Pawedness and Motor Asymmetries in Toads

Effects of predation risk on the sensory asymmetries and defensive strategies of Bufotes balearicus tadpoles

Lateralization consists of the differential use of bilateral organs or limbs and is well described in many taxa and in several contexts. Common ecological frameworks where it can be observed are foraging and predatory ones, with benefits related to both visual and auditory lateralization such as faster response or increasing neural processing ability. Anuran amphibians are considered relevant models for investigating lateralization, due to their great ecological variety and the possibility of easily being raised under laboratory conditions. By adopting the "rotational preference test", we used Balearic green toad tadpoles to test the effects of behavioural defensive responses triggered by different predator types (native vs alien, i.e. dragonfly larvae Aeshna cyanea and adult red swamp crayfish Procambarus clarkii) and diets (fasted vs. tadpole-fed predators) on their lateralization. We recorded tadpoles' responses to five different chemical cues: clean water (control treatment), fasted dragonfly larvae and crayfish, and tadpole-fed dragonfly larvae and crayfish. Green toad tadpoles did not show a bias in a predominant direction, although lateralization occurred at the individual level, as shown by the intensity index (L_A). Perceived predation risk was the highest in tadpoles exposed to the combined chemical cues of conspecific prey and native predators, which elicited both changes in the intensity of lateralization and a marked reduction in tadpoles' activity level. Our results suggest that contextual predation threat may induce very rapid changes in the expression of asymmetries at the individual level, and might play a role as part of the complex defensive strategies adopted by prey in the attempt to escape predators.

Lateralized motor behaviour in the righting responses of the cane toad (Rhinella marina)

This paper reports a series of tests for fore- and hind-limb preferences used by cane toads, Rhinella marina, to assist returning to the righted position after being overturned. We confirm the strong and significant right-handedness reported in this species, which under certain conditions exceeded 90% right-hand preference at the group level. Toads were tested under a variety of conditions including horizontal and inclined surfaces, with and without the opportunity for the forelimbs to grasp a support, in order to assess the effects of different vestibular and proprioceptive input on the strength and direction of fore- and hind-limb preferences. A range of behavioural strategies indicated learning effects; however, the strength or direction of limb preferences did not increase significantly with experience, even in toads retested multiple times. Comparisons with the mammalian condition for limb preferences are discussed with relevance to practice effects and established limb preferences, and to effects associated with arousal or stress. In contrast to the expectation that handedness in toads represents intentional or voluntary preferences, the presence of lateralized central pattern generators in the toads is postulated to explain the different forms of lateralization revealed by our tests.

A function for the bicameral mind

Why do the left and right sides of the brain have different functions? Having a lateralized brain, in which each hemisphere processes sensory inputs differently and carries out different functions, is common in vertebrates, and it has now been reported for invertebrates too. Experiments with several animal species have shown that having a lateralized brain can enhance the capacity to perform two tasks at the same time. Thus, the different specializations of the left and right sides of the brain seem to increase brain efficiency. Other advantages may involve control of action that, in Bilateria, may be confounded by separate and independent sensory processing and motor outputs on the left and right sides. Also, the opportunity for increased perceptual training associated with preferential use of only one sensory or motoric organ may result in a time advantage for the dominant side. Although brain efficiency of individuals can be achieved without the need for alignment of lateralization in the population, lateral biases (such as preferences in the use of a laterally-placed eye) usually occur at the population level, with most individuals showing a similar direction of bias. Why is this the case? Not only humans, but also most non-human animals, show a similar pattern of population bias (i.e., directional asymmetry). For instance, in several vertebrate species (from fish to mammals) most individuals react faster when a predator approaches from their left side, although some individuals (a minority usually ranging from 10 to 35%) escape faster from predators arriving from their right side. Invoking individual efficiency (lateralization may increase fitness), evolutionary chance or simply genetic inheritance cannot explain this widespread pattern. Using mathematical theory of games, it has been argued that the population structure of lateralization (with either antisymmetry or directional asymmetry) may result from the type of interactions asymmetric organisms face with each other.

Sheep Quickstep while the Floor Rock and Rolls: Visuomotor Lateralization during Simulated Sea Travel

Unpredictable floor motions during transport disturbs animals' balance, requiring stepping to move the centre of gravity in the direction of body movement. When repeated regularly, this may be stressful, requiring involvement of the right brain hemisphere, hence we investigated the existence of behavioral laterality in sheep during prolonged floor motions. Six sheep were restrained in pairs on a programmable rocking platform, in which they were unable to turn around. They were exposed to three continuous rocking motion treatments (roll, pitch or both) in a regular or irregular pattern for 1 h periods in a changeover design. Right forelimb and left hindlimb diagonal stepping was more frequent in response to the motion treatment of irregular roll and pitch, which previous research has suggested to be the most stressful from heart rate measurements. An overall strategy to maintain balance appeared to be the use of the right hindlimb as a stabilizer, which was repositioned least often of all limbs until towards the end of the hour of experimental treatment. Of each tested pair, sheep restrained on the left side of the rocking floor stepped significantly often than its partner restrained on the right side, and we postulate the existence of visuomotor lateralization as left restrained sheep were unable to view their partner within the field of view of their left eye. We also investigated which side sheep lie down on, which if left lateralized could explain our observed bipedal diagonal control of sheep balance under stress. From the observation of 412 web-based images of sheep, there was an overall left-sided laterality to their lying, as has been observed in cattle. We conclude that stepping activity in sheep in response to a motion stressor is lateralized, providing evidence that floor motion experienced in transport may induce stress responses.

Asymmetry of righting reflexes in sea turtles and its behavioral correlates

The righting responses, when the animal rights itself over one side of the body after been overturned on the back, are one of the simplest ways to test for laterality, especially in lower vertebrates. In anuran amphibians unilateral preferences in righting responses correlated to the degree of the use of alternating-limb (asynchronous) movements during locomotion. Turtles is one of the underrepresented vertebrate groups in the studies of laterality, while possess also different types of locomotion (with synchronous or asynchronous use of the contralateral limbs), which allows testing the hypothesis on functional relationship between the mode of locomotion and the strength of laterality. We studied two species of sea turtles, Green turtle (Chelonia mydas) and Olive Ridley turtle (Lepidochelys olivacea), which differ from the majority of other representatives of the order in that they mostly utilize synchronous locomotion, when all four limbs move simultaneously in strokes (scratching). In righting response tests turtles demonstrated individual and weak population level laterality, which differed in strength. The Green turtle was less lateralized with the majority of individuals being ambipreferent. The Olive Ridley turtle had a greater number of lateralized individuals and a greater average strength of laterality. Interspecies comparison to land tortoises, which use only asynchronous (alternating-limb) walking (crawling), confirmed the rule found in amphibians: the more asynchronous locomotion is used, the greater is the strength of laterality in righting. Hence, data from turtles and amphibians may represent a phenomenon common for all quadruped vertebrates. We also discuss possible biomechanical and neurological correlates of this evolutionary change in locomotory patterns and lateralization in sea turtles when adapting to sea life.

The biological significance of acoustic stimuli determines ear preference in the music frog

Behavioral and neurophysiological studies support the idea that right ear advantage (REA) exists for perception of conspecific vocal signals in birds and mammals. Nevertheless, few studies have focused on anuran species that typically communicate through vocalization. The present study examined the direction and latencies of orientation behaviors in Emei music frogs (Babina daunchina) produced in response to six auditory stimuli emitted by a speaker placed directly behind the subjects. The stimuli included male advertisement calls produced from within burrow nests, which have been shown to be highly sexually attractive (HSA), calls produced from outside burrows, which are of low sexual attractiveness (LSA), screech calls produced when frogs are attacked by snakes, white noise, thunder and silence. For all sound stimuli except the screech, the frogs preferentially turned to the right. Right ear preference was strongest for HSA calls. For the screech and thunder stimuli, there was an increased tendency for subjects to move further from the speaker rather than turning. These results support the idea that in anurans, right ear preference is associated with perception of positive or neutral signals such as the conspecific advertisement call and white noise, while a left ear preference is associated with perception of negative signals such as predatory attack.

Relating lateralization of eye use to body motion in the avoidance behavior of the chameleon (Chamaeleo chameleon)

Lateralization is mostly analyzed for single traits, but seldom for two or more traits while performing a given task (e.g. object manipulation). We examined lateralization in eye use and in body motion that co-occur during avoidance behaviour of the common chameleon, Chamaeleo chameleon. A chameleon facing a moving threat smoothly repositions its body on the side of its perch distal to the threat, to minimize its visual exposure. We previously demonstrated that during the response (i) eye use and body motion were, each, lateralized at the tested group level (N = 26), (ii) in body motion, we observed two similar-sized sub-groups, one exhibiting a greater reduction in body exposure to threat approaching from the left and one--to threat approaching from the right (left- and right-biased subgroups), (iii) the left-biased sub-group exhibited weak lateralization of body exposure under binocular threat viewing and none under monocular viewing while the right-biased sub-group exhibited strong lateralization under both monocular and binocular threat viewing. In avoidance, how is eye use related to body motion at the entire group and at the sub-group levels? We demonstrate that (i) in the left-biased sub-group, eye use is not lateralized, (ii) in the right-biased sub-group, eye use is lateralized under binocular, but not monocular viewing of the threat, (iii) the dominance of the right-biased sub-group determines the lateralization of the entire group tested. We conclude that in chameleons, patterns of lateralization of visual function and body motion are inter-related at a subtle level. Presently, the patterns cannot be compared with humans' or related to the unique visual system of chameleons, with highly independent eye movements, complete optic nerve decussation and relatively few inter-hemispheric commissures. We present a model to explain the possible inter-hemispheric differences in dominance in chameleons' visual control of body motion during avoidance.

Right paw foraging bias in wild black bear (Ursus americanus kermodei)

Using field observations of ~15 wild adult black bear (Ursus americanus kermodei) foraging on a salmon stream during two autumns on the central coast of British Columbia, we tested for laterality of forelimb use during lunging and during handling of salmon. Of 288 lunging events observed overall, 53% were non biased, 26% were right-limb biased, and 21% left-limb biased (p = .53 between left and right bias). Among six bears in which we could ascertain individual identity (182 lunging events), there was heterogeneity among individuals (p <.05) of which two were significantly right biased and one significantly left biased (p<.005). Of 186 carcass-handling (pick-up) events, 68% were right-pawed (p <.005) and there was no heterogeneity among five individually identifiable bears (p = .19). There was no forelimb laterality in adjustment of the prey in the mouth or in securing the prey to the substrate. This is the first report of task-specific behavioural lateralisation of a wild carnivore and is suggestive of a right bias (left-hemisphere dominance) in object manipulation.

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.

Environmental stress increases skeletal fluctuating asymmetry in the moor frog Rana arvalis

Whether fluctuating asymmetry (FA) provides a useful metric indicator of the degree of environmental stress experienced by populations is still a contentious issue. We investigated whether the degree of FA in skeletal elements is useful in elucidating the degree of environmental stress experienced by frog populations, and further, tested the proposition that a trait's sensitivity to stress--as reflected in the degree of FA--is related to the degree of directional selection experienced by the given trait. We compared the degree of FA in four bilateral skeletal elements of male and female moor frogs (Rana arvalis) originating from low (acidified) and neutral pH populations. While the degree of uncorrected FA was unrelated to the degree of acidity, the growth rate and age of the individuals, the size-corrected FA was significantly higher in low than in neutral pH populations and decreased with individual ages and growth rates. In addition, both measures of FA were significantly higher in males and in particular in traits presumably under high sexual selection as indicated by the degree of sexual size dimorphism. All in all, the results indicate that individuals from acidified localities are smaller, younger and exhibit a significantly higher degree of FA than individuals from neutral pH populations. These results constitute the first assessment of FA in amphibians and suggest that the degree of FA in skeletal traits can be a useful indicator of the degree of environmental stress experienced by amphibian populations.

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.

Footedness in binocular and monocular chicks

The first foot used during bouts of ground scratching in 16-day-old chicks searching for food in the floor of an arena covered with sawdust was recorded in animals with normal binocular vision and in animals with an eye temporarily occluded by an eye-patch. Binocular chicks showed a significant right foot bias, whereas monocular chicks tended to use the foot contralateral to the eye in use. Data for monocular chicks thus suggest that the activated hemisphere (contralateral to the eye in use) is the one that takes control of posture, leaving to the other hemisphere reflex-like responses associated with ground scratching or body wiping. It is argued that footedness in chicks might have arisen from the limb that is used to maintain postural and positional control, rather than from the limb that is used during motor activities.

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.

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.

Limb preference and skeletal asymmetry in the cane toad, Bufo marinus (Anura: Bufonidae)

Two forms of skeletal asymmetry were identified in a population of cane toads, Bufo marinus, an exotic species in Australia. Fluctuating asymmetry characterised the lengths and weights of the long bones of the forelimbs and hindlimbs. Directional asymmetry was observed in the structure of the pectoral girdle of the toads, with the right epicoracoid positioned ventral to the left epicoracoid in 88% of the skeletons examined. Morphological data from a cohort of individuals were correlated with limb preferences determined from 10 consecutive trials in which the toads were inverted and briefly submerged in water while bilaterally clasping the experimenter's fingers. The toad's left forelimb was released first to enable the right forelimb to exert force against the experimenter's fingers and so control righting the body of the toad in 90% of trials. Asymmetries in the long bones of the forelimbs and pectoral girdles of the toads did not correlate significantly with the strength of preference for the right forelimb, although asymmetry of the weight of the tibiafibulae did correlate significantly with percent right forelimb preference. Age, or nutritional status, was a factor in the right forelimb preference: the preference for the use of the right forelimb was strongest in toads possessing longer and heavier long bones of both the forelimbs and hindlimbs. These results provide insight into the interaction between skeletal development and lateralised motor behaviour in an anuran species.

Lateralised brain function in anurans: Comparison to lateralisation in other vertebrates

In recent years researchers have begun to investigate lateralisation of behaviour in amphibians. Given the mounting evidence of lateralisation in birds and mammals, and even reptiles, over the past two or more decades, it is not surprising that amphibians have attracted attention in this context. In particular, the evidence for lateralisation in fish has provided a strong basis for this research. This paper summarises the currently available information on lateralisation in anuran amphibians and discusses it in comparison to lateralisation in other vertebrate species, beginning with examples of motor lateralisation and then discussing functional asymmetries that occur between the left and right sides of the brain. The latter are manifested as side biases in responding to different stimuli or, in a number of non-amphibian species, revealed by monocular testing. Most of the examples discussed refer to lateralisation present at the level of the forebrain hemispheres, and so represent hemispheric specialisation. Lateralisation usually refers to examples in which there is a population bias for the majority of individuals in a population to be lateralised in the same direction. In other words, there is a significant skew in the frequency distribution. Such population biases in lateralisation are now known to be widespread among the vertebrates and, as shown, there are some surprisingly similar patterns of lateralisation in those species of fish, amphibians, reptiles, birds, and mammals that have been studied so far. It is also noted that, despite their ubiquity in vertebrates, far from all forms of lateralisation develop solely, or even largely, according to genetic determinants. In fact, the clear and powerful influences of environmental stimulation on development of some kinds of lateralisation in birds provide a basis for similar investigations in anurans.

Preferential limb use in relation to epicoracoid overlap in the shoulder girdle of toads

We studied left-right asymmetry in forelimb and hindlimb use in green toads (Bufo viridis) and fire-bellied toads (Bombina bombina) and investigated its possible relationship to the asymmetric structure of the shoulder girdle (epicoracoid overlap) in the latter species. To estimate forelimb use preference we used a modified ''snout-wiping test'' (Bisazza et al., 1997) and to estimate hindlimb use preference we used the ''righting response test'' (Robins et al., 1998). The position of epicoracoids in living animals was determined as proposed earlier (Borkhvardt & Malashichev, 1997). We also examined behavioural laterality in B. viridis to check whether B. viridis is a left-handed species, as it was not clear from the previous study. Our results showed that B. viridis predominantly used the left forelimb and left hindlimb in experimental situations at both the population and individual levels. The same tests were applied to fire-bellied toads, B. bombina, with right or left epicoracoids in the top (dorsal) position. We found that (1) B. bombina is mostly a symmetric species, sometimes using both hands or feet simultaneously; (2) it is ambidextrous in hand and foot use with non-significant left side preference at the population level; (3) there is a positive and significant concordance between the position of epicoracoids and the forelimb preference in B. bombina. Animals with the right epicoracoid in the dorsal position (R. top = L. superficial) prefer to use the right forelimb in the ''snout-wiping test'' and L. top animals predominantly use their left forelimb.

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.

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.

Lateralized agonistic responses and hindlimb use in toads

The recent discovery of forepaw preferences (handedness) in toad species has provided some insight into the evolution of brain lateralization. We tested the prediction that, as in higher vertebrates, visual lateralization and other motor preferences (footedness) also exists in toad species. During feeding periods, South American cane toads, Bufo marinus, showed a population bias to strike with the tongue at other toads occupying their left visual field. This is the first demonstration of lateralized visual behaviour in an amphibian species. Tongue striking at an individual's eyes or head may sometimes delay its approach to prey already seen by the attacker, or may dislodge prey from its mouth. In addition, we report hindlimb preferences (footedness) for contact righting in three species of toad (B. marinus, the European green toad, B. viridis, and the European common toad, B. bufo). After being fully overturned on to their back on a horizontal surface, toads initiated and completed righting using the hindlimbs and with only perfunctory use of the forepaws. Together, the findings of visual lateralization and footedness demonstrate that in toads, as in higher vertebrates, behavioural lateralization is not restricted to handedness. The hypothesis that lateralized brain functions in birds and mammals might have arisen from a common lateralized ancestor is therefore supported. Copyright 1998 The Association for the Study of Animal Behaviour.

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