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.     

Rotational stimulation-related changes of the motor asymmetry in the goldfish

We studied changes in the motor asymmetry of the goldfish induced by single-session long-lasting vestibular stimulations (clockwise and counter clockwise rotations around the rostro-caudal body axis) and repetitive everyday short sessions of such stimulation (training); the latter mode led to the development of adaptation (resistance to fatigue). Rotational stimulation of different durations and directions elicited effects of different patterns and intensities. Such stimulation enhanced or, vice versa, smoothed the motor asymmetry in “dextral” and “ sinistral” fishes, up to full symmetry or even a change of the preferred turning direction. Adaptation to unilateral rotational stimulation allows an experimenter to selectively and gradually induce the resistivity of the left-or right-ward asymmetry to fatigue effects. Earlier, we found that the motor asymmetry in the goldfish, which is determined by the functional asymmetry of the brain, correlates with the morphological asymmetry of Mauthner neurons localized in the medulla in a mirror manner and playing a crucial role in the control of turnings in the course of locomotion (swimming). Experimental rotational stimulation-induced gradual modification of the motor asymmetry in the goldfish can serve as a physiological model for more detailed studies of the structural base of the functional brain asymmetry and some mechanisms of adaptation on the level of single neurons. Neirofiziologiya/Neurophysiology, Vol. 37, Nos. 5/6, pp. 432–442, September–December, 2005.     

Feeding behaviour of reared and wild cod and the effect of learning: two strategies of feeding on the two-spotted goby

This study investigates possible differences in the feeding behaviour of reared and wild cod Gadus morhua and the effect of learning in connection with sea-ranching experiments. In two laboratory experiments, single individuals, reared or wild, were allowed to prey upon 15 two-spotted gobies Gobiusculus flavescens in trials of 30 min duration. Reared and wild cod seldom attacked stationary gobies and generally attacked moving gobies, and reaction times were similar (c. 0·25 s). Reared and wild cod ingested similar numbers of gobies per trial. Reared cod, however, caught more gobies in pursuits, while wild cod took more gobies in lunges. Reared cod had higher costs as measured by a higher index of energy expenditure and a higher opercular beat frequency, and wild cod were thus more efficient (benefit divided by cost). The efficiency of both groups tended to increase as they gained experience. The results indicate that reared cod more often used a pursuit strategy and wild cod more often a lunge strategy. Differences in previous experience may have initiated the strategies, and the success of each strategy in the experimental situation, in addition to the potential cost of changing strategy, may have maintained them. For cod released into a natural habitat, a pursuit strategy may lead to low efficiency vis-à-vis mobile prey and could also involve a high risk of predation, forcing reared Cod to change strategy.     

Early hominid feeding mechanisms.

Three predominant influences mark the evolution of human head form: big brain, erect bipedalism, modified oral apparatus. Confusing interplay between different adaptive requirements of each feature has made explanation of skull structure extremely difficult in the past. It now seems possible to isolate each influence in early fossil forms. A model of mammalian modes of feeding adaptation is proposed in the form of a “Natural Experiment” for tighter analysis of fossil forms. Two forms of australopithecines are recognized, “gracile” and “robust.” Both had closely similar brains, both had erect bipedalism, but each had different masticatory construction. Separation of the first two similar influences isolates the adaptive differences in oral mechanics. The gracile form had a projecting oral apparatus, distinct canine and zygomatic buttresses, moderate jaw-lever development, jaw joint not unlike most higher primates, large unusual anterior teeth, moderately sized posterior teeth. The robust form had a retruded, greatly deepened oral apparatus, “dished-in” face with fused canine and zygomatic buttresses, powerful jaw-lever development, distinctively different joint construction, remarkably small anterior teeth, enormous posterior teeth. Striking evidence for extraordinary jaw movements emerges from these features in the robust form. This is strongly supported by remarkably close parallels in Ursidae: grizzly bear and giant panda.     

Mixture analysis of asymmetry: modelling directional asymmetry, antisymmetry and heterogeneity in fluctuating asymmetry

The occurrence of different forms of asymmetry complicates the analysis and interpretation of patterns in asymmetry. Furthermore, between-individual heterogeneity in developmental stability (DS) and thus fluctuating asymmetry (FA), is required to find relationships between DS and other factors. Separating directional asymmetry (DA) and antisymmetry (AS) from real FA and understanding between-individual heterogeneity in FA is therefore crucial in the analysis and interpretation of patterns in asymmetry. In this paper we introduce and explore mixture analysis to (i) identify FA, DA and AS from the distribution of the signed asymmetry, and (ii) to model and quantify between-individual heterogeneity in developmental stability and FA. In addition, we expand mixtures to the estimation of the proportion of variation in the unsigned FA that can be attributed to between-individual heterogeneity in the presumed underlying developmental stability (the so-called hypothetical repeatability). Finally, we construct weighted normal probability plots to investigate the assumption of underlying normality of the different components. We specifically show that (i) model selection based on the likelihood ratio test has the potential to yield models that incorporate nearly all heterogeneity in FA; (ii) mixtures appear to be a powerful and sensitive statistical technique to identify the different forms of asymmetry; (iii) restricted measurement accuracy and the occurrence of many zero observations results in an overestimation of the hypothetical repeatability on the basis of the model parameters; and (iv) as judged from the high correlation coefficients of the normal probability plots, the underlying normality assumption appears to hold for the empirical data we analysed. In conclusion, mixtures provide a useful statistical tool to study patterns in asymmetry.     

Bacterivory by heterotrophic flagellates: community structure and feeding strategies

Heterotrophic flagellates (HF) are known as most important grazers of bacteria in many aquatic ecosystem. HF cannot be treated as a black box since HF generally contain a diverse community of species significantly differing in their feeding behaviour and other ecological properties. Today it seems that the dominant taxonomic groups among heterotrophic nano- and microflagellate communities within different marine, brackish and limnetic pelagic communities (heterokont taxa, dinoflagellates, choanoflagellates, kathablepharids) and benthic communities (euglenids, bodonids, thaumatomonads, apusomonads, cercomonads) are relatively similar. HF among protista incertae sedis, often neglected in ecological studies, are abundant bacterivores in all investigated habitats. Recent studies of flagellate feeding processes indicated that there are significant species-specific differences and individual variability regarding the food uptake and food selection of bacterivorous flagellates: Variability of bacterivory is discussed regarding the prevailing feeding modes, the energy budgets, the considerable importance of slight deviations in the time budgets of feeding phases, the ingestion rates and the feeding microhabitat, respectively. The significant flexibility of the grazing impact of bacterivorous flagellate communities creates a complex top-down pressure on bacteria which should have lead to the evolution of efficient predator avoidance mechanisms in bacteria and should be at least partly responsible for the diversity of present bacteria. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Morphological studies of facial skeleton asymmetry in pongidae and hominid primates

On the question of asymmetry in the upper facial skeleton, ten samples of hominoid primates were investigated in a comparative metrical analysis. Generally, there was a slight dominance in the right-handed measurements. With one exception these findings could be confirmed statistically, whereas sexual dimorphism could not be shown to be significant in this respect. The question, whether the differences between right and left measurements show a bimodal distribution and so suggest a certain amount of reversed asymmetry, could not be answered clearly because the sample size was limited. Most of the distributions are explicable in accordance with this assumption.     

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.     

Patterns in the life histories and feeding strategies of British macrolepidoptera

Temperate Lepidoptera typically have life cycles of a year or less. The time available to feed and attain a suitable state for reproduction might thus constrain potential life-history patterns, and species characteristics such as adult size, overwintering stage, first month of larval feeding and feeding specificity may only occur in particular combinations. Several studies have documented correlates of feeding ecology which suggest this is indeed the case. We use data for more than 900 British macrolepidoptera to establish relationships among several ecological and life-history variables to determine whether only particular combinations can occur. Few patterns of feeding characteristics predicted in the literature are observed. Distinct, consistent life-history syndromes cannot be defined; almost any combination of the life-history characteristics we looked at can occur. So long as it is possible to fit in with timing constraints at certain critical times of year, there seems to be a great deal of flexibility in how the rest of the time can be filled. However, several broad and potentially interesting patterns still emerge. Polyphagous species are larger than specialists; the month in which species start to feed inlinked to both their overwintering stage and the growth form of the plant they feed upon; and there are no species overwintering in the egg stage and having two broods per year.     

Condition-dependent asymmetry is fluctuating asymmetry

Asymmetry has been demonstrated to play a role in signalling systems such as sexual selection and pollination, with receivers showing a preference for symmetrical signals. Large signals often have the smallest degree of asymmetry, a finding that is consistent with signal asymmetry being condition-dependent. The kind of asymmetry displayed by signals was supposed or shown to be fluctuating asymmetry, and signals revealing individual differences in the ability to stabilize developmental processes, despite a hostile developmental environment, was supposed to be the basis for the preference for symmetric signals. Recently, it has been suggested that condition-dependent signals display antisymmetry rather than fluctuating asymmetry, based on analyses of the relationship between asymmetry and mean length of the left and the right character in a few published graphs of absolute asymmetry of signals. Here I demonstrate on the basis of a much larger number of data sets, including those previously published, that the previous results are biased because of the methods used for the analyses, and that characters with condition-dependent asymmetry show fluctuating asymmetry rather than antisymmetry. In particular, frequency distributions of signed left-minus-right character values display leptokurtosis, as predicted if asymmetry distributions reflected individual differences in developmental precision, rather than platykurtosis. Platykurtosis is predicted if the traits are antisymmetric. The preponderance of leptokurtic distributions is consistent with recent modelling showing that inherent differences in the ability of individuals to control developmental processes invariably leads to leptokurtic distributions of signed left-minus-right character values.     

The usefulness of destructive host feeding parasitoids in classical biological control: theory and observation conflict

Abstract.

• 1 We examine the conventional wisdom among biological control practitioners that destructive host feeding is a desirable attribute in parasitoids employed for classical biological control, using both the predictions of population dynamics theory and historical data on biological control introductions of Hymenoptera against Homoptera.
• 2 Population dynamics theory predicts that destructive host feeders, compared with other parasitoids, are (a) either just as likely or more likely to become established, and (b) unable to depress host equilibria as strongly.
• 3 Analyses of the B IOC AT database suggest that among parasitoids of Homoptera destructive host feeders are superior to other parasitoids with respect to both establishment rate and success rate.
• 4 We present likely explanations for the disparity between the predictions of population dynamics theory and the results of database analysis. A partial explanation for the mismatch between theory and observation with respect to the degree of pest suppression may be that females of destructive host feeding parasitoids rely less upon hosts as a food source when alternative foods such as honeydew and nectar are plentiful.
• 5 We conclude that, despite the predictions of population dynamics theory, destructive host feeders are probably better biological control agents than other parasitoids, and certainly no worse, but that it would imprudent to use destructive host feeding as the sole, or even primary, selection criterion when seeking agents for classical biological control.

     

Directional asymmetry in the forelimb of Macaca mulatta

Asymmetry was investigated in the forelimbs of 150 rhesus monkey (Macaca mulatta) skeletons using measurements of right and left humerii, radii, ulnae, second metacarpals, and femora. Seven of the ten forelimb dimensions were larger on the right than on the left side. Paired t-tests revealed that the mean of the right side was significantly larger than that for the left for two measurements of the ulna and two of the humerus. No measurement was significantly larger on the left than on the right side. These results indicate a small but significant asymmetry in the forelimb bones of rhesus monkeys and, as is the case for humans, the direction of asymmetry favors the right side. Our findings are consistent with an interpretation of hypertrophy of certain muscles and opens the question of whether rhesus monkeys preferentially use their right forelimbs for manipulative tasks that require manual dexterity, as is the case for humans. These forelimb skeletal asymmetries are discussed in light of the recent literature on cortical asymmetry and handedness in nonhuman primates.     

Fluctuating asymmetry and sexual selection

Fluctuating asymmetry occurs when an individual is unable to undergo identical development on both sides of a bilaterally symmetrical trait. Fluctuating asymmetry measures the sensitivity of development to a wide array of genetic and environmental stresses. We propose that fluctuating asymmetry is used in many signalling contexts for assessment of an individual's ability to cope with its environment. We hypothesize that fluctuating asymmetry is used in sexual selection, both in fighting and mate choice, and in competition for access to resources. Evidence is reviewed showing that the patterns of fluctuating asymmetry in secondary sexual characters differ from those seen in other morphological traits. Secondary sexual characters show much higher levels of fluctuating asymmetry. Also, there is often a negative relationship between fluctuating asymmetry and the absolute size of ornaments, whereas the relationship is typically U-shaped in other morphological traits. The common negative relationship between fluctuating asymmetry and ornament size suggests that many ornaments reliably reflect individual quality.     

Fluctuating asymmetry and aggression in boys

Fluctuating asymmetry (FA) is small deviations from perfect symmetry in normally bilaterally symmetrical traits. We examined the relationship between FA of five body traits (ear height, length of three digits, and ankle circumference) and self-reported scores of physical and verbal aggression in a sample of 90 boys aged 10 to 15 years. The relationships between FA and scores of aggression (particularly physical aggression) were found to be negative; in other words, the most symmetrical boys showed highest aggression. One trait (ankle circumference) showed the characteristics of “ideal” FA—parametric mean of zero and a normal distribution. Mean asymmetries calculated from six repeated measures of ankle FA in 30 subjects taken over a period of five months showed strong negative associations with scores of physical aggression which were independent of age, height, and weight. It is argued that soft tissue “cyclical” FA (as opposed to “fixed” bony FA) is dependent on the secretion of hormones: for example, cortisol. Causal associations between behavioral traits such as aggresion and hormones will lead to similar correlations between FA and behavior. John Manning is a senior lecturer in the School of Biological Sciences at the University of Liverpool. His research interests are in symmetry as an indicator of good genes, disease resistance, fertility, and hormonal status in human and nonhuman animals. Daniel Wood has a B.Sc. in anatomy and biology from Liverpool University. At present he is a postgraduate student in the School of Biological Sciences. His research interests are in fluctuating asymmetry and its behavioral correlates in adolescent boys.     

Commissural asymmetry in brachiopods

Consistent asymmetric folding of the commissure is a characteristic feature of a small but significant number of brachiopod species. The feature may be obligate or facultative and is almost entirely confined to rhynchonellids, most of which are Mesozoic. The detailed nature of the asymmetry is very variable, but does not extend to internal hard parts such as crura. Taken as a whole, asymmetric brachiopod species show no preference for any particular environment or geographic region, and in no circumstances seem to have been markedly more or less successful than symmetric species. We are thus led to suggest that asymmetry was a genetically based condition which cropped up periodically in brachiopod evolution, and which possibly was selected neither particularly for nor against.     

Mandible asymmetry and genetic diversity in island populations of the common shrew, Sorex araneus

Mandibles from 13 island and six mainland populations of common shrews from the west coast of Scotland were subjected to geometric morphometric analysis in order to investigate the relationship between genetic diversity and fluctuating asymmetry. Although population mean shape fluctuating asymmetry (FA) and size FA were significantly inversely correlated with population genetic diversity this result was substantially due to one island. Sanda, the smallest island with by far the lowest genetic diversity, also had the highest FA. When Sanda was removed from the analysis, the relationship was not significant. There was no relationship between genetic diversity and FA at the individual level, whether measured as mean locus heterozygosity or d(2). In general, if genetic variation affects FA at all, the effect is weak and may only be of biological interest in very small populations.     

Surface deposit feeding versus filter feeding in the amphipod Corophium volutator

The previously indicated ability of the amphipod Corophium volutator to switch between deposit feeding and filter feeding was confirmed and studied in more detail in controlled laboratory experiments in which filtration rate measurements were combined with simultaneous video recordings of surface-feeding activity of the amphipod exposed to different known concentrations of algal (Tetraselmis sp.) cells. When algal cells were added to the ambient water, this stimulated C. volutator, buried in natural sediment or transferred to glass tubes, to commence filter feeding, which was maintained as long as the algal concentration was kept above a certain threshold level. However, shortly after the algal concentration was grazed below the threshold level, filter feeding was abandoned and replaced by surface deposit feeding, as evident from a video observed increase in surface scraping frequency. The average frequency of surface scraping was 0.64±0.27 min^-1, with a residence time of 3.7±1.4 s on the sediment surface where the amphipod grabbed material within a semicircle. Such detailed knowledge of filter feeding versus deposit feeding in C. volutator is of importance for a better understanding of the ecological role of this key organism in many shallow-water ecosystems where the feeding conditions are frequently changing.