Effects of optokinetic stimulation on motor asymmetry in the goldfish

In goldfish fries, we examined the effect of the optomotor reaction (drive to swim toward moving images of vertical dark bars) on the behavioral motor asymmetry. Contralateral optokinetic stimulation of fishes (rotation of the bars against the direction preferred by fishes in their turnings) gradually smoothed and, later on, inverted the motor asymmetry, while the asymmetry underwent no modifications in the case of ipsilateral optokinetic stimulation (rotation of the bars in the direction similar to that preferred for turnings). Contralateral optokinetic stimulation also induced long-lasting inversion of the motor asymmetry of immobilized fishes deprived of the possibility to follow the movement of bar images. Ipsilateral optokinetic stimulation of fishes with the enucleation of the ipsilateral eye enhanced their motor asymmetry, while contralateral stimulation either did not modify the motor asymmetry of such individuals or inverted this feature. These data agree with the concept that, in fishes, one eye dominates and more actively provides tracking of the movement of bars, while another eye is a subdominant one. In general, we first found that the use of specific visual stimulation allows one to modify for a long time the behavioral motor asymmetry of the fishes, which, as is known, correlates with the morphofunctional asymmetry of Mauthner neurons (MNs). Visual information that activates MNs influences mostly the ventral dendrites of these neurons; thus, our findings allow us to believe that stimulations, which initiate the optomotor reaction, can serve as an adequate physiological model of natural visual stimulation of MNs (with projection of the respective influences on the ventral dendrites of the above cells). The use of such an experimental paradigm opens up new possibilities for studies of the role of these dendrites in the functions of MNs and of the plasticity of morphofunctional organization of these cells. Neirofiziologiya/Neurophysiology, Vol. 39, No. 2, pp. 133–145, March–April, 2007.     

Stabilization of motor asymmetry in the goldfish under the influence of optokinetic stimulation

Adaptation as a memory model appears, at the cellular level, as an increase in the resistivity of neurons to fatigue under the influence of repetitive natural training stimulation. Selective induction of adaptational changes in separate compartments of one and the same neuron can also serve as an important instrument for identification of the roles of these compartments in the integrative function of the individual neuron. Mauthner neurons (MNs) of fishes (the goldfish in particular) possess a clearly differentiated soma and two dendrites, lateral and ventral ones. The soma and lateral dendrite of each MN receive afferentation from the ipsilateral vestibular apparatus; at present, the functional and morphological aspects of selective adaptational modifications induced in these compartments by adequate vestibular stimulation have been examined in detail. As to the ventral MN dendrite receiving visual afferentation from the contralateral eye via the ipsilateral tectum, it remained impossible until now to realize the respective approach. We found that training sessions of visual optokinetic stimulation performed in certain modes provide selective activation of one MN through its ventral dendrite and increase the resistivity of this cell to fatiguing stimulation. Therefore, we first demonstrated the possibility of adaptational changes in an individual ventral dendrite of the MN. If fishes were preliminarily adapted with respect to vestibular stimulation, and the resistivity of the soma and lateral dendrite was selectively increased, the resistivity to fatiguing visual test stimulation also increased. On the other hand, if fishes were preliminarily adapted with respect to visual stimulation, the resistivity to fatiguing vestibular stimulation also increased. The observed increase in the resistivity of MNs of fishes adapted due to sensory stimulation of one afferent input with respect to sensory stimulation of other sensory input, as well as an increase in the resistivity to sensory stimulation of one modality, probably show that the mechanism of increase in the resistivity is the same in both cases. Neirofiziologiya/Neurophysiology, Vol. 40, No. 3, pp. 211–220, May–June, 2008.     

Which way to turn? Effect of direction of body asymmetry on turning and prey strike orientation in starry flounder Platichthys stellatus (Pallas) (Pleuronectidae)

Starry flounder Platichthys stellatus , a rare polymorphic flatfish exhibiting a large-scale geographic cline in the frequency of right-eyed (dextral) and left-eyed (sinistral) morphs, was studied to investigate whether foraging behaviour (turning angle and prey strike orientation) differed between dextral and sinistral laboratory-raised juveniles. Platichthys stellatus foraging on brine shrimp Artemia sp. nauplii tended to strike dorsally at prey ('left' to an observer for dextral flounder and 'right' to an observer for sinistral flounder), although this effect was stronger for sinistral fish. This dorsal tendency also increased with body size. Non-strike behaviours (movements between strikes) were ventrally biased for both morphs. Maximum turn angles were larger for both morphs towards the dorsal side than the ventral side during prey strikes but were the same during non-strike behaviours. The positioning of the eyes of the juvenile starry flounder was skewed towards the dorsal midline rather than being symmetrically placed between dorsal and ventral margins on the eyed side of each fish. The migrating eyes of dextral fish, however, were significantly closer to the dorsal midline than in sinistral fish. This, in addition to the more dorsally oriented prey strikes in sinistral fish, suggests that the morphs are not simple behavioural mirror images of one another and therefore may differ ecologically.     

Metamorphic pitx2 expression in the left habenula correlated with lateralization of eye‐sidedness in flounder

The bilateral symmetry of flounder larvae changes through the process of morphogenesis to produce external asymmetry at metamorphosis. The process is characterized by the lateral migration of one eye and pigmentation at the ocular side. Migration of the left or right eye to produce either dextral or sinistral forms, respectively, is usually fixed within a species. Here we propose a mechanism for the mediation of lateralization by the nodal‐lefty‐pitx2 (NLP) pathway in flounders, in which pitx2, the final left‐right determinant of the NLP pathway, is re‐expressed in the left habenula at pre‐metamorphosis. After the initiation of left‐sided pitx2 re‐expression, the eye commences migration, when the habenulae shift their position on the ventral diencephalon rightwards in sinistral flounder (Paralichthys olivaceus) and leftwards in dextral flounder (Verasper variegatus). In addition, the right habenula increases in size relative to the left habenula in both species. Loss of pitx2 re‐expression induces randomization of eye‐sidedness, manifesting as normal, reversed or bilateral symmetry, with laterality of the structural asymmetry of habenulae being entirely inverted in reversed flounders compared with normal ones. Thus, flounder pitx2 appears to be re‐expressed in the left habenula at metamorphosis to direct eye‐sidedness by lateralizing the morphological asymmetry of the habenulae.     

Morphological parameters of mauthner neurons of goldfishes with modified asymmetry of motor behavior

We examined the morphological peculiarities of Mauthner neurons, MNs, in goldfishes with a phenotypically different or an experimentally modified preference to perform rightward vs leftward turnings in the course of motor behavior; this preference was characterized by values of the motor asymmetry coefficient (MAC). 3D reconstruction of MNs was performed based on several histological sections; volumes of the soma, lateral and ventral dendrites (LD and VD, respectively), initial segment of the axon, as well as full volumes of the right and left neurons, were calculated. Differences between the above parameters were expressed as structural asymmetry coefficients (SACs). It was shown that clear orientation asymmetry of motor behavior of the fish is accompanied by differences in the dimensions of MNs and their compartments; MNs localized contralaterally with respect to the preferred turning side were considerably bigger than ipsilateral neurons. Experimental influences inducing inversion of the motor asymmetry of fishes inverted structural asymmetry of their MNs. In fishes with no phenotypical preference of the turning side and in individuals whose motor asymmetry was smoothed due to experimental influences (rotational stimulations), structural asymmetry of the MNs was also smoothed. Changes of the structural proportions developed, as a rule, due to decreases in the dimensions of one or both MNs and their compartments. The MAC value was in direct correlation with the value of SAC of the MNs and with values of this coefficient for the soma and the sum soma + LD. At the same time, reciprocal relations were found for the MAC and structural asymmetry of the VD; the decrease in the volume of VD was related to an increase in the preference of the contralateral turning side by the fish, and vice versa. In general, the results of our study demonstrate that both morphological and functional peculiarities of MNs correlate to a significant extent with such a form of motor behavior of fishes as realization of spontaneous turnings. Neirofiziologiya/Neurophysiology, Vol. 38, No. 1, pp. 18–31, January–February, 2006.     

Sensory development of the Antarctic silverfish Pleuragramma antarcticum: a test for the ontogenetic shift hypothesis

In 1996 Montgomery proposed an ontogenetic shift in the use of visual and non-visual senses in Antarctic notothenioid fishes, with visual dominance in larval fishes giving way to non-visual senses in adults. One prediction of the hypothesis is timing differences in the development of the respective sensory systems, with the visual system expected to develop earlier than the other systems. The volume of certain brain centres can be determined from fixed material and should correlate with sensory development. This study determined the relative volumes of visual and lateral line brain areas, and relative eye size as a function of fish length in Pleuragramma antarcticum.The relative volume of optic tectum was largest in larval fish, exhibiting a negative allometry with growth. The eminentia granularis, and crista cerebellaris (lateral line associated areas) were not recognisable in the smallest larvae; they became differentiated at standard lengths of 10–20 mm and their relative volumes continued to increase over the size range of fish studied (up to 150 mm standard length). Relative eye diameter decreased dramatically over the size range 5–25 mm and then increased such that relative eye diameter doubled over the size range 25–30 mm. A similar, but less extreme, pattern was seen over the size range 30–60 mm. Above 60 mm relative eye diameter increased slightly with size. Our interpretation is that eye growth and somatic growth are on separate trajectories, and the breaks in the relative eye diameter curve result from overwinter periods when somatic growth is static, but the eye continues to grow. These results provide support for the ontogenetic shift hypothesis, and indicate that the timing of the shift probably occurs after the second winter. Received: 22 October 1996 / Accepted: 10 January 1997     

Embryogenesis and expression profiles of charon and nodal-pathway genes in sinistral (Paralichthys olivaceus) and dextral (Verasper variegatus) flounders

Although it is well known that flounder form external asymmetry by migration of one eye at metamorphosis, the control system that forms this asymmetry is unknown. To help elucidate this mechanism, we here describe the embryogenesis and expression profiles of the Nodal-pathway genes in the Japanese flounder, Paralichthys olivaceus. We also perform a comparative study of the laterality of the expression of these genes in sinistral (P. olivaceus) and dextral (Verasper variegatus) flounders. In P. olivaceus, Kupffer's vesicle forms at the 2-somite stage, after which left-sided expression of spaw starts at the 8-somite stage. Left-sided expression of pitx2 occurs in the gut field at the 15-somite to high-pec stages, in the heart field at the 21-somite stage, and in the dorsal diencephalon at the 27-somite to high-pec stages. In response to left-sided pitx2 expression, the heart, gut, and diencephalon begin asymmetric organogenesis at the pharyngula (heart) and the long-pec (gut and diencephalon) stages, whereas the eyes do not show signs of asymmetry at these stages. In both sinistral and dextral flounders, the Nodal-pathway genes are expressed at the left side of the dorsal diencephalon and left lateral-plate mesoderm. Considering these data together with our previous finding that reversal of eye laterality occurs to some extent in the P. olivaceus mutant reversed, in which embryonic pitx2 expression is randomized, we propose that although the Nodal pathway seems to function to fix eye laterality, embryonic expression of these genes does not act as a direct positional cue for eye laterality.     

Hemispheric participation in the shaping of spatial-motor asymmetry in visual recognition in rats

Asymmetry of movement direction was found in Wistar rats at establishing of motor alimentary conditioned reflex to simultaneously presented visual stimuli. In the course of learning the asymmetry weakened on the whole, but some individuals retained right- or left side preference. The analysis of asymmetry change before and after unilateral cortical inactivation revealed a special role of right hemisphere influences for the formation of right-side preference and of the left hemisphere--for the choice of the left direction. The lack of asymmetry was observed at the presence of the influences from the left hemisphere cortex depressing ipsilateral nigro-striate system and activating the contralateral one. Influences of the cortex of both hemispheres reduce the absolute value of the asymmetry coefficient; the left hemisphere has a special significance for manifestation of temporal asymmetry parameters. Photic interference is a factor modulating the asymmetry. It reduces the right hemisphere activity more than that of the left one; it intensifies right hemisphere influences, contributes to the involvement of the transcallosal conduction channel in the formation of spatial-motor asymmetry.     

Can an eel be a flatfish? Observations on enigmatic asymmetrical heterenchelyids from the Guinea coast of West Africa

Morphological asymmetry is described in the heterenchelyid mud eel Pythonichthys cf. macrurus from inshore coastal waters of Guinea, West Africa. The intensity of asymmetry differs between two examined specimens, with the more extreme case exhibiting strong asymmetry in both external and internal features, including unilateral depigmentation, reductive degeneration and embedding of a blind‐side eye, skewed jaws with reduced dentition and tooth loss. The extent and nature of asymmetry suggests that this individual probably lived primarily on its left lateral side, not unlike sinistral pleuronectiform flatfishes.     

The developmental genetics of dextrality and sinistrality in the gastropodLymnaea peregra

Summary The genetics of body asymmetry inLymnaea peregra follows a maternal mode of inheritance involving a single locus with dextrality being dominant to sinistrality. Maternal inheritance implies that all members of a brood have the same phenotype, however, some broods contain a few individuals of opposite coil. One purpose of this paper is to explain the origin of these anomalous individuals. Genetic analyses of sinistral broods with a few dextral individuals have led to the development of a cross-over model, with the anomalous dextrals originating as a consequence of crossing over either during meiosis or mitosis in the female germ line. The crossover either reconstitutes the dextral gene from previously dissociated parts, or creates a dextral gene by means of a position effect. The probability of a crossover event depends upon the appropriate combination of complementary sinistral chromosomes. Each crossover event has the potential of creating a unique dextral gene. Genetic analyses of dextral broods containing a few sinistral individuals have demonstrated that different dextral genes vary in penetrance.The dextral gene produces a product during oogenesis which influences the pattern of cleavage in the embryo; this cleavage pattern is translated into the appropriate body asymmetry. The other purpose of this paper is to provide an assay for this gene product. Cytoplasm from dextral eggs injected into uncleaved sinistral eggs causes these eggs to cleave in a dextral pattern. Cytoplasm from sinistral eggs has no effect on the cleavage pattern of dextral eggs. While the dextral gene product is made during oogenesis, it does not function in controlling cleavage until just before this process begins.     

The dorsomedial nuclear group of cranial nerves in the frog.

The dorsomedial motor nuclei were demonstrated by the cobalt-labeling technique applied to the so-called somatic motor cranial nerves. The motoneurons constituting these nuclei are oval-shaped and smaller than the motoneurons in the ventrolateral motor nuclei. They give rise to ventral and dorsal dendrite groups which have extensive arborization areas. A dorsolateral cell group in the rostral three quarters of the oculomotorius nucleus innervates ipsilateral eye muscles (m.obl.inf., m.rect.inf., m.rect.med.) and a ventromedial cell group innervates the contralateral m. rectus superior. Ipsilateral axons originate from ventral dendrites, contralateral axons emerge from the medial aspect of cell bodies, or from dorsal dendrites, and form a "knee" as they turn around the nucleus on their way to join the ipsilateral axons. A few labeled small cells found dorsal and lateral to the main nucleus in the central gray matter are regarded as representing the nucleus of Edinger-Westphal. The trochlearis nucleus is continuous with the ventromedial cell group of the oculomotorius nucleus. The axons originate in dorsal dendrites, run dorsally along the border of the gray matter and pierce the velum medullare on the contralateral side. A compact dendritic bundle of oculomotorius neurons traverse the nucleus, and side branches appear to be in close apposition to the trochlearis neurons. A dorsomedial and a ventrolateral cell group becomes labeled via the abducens nerve. The former supplies the m. rectus lateralis, while the latter corresponds to the accessorius abducens nucleus which innervates the mm. rectractores. Neurons in this latter nucleus are large and multipolar, resembling the neurons in the ventrolateral motor nuclei. Their axons originate from dorsal dendrites and form a "knee" around the dorsomedial aspect of the abducens nucleus. Cobalt applied to the hypoglossus nerve reaches a dorsomedial cell group (the nucleus proper), spinal motoneurons and sympathetic preganglionic neurons. Of the dorsomedial motor cells, the hypoglossus neurons are the largest, and a branch of their ventral dendrites terminates on the contralateral side. Some functional and developmental biological aspects of the morphological findings, such as the crossing axons and the peculiar morphology of the accessory abducens nucleus, are discussed.     

Ipsilateral retinal projections into the tectum during regeneration of the optic nerve in the cichlid fish Haplochromis burtoni: a Dil study in fixed tissue.

Retinal projections were experimentally manipulated in a bony fish to reveal conditions under which considerably enlarged ipsilateral projections developed and persisted. Three experimental groups were studied: animals after unilateral enucleation, after unilateral nerve crush, and after enucleation and crush of the remaining optic nerve. At 29 days after unilateral enucleation alone, no enhanced ipsilateral projection had developed. After nerve crush, however, large numbers of retinal fibers regenerated into the ipsilateral tectum. Retrogradely filled, ipsilaterally projecting ganglion cells were distributed throughout the entire retina. After 15 days regenerating retinal fibers covered the entire ipsilateral tectum. At later stages the ipsilateral projection showed progressive reduction in coverage of the tectum. Combining enucleation with nerve crush led to an ipsilateral projection that covered the tectum at 28 days and later. In this experimental situation the development of an ipsilateral projection appears to be a two-step process: (1) Fibers are rerouted to the ipsilateral side at the diencephalon, and (2) ipsilateral fibers persist in the tectum only in the absence of a contralateral projection while they appear to be eliminated in the other cases.     

Right-handed snakes: convergent evolution of asymmetry for functional specialization

External asymmetry found in diverse animals bears critical functions to fulfil ecological requirements. Some snail-eating arthropods exhibit directional asymmetry in their feeding apparatus for foraging efficiency because dextral (clockwise) species are overwhelmingly predominant in snails. Here, we show convergence of directional asymmetry in the dentition of snail-eating vertebrates. We found that snakes in the subfamily Pareatinae, except for non-snail-eating specialists, have more teeth on the right mandible than the left. In feeding experiments, a snail-eating specialist Pareas iwasakii completed extracting a dextral soft body faster with fewer mandible retractions than a sinistral body. The snakes failed in holding and dropped sinistral snails more often owing to behavioural asymmetry when striking. Our results demonstrate that symmetry break in dentition is a key innovation that has opened a unique ecological niche for snake predators.     

Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

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Morphological evidence of correlational selection and ecological segregation between dextral and sinistral forms in a polymorphic flatfish, Platichthys stellatus

Phenotypic polymorphisms in natural systems are often maintained by ecological selection, but only if niche segregation between morphs exists. Polymorphism for eyed-side direction is rare among the approximately 700 species of flatfish (Pleuronectiformes), and the evolutionary mechanisms that maintain it are unknown. Platichthys stellatus (starry flounder) is a polymorphic pleuronectid flatfish exhibiting large, clinal variation in proportion of left-eyed (sinistral) morphs, from 50% in California to 100% in Japan. Here I examined multiple traits related to swimming and foraging performance between sinistral and dextral morphs of P. stellatus from 12 sites to investigate if the two morphs differ in ways that may affect function and ecology. Direction of body asymmetry was correlated with several other characters: on an average, dextral morphs had longer, wider caudal peduncles, shorter snouts and fewer gill rakers than sinistral morphs. Although the differences were small in magnitude, they were consistent in direction across samples, implying that dextral and sinistral starry flounder may be targeting different prey types. Morphological differences between morphs were greatest in samples where the chances of competitive interactions between them were the greatest. These results suggest that the two morphs are not ecologically identical, may represent a rare example of divergent selection maintaining polymorphism of asymmetric forms, and that correlational selection between body asymmetry and other characters may be driven by competitive interactions between sinistral and dextral flatfish. This study is one of very few that demonstrates the ecological significance of direction in a species with polymorphic asymmetric forms.     

Lateral asymmetry of eye use in Octopus vulgaris

The lateralization of sensory and motor functions has been recently demonstrated in various groups of vertebrates. We examined lateral asymmetry of eye use in Octopus vulgaris by behavioural methods. Octopus vulgaris uses monocular vision almost exclusively and can move its eyes independently. The amount of binocular vision is small because the eyes are on the sides of the head. We tested eight octopuses in two conditions (one with and one without moving stimuli) where the use of the eye for frontal vision could be determined unequivocally. Data were recorded on videotape. All animals showed a preference for one eye (five left, three right). There was no correlation between eye use and the animal's direction of movement. Pigmentation of the ventral side of the arms tended to be most intense on the side of the preferred eye and the body was most pigmented on the side of the eye currently in use. We found no sex differences for visual lateralization. Pigmentation of the ventral side of the arms was lighter in females than in males. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Whole-body enantiomorphy and maternal inheritance of chiral reversal in the pond snail Lymnaea stagnalis

Sinistral and dextral snails have repeatedly evolved by left-right reversal of bilateral asymmetry as well as coiling direction. However, in most snail species, populations are fixed for either enantiomorph and laboratory breeding is difficult even if chiral variants are found. Thus, only few experimental models of chiral variation within species have been available to study the evolution of the primary asymmetry. We have established laboratory lines of enantiomorphs of the pond snail Lymnaea stagnalis starting from a wild population. Crossing experiments demonstrated that the primary asymmetry of L. stagnalis is determined by the maternal genotype at a single nuclear locus where the dextral allele is dominant to the sinistral allele. Field surveys revealed that the sinistral allele has persisted for at least 10 years, that is, about 10 generations. The frequency of the sinistral allele showed large fluctuations, reaching as frequent as 0.156 in estimate under the assumption of Hardy-Weinberg equilibrium. The frequency shifts suggest that selection against chiral reversal was not strong enough to counterbalance genetic drift in an ephemeral small pond. Because of the advantages as a model animal, enantiomorphs of L. stagnalis can be a unique system to study aspects of chirality in diverse biological disciplines.     

Asymmetry of Motor Behavior of the Goldfish in a Narrow Channel

We studied swimming of goldfish fries about 3 cm long in a narrow channel by calculating the numbers of spontaneous turns on different sides. The ratio of fishes preferring to turn to the right vs to the left was 1.5:1.0, respectively; two-thirds of the fishes demonstrated an ambilateral behavior. Experiments with compulsory 10-min-long rotation of the fishes (clockwise around the longitudinal body axis for fishes preferring right-side turns and anticlockwise for fishes preferring left-side turns) showed that the behavioral asymmetry smoothed somewhat after such a procedure, and a greater number of the fishes became ambilateral in their preference to turn to one side or another. After a one- or two-day-long test, the initial asymmetry of motor behavior completely recovered. Compulsory rotation of similar fishes in the opposite direction exerted no influence on the asymmetry in the choice of the turning direction. Adaptation-induced training of the fishes (using fatiguing long-lasting vestibular stimulation) resulted in some smoothing of motor asymmetry but did not change its general pattern. Thus, our findings allow us to believe that a noticeable proportion of the goldfish individuals (similarly to other animals and humans) is characterized by an innate asymmetry of the motor function with a clear preference for either right- or left-side turnings. These relations can be smoothed under experimental influences but are recovered later on, i.e., they are stable and are not fundamentally transformed. We assume that the asymmetry of motor behavior of fishes in a narrow channel can be an adequate pre-requisite for further examination of the asymmetry of the brain and motor centers controlling changes in locomotion (body turnings)Neirofiziologiya/Neurophysiology, Vol. 37, No. 1, pp. 52–60, January–February, 2005.     

Multiple reversals of chirality in the land snail genus Albinaria (Gastropoda,Clausiliidae)

Reversed chirality has frequently evolved in snails, although the vast majority coils dextrally. However, there are often sinistral species within a dextral genus or almost exclusively sinistral families, such as the Clausiliidae. Some populations of the predominantly sinistral clausiliid genus Albinaria, in the southern Greek mainland, coil dextrally. The origin, evolution and distribution of the dextral Albinaria are puzzling, and as there is no reliable phylogenetic reconstruction for this speciose genus, it remains unclear how many times a shift in chirality has really occurred. In this study, our aim was to elucidate the evolutionary pathways of dextrality in Albinaria. We undertook a molecular phylogenetic analysis of two mtDNA (16S and COI) and one nDNA marker (ITS1) and included dextral and sinistral representatives found in syntopy or not. Both mtDNA and nDNA tree topologies imply that dextrals did not evolve as a monophyletic lineage. Instead, dextral lineages have evolved from sinistral ancestors multiple times independently. The fragmented population structure in Albinaria facilitates genetic drift and contributes to fixation of the opposite chirality and overcoming of the mating disadvantage of left–right reversal. Stochastic phenomena and biogeographical barriers have trapped those reversals in a limited geographical area.