent responses to resist the temptation of a stimulus in certain situations, such as a novel food item, can directly affect an animal's survival. In humans and dogs, response inhibition varies between contexts and between individuals. We used two contextually different experiments to investigate response inhibition in the eastern water skink (Eulamprus quoyii): reversal of a visual two-choice discrimination and a cylinder detour task. During the two-choice task, half of our lizards were able to reach an initial learning criterion, but, thereafter, did not show consistent performance. Only two individuals reached a more stringent criterion, but subsequently failed during reversals. Furthermore, half of our animals were not able to inhibit a pre-existing side preference which affected their ability to learn during the two-choice task. Skinks were, however, able to achieve a detour around a cylinder performing at levels comparable to brown lemurs, marmosets, and some parrot species. A comparison between the tasks showed that reaching the initial criterion was associated with low success during the detour task, indicating that response inhibition could be context-specific in the water skink. To the best of our knowledge, this is the first study to examine inhibitory control and motor self-regulation in a lizard species.

Perception of artificial conspecifics by bearded dragons (Pogona vitticeps)

Artificial animals are increasingly used as conspecific stimuli in animal behavior research. However, researchers often have an incomplete understanding of how the species under study perceives conspecifics, and, hence, which features are needed for a stimulus to be perceived appropriately. To investigate the features that bearded dragons (Pogona vitticeps) attend to, we measured their lateralized eye use when assessing a successive range of stimuli. These ranged through several stages of realism in artificial conspecifics, to see how features such as color, the presence of eyes, body shape and motion influence behavior. We found differences in lateralized eye use depending on the sex of the observing bearded dragon and the artificial conspecific, as well as the artificial conspecific's behavior. Therefore, this approach can inform the design of robotic animals that elicit biologically-meaningful responses in live animals.

Lizards assess complex social signals by lateralizing colour but not motion detection

Vertebrates lateralize many behaviours including social interactions. Social displays typically comprise multiple components, yet our understanding of how these are processed come from studies that typically examine responses to the dominant component or the complex signal as a whole. Here, we examine laterality in lizard responses to determine whether receivers separate the processing of motion and colour signal components in different brain hemispheres. In Psammophilus dorsalis, males display colours that dynamically change during courtship and aggressive interactions. We tested the visual grasp reflex of both sexes using robotic stimuli that mimicked two signal components: (1) multiple speeds of head-bobbing behaviour and (2) multiple colours. We find no laterality in response to different motion stimuli, indicating that motion similarly attracts attention from both visual fields across sexes. Notably, receivers showed left visual field dominance to colours, especially when males were exposed to “aggression-specific” colours and females to “courtship-specific” colours.

Context-dependent behavioural lateralization in the European pond turtle Emys orbicularis (Testudines, Emydidae)

Lateralization presents clear advantages in ecological contexts since dominance of one brain side prevents the simultaneous activation of contrasting responses in organisms with laterally located eyes. This is crucial in selecting a safe refuge during a predatory attack and may strongly affect predator–prey interactions. We explored the possible presence of lateralization in the antipredatory behaviour of European pond turtles, considering their escape facing a possible predatory attack. Thirty individuals (17 males, 13 females) were exposed to three different environmental situations of gradual increasing predatory threat: escape underwater from an unsafe shelter, diving into the water from a basking site, righting after being overturned. All turtles were tested 20 times for each of the three experiments (60 trials per individual and 1800 overall trials). We recorded multiple behavioural responses in the general context of predation risk. This was done in order to assess both the existence of lateralization and possible correlations among different behaviours as function of lateralization. The number of significant responses to the left side was always prevalent in each of the three simulated anti-predatory situations, suggesting the existence of a lateralized behaviour in this species. At the individual level, the differences we found in the three experiments could be related to different ecological contexts and consequent risk of predation. Our findings, among the few on Chelonians, support the possible involvement of the right hemisphere activity and, most importantly, reveal how the complexity of a general predatory context can affect the laterality of escape behaviour.

Tortoises in front of mirrors: Brain asymmetries and lateralized behaviours in the tortoise (Testudo hermanni)

Brain lateralization in response to social stimuli is well known for its involvement of the right hemisphere in several vertebrate species, including humans. This study aimed to investigate the laterality of the social behavior during the mirror-images inspection in tortoises (Testudo hermanni). In a rectangular apparatus, in presence or in absence of two mirrors as the longer walls, we assessed: 1) the animal's position and 2) the monocular viewing compared to the longer walls, 3) the paw used to start a movement from a resting position. Here we provide the first evidence of lateralization towards social stimuli in tortoises, a reptile that is likely to lead mostly a solitary life, but also able to show a few basic abilities in social cognition. Results revealed a preference to spend significantly more time in peripheral positions, mainly in the presence of mirrors. Moreover, a consistent left-eye preference to inspect the mirrors was observed, especially when close to them. In contrast, a significant right-eye preference appeared in absence of mirrors, when tortoises occupied the central areas. Findings show a significant preference for right-paw use in starting movements, when mirrors were present. Results are discussed with reference to other evidence of brain asymmetry.

Is righting response lateralized in two species of freshwater turtles?

Laterality has been found in a variety of reptiles. In turtles, one important behaviour is the righting response. Here, we studied laterality of righting response of two species of freshwater turtles, the Painted Turtle (Chrysemys picta) and the Eastern Musk Turtle (Sternotherus odoratus). We found evidence of individual-level laterality in righting response in C. picta, but not S. odoratus. Neither species showed evidence of population-level laterality in righting response. Our results suggest that there is variation in the extent of laterality of righting response in turtles. Possible explanations for variation in laterality of righting response in turtles include shell shape and use of terrestrial habitats. However, more species of turtles need to be examined to demonstrate any general patterns in laterality of righting response in turtles.

Examining the link between personality and laterality in a feral guppy Poecilia reticulata population

This study examined whether variation in the strength and direction of lateralization in a detour task was linked with variation in three common personality measurements: boldness, activity and sociability, in a population of wild guppies Poecilia reticulata. Additionally, the aim was to determine whether any consistent correlations between these behavioural traits, known as behavioural syndromes, were present in the study population. The results revealed that all three personality traits were highly repeatable over time in both sexes. Evidence of a complex syndrome in the form of a correlation between boldness, sociability and activity was found; however, this relationship was only present in males. Males that were more active in a familiar environment emerged more quickly from shelter into a novel environment and were more social. In general, male P. reticulata were bold, active and antisocial compared to females, with these differences probably a reflection of opposing life-history strategies. Only a weak link between the strength of cerebral lateralisation and personality was discovered and this was mediated by sex.

Visually guided avoidance in the chameleon (Chamaeleo chameleon): response patterns and lateralization

The common chameleon, Chamaeleo chameleon, is an arboreal lizard with highly independent, large-amplitude eye movements. In response to a moving threat, a chameleon on a perch responds with distinct avoidance movements that are expressed in its continuous positioning on the side of the perch distal to the threat. We analyzed body-exposure patterns during threat avoidance for evidence of lateralization, that is, asymmetry at the functional/behavioral levels. Chameleons were exposed to a threat approaching horizontally from the left or right, as they held onto a vertical pole that was either wider or narrower than the width of their head, providing, respectively, monocular or binocular viewing of the threat. We found two equal-sized sub-groups, each displaying lateralization of motor responses to a given direction of stimulus approach. Such an anti-symmetrical distribution of lateralization in a population may be indicative of situations in which organisms are regularly exposed to crucial stimuli from all spatial directions. This is because a bimodal distribution of responses to threat in a natural population will reduce the spatial advantage of predators.

Threat perception in the chameleon (Chamaeleo chameleon): evidence for lateralized eye use

Chameleons are arboreal lizards with highly independent, large amplitude eye movements. In response to an approaching threat, a chameleon on a vertical pole moves so as to keep itself away from the threat. In so doing, it shifts between monocular and binocular scanning of the threat and of the environment. We analyzed eye movements in the Common chameleon, Chamaeleo chameleon, during avoidance response for lateralization, that is, asymmetry at the functional/behavioral levels. The chameleons were exposed to a threat, approaching horizontally from clockwise or anti-clockwise directions, and that could be viewed monocularly or binocularly. Our results show three broad patterns of eye use, as determined by durations spent viewing the threat and by frequency of eye shifts. Under binocular viewing, two of the patterns were found to be both side dependent, that is, lateralized and role dependent ("leading" or "following"). However, under monocular viewing, no such lateralization was detected. We discuss these findings in light of the situation not uncommon in vertebrates, of independent eye movements and a high degree of optic nerve decussation and that lateralization may well occur in organisms that are regularly exposed to critical stimuli from all spatial directions. We point to the need of further investigating lateralization at fine behavioral levels.

Visual laterality of calf-mother interactions in wild whales

BACKGROUND

Behavioral laterality is known for a variety of vertebrate and invertebrate animals. Laterality in social interactions has been described for a wide range of species including humans. Although evidence and theoretical predictions indicate that in social species the degree of population level laterality is greater than in solitary ones, the origin of these unilateral biases is not fully understood. It is especially poorly studied in the wild animals. Little is known about the role, which laterality in social interactions plays in natural populations. A number of brain characteristics make cetaceans most suitable for investigation of lateralization in social contacts.

METHODOLOGY/PRINCIPAL FINDINGS

Observations were made on wild beluga whales (Delphinapterus leucas) in the greatest breeding aggregation in the White Sea. Here we show that young calves (in 29 individually identified and in over a hundred of individually not recognized mother-calf pairs) swim and rest significantly longer on a mother's right side. Further observations along with the data from other cetaceans indicate that found laterality is a result of the calves' preference to observe their mothers with the left eye, i.e., to analyze the information on a socially significant object in the right brain hemisphere.

CONCLUSIONS/SIGNIFICANCE

Data from our and previous work on cetacean laterality suggest that basic brain lateralizations are expressed in the same way in cetaceans and other vertebrates. While the information on social partners and novel objects is analyzed in the right brain hemisphere, the control of feeding behavior is performed by the left brain hemisphere. Continuous unilateral visual contacts of calves to mothers with the left eye may influence social development of the young by activation of the contralateral (right) brain hemisphere, indicating a possible mechanism on how behavioral lateralization may influence species life and welfare. This hypothesis is supported by evidence from other vertebrates.

Mind your left: spatial bias in subcortical fear processing

Hemispheric lateralization of emotional processing has long been suggested, but its underlying neural mechanisms have not yet been defined. In this functional magnetic resonance imaging study, facial expressions were presented to 10 right-handed healthy adult females in an event-related visual half-field presentation paradigm. Differential activations to fearful versus neutral faces were observed in the amygdala, pulvinar, and superior colliculus only for faces presented in the left hemifield. Interestingly, the left hemifield advantage for fear processing was observed in both hemispheres. These results suggest a leftward bias in subcortical fear processing, consistent with the well-documented leftward bias of danger-associated behaviors in animals. The current finding highlights the importance of hemifield advantage in emotional lateralization, which might reflect the combination of hemispheric dominance and asymmetric interhemispheric information transfer.

Lateralised visual processing in domestic cattle herds responding to novel and familiar stimuli

We investigated whether cattle exhibit preferences to monitor challenging and novel stimuli. Experiments were conducted on dairy and beef cattle herds and revealed significant left eye preferences in the cattle for viewing an experimenter walking to repeatedly split the herd through its centre. Visual lateralisation was demonstrated in the preference to use the left monocular field to monitor the experimenter, alone or equipped with a range of novel stimuli. This finding is consistent with left eye preferences found in various species of mammals, birds, and amphibians responding to predators and novel stimuli. A cohort of the familiarized cattle herds was then subjected to additional herd-splitting tests with the same stimuli and demonstrated a reversal of viewing preferences, preferring to monitor the experimenter and stimuli within the right and not left monocular field. This directional shift in viewing preferences is consistent with experience-dependent learning found in lateralised visual processing in other, non-mammalian, species, and to our knowledge is the first of such studies to suggest that such lateralised learning processes also exist in mammals. Together the data support a number of key hypotheses concerning the evolution and conservation of lateralised brain function in vertebrates, and also provide important considerations for livestock handling.