Rotational Bias in Mosquitofish (Gambusia holbrooki): The Role of Laterality and Sun-compass Navigation

Hemispheric asymmetries for emotions in non-human primates: A systematic review

A systematic review of investigations evaluating hemispheric asymmetries for emotions in primates was undertaken to individuate the most consistent lines of research allowing to check the hypothesis of a continuum in emotional lateralization across vertebrates. We reviewed studies on the lateralization of emotional expression (N = 31) and perception (N = 32) and of markers of emotional activation (N = 9), trying to distinguish those which had given respectively more consistent or more conflicting outcomes. Furthermore, we tried to identify the most strongly supported model of emotional lateralization. The most consistent results were obtained in studies investigating asymmetries in emotional expression at the facial level and in the perception of emotional facial expressions, whereas the most disappointing data were obtained in investigations evaluating possible neurophysiological markers of lateralized emotional activation. These results supported more the hypothesis of a continuity between humans and non-human primates than the more general hypothesis of a continuum between humans and all vertebrates. Furthermore, results supported more the 'right hemisphere' than the 'valence' model of emotional lateralization.

Brain and Behavioral Asymmetry: A Lesson From Fish

It is widely acknowledged that the left and right hemispheres of human brains display both anatomical and functional asymmetries. For more than a century, brain and behavioral lateralization have been considered a uniquely human feature linked to language and handedness. However, over the past decades this idea has been challenged by an increasing number of studies describing structural asymmetries and lateralized behaviors in non-human species extending from primates to fish. Evidence suggesting that a similar pattern of brain lateralization occurs in all vertebrates, humans included, has allowed the emergence of different model systems to investigate the development of brain asymmetries and their impact on behavior. Among animal models, fish have contributed much to the research on lateralization as several fish species exhibit lateralized behaviors. For instance, behavioral studies have shown that the advantages of having an asymmetric brain, such as the ability of simultaneously processing different information and perform parallel tasks compensate the potential costs associated with poor integration of information between the two hemispheres thus helping to better understand the possible evolutionary significance of lateralization. However, these studies inferred how the two sides of the brains are differentially specialized by measuring the differences in the behavioral responses but did not allow to directly investigate the relation between anatomical and functional asymmetries. With respect to this issue, in recent years zebrafish has become a powerful model to address lateralization at different level of complexity, from genes to neural circuitry and behavior. The possibility of combining genetic manipulation of brain asymmetries with cutting-edge in vivo imaging technique and behavioral tests makes the zebrafish a valuable model to investigate the phylogeny and ontogeny of brain lateralization and its relevance for normal brain function and behavior.

The Impact of Brain Lateralization and Anxiety-Like Behaviour in an Extensive Operant Conditioning Task in Zebrafish (Danio rerio)

Several studies in mammals, birds, and fish have documented better cognitive abilities associated with an asymmetrical distribution of cognitive functions in the two halves of the brain, also known as ‘functional brain lateralization’. However, the role of brain lateralization in learning abilities is still unclear. In addition, although recent studies suggest a link between some personality traits and accuracy in cognitive tasks, the relation between anxiety and learning skills in Skinner boxes needs to be clarified. In the present study, we tested the impact of brain lateralization and anxiety-like behaviour in the performance of an extensive operant conditioning task. Zebrafish tested in a Skinner box underwent 500 trials in a colour discrimination task (red vs. yellow and green vs. blue). To assess the degree of lateralization, fish were observed in a detour test in the presence of a dummy predator, and anxiety-like behaviour was studied by observing scototaxis response in an experimental tank divided into light and dark compartments. Although the low performance in the colour discrimination task did not permit the drawing of firm conclusions, no correlation was found between the accuracy in the colour discrimination task and the behaviour in the detour and scototaxis tests. This suggests that neither different degrees of asymmetries in brain lateralization nor anxiety may significantly impact the learning skills of zebrafish.

Lateralisation of rotational swimming but not fast escape response in the juvenile sterlet sturgeon, Acipenser ruthenus (Chondrostei: Acipenseridae)

For the first time, behavioural lateralisation was shown in a chondrostean fish (sterlet sturgeon Acipenser ruthenus). A significant directional bias was found in young A. ruthenus swimming along a circular swimway. This laterality manifested itself as an individual preference for a certain movement direction (either clockwise or counterclockwise) which was consistent at the retest 10 days later. On the other hand, no significant rotational bias was observed at the population level. The same sterlet individuals displayed the C-start (the first stage of escape response) elicited by sudden low-frequency sound vibrations (50 Hz). However, the experiments failed to reveal either individual or population laterality of this response: the frequencies of leftward and rightward bends in startled fish were virtually equal. These results demonstrate that the two types of laterality can be independent in fish.

Jaw laterality and related handedness in the hunting behavior of a scale-eating characin, Exodon paradoxus

BACKGROUND

Asymmetry in animal bodies and behavior has evolved several times, but our knowledge of their linkage is limited. Tanganyikan scale-eating cichlids have well-known antisymmetry in their bodies and behavior; individuals open their mouths leftward (righty) or rightward (lefty), and righties always attack the right flank of the prey, whereas lefties attack the left. This study analyzed the morphological asymmetry in a scale-eating characiform, Exodon paradoxus, and its behavioral handedness.

METHODOLOGY/PRINCIPAL FINDINGS

Each eight E. paradoxus was observed for 1-h with a prey goldfish in an aquarium to detect the behavioral handedness. Following the experiment, the lateral differences in the mandibles and head-inclination of these eight and ten additional specimens were analyzed. Both measurements on the morphology showed a bimodal distribution, and the laterality identified by these two methods was always consistent within a given individual, indicating that the characin has morphological antisymmetry. Furthermore, this laterality significantly corresponded to behavioral handedness; that is, lefties more often rasped scales from the right flank of the prey and vice versa. However, the correlation between laterality and handedness is the opposite of that in the cichlids. This is due to differences in the feeding apparatus and technique. The characin has cuspids pointing forward on the external side of the premaxilla, and it thrusts its dominant body side outward from its body axis on the flank of the prey to tear off scales. By contrast, the cichlids draw their dominant body side inward toward the axis or rotate it to scrape or wrench off scales with the teeth lined in the opened mouth.

CONCLUSIONS/SIGNIFICANCE

This study demonstrated that the antisymmetry in external morphology and the corresponding behavioral handedness have evolved in two lineages of scale-eating fishes independently, and these fishes adopt different utilization of their body asymmetry to tear off scales.

Origins and functions of laterality: interactions of motoric systems

To evaluate lateral motoric bias in response systems at different levels of the neuraxis and assess the extent of interaction between these levels in the small-eared bushbaby (Otolemur garnettii), 27 animals were tested for lateral bias in hand use and whole-body turn bias in two postural conditions. Subjects retrieved mealworms quadrupedally by reaching downwards into glass jars and bipedally by reaching upwards to baited straws. Eye bias was assessed separately. Behaviours were scored from videotape. Two subgroups were identified: SHIFTERS changed hand preference with posture and had correlations of hand/eye bias in quadrupedal posture and of hand/turn bias, with more bimanual reaching, in bipedal posture; NONSHIFTERS were consistent in hand preference and more strongly lateralised in reach and turn than SHIFTERS. Subgroups did not differ in reach efficiency. Results are interpreted to support the value of the analysis of motoric levels and their interactions in the study of the evolution of laterality. Assuming natural selection for coordinated and targeted behaviours to be the source of lateralisation, several proposals in support of a motoric theory of laterality origins and functions are advanced.

Ground scratching and preferred leg use in domestic chicks: changes in motor control in the first two weeks post-hatching

Lateralisation of a variety of visual functions: food discrimination, fear response, copulation, and performance of topographical and other tasks, such as olfactory and auditory functions, have been described in the domestic chick, Gallus gallus domesticus. A bias to left hemisphere control on day 8 and to the right on day 11 has also been demonstrated in the domestic chick. In this study we show that motor control as to foot preference in initiating a scratching bout and a tape-removing task is lateralised in both adults and chicks. There was a preference for the right leg to initiate a bout of ground scratching in both male and female adult birds. Second, foot preference is also affected by the changes in shifts of bias on day 8 and day 11. The right leg preference in initiating a ground scratching bout observed on day 5 is reversed to a left leg preference on day 8. This then reverts to the right leg preference after day 11. Hence it is postulated that the hemisphere that is not activated due to the bias of age controls the first leg to be used in initiating routine movements such as ground scratching. For the tape-removing task the right leg was used to remove a tape adhered to the beak of the chick for the trained group on day 8; but there was no preference in the naive group. Similarly, on day 11 a left foot bias was observed for the trained group and right foot bias for the naive group. To remove a tape the activated hemisphere on days of bias is used; whereas in a novel situation the foot use is reversed. Thus, footedness is affected by age, type of task, and changing hemispheric dominance.

Population lateralisation and social behaviour: a study with 16 species of fish

We investigated turning responses in 16 species of fish faced with a vertical-bar barrier through which a learned dummy predator was visible. Ten of these species showed a consistent lateral bias to turn preferentially to the right or to the left. Species belonging to the same family showed similar directions of lateral biases. We performed an independent test of shoaling tendency and found that all gregarious species showed population lateralisation, whereas only 40% of the non-gregarious species did so. The results provide some support to the Rogers (1989) hypothesis that population lateralisation might have been developed in relation to the need to maintain coordination among individuals in behaviours associated with social life.

Grip morphology and hand use in chimpanzees (Pan troglodytes): evidence of a left hemisphere specialization in motor skill

Three experiments on grip morphology and hand use were conducted in a sample of chimpanzees. In Experiment 1, grip morphology when grasping food items was recorded, and it was found that subjects who adopted a precision grip were more right-handed than chimpanzees using other grips. In Experiment 2, the effect of food type on grasping was assessed. Smaller food items elicited significantly more precision grips for the right hand. In Experiment 3, error rates in grasping foods were compared between the left and right hands. Significantly more errors were made for the left compared with the right hand. The cumulative results indicate that chimpanzees show a left-hemisphere asymmetry in motor skill that is associated with the use of precision grips.

Consistency among different tasks of left-right asymmetries in lines of fish originally selected for opposite direction of lateralization in a detour task

Lines of fish, Girardinus falcatus preferentially turning rightward (RD) or leftward (LD) when facing a dummy predator visible behind a barrier have been obtained through selective breeding. To check whether lateralization was maintained in other behavioral responses, five different tests were carried out. They comprised measures of (1) turning direction in a T-maze; (2) proportion of clockwise and anticlockwise direction of rotation in a circular arena; (3) preferential eye use by females during shoaling behavior (i.e. while looking at their own mirror image reflection); (4) preferential eye use by males during sexual behavior (i.e. while turning around a barrier to join a group of females); and (5) preferential eye use by males during agonistic behavior (i.e. while attacking a rival visible in a mirror). In all five tests the two selected lines showed opposite direction of lateralization. Results thus indicate that behavioral asymmetries in the detour test are predictive of lateralization in other types of behavioral tests. Moreover, results show that RD and LD fish have a similar but left-right reversed pattern of subdivision of cognitive/ behavioral functions, which is suggestive of a similarly left-right reversed (mirror image) brain organization.

Asymmetrical hatching behaviors influence the development of postnatal laterality in domestic chicks (Gallus gallus)

Lateralized motor behaviors have been reported in some avian species. For instance, footedness has been reported in parrots and domestic chicks, and turning biases have been reported in such species as quail and domestic chicks. This study examined the effects of asymmetrical hatching behaviors on the development of lateralized turning bias and footedness in domestic chicks. Asymmetrical hatching behaviors are counter-clockwise full body turns that many precocial birds make to escape the egg. To study the role of such coordinated prenatal motor behaviors in the development of lateralization, hatching behaviors were systematically disrupted following pipping. Subjects were subsequently tested on two measures of laterality: footedness and turning bias. Results indicated a significant reduction in individual and group lateralization for both measures. These findings suggest that the hatching behaviors found in domestic chicks serve to induce the development of strong motor biases at both the individual and population level.

The origins of cerebral asymmetry: a review of evidence of behavioural and brain lateralization in fishes, reptiles and amphibians

Early evidence for lateralization at a population and/or individual level in 'lower' vertebrates is reviewed. The lateralities include structural asymmetries in the epithalamus of several species of fish and amphibians, asymmetries in the location of both eyes on the same side of the head and of the dorsal/ventral crossing at optic-chiasma in flatfish, asymmetries in copulatory organs of several species of fishes, asymmetries in lung size and direction of coiling in reptiles, and asymmetrical distribution of scarring in whitefish. More recent data on functional lateralization at population level in lower vertebrates are also reviewed. These include: lateral asymmetries in the direction of turning during escape behaviour and in eye use in poeciliid fish; lateralization of pectoral stridulation sounds in catfish; neural lateralization for control of vocalization in the frogs; pawedness in toads; lateralization of courtship behaviour in newts; and lateralization of aggressive responses in lizards. Several cases of behavioural asymmetries at the individual level are also described, and possible relationships between lateralization at the individual level and fluctuating asymmetries arising from reduced heterozygosity are discussed. It is argued that the overall evidence now available supports the hypothesis of an early origin of brain lateralization in vertebrates.

Asymmetrical turning during spermatophore transfer in the male smooth newt

During mating, male smooth newts, Triturus vulgarisshowed a population bias for turning left during spermatophore transfer. This is the first demonstration of asymmetrical sexual behaviour in an amphibian population. An experiment with a perfect female model showed that it was due to male rather than female lateralization. Left turning bias decreased progressively as more spermatophores were deposited, and no significant bias was detectable by the third deposition. The hypothesis that this was due to neuromuscular fatigue was tested but not supported. Turning orientation had no influence on the probability of the female picking up the spermatophore in her cloaca. The left turning bias has not been found in the great crested newt, T. cristatus