Left–right asymmetries of behaviour and nervous system in invertebrates

Looking for the right mate-What we really know on the courtship and mating of Lucilia sericata (Meigen)?

Lucilia sericata is well known for causing myiasis in humans, livestock, pets and wildlife. It also vectors microbial pathogens, including paratuberculosis agents. This species can be exploited in maggot therapy to treat necrotic wounds, particularly those infected by multidrug-resistant pathogens. Despite its high medical and veterinary importance, our knowledge about its courtship and mating behavior is still limited. In this study, we quantified the courtship and mating behavior of L. sericata, shedding light on the potential impact of lateralization of selected behavioral traits during sexual interactions. When a male identified a female, he approached her with head pushing followed by foreleg tapping acts. Courtship lasted 7.65 ± 0.4 s. During copulation attempts, the male continued foreleg tapping acts on the female body, and tried to achieve genital contact. Copula lasted 14.88 ± 0.41 min, while male mating success was 85%. Several courtship and mating traits were found lateralized at population-level. Most of males approached the female with head pushing acts on her left side of the body. Both during courtship and copulation attempt phases, males mainly used the right foreleg to perform leg tapping acts on females. However, the impact of lateralized head pushing and foreleg tapping on the main behavioral parameters characterizing L. sericata courtship and mating was not significant, except for a higher number of foreleg tapping acts during copulation attempts displayed by right-biased males over left-biased ones. Overall, these results contribute to improve our basic knowledge on the reproductive behavior of L. sericata. Besides, selected behavioral parameters characterized here can be exploited as benchmarks to monitor mate quality during mass-rearing, as well as to select males with boosted mating competitiveness, helping to improve the success of SIT programs and behavior-based control tools.

Individual-Level and Population-Level Lateralization: Two Sides of the Same Coin

Lateralization, i.e., the different functional roles played by the left and right sides of the brain, is expressed in two main ways: (1) in single individuals, regardless of a common direction (bias) in the population (aka individual-level lateralization); or (2) in single individuals and in the same direction in most of them, so that the population is biased (aka population-level lateralization). Indeed, lateralization often occurs at the population-level, with 60–90% of individuals showing the same direction (right or left) of bias, depending on species and tasks. It is usually maintained that lateralization can increase the brain’s efficiency. However, this may explain individual-level lateralization, but not population-level lateralization, for individual brain efficiency is unrelated to the direction of the asymmetry in other individuals. From a theoretical point of view, a possible explanation for population-level lateralization is that it may reflect an evolutionarily stable strategy (ESS) that can develop when individually asymmetrical organisms are under specific selective pressures to coordinate their behavior with that of other asymmetrical organisms. This prediction has been sometimes misunderstood as it is equated with the idea that population-level lateralization should only be present in social species. However, population-level asymmetries have been observed in aggressive and mating displays in so-called “solitary” insects, suggesting that engagement in specific inter-individual interactions rather than “sociality” per se may promote population-level lateralization. Here, we clarify that the nature of inter-individuals interaction can generate evolutionarily stable strategies of lateralization at the individual- or population-level, depending on ecological contexts, showing that individual-level and population-level lateralization should be considered as two aspects of the same continuum.

Ex vivo recordings reveal desert locust forelimb control is asymmetric

Lateralized behaviours are widespread among the animals, including insects with their miniature brains, perhaps being a way of maximising neural capacity (reviewed in [1,2]). However, evidence for functional asymmetries in the neural circuitry itself is scarce. Here, using bilateral simultaneous recordings from the ex vivo nervous system of desert locusts, we show that the neural control of their forelimbs is asymmetric. This asymmetry was retained throughout the experimental period and either with or without the suboesophageal ganglion (SOG). These findings provide evidence for hard-wired neural sidedness and contribute to our understanding of the lateralization observed in in-vivo motor behaviours.

Lateralization influences contest behaviour in domestic pigs

Cerebral lateralization, i.e. hemispheric asymmetries in structure and function, relates in many species to a preference to attack from their left. Lateralization increases cognitive capacity, enabling the simultaneous processing of multiple sources of information. Therefore, lateralization may constitute a component of fighting ability (Resource Holding Potential), and/or influence the efficiency of information-gathering during a contest. We hypothesized that lateralization will affect contest outcome and duration, with an advantage for more strongly lateralized individuals. In 52 dyadic contests between weight-matched pigs (Sus scrofa; n = 104; 10 wk age), the direction of orientation towards the opponent was scan sampled every 10 s. Laterality indexes (LI) were calculated for the direction and strength of lateralization. Up to 12.5% of the individuals showed significant lateralization towards either the right or left but lateralization was absent at the population level. In line with our hypothesis, animals showing strong lateralization (irrespective of direction) had a shorter contest duration than animals showing weak lateralization. Winners did not differ from losers in their strength or direction of lateralization. Overall the results suggest that cerebral lateralization may aid in conflict resolution, but does not directly contribute to fighting ability, and will be of value in the study of animal contests.

Attentional state and brain processes: state-dependent lateralization of EEG profiles in horses

Lateralization of brain functions has been suggested to provide individuals with advantages, such as an increase of neural efficiency. The right hemisphere is likely to be specialized for processing attention for details and the left hemisphere for categorization of stimuli. Thus attentional processes actually may underlie lateralization. In the present study, we hypothesized that the attentional state of horses could be reflected in the lateralization of brain responses. We used i) a recently developed attention test to measure horses’ visual attentional responses towards a standardized stimulus and ii) a recently developed portable EEG telemetric tool to measure brain responses. A particular emphasis was given to the types of waves (EEG power profile) and their side of production when horses were either attentive towards a visual stimulus or quiet standing. The results confirmed that a higher attentional state is associated with a higher proportion of gamma waves. There was moreover an interaction between the attentional state, the hemisphere and the EEG profile: attention towards the visual stimulus was associated with a significant increase of gamma wave proportion in the right hemisphere while “inattention” was associated with more alpha and beta waves in the left hemisphere. These first results are highly promising and contribute to the large debate on functional lateralization.

The left cradling bias: An evolutionary facilitator of social cognition?

A robust left side cradling bias (LCB) in humans is argued to reflect an evolutionarily old left visual field bias and right hemisphere dominance for processing social stimuli. A left visual field bias for face processing, invoked via the LCB, is known to reflect a human population-level right cerebral hemisphere specialization for processing social stimuli. We explored the relationship between cradling side biases, hand dominance and socio-communicative abilities. Four and five year old typically-developing children (N = 98) participated in a battery of manual motor tasks interspersed by cradling trials comprising a(n): infant human doll, infant primate doll, proto-face pillow and no-face pillow. Mean social and communication ability scores were obtained via a survey completed by each child's key teacher. We found a population-level LCB for holding an infant human doll that was not influenced by hand dominance, sex, age or experience of having a younger sibling. Children demonstrating a LCB, did however, obtain a significantly higher mean social ability score compared with their right side cradling counterparts. Like the infant human doll, the proto-face pillow's schematic face symbol was sufficient to elicit a population-level LCB. By contrast, the infant primate doll elicited a population-level right side cradling bias, influenced by both hand dominance and sex. The findings suggest that the LCB is present and visible early in development and is likely therefore, to represent evolutionarily old domain-specific organization and function of the right cerebral hemisphere. Additionally, results suggest that a LCB requires minimal triggering but can be reversed in some situations, possibly in response to species-type or levels of novelty or stress as perceived by the viewer. Patterns of behavioral biases within the context of social stimuli and their associations with cognitive ability are important for understanding how socio-communication abilities emerge in developing children.

Asymmetric ommatidia count and behavioural lateralization in the ant Temnothorax albipennis

Workers of the house-hunting ant Temnothorax albipennis rely on visual edge following and landmark recognition to navigate their rocky environment, and they also exhibit a leftward turning bias when exploring unknown nest sites. We used electron microscopy to count the number of ommatidia composing the compound eyes of workers, males and queens, to make an approximate assessment of their relative sampling resolution; and to establish whether there is an asymmetry in the number of ommatidia composing the workers' eyes, which might provide an observable, mechanistic explanation for the turning bias. We hypothesise that even small asymmetries in relative visual acuity between left and right eyes could be magnified by developmental experience into a symmetry-breaking turning preference that results in the inferior eye pointing toward the wall. Fifty-six workers were examined: 45% had more ommatidia in the right eye, 36% more in the left, and 20% an equal number. A tentative connection between relative ommatidia count for each eye and turning behaviour was identified, with a stronger assessment of behavioural lateralization before imaging and a larger sample suggested for further work. There was a clear sexual dimorphism in ommatidia counts between queens and males.

Lateralization of Sucrose Responsiveness and Non-associative Learning in Honeybees

Lateralization is a fundamental property of the human brain that affects perceptual, motor, and cognitive processes. It is now acknowledged that left–right laterality is widespread across vertebrates and even some invertebrates such as fruit flies and bees. Honeybees, which learn to associate an odorant (the conditioned stimulus, CS) with sucrose solution (the unconditioned stimulus, US), recall this association better when trained using their right antenna than they do when using their left antenna. Correspondingly, olfactory sensilla are more abundant on the right antenna and odor encoding by projection neurons of the right antennal lobe results in better odor differentiation than those of the left one. Thus, lateralization arises from asymmetries both in the peripheral and central olfactory system, responsible for detecting the CS. Here, we focused on the US component and studied if lateralization exists in the gustatory system of Apis mellifera. We investigated whether sucrose sensitivity is lateralized both at the level of the antennae and the fore-tarsi in two independent groups of bees. Sucrose sensitivity was assessed by presenting bees with a series of increasing concentrations of sucrose solution delivered either to the left or the right antenna/tarsus and measuring the proboscis extension response to these stimuli. Bees experienced two series of stimulations, one on the left and the other on the right antenna/tarsus. We found that tarsal responsiveness was similar on both sides and that the order of testing affects sucrose responsiveness. On the contrary, antennal responsiveness to sucrose was higher on the right than on the left side, and this effect was independent of the order of antennal stimulation. Given this asymmetry, we also investigated antennal lateralization of habituation to sucrose. We found that the right antenna was more resistant to habituation, which is consistent with its higher sucrose sensitivity. Our results reveal that the gustatory system presents a peripheral lateralization that affects stimulus detection and non-associative learning. Contrary to the olfactory system, which is organized in two distinct brain hemispheres, gustatory receptor neurons converge into a single central region termed the subesophagic zone (SEZ). Whether the SEZ presents lateralized gustatory processing remains to be determined.

The right thalamus may play an important role in anesthesia-awakening regulation in frogs

Background

Previous studies have shown that the mammalian thalamus is a key structure for anesthesia-induced unconsciousness and anesthesia-awakening regulation. However, both the dynamic characteristics and probable lateralization of thalamic functioning during anesthesia-awakening regulation are not fully understood, and little is known of the evolutionary basis of the role of the thalamus in anesthesia-awakening regulation.

Methods

An amphibian species, the South African clawed frog (Xenopus laevis) was used in the present study. The frogs were immersed in triciane methanesulfonate (MS-222) for general anesthesia. Electroencephalogram (EEG) signals were recorded continuously from both sides of the telencephalon, diencephalon (thalamus) and mesencephalon during the pre-anesthesia stage, administration stage, recovery stage and post-anesthesia stage. EEG data was analyzed including calculation of approximate entropy (ApEn) and permutation entropy (PE).

Results

Both ApEn and PE values differed significantly between anesthesia stages, with the highest values occurring during the awakening period and the lowest values during the anesthesia period. There was a significant correlation between the stage durations and ApEn or PE values during anesthesia-awakening cycle primarily for the right diencephalon (right thalamus). ApEn and PE values for females were significantly higher than those for males.

Discussion

ApEn and PE measurements are suitable for estimating depth of anesthesia and complexity of amphibian brain activity. The right thalamus appears physiologically positioned to play an important role in anesthesia-awakening regulation in frogs indicating an early evolutionary origin of the role of the thalamus in arousal and consciousness in land vertebrates. Sex differences exist in the neural regulation of general anesthesia in frogs.

Complementary landmarks facilitate ant navigation

Visual landmarks are important navigational aids to many animals, and when more than one is available their juxtaposition can convey valuable new information to a navigator about progress toward a goal, depending on the landmarks' comparative distinctiveness. We investigated the effect of presenting rock ant colonies (Temnothorax albipennis) with identical horizontal landmarks either side of their route, versus one horizontal landmark paired with a sloping landmark, as they navigated to a new nest site. Our findings suggest that ants can obtain more navigational information from a combination of dissimilar landmarks: the average tortuosity of the route taken between old and new nests was significantly lower when a horizontal landmark was paired with a monotonically downward sloping landmark (the paths were more direct). The impact on available navigational information from the similarity or dissimilarity of nearby landmarks is likely made through more distinctive visual panoramas, and could be an influential factor in individual and collective animal decision-making about which routes are followed. Furthermore, the effect of landmark complementarity may be relevant to a wide range of species, including other insects or birds, and highlights the possibility that there is an intrinsic difference in the informational content of natural vs. artificial environments.

Mating behavior of the West Nile virus vector Culex pipiens - role of behavioral asymmetries

Culex pipiens is a vector of West Nile, Rift Valley fever, Japanese encephalitis and Usutu viruses. In agreement with the criteria of Integrated Vector Management, several research efforts have been devoted to develop behavior-based control tools to fight mosquito vectors. However, our knowledge of mosquito mating biology and sexual communication is still patchy. Despite the high relevance of C. pipiens as a vector of medical and veterinary importance, no studies on its mating behavior and the factors routing mating success have been conducted. In this study, I quantified the mating behavior of an Italian strain of C. pipiens, evaluating the male mating success and its potential connections with population-level lateralized traits occurring during the mating sequence. Mean copula duration exceeded 100 s. Courting males can be straightly accepted by the female after the first genital contact (38.95%), as well as after some rejection kicks performed by females with hind legs (17.89%). No copula duration differences were detected between these two cases. The overall male mating success in laboratory conditions was 56.84%. The females performing rejection kicks preferentially used right hind legs at population-level. This was confirmed over four subsequent testing phases. The number of kicks per rejection event and the rejection success were higher when right legs are used over left ones, showing a functional advantage linked with the employ of right legs. Overall, the present study represents the first quantification of the courtship and mating behavior of C. pipiens. Data on male mating success and the role population-level lateralized mating traits provides basic biological knowledge that can be helpful to optimize autocidal and behavior-based control tools.

Behavioral asymmetries in ticks - Lateralized questing of Ixodes ricinus to a mechatronic apparatus delivering host-borne cues

Ticks are considered among the most dangerous arthropod vectors of disease agents to both humans and animals worldwide. Lateralization contributes to biological fitness in many animals, conferring important functional advantages, therefore studying its role in tick perception would critically improve our knowledge about their host-seeking behavior. In this research, we evaluated if Ixodes ricinus (L.) (Ixodiidae) ticks have a preference in using the right or the left foreleg to climb on a host. We developed a mechatronic device moving a tuft of fox skin with fur as host-mimicking combination of cues. This engineered approach allows to display a realistic combination of both visual and olfactory host-borne stimuli, which is prolonged over the time and standardized for each replicate. In the first experiment, the mechatronic apparatus delivered host-borne cues frontally, to evaluate the leg preference during questing as response to a symmetrical stimulus. In the second experiment, host-borne cues were provided laterally, in an equal proportion to the left and to the right of the tick, to investigate if the host direction affected the questing behavior. In both experiments, the large majority of the tested ticks showed individual-level left-biased questing acts, if compared to the ticks showing right-biased ones. Furthermore, population-level left-biased questing responses were observed post-exposure to host-mimicking cues provided frontally or laterally to the tick. Overall, this is the first report on behavioral asymmetries in ticks of medical and veterinary importance. Moreover, the mechatronic apparatus developed in this research can be exploited to evaluate the impact of repellents on tick questing in highly reproducible standardized conditions.

Detailed movement and laterality of fin-biting behaviour with special mouth morphology in Genyochromis mento in Lake Malawi

Several vertebrates, including fish, exhibit behavioural laterality and associated morphological asymmetry. Laterality may increase individual fitness, and foraging strength, accuracy, and speed. However, little is known about which behaviours are affected by laterality or what fish species exhibit obvious laterality. Previous research on the predatory behaviour of the scale-eating Lake Tanganyika cichlid Perissodus microlepis indicates behavioural laterality that reflects asymmetric jaw morphology. The Lake Malawi cichlid Genyochromis mento feeds on the fins of other fish, a behaviour that G. mento developed independently from the Tanganyikan Perissodini scale-eaters. We investigated stomach contents and behavioural laterality of predation in aquarium to clarify the functional roles and evolution of laterality in cichlids. We also compared the behavioural laterality and mouth asymmetry of G. mento and P. microlepis. The diet of G. mento mostly includes fin fragments, but also scales of several fish species. Most individual G. mento specimens showed significant attack bias favouring the skew mouth direction. However, there was no difference in success rate between attacks from the preferred side and those from the non-preferred side, and no lateralized kinetic elements in predation behaviour. G. mento showed weaker laterality than P. microlepis, partly because of their different feeding habits, the phylogenetic constraints from their shorter evolutionary history, and their origin from ancestor Haplochromini omnivorous/herbivorous species. Taken together, this study provides new insights into the functional roles of behavioural laterality: Predatory fish aiming for prey that show escape behaviours frequently exhibit lateralized behaviour in predation.

Learning Where to Look for High Value Improves Decision Making Asymmetrically

Decision making in any brain is imperfect and costly in terms of time and energy. Operating under such constraints, an organism could be in a position to improve performance if an opportunity arose to exploit informative patterns in the environment being searched. Such an improvement of performance could entail both faster and more accurate (i.e., reward-maximizing) decisions. The present study investigated the extent to which human participants could learn to take advantage of immediate patterns in the spatial arrangement of serially presented foods such that a region of space would consistently be associated with greater subjective value. Eye movements leading up to choices demonstrated rapidly induced biases in the selective allocation of visual fixation and attention that were accompanied by both faster and more accurate choices of desired goods as implicit learning occurred. However, for the control condition with its spatially balanced reward environment, these subjects exhibited preexisting lateralized biases for eye and hand movements (i.e., leftward and rightward, respectively) that could act in opposition not only to each other but also to the orienting biases elicited by the experimental manipulation, producing an asymmetry between the left and right hemifields with respect to performance. Potentially owing at least in part to learned cultural conventions (e.g., reading from left to right), the findings herein particularly revealed an intrinsic leftward bias underlying initial saccades in the midst of more immediate feedback-directed processes for which spatial biases can be learned flexibly to optimize oculomotor and manual control in value-based decision making. The present study thus replicates general findings of learned attentional biases in a novel context with inherently rewarding stimuli and goes on to further elucidate the interactions between endogenous and exogenous biases.

Visuospatial attention in the lateralised brain of pigeons - a matter of ontogenetic light experiences

The ontogenetic mechanisms leading to complementary hemispheric specialisations of the two brain halves are poorly understood. In pigeons, asymmetrical light stimulation during development triggers the left-hemispheric dominance for visuomotor control but light effects on right-hemispheric specialisations are largely unknown. We therefore tested adult pigeons with and without embryonic light experience in a visual search task in which the birds pecked peas regularly scattered on an area in front of them. Comparing the pecking pattern of both groups indicates that the embryonic light conditions differentially influence biased visuospatial attention under mono- and binocular seeing conditions. When one eye was occluded, dark-incubated pigeons peck only within the limits of the visual hemifield of the seeing eye. Light-exposed pigeons also peck into the contralateral field indicating enlarged monocular visual fields of both hemispheres. While dark-incubated birds evinced an attentional bias to the right halfspace when seeing with both eyes, embryonic light exposure shifted this to the left. Thus, embryonic light experience modifies processes regulating biased visuospatial attention of the adult birds depending on the seeing conditions during testing. These data support the impact of light onto the emergence of functional dominances in both hemispheres and point to the critical role of interhemispheric processes.

Obstacle traversal and route choice in flying honeybees: Evidence for individual handedness

Flying insects constantly face the challenge of choosing efficient, safe and collision-free routes while navigating through dense foliage. We examined the route-choice behavior of foraging honeybees when they encountered a barrier which could be traversed by flying through one of two apertures, positioned side by side. When the bees' choice behavior was averaged over the entire tested population, the two apertures were chosen with equal frequency when they were equally wide. When the apertures were of different width, the bees, on average, showed a preference for the wider aperture, which increased sharply with the difference between the aperture widths. Thus, bees are able to discriminate the widths of oncoming gaps and choose the passage which is presumably safer and quicker to transit. Examination of the behavior of individual bees revealed that, when the two apertures were equally wide, ca. 55% of the bees displayed no side bias in their choices. However, the remaining 45% showed varying degrees of bias, with one half of them preferring the left-hand aperture, and the other half the right-hand aperture. The existence of distinct individual biases was confirmed by measuring the times required by biased bees to transit various aperture configurations: The transit time was longer if a bee's intrinsic bias forced it to engage with the narrower aperture. Our results show that, at the population level, bees do not exhibit 'handedness' in choosing routes; however, individual bees display an idiosyncratic bias that can range from a strong left bias, through zero bias, to a strong right bias. In honeybees, previous studies of olfactory and visual learning have demonstrated clear biases at the population level. To our knowledge, our study is the first to uncover the existence of individually distinct biases in honeybees. We also show how a distribution of biases among individual honeybees can be advantageous in facilitating rapid transit of a group of bees through a cluttered environment, without any centralized decision-making or control.

Escape and surveillance asymmetries in locusts exposed to a Guinea fowl-mimicking robot predator

Escape and surveillance responses to predators are lateralized in several vertebrate species. However, little is known on the laterality of escapes and predator surveillance in arthropods. In this study, we investigated the lateralization of escape and surveillance responses in young instars and adults of Locusta migratoria during biomimetic interactions with a robot-predator inspired to the Guinea fowl, Numida meleagris. Results showed individual-level lateralization in the jumping escape of locusts exposed to the robot-predator attack. The laterality of this response was higher in L. migratoria adults over young instars. Furthermore, population-level lateralization of predator surveillance was found testing both L. migratoria adults and young instars; locusts used the right compound eye to oversee the robot-predator. Right-biased individuals were more stationary over left-biased ones during surveillance of the robot-predator. Individual-level lateralization could avoid predictability during the jumping escape. Population-level lateralization may improve coordination in the swarm during specific group tasks such as predator surveillance. To the best of our knowledge, this is the first report of lateralized predator-prey interactions in insects. Our findings outline the possibility of using biomimetic robots to study predator-prey interaction, avoiding the use of real predators, thus achieving standardized experimental conditions to investigate complex and flexible behaviours.

Handedness and Reach-to-Place Kinematics in Adults: Left-Handers Are Not Reversed Right-Handers

The primary goal of this study was to examine the relations between limb control and handedness in adults. Participants were categorized as left or right handed for analyses using the Edinburgh Handedness Inventory. Three-dimensional recordings were made of each arm on two reach-to-place tasks: adults reached to a ball and placed it into the opening of a toy (fitting task), or reached to a Cheerio inside a cup, which they placed on a designated mark after each trial (cup task). We hypothesized that limb control and handedness were related, and we predicted that we would observe side differences favoring the dominant limb based on the dynamic dominance hypothesis of motor lateralization. Specifically, we predicted that the dominant limb would be straighter and smoother on both tasks compared with the nondominant limb (i.e., right arm in right-handers and left arm in left-handers). Our results only partially supported these predictions for right-handers, but not for left-handers. When differences between hands were observed, the right hand was favored regardless of handedness group. Our findings suggest that left-handers are not reversed right-handers when compared on interlimb kinematics for reach-to-place tasks, and reaffirm that task selection is critical when evaluating manual asymmetries.

Exposure to agricultural pesticide impairs visual lateralization in a larval coral reef fish

Lateralization, i.e. the preferential use of one side of the body, may convey fitness benefits for organisms within rapidly-changing environments, by optimizing separate and parallel processing of different information between the two brain hemispheres. In coral reef-fishes, the movement of larvae from planktonic to reef environments (recruitment) represents a major life-history transition. This transition requires larvae to rapidly identify and respond to sensory cues to select a suitable habitat that facilitates survival and growth. This 'recruitment' is critical for population persistence and resilience. In aquarium experiments, larval Acanthurus triostegus preferentially used their right-eye to investigate a variety of visual stimuli. Despite this, when held in in situ cages with predators, those larvae that previously favored their left-eye exhibited higher survival. These results support the "brain's right-hemisphere" theory, which predicts that the right-eye (i.e. left-hemisphere) is used to categorize stimuli while the left-eye (i.e. right-hemisphere) is used to inspect novel items and initiate rapid behavioral-responses. While these experiments confirm that being highly lateralized is ecologically advantageous, exposure to chlorpyrifos, a pesticide often inadvertently added to coral-reef waters, impaired visual-lateralization. This suggests that chemical pollutants could impair the brain function of larval fishes during a critical life-history transition, potentially impacting recruitment success.

Lateralized scale-eating behaviour of cichlid is acquired by learning to use the naturally stronger side

The scale-eating cichlid Perissodus microlepis exhibits significant lateralised predation behaviour using an asymmetric mouth. But how the acquisition of the behavioural laterality depends, if at all, on experience during development remains obscure. Here, naïve juveniles were tested in a series of predation sessions. Initially, they attacked both sides of the prey, but during subsequent sessions, attack direction gradually lateralised to the skewed mouth (dominant) side. Attack side preference of juveniles that had accumulated scale-eating experience during successive sessions was significantly higher than that of naïve juveniles at the same age and naïve adults. Thus, the lateralised behaviour was a learned experience, and did not develop with age. Surprisingly, however, both maximum amplitude and angular velocity of body flexion during attack of naïve fish was dominant on one side. Therefore, scale-eating fish have a naturally stronger side for attacking prey fish, and they learn to use the dominant side through experience.

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.

Visual Ecology and the Development of Visually Guided Behavior in the Cuttlefish

Cuttlefish are highly visual animals, a fact reflected in the large size of their eyes and visual-processing centers of their brain. Adults detect their prey visually, navigate using visual cues such as landmarks or the e-vector of polarized light and display intense visual patterns during mating and agonistic encounters. Although much is known about the visual system in adult cuttlefish, few studies have investigated its development and that of visually-guided behavior in juveniles. This review summarizes the results of studies of visual development in embryos and young juveniles. The visual system is the last to develop, as in vertebrates, and is functional before hatching. Indeed, embryonic exposure to prey, shelters or complex background alters postembryonic behavior. Visual acuity and lateralization, and polarization sensitivity improve throughout the first months after hatching. The production of body patterning in juveniles is not the simple stimulus-response process commonly presented in the literature. Rather, it likely requires the complex integration of visual information, and is subject to inter-individual differences. Though the focus of this review is vision in cuttlefish, it is important to note that other senses, particularly sensitivity to vibration and to waterborne chemical signals, also play a role in behavior. Considering the multimodal sensory dimensions of natural stimuli and their integration and processing by individuals offer new exciting avenues of future inquiry.

Melanism is related to behavioural lateralization in nestling barn owls

Behavioural laterality is a commonly observed phenomenon in many species suggesting there might be an advantage of using dominantly one side over the other for certain tasks. Indeed, lateralized individuals were often shown to be more successful in cognitive tasks compared to non-lateralized conspecifics. However, stressed individuals are also often, but not always, more strongly lateralized. Because barn owl (Tyto alba) females displaying larger black spots on the tip of their ventral feathers produce offspring that are more resistant to a variety of environmental stressful factors, we examined whether laterality is associated with melanin-based coloration. We recorded whether nestlings use more often the right or left foot to scratch their body and whether they preen more often one side of the body or the other using their bills. We found that the strength of lateralization of preening and scratching was less pronounced in individuals born from heavily spotted mothers. This result might be explained by plumage-related variation in the ability to resist stressful rearing conditions.

Effects of elevated carbon dioxide and temperature on locomotion and the repeatability of lateralization in a keystone marine mollusc

Recent work has shown that the behaviour of marine organisms can be affected by elevated PCO2, although little is known about the effect of multiple stressors. We therefore investigated the effect of elevated PCO2 and temperature on locomotion and behaviour during prey searching in the marine gastropod Concholepas concholepas, a predator characteristic of the southeastern Pacific coast. Movement duration, decision time, route finding and lateralization were measured using a T-maze tank with a prey positioned behind a barrier. Four treatments, representing present day and near-future scenarios of ocean acidification and warming were used in rearing the individuals for 6 months. Regardless of the treatment, no significant differences were found in relative and absolute lateralization before and after exposure for 6 months. However, relative lateralization was not repeatable for animals tested after 6 months at elevated PCO2 at both experimental temperatures, whereas it was repeatable in individuals kept at the present day level of PCO2. We suggest that these effects may be related to a behavioural malfunction caused by elevated PCO2. Movement duration, decision time and route finding were not repeatable. However, movement duration and decision time increased and route finding decreased in elevated PCO2 (at 15°C), suggesting that elevated PCO2 has negative effects on the locomotor and sensory performance of C. concholepas in the presence of a prey odour, thereby decreasing their ability to forage efficiently.

The Evolution of Lateralization in Group Hunting Sailfish

Lateralization is widespread throughout the animal kingdom [1-7] and can increase task efficiency via shortening reaction times and saving on neural tissue [8-16]. However, lateralization might be costly because it increases predictability [17-21]. In predator-prey interactions, for example, predators might increase capture success because of specialization in a lateralized attack, but at the cost of increased predictability to their prey, constraining the evolution of lateralization. One unexplored mechanism for evading such costs is group hunting: this would allow individual-level specialization, while still allowing for group-level unpredictability. We investigated this mechanism in group hunting sailfish, Istiophorus platypterus, attacking schooling sardines, Sardinella aurita. During these attacks, sailfish alternate in attacking the prey using their elongated bills to slash or tap the prey [22-24]. This rapid bill movement is either leftward or rightward. Using behavioral observations of identifiable individual sailfish hunting in groups, we provide evidence for individual-level attack lateralization in sailfish. More strongly lateralized individuals had a higher capture success. Further evidence of lateralization comes from morphological analyses of sailfish bills that show strong evidence of one-sided micro-teeth abrasions. Finally, we show that attacks by single sailfish are indeed highly predictable, but predictability rapidly declines with increasing group size because of a lack of population-level lateralization. Our results present a novel benefit of group hunting: by alternating attacks, individual-level attack lateralization can evolve, without the negative consequences of individual-level predictability. More generally, our results suggest that group hunting in predators might provide more suitable conditions for the evolution of strategy diversity compared to solitary life.

Ambidextrous ungulates have more flexible behaviour, bolder personalities and migrate less

Studies of wildlife have shown consistent individual variation in behavioural plasticity, which affects the rate of adaptation to changing environments. More flexible individuals may thus be more prone to habituation and conflict behaviour, but these applications of personality to wildlife management are little explored. Behavioural lateralization reflects cerebral specialization that may predict diverse expressions of behavioural plasticity. We recorded front-limb biases (i.e. handedness) in wild elk (Cervus canadensis), a species with facultative migration and high rates of habituation inside protected areas. Less lateralized elk responded more strongly to the application of aversive conditioning (predator-resembling chases by humans) by increasing their average flight response distances, but these same animals were also quicker to reduce their flight responses (i.e. habituate) when human approaches were benign. Greater laterality was correlated with, but not completely predicted by, bolder personalities, which we quantified via five correlated behavioural metrics. Lastly, lateralized elk were three times more likely to migrate, whereas less lateralized animals were similarly likely to remain near humans year-round. Lateralized behaviours can provide insight into behavioural flexibility enabling certain individuals to more quickly adapt to human-disturbed landscapes, and offer an especially productive arena for collaborative work by behaviourists, conservation biologists and wildlife managers.

Epigenetic regulation of lateralized fetal spinal gene expression underlies hemispheric asymmetries

Lateralization is a fundamental principle of nervous system organization but its molecular determinants are mostly unknown. In humans, asymmetric gene expression in the fetal cortex has been suggested as the molecular basis of handedness. However, human fetuses already show considerable asymmetries in arm movements before the motor cortex is functionally linked to the spinal cord, making it more likely that spinal gene expression asymmetries form the molecular basis of handedness. We analyzed genome-wide mRNA expression and DNA methylation in cervical and anterior thoracal spinal cord segments of five human fetuses and show development-dependent gene expression asymmetries. These gene expression asymmetries were epigenetically regulated by miRNA expression asymmetries in the TGF-β signaling pathway and lateralized methylation of CpG islands. Our findings suggest that molecular mechanisms for epigenetic regulation within the spinal cord constitute the starting point for handedness, implying a fundamental shift in our understanding of the ontogenesis of hemispheric asymmetries in humans.

DOI:http://dx.doi.org/10.7554/eLife.22784.001

Conserved roles for cytoskeletal components in determining laterality

Consistently-biased left-right (LR) patterning is required for the proper placement of organs including the heart and viscera. The LR axis is especially fascinating as an example of multi-scale pattern formation, since here chiral events at the subcellular level are integrated and amplified into asymmetric transcriptional cascades and ultimately into the anatomical patterning of the entire body. In contrast to the other two body axes, there is considerable controversy about the earliest mechanisms of embryonic laterality. Many molecular components of asymmetry have not been widely tested among phyla with diverse bodyplans, and it is unknown whether parallel (redundant) pathways may exist that could reverse abnormal asymmetry states at specific checkpoints in development. To address conservation of the early steps of LR patterning, we used the Xenopus laevis (frog) embryo to functionally test a number of protein targets known to direct asymmetry in plants, fruit fly, and rodent. Using the same reagents that randomize asymmetry in Arabidopsis, Drosophila, and mouse embryos, we show that manipulation of the microtubule and actin cytoskeleton immediately post-fertilization, but not later, results in laterality defects in Xenopus embryos. Moreover, we observed organ-specific randomization effects and a striking dissociation of organ situs from effects on the expression of left side control genes, which parallel data from Drosophila and mouse. Remarkably, some early manipulations that disrupt laterality of transcriptional asymmetry determinants can be subsequently "rescued" by the embryo, resulting in normal organ situs. These data reveal the existence of novel corrective mechanisms, demonstrate that asymmetric expression of Nodal is not a definitive marker of laterality, and suggest the existence of amplification pathways that connect early cytoskeletal processes to control of organ situs bypassing Nodal. Counter to alternative models of symmetry breaking during neurulation (via ciliary structures absent in many phyla), our data suggest a widely-conserved role for the cytoskeleton in regulating left-right axis formation immediately after fertilization of the egg. The novel mechanisms that rescue organ situs, even after incorrect expression of genes previously considered to be left-side master regulators, suggest LR patterning as a new context in which to explore multi-scale redundancy and integration of patterning from the subcellular structure to the entire bodyplan.