Asymmetrical turning during spermatophore transfer in the male smooth newt

The Difficult Integration between Human and Animal Studies on Emotional Lateralization: A Perspective Article

Even if for many years hemispheric asymmetries have been considered as a uniquely human feature, an increasing number of studies have described hemispheric asymmetries for various behavioral functions in several nonhuman species. An aspect of animal lateralization that has attracted particular attention has concerned the hemispheric asymmetries for emotions, but human and animal studies on this subject have been developed as independent lines of investigation, without attempts for their integration. In this perspective article, after an illustration of factors that have hampered the integration between human and animal studies on emotional lateralization, I will pass to analyze components and stages of the processing of emotions to distinguish those which point to a continuum between humans and many animal species, from those which suggest a similarity only between humans and great apes. The right lateralization of sympathetic functions (involved in brain and bodily activities necessary in emergency situations) seems consistent across many animal species, whereas asymmetries in emotional communication and in structures involved in emotional experience, similar to those observed in humans, have been documented only in primates.

Population-level lateralized aggressive and courtship displays make better fighters not lovers: evidence from a fly

Lateralization (i.e., left-right asymmetries in the brain and behavior) of aggressive and courtship displays has been examined in many vertebrate species, while evidence for invertebrates is limited. We investigated lateralization of aggressive and courtship displays in a lekking tephritid species, the olive fruit fly, Bactrocera oleae. Results showed a left-biased population-level lateralization of aggressive displays, with no differences between the sexes. In both male-male and female-female contests, aggressive behaviors performed with left body parts led to greater fighting success than those performed with right body parts, while no differences in fighting duration were found. Olive fruit fly males also showed a side bias during courtship and mating behavior, courting females more frequently from the left than the right, front, or back sides. No differences were detected between courtship duration and copulation duration following the different male directional approaches. Male mating success was comparable whether females were approached from the left, right, front, or back side. Lateralized aggressive and courtship displays at the population-level may be connected to the prolonged social interactions occurring among lekking flies. Further research is needed on possible benefits arising from lateralization of courtship traits in insects.

Assessing and interpreting lateralised behaviours in anuran larvae

We review here what is known about lateralised behaviours in tadpoles, focusing on turning biases and methods for testing them. Two testing protocols have been used that are specific for explosive turns which are likely to be Mauthner cell-mediated. They involve recording the turns made by tadpoles: (1) upon descent after they take a breath of air, and (2) after they are mechanically startled. Turning bias has also been explored for tadpoles: (3) in a T-maze, (4) as they exit a tube into a larger arena, and (5) as they turn away from a barrier or object brought towards their snout. Slower turns observed under the last three protocols may not be regulated by the same neuromotor pathways as the faster turns elicited in the first two protocols. Turning biases do not occur in tadpoles of all species. In species where turning biases have been observed during explosive turns, the biases are typically towards the left side. The majority of tadpoles have a single asymmetric left-sided spiracle, yet lateralised behaviours in these tadpoles do not appear to be obligatorily linked to this morphological asymmetry. Tadpole turning biases are usually of the order of 60-90% towards the preferred side and are rarely absolute for individuals, and never for populations. Turning biases, when present, usually appear shortly after hatching and disappear before metamorphosis. Turning biases that appear during metamorphosis may depend on appendicular rather than axial muscle, and thus are fundamentally different behaviours; i.e., involving different neuromuscular components. Lateralised behaviours may occur in anurans before they reach the free-living larval stage. This could include bias in the side towards which a frog embryo coils its tail within the egg case, or the side towards which a newly hatched tadpole leans when lying on the bottom How lateralised behaviours of anurans that change with ontogeny relate to each other is not known Although it has been suggested that turning biases are absent in the more archaic frog genera only two 'archaic' genera have been examined Xenopus and Bombina and the data are too few to discern any clear phylogenetic patterns Lastly we present a model suggesting why tadpoles might have turning biases in situations where maximum speed is paramount This model assumes that the fastest neuromotor programs will be 'hardwired' in the central nervous system The model predicts that the amount of morphological asymmetry in the Mauthner neurons will be directly proportional to the amount of turning bias seen in tadpoles.

Asymmetries in amphibians: a review of morphology and behaviour

Morphological and behavioural asymmetries in amphibians are reviewed. Among the characteristics considered are: (1) the asymmetry of the shoulder girdle (epicoracoid overlap); (2) the distribution of the left and right variants of its structure in amphibian populations; (3) asymmetry in the position of the spiracle(s); (4) asymmetric order of forelimb emergence from opercular chambers in tadpoles; and (5) preferential forelimb use in adult amphibians. I show that there are no direct cause-and-effect relationships between these characteristics, which would explain their development. Other asymmetries, such as asymmetry of the visceral organs, turning behaviour of tadpoles, asymmetries in the length and weights of the long bones, and some neuromorphological traits, also show few examples of relationships. However, the simultaneous absence of many asymmetries in some amphibians and their presence in others suggests a common cause, which affects all of these asymmetries indirectly, presumably very early in ontogenesis.

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.

Asymmetrical hatching behaviors: The development of postnatal motor laterality in three precocial bird species

The effects of asymmetrical hatching behaviors on the development of turning bias and footedness in domestic chicks, bobwhite quail, and Japanese quail chicks were examined. Control tests with incubator reared domestic chicks and bobwhite quail revealed significant individual and population left-side turning bias and right footedness. When late stage hatching behaviors were disrupted, population laterality was not evident and individual laterality was reduced. By contrast, Japanese quail chicks demonstrated no population turning bias or footedness and only weak individual biases. Disruption of hatch behaviors further decreased laterality. Examination of discarded eggshells showed significant differences in the degree of rotation made to cut out of the egg by Japanese quail versus domestic chicks and bobwhite quail. Taken together these findings suggest that the counterclockwise hatching behaviors that are characteristic of many precocial bird species serve to facilitate the development of motor laterality at both the individual and population level.

Left and right in the amphibian world: which way to develop and where to turn?

The last decade has seen a dramatic increase in studies on the development, function and evolution of asymmetries in vertebrates, including amphibians. Here we discuss current knowledge of behavioral and anatomical asymmetries in amphibians. Behavioral laterality in the response of both adult and larval anurans to presumed predators and competitors is strong and may be related, respectively, to laterality in the telencephalon of adults and the Mauthner neurons of tadpoles. These behavior lateralities, however, do not seem to correlate with visceral asymmetries in the same animals. We briefly compare what is known about the evolution and development of asymmetry in the structure and function of amphibians with what is known about asymmetries in other chordate and non-chordate groups. Available data suggest that the majority of asymmetries in amphibians fall into two independent groups: (1) related to situs viscerum and (2) of a neurobehavioral nature. We find little evidence linking these two groups, which implies different developmental regulatory pathways and independent evolutionary histories for visceral and telencephalic lateralizations. Studies of animals other than standard model species are essential to test hypotheses about the evolution of laterality in amphibians and other chordates.

Display lateralisation in the courtship behaviour of the alpine newt (Triturus alpestris)

Among urodelan amphibians, European newts of the genus Triturus have evolved a complex sequence of displays to the effect of stimulating the female to actively pick up the spermatophore deposited by the male. Courtship is varied, with plenty of potential for asymmetric uses of tails and of asymmetric turns. The analysis of the temporal structure of the behavioural sequences showed that both males and females significantly utilise the same side during a single courtship sequence. Moreover, if an individual prefers to exhibit one side during its lateral displays, then the duration of its displays on that side is longer than the duration of its displays on the other side. The only significantly contralateral display is creep-on. Less than 50% of the alpine newts show a significant left- or right-side preference and no lateral bias at population level was found. At the population level, male Triturus vulgaris showed a marked bias towards left turning after spermatophore deposition, in spite of the existence of both "left-turning" and "right-turning" individuals in the population (Green, 1997). The presence of population biases may be adaptive if it can influence the sensory processes and the motor responses involved in social interactions. In fact, Triturus vulgaris is characterised by a more complex courtship sequence than T. alpestris and by complex male-male interference mechanisms, but no selective advantages were shown for either left- or right-turning males (Green, 1997).

Lateralisation of predator avoidance responses in three species of toads

Lateralisation of responses to presentation of a simulated predator was investigated in three species of toads: two European species (the common toad, Bufo bufo, and the green toad, Bufo viridis) and one species introduced to Australia from South America, the cane toad Bufo marinus . First a simulated snake was presented moving rapidly towards the toad in the frontal field of vision and the toad's escape responses, including jumps to the right and to the left, were recorded. No significant bias in left or right side jumping was apparent in this test. Next the simulated snake was presented in the left or right lateral field of vision in random order. Escape and defensive responses were elicited more strongly, in all three species, when the stimulus was on the toad's left side compared to its right side. Reaction times scored in the experiments with B. marinus, alone, did not differ from left to right. There were, however, species differences in the types of escape responses with respect to the laterality: B. viridis and B. marinus showed similar patterns of more sideways jumps with left presentation and more frontal jumps with right presentation. Sideways jumps were not lateralised in B. bufo, but this species showed more frontal jumps when the presentation was on the left side. These findings suggest that the selective involvement of structures located in the right side of the brain (left monocular visual field) in emotional responses (particularly fear responses) could be a phylogenetic ancient trait.

Cross-species investigations of prenatal experience, hatching behavior, and postnatal behavioral laterality

Turning biases have been reported in some mammalian species, but less is known about such biases in nonmammalians. This study investigated turning biases in domestic chicks, bobwhite and Japanese quail, leopard geckos, and snapping turtles. Domestic chicks (white leghorn and bantam) and bobwhite quail demonstrate strong group laterality. Japanese quail chicks, snapping turtles, and leopard geckos demonstrate no significant group bias. Results are discussed with regard to differences in embryonic experience, hatching behavior, and postnatal environment.

Lateralization of ventral fins use during object exploration in the blue gourami (Trichogaster trichopterus)

Blue gourami fish have a pair of modified ventral fins that are used to obtain tactile information about surrounding objects. Use of ventral fins by blue gourami was investigated during initial exploration of novel objects. When exposed to a sequence of novel plastic objects, varying in shape and colour, the blue gourami showed preferential use of the left fin during initial contacts. Laterality apparently depends on the nature of the stimulus: Fish exposed to a randomized series of natural objects showed preferential use of the left fin for inanimate mineral objects, but no asymmetry was apparent for investigating animate objects. This would suggest that some form of 'handedness' may have been present prior to the appearance of tetrapods. On the other hand, measurements of fish monocular viewing revealed that the fin use was strongly associated with preferential use of the ipsilateral eye before the touching of the stimulus took place, thus, suggesting that the asymmetry in fin use may also be related to lateralization of the visual system.

What causes lateralization of detour behavior in fish? Evidence for asymmetries in eye use

A consistent population bias to detour a vertical-bar barrier preferentially leftwise during approach to inspect a dummy predator was demonstrated in the poeciliid fish Girardinus falcatus. The asymmetry seems to be due to a preferential use of the lateral visual field of the right eye during fixation of biologically relevant stimuli such as a predator. Viewing tests revealed in fact that fish which tended to detour the barrier on the left side used the right eye to scrutiny a dummy predator and the left eye to scrutiny a neutral stimulus, whereas fish which tended to detour the barrier on the right side showed the reverse pattern of eye use; fish that did not show any consistent bias in the detour test did not reveal any significant preference in the viewing test.

Possible evolutionary origins of cognitive brain lateralization

Despite the substantial literature on the functional architecture of the asymmetries of the human brain, which has been accumulating for more than 130 years since Dax and Broca's early reports, the biological foundations of cerebral asymmetries are still poorly understood. Recent advances in comparative cognitive neurosciences have made available new animal models that have started to provide unexpected insights into the evolutionary origins and neuronal mechanisms of cerebral asymmetries. Animal model-systems, particularly those provided by the avian brain, highlight the interrelations of genetic, hormonal and environmental events to produce neural and behavioural asymmetries. Novel evidences showing that functional and structural lateralization of the brain is widespread among vertebrates (including fish, reptiles and amphibians) have accumulated rapidly. Perceptual asymmetries, in particular, seem to be ubiquitous in everyday behaviour of most species of animals with laterally placed eyes; in organisms with wider binocular overlap (e.g., amphibians), they appear to be retained for initial detection of stimuli in the extreme lateral fields. We speculate that adjustment of head position and eye movements may play a similar role in mammals with frontal vision as does the choice for right or left lateral visual fields in animals with laterally placed eyes. A first attempt to trace back the origins of brain asymmetry to early vertebrates is presented, based on the hypothesis that functional incompatibility between the logical demands associated with very basic cognitive functions is central to the phenomenon of cerebral lateralization.

Lateralization of detour behaviour in poeciliid fish: the effect of species, gender and sexual motivation

We studied detour responses of two species of poeciliid fish (Gambusia hoolbroki and Girardinus falcatus) faced with a vertical-bar barrier, through which conspecifics of the same or different sex or a simulated-predator (which induced detour behaviour for predator-inspection responses) were visible. Both species showed a consistent bias to turn leftward when faced with the predator, and a consistent bias to turn rightward when faced with an opaque barrier. Sexual stimuli (conspecifics of different sex) elicited a leftward bias in females that had been deprived of the presence of males for 2 months, whilst no bias was apparent in non-deprived females. Social stimuli (conspecifics of the same sex) elicited a consistent rightward bias in females but not in males in both species. Results suggest that males and females of both species show basically the same pattern of laterality and that sex differences, when present, can be accounted for in terms of differences in sexual and/or social motivation.

Rotational swimming preferences in mosquitofish: evidence for brain lateralization?

Rotational preferences of mosquitofish (Gambusia holbrooki) were investigated in circular tanks with a group of females or a group of predators located at the centre, or during spontaneous swimming in absence of any particular target. Mosquitofish swam preferentially clockwise in presence of the predators, whilst no significant preferences appeared with the females or during spontaneous swimming. Similar rotational biases have been reported previously only for rodents and marine mammals: the present findings suggest that even teleost fish may possess lateralized brains.

Detour tests reveal task- and stimulus-specific behavioral lateralization in mosquitofish (Gambusia holbrooki)

We studied detour responses of male mosquitofish faced with a vertical-bar barrier through which a group of females was visible. Mosquitofish showed a consistent population bias to detour the barrier preferentially leftwise when a straight barrier was used, whilst the asymmetry disappeared if a U-shaped barrier was used. The leftward bias was apparent even when using a simulated-predator as a target (which induced detour behaviour for predatory-inspection responses), but not when using an empty environment or a group of males as a target. Moreover, when faced with an opaque barrier, mosquitofish tended to turn on their right side. These lateral biases could be accounted for in terms of a right eye preference during lateral (monocular) fixation of any stimulus of interest, suggesting functional lateralization in a teleost species for the analysis of visual information.

Laterality in detour behaviour: interspecific variation in poeciliid fish

We measured whether males of five species of poeciliid fish made detours to the right or left of a vertical-bar obstacle in order to approach a group of females. Three of these species, Gambusia holbrookiGambusia nicaraguensis and Poecilia reticulata showed a significant bias to the left, whereas Brachyrhaphis roseni and Girardinus falcatus showed a significant bias to the right. When tested for direction of turning in front of an opaque barrier, or when a dummy predator was used as a target in a detour test, G. holbrooki and G. falcatus showed similar biases to the right (opaque barrier) and left (predator), thus suggesting that the difference observed when females were used as a target could arise from species differences in the degree of sexual motivation in a novel environment. The two species that showed bias to the right with the females were less likely to exhibit sexual behaviour when placed in a novel environment. Moreover, manipulation of the factors affecting the relative strength of sexual motivation and of fear of a novel environment, such as how long fish were maintained in captivity or in the test apparatus before being tested, caused shifts in the direction of the lateral asymmetries. These results suggest that the presence of functional asymmetries in behaviour could be widespread among vertebrates and that the direction of such asymmetries tends to be strikingly similar in closely related species, thus supporting the hypothesis of an early evolution of laterality in brain and behaviour.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour