Preferred Zones Research Articles

The turbulent life of Sirevirus retrotransposons and the evolution of the maize genome: more than ten thousand elements tell the story

Sireviruses are one of the three genera of Copia long terminal repeat (LTR) retrotransposons, exclusive to and highly abundant in plants, and with a unique, among retrotransposons, genome structure. Yet, perhaps due to the few references to the Sirevirus origin of some families, compounded by the difficulty in correctly assigning retrotransposon families into genera, Sireviruses have hardly featured in recent research. As a result, analysis at this key level of classification and details of their colonization and impact on plant genomes are currently lacking. Recently, however, it became possible to accurately assign elements from diverse families to this genus in one step, based on highly conserved sequence motifs. Hence, Sirevirus dynamics in the relatively obese maize genome can now be comprehensively studied. Overall, we identified >10 600 intact and approximately 28 000 degenerate Sirevirus elements from a plethora of families, some brought into the genus for the first time. Sireviruses make up approximately 90% of the Copia population and it is the only genus that has successfully infiltrated the genome, possibly by experiencing intense amplification during the last 600 000 years, while being constantly recycled by host mechanisms. They accumulate in chromosome-distal gene-rich areas, where they insert in between gene islands, mainly in preferred zones within their own genomes. Sirevirus LTRs are heavily methylated, while there is evidence for a palindromic consensus target sequence. This work brings Sireviruses in the spotlight, elucidating their lifestyle and history, and suggesting their crucial role in the current genomic make-up of maize, and possibly other plant hosts.

The complex impact structure Serra da Cangalha, Tocantins State, Brazil

Abstract– Serra da Cangalha is a complex impact structure with a crater diameter of 13,700 m and a central uplift diameter of 5800 m. New findings of shatter cones, planar fractures, feather features, and possible planar deformation features are presented. Several ring‐like features that are visible on remote sensing imagery are caused by selective erosion of tilted strata. The target at Serra da Cangalha is composed of Devonian to Permian sedimentary rocks, mainly sandstones that are interlayered with siltstone and claystones. NNE–SSW and WNW–ESE‐striking joint sets were present prior to the impact and also overprinted the structure after its formation. As preferred zones of weakness, these joint sets partly controlled the shape of the outer perimeter of the structure and, in particular, affected the deformation within the central uplift. Joints in radial orientation to the impact center did not undergo a change in orientation during tilting of strata when the central uplift was formed. These planes were used as major displacement zones. The asymmetry of the central uplift, with preferred overturning of strata in the northern to western sector, may suggest a moderately oblique impact from a southerly direction. Buckle folding of tilted strata, as well as strata overturning, indicates that the central uplift became gravitationally unstable at the end of crater formation.

How do disconnected macropores in sloping soils facilitate preferential flow?

AbstractRunoff from hillslopes is generated by processes such as infiltration‐excess and saturation overland flow, subsurface stormflow and subsurface return flow. Preferential flow through macropores can affect any one of these runoff generation processes. Field studies at the Hitachi Ohta Experimental Watershed in Japan have noted that self‐organization processes may manifest the connectivity of such subsurface flow paths, particularly via macropores, from hillslopes to stream channels. It is well established from soil physics principles that the connectivity of macropore networks depends on soil wetness and this has been shown experimentally at Hitachi Ohta where subsurface flow and streamflow respond to thresholds of wetness. Numerical solutions to the three‐dimensional Richards equation are derived for a sloping soil block containing a population of disconnected macropores of various sizes, shapes and orientations. Solutions for the case of steady water flux applied to the surface of the soil block are evaluated to determine the conditions where the disconnected macropores become active in the flow process. Results show that subsurface flow is directed through the preferential flow network in the saturated portion of the soil but bypasses the macropores in the drier regions. The preferential flow network expands as the degree of saturation increases. The expanding network of active macropores leads to less resistance to overall flow in the domain and access to increased volumes of the flow domain. Although the individual macropores are disconnected, it is argued that large localized hydraulic gradients can potentially lead to preferred zones of subsurface erosion. In addition to the importance of these findings related to stormflow generation in catchments, they add support to the concept of self‐organization of subsurface flow systems in soils. Copyright © 2010 John Wiley & Sons, Ltd.

Tricksters Trot to America: Areal Distribution of Folklore Motifs

The folklore Trickster is usually considered a universally known com- bination of features intrinsic to human nature. However, there are strong anoma- lies in the areal distribution of such a figure. Sub-Saharan Africa, North America (except for the Arctic), Northeast Asia and South American Chaco not only are the preferred zones of tricksters' activity but also share some peculiar trickster motifs unknown in most of the other regions. The range of animals which play the role of tricksters is also restricted and not always easily explained, E.g. the Hare and Spider, known in both Africa and North America, are neither media- tors between life and death (suggested by C. Levi-Strauss for Coyote) nor re- ally tricky (materialistic hypothesis of M. Harris). The set of trickster motifs and the zoo- or anthropomorphic impersonations of the Trickster are independ- ent variables. The same episodes are easily linked to different tricksters while every trickster usually attracts episodes characteristic of a particular region. Though the original emergence of Trickster as a mental construct can indeed be rooted in human psychology (and where else?), the distribution of tricksters in folklore is discretionary and depends of many uncertain, i.e. chance, factors. The wide spread or lack of tricksters in certain cultural areas hardly reflect any fundamental differences in the psychology of inhabitants of these regions. The study of trickster motifs, just as of any other folklore motifs, helps us recon- struct possible historic links between populations. The African - North Ameri- can links remain enigmatic (independent emergence is possible but slight his- torical links cannot be completely excluded) but the parallels between (Western and Northeast) Siberian - North American tricksters are almost certainly due to former cultural ties across Northern Asia. Another interesting case is the proliferation of tricksters with different zoomorphic and other identities (Mink, Blue Jay, Raccoon, Ice, South Wind, etc.) inside a small area of North America (Plateau and the adjacent part of the Northwest Coast) between two large zones of the Raven and of Coyote. Study of such cases helps us reconstruct cultural processes that little is known about, and some of them are very ancient.

Likelihood ratio test-based interval estimate of the number of signals present in a measurement

A multi-step procedure is proposed to construct a confidence interval for the number of signals present and a comparative analysis of our procedure with other existing procedures is conducted. The proposed procedure uses likelihood ratio statistics and its simulated percentiles sequentially to determine the upper and lower limits for the confidence interval. A preference zone in the parameter space of the population eigenvalues is defined and it is used to separate the signals and the noise. The least favourable configuration (LFC) is derived asymptotically under the preference zone. Under the LFC, the procedure parameters necessary to attain the required confidence level are determined. A comparative analysis with other procedures is presented in tables.

Dynamics of a strongly nonlinear vibration absorber coupled to a harmonically excited two-degree-of-freedom system

This paper investigates suppression of vibrations in 2dof forced linear system with a nonlinear energy sink (NES) attached. Ability of the properly tuned single NES to successfully absorb energy from both excited modes of the linear subsystem is demonstrated. The proposed methodology of the NES tuning is based on the results of analytic treatment. The strongly nonlinear vibration absorber is compared to the best-tuned linear one and excitation zones of preference of the nonlinear absorber are revealed.

Control panel with activation zone

An interchangeable hearing aid control panel with at least one activation zone arranged in connection with a layered structure. The layered structure has an electrically non-conducting substrate, an electrically conducting path arranged in connection with the substrate, and an electrically conducting member, such as a conducting foil, arranged at a predetermined distance from the activation zone. The activation zone can be either in a deactuated or in an actuated state. In the actuated state the conducting member and the conducting path are electrically connected while disconnected in the deactuated state. Electrical connection to an associated hearing aid is by means of a connector, such as a plug, enabling the control panel to be easily changed. Preferably, the connector is formed by a piece of flexprint. The layered structure may comprise a second conducting path. In preferred embodiments activation zones are indicated by “poppel domes” formed by a surface layer covering the layered structure. The activation zones may form an MTO control or a volume control. To fit BTE hearing aids, the layered structure preferably has an elongated structure with a length of 1-4 cm. Other shapes can be formed to fit ITE, ITC and CIC hearing aids. In preferred embodiments, the control panel comprises one or more Silicon-based microphones protected behind a surface layer of the control panel.

Coastline topography affects the distribution of indigenous and invasive mussels

Coastline topography has important effects on nearshore oceanography, larval trans- port, settlement and the adult distribution of benthic organisms. The resultant physical regime also influences interactions between invasive and indigenous species. Such interactions can alter inter- tidal communities dramatically, including the local extinction and replacement of native species. We examined the effect of bays and their associated headlands on the distribution of indigenous (Perna perna) and invasive (Mytilus galloprovincialis) mussels along 500 km of the south coast of South Africa. Within this single biogeographic region, mussel cover was estimated at 22 sites across 4 bays and the intervening open coast. Given that mussel biomass is greater at intermediate levels of wave exposure and that wave exposure is strongly dependent upon coastline topography, we hypothesised that mussel cover would be greater in bays, and that bays would specifically favour M. galloprovin- cialis which is more easily disturbed by strong waves. The 2 species show partial vertical separation into 3 zones within the lower eulittoral zone. Both species had significantly greater cover within bays. There was, however, an interaction between bay and zone for P. perna, and the effect of bays was strongest within the preferred zones of each species. Although the overall effect of bay was stronger for M. galloprovincialis than for P. perna, this resulted from the strong spatial structure identified for the M. galloprovincialis distribution using semivariogram analysis. Overall findings illustrate how coastline topography and local processes operate in synchrony to affect the dynamics of invasive and indigenous intertidal species.

The dry season governs the reproduction of three pseudostigmatid zygopterans in Costa Rica (Odonata: Pseudostigmatidae)

The large Neotropical zygopterans Megaloprepus caerulatus, Mecistogaster linearis and M. ornata (Pesudostigmatidae) were surveyed during five years, and striking differences in their reproduction patterns were shown: (1) At two study sites in seasonal, tropical semi-dry forests in Pacific Costa Rica, adult M. ornata could be observed throughout the year, occasionally during the dry season up to 24 indivi duals at one time. Larvae were found from the middle to the end of the wet season suggesting a generation time of one year. (2) At two other study sites in aseasonal tropical wet forest in Caribbean Costa Rica, adults of M. caerulatus were observed year round, often in rather low numbers. Larvae of this species as well as M. linearis appeared throughout the year. While dry periods and rainfall certainly are key factors in governing the reproductive patterns of these species in relation to the climatic regimes of their preferred life zones, it is also concluded that competition from other container dwellers, including tadpoles of poison arrow frogs, may be additional factors in explaining their seasonal variation. It is also argued that all three species seem to have a high plasticity in their life cycles and hence are able to adapt to local conditions rather than displaying the same behaviour throughout their range.

Comparison of two multicriteria decision aid methods: Net Flow and Rough Set Methods in a high yield pulping process

This investigation presents a synthesis of two multicriteria analysis methods, Rough Set Method (RSM) and Net Flow Method (NFM), applied to the multicriteria optimisation for the manufacture of paper using jack pine as the source of fibres. This work is the result of a collaboration between different Canadian and French laboratories. The two optimisation methods, based on different approaches, are applied to the same Pareto domain of non-dominated operating conditions. The Rough Set Method (RSM) uses a set of decision rules that are based on the preferences of experts, when presented with a small set of diverse conditions extracted from the Pareto domain. These rules are then applied to the entire Pareto domain to determine the preferred zone of operation. In the Net Flow Method (NFM), the preferences of experts are defined with three threshold values and one set of weights that are used to classify the entire Pareto domain. The NFM is a hybrid of two methods between ELECTRE and PROMETHEE. To compare these two methods, they were used to optimise the identical process. Results clearly show that the two methods gave nearly identical optimal solutions and well within inherent experimental errors.

Zones of bimanual and unimanual preference within human primary sensorimotor cortex during object manipulation

We asked which brain areas are engaged in the coordination of our hands in dexterous object manipulations where they cooperate for achieving a common goal. Well-trained right-handers steered a cursor on a screen to hit successively displayed targets by applying isometric forces and torques to a rigid tool. In two bimanual conditions, the object was held freely in the air and the hands thus generated coupled opposing forces. Yet, depending on the mapping rule linking hand forces and cursor movements, all subjects selected either the left or the right hand as prime actor. In two unimanual conditions, the subjects performed the same task with either the left or the right hand operating on a fixed tool. Functional magnetic resonance imaging revealed common activation across all four conditions in a dorsal fronto-parietal network biased to the left hemisphere and in bilateral occipitotemporal cortex. Contrary to the notion that medial wall premotor areas are especially active in complex bimanual actions, their activation depended on acting hand (left, right) rather than on grip type (bimanual, unimanual). We observed effects of grip type only in the primary sensorimotor cortex (SMC). In particular, with either hand as prime actor, bimanual actions preferentially activated subregions of the SMC contralateral to the acting hand. A sizeable subregion with preference for unimanual activity was found only in the left SMC in our right-handed subjects. Collectively, these results indicate a hemispheric asymmetry for the SMC and that partially different neural populations support the control of bimanual versus unimanual object manipulations.

Effect of fluvial and geomorphic disturbances on habitat segregation of tree species in a sedimentation-dominated riparian forest in warm-temperate mountainous region in southern Japan

We investigated habitat segregation and patterns of species diversity of trees in relation to variations in fluvial and geomorphic disturbances (erosion or sedimentation) along a longitudinal stream gradient from V-shaped valley to alluvial fan and between valley and adjacent hill slopes in a warm-temperate mountainous riparian forest in Kyushu, southwestern Japan. We longitudinally divided the riparian area into four geomorphic zones: V-shaped valley (VV-zone), upper fan (UF-zone), middle fan (MF-zone), and lower fan (LF-zone). We surveyed the distribution of tree species (diameter at breast height ≥3 cm) in the four riparian zones and in additional plots on hill slopes (SL-zone) representing the broader, nonriparian forest matrix. Detrended correspondence analysis ordination demonstrated variations in species composition along the longitudinal stream gradient. Species guild analysis based on the detection of the species preferred zone by a bootstrap method revealed a guild structure corresponding to each geomorphic zone. The four riparian zones were differentiated from the SL-zone by having a low proportion of SL-guild species and a high proportion of infrequent species that were characterized by deciduous leaf habit. The LF-zone was the most differentiated and was characterized by low tree density and specialist species established on the flat and unstable soil surface created by frequent deposition of sediment. The UF- and MF-zones were characterized by a high tree density and species richness (particularly of infrequent species) established on the stable ground surface of a high alluvial terrace. Microsite heterogeneity produced by channel formation may also maintain a high species diversity in the riparian zones.

Suggesting the possible role of Turkey Herpesvirus or HVT-like as a predisposing factor or causative agent in multiple sclerosis

Wild birds are referred to as 'vectors' of an exogenous causative agent of MS, in particular the Marek's disease virus, but this has yet to be confirmed. The epidemiology of MS shows that it occurs worldwide but that there is a high incidence of MS clusters within specific geographical distributions such as in cooler, temperate, zones in a North/South gradient from the equator. Furthermore, these regions are well known as preferred zones for wintering/breeding/feeding purposes and for having a high density of wild birds. A significant observation is that these MS clusters are located on the main global flyways of migratory birds. In 1973, herpesvirus of turkeys (HVT) was isolated for the first time in Florida in asymptomatic wild turkeys and serological studies indicated that it was widespread throughout this region. Experimental data for HVT showed that in chickens it causes prolonged latent infection and no clinical disease, and as showed in latent infected chickens viral RNA was detected in lymphocytes, feather follicles and peripheral nerves. Also in ovo infection or in young infected chickens the HVT can cause demyelination in peripheral nerves. Possible latency and demyelination have both been referred in MS. This study attempts to draw a link between HVT or HVT-like, probably spread with the global migration wild bird flyways, and its possible involvement in multiple sclerosis (MS) aetiology, as an initiate or causative agent. A map with the world's main migratory bird flyways and key MS related regions are included.

Theoretical analysis on the effects of crystal anisotropy on wiresawing process and application to wafer slicing

Most of the crystals sliced using wiresaw are anisotropic to an extent. The effect of crystal anisotropy on the process of slicing using wiresaw is studied and presented in this paper. A method is proposed to determine the direction of approach (DOA) which will give a better surface finish and reduce deviation from the desired surface normal by maintaining symmetry in material removal rates on the two sides of the wire. The effect of cleavage anisotropy on wiresaw slicing is also studied. If the DOA is perpendicular to a cleavage direction, then the longitudinal direction of the wire aligns with the cleavage direction which increases the tendency of wafer breakage, resulting in lower yield of the wafers. This can be easily avoided by choosing an appropriate DOA. Theoretical analysis is carried out using the proposed methods for slicing silicon wafers. Recommendations are made for three most commonly sliced orientations of silicon: (100), (110) and (111). DOA can be any direction for (100) and (110) wafers from the symmetry point of view but preferred DOAs do exist for these wafers from cleavage point of view. For (111) crystal there are exactly six DOAs with symmetry. However, these six DOAs do not lie in the preferred zones suggested by cleavage criterion. It is suggested that in such situations the symmetry criterion should be given precedence over the cleavage criterion during wiresawing process, as the semiconductor industry has strict tolerances in place for surface normal deviation and flatness.

Biliary cholesterol crystallization characterized by single-crystal cryogenic electron diffraction

Cholesterol crystals are the building blocks of cholesterol gallstones. The exact structure of early-forming crystals is still controversial. We combined cryogenic-temperature transmission electron microscopy with cryogenic-temperature electron diffraction to sequentially study crystal development and structure in nucleating model and native gallbladder biles. The growth and long-term stability of classic cholesterol monohydrate (ChM) crystals in native and model biles was determined. In solutions of model bile with low phospholipid-to-cholesterol ratio, electron diffraction provided direct proof of a novel transient polymorph that had an elongated habit and unit cell parameters differing from those of classic triclinic ChM. This crystal is exactly the monoclinic ChM phase described by Solomonov and coworkers (Biophysical J., In press) in cholesterol monolayers compressed on the air-water interface. We observed no evidence of anhydrous cholesterol crystallization in any of the biles studied. In conclusion, classic ChM is the predominant and stable form in native and model biles. However, under certain (low phospholipid) conditions, transient intermediate polymorphs may form. These findings, documenting single-crystal analysis in bulk solution, provide an experimental approach to investigating factors influencing biliary cholesterol crystal nucleation and growth as well as other processes of nucleation and crystallization in liquid systems.

Inferior olivary neurons innervate multiple zones of the flocculus in pigeons (Columba livia)

Complex spike activity of floccular Purkinje cells responds to patterns of rotational optic flow about the vertical axis (rVA neurons) or a horizontal axis 45 degrees to the midline (rH45 neurons). The pigeon flocculus is organized into four parasagittal zones: two rVA zones (zones 0 and 2) interdigitated with two rH45 zones (zones 1 and 3). Climbing fiber input to the rVA and rH45 zones arises in the caudal and rostral regions of the medial column of the inferior olive (mcIO), respectively. To determine whether the two rVA zones and the two rH45 zones receive input from different areas of the caudal and rostral mcIO and whether individual neurons project to both zones of the same rotational preference, different colors of fluorescent retrograde tracer were injected into the two rVA or two rH45 zones. For the rVA injections, retrogradely labeled cells from the two zones were intermingled in the caudal mcIO, but the distribution of cells labeled from zone 0 was slightly caudal to that from zone 2. On average, 18% of neurons were double labeled. For the rH45 injections, cells retrogradely labeled from the two zones were intermingled in the rostral mcIO, but the distribution of cells labeled from zone 1 was slightly rostral to that from zone 3. On average, 22% of neurons were double labeled. In sum, each of the two rVA zones and the two rH45 zones receives input from slightly different regions of the mcIO, and about 20% of the neurons project to both zones.

Gold Mineralization in Kottathara Prospect, Attappadi Valley, Kerala, India: a Preliminary Appraisal

The Kottathara gold prospect of Attappadi Valley in Kerala is located within the Southern Indian Granulite Terrain comprising charnockite and gneisses with enclaves of high-grade supracrustals. The gold mineralization associated with the basic members of the Attappadi supracrustals and the quartz veins traversing them are confined within the Bhavani Shear Zone. Primarily the gold-quartz lode is emplaced in rheologically preferred zones along the contact of the basic members with the enclosing gneisses subsequent to a period of retrogression and shearing. Ore-mineralogical studies reveal that gold got remobilized and this remobilization is identified with the regional Bhavani Shear. SEM studies indicate that gold occurs in free state and also within sulphides especially pyrite. Variation in grain morphology is clearly discernible in gold occurring within oxidised and in non-oxidised zones. Sequencing of deformational events with associated emplacements of known ages suggests the age of gold mineralization of Attappadi area as between 2 Ga. and 2.5 Ga. The secondary mobilization has to be <2.0 Ga or younger possibly of younger Pan-African age related with the Moyar-Bhavani Shear System. The inherent gold content of the komatiitic metapyroxenites together with the auriferous quartz lodes assigns a lithological control on gold mineralisation. Subsequent folding and remobilization due to the regional shear constrained the geometry of the lode zones implying structural control.

An interval estimation for the number of signals

We propose a multi-step procedure for constructing a confidence interval for the number of signals present. The proposed procedure uses the ratios of a sample eigen-value and the sum of different sample eigen-values sequentially to determine the upper and lower limits for the confidence interval. A preference zone in the parameter space of the population eigen-values is defined to separate the signals and the noise. We derive the probability of a correct estimation, P (CE), and the least favorable configuration (LFC) asymptotically under the preference zone. Some important procedure properties are shown. Under the asymptotic LFC, the P (CE) attains its minimum over the preference zone in the parameter space of all eigen-values. Therefore a minimum sample size can be determined in order to implement our procedure with a guaranteed probability requirement.

Winter distribution of birds in the West Siberian Plain

Long-term studies on the winter population of birds in the West Siberian Plain on a landscape basis allowed us to reveal the regional and seasonal patterns of their distribution. The highest proportion of species demonstrated forest-steppe and forest preference, while the lowest proportion demonstrated aquatic-semiaquatic and tundra-forest-tundra preference. The preference zones did not change or extend in the winter period relative to summer postnesting period only in a small fraction of species; while the preference zones of most species were reduced or shifted. Commonly, the zonal borders of preferred habitats shifted southward to better climatic, feeding, and safety conditions. Only rare species with seasonally changing and specialized feeding demonstrated a northward shift of these borders.

The influence of social status on shoaling preferences in the freshwater angelfish (Pterophyllum scalare)

[Shoal choice studies have revealed that fish have cognitive abilities to discriminate between groups of different composition. In this work, the role of social status (based on aggressive acts) of both the test fish and the fish in the stimulus shoals was examined because of the fitness-related consequences that group association may have for the test individual. Single angelfish of high and low social status (dominant and subordinate) were presented with a choice between two stimulus shoals composed of three conspecifics of equal size and familiarity but of social status equal to, and different from that of the test fish in the same dominance hierarchy. Test fish, irrespective of the social status, spent significantly more time shoaling with subordinates than with dominants. They also initiated shoaling behaviour with subordinates more readily and the number of visits to the preference zone close to the subordinates was greater than that to dominants. The tendency was greater in subordinate fish, which showed longer latency in approaching the shoals of dominants, and spent more time in proximity to the subordinates per visit than did dominant fish. A replicate preference test indicated that this general pattern was relatively stable for at least 2f hr. A possible factor mediating this association preference, that of familiarity, was then tested. The same protocol as before was used but unfamiliar conspecific dominants and subordinates served as stimulus shoals. In this second experiment, generally test fish did not show any significant shoaling preference. The results indicate that angelfish are capable of distinguishing the social status of conspecifics and can discriminate between shoals composed of dominants and subordinates on the basis of previous interactions. It is suggested that the tendency to avoid shoals of dominant companions may be due to the disadvantage of enhanced competition, subordinates being more affected., Shoal choice studies have revealed that fish have cognitive abilities to discriminate between groups of different composition. In this work, the role of social status (based on aggressive acts) of both the test fish and the fish in the stimulus shoals was examined because of the fitness-related consequences that group association may have for the test individual. Single angelfish of high and low social status (dominant and subordinate) were presented with a choice between two stimulus shoals composed of three conspecifics of equal size and familiarity but of social status equal to, and different from that of the test fish in the same dominance hierarchy. Test fish, irrespective of the social status, spent significantly more time shoaling with subordinates than with dominants. They also initiated shoaling behaviour with subordinates more readily and the number of visits to the preference zone close to the subordinates was greater than that to dominants. The tendency was greater in subordinate fish, which showed longer latency in approaching the shoals of dominants, and spent more time in proximity to the subordinates per visit than did dominant fish. A replicate preference test indicated that this general pattern was relatively stable for at least 2½ hr. A possible factor mediating this association preference, that of familiarity, was then tested. The same protocol as before was used but unfamiliar conspecific dominants and subordinates served as stimulus shoals. In this second experiment, generally test fish did not show any significant shoaling preference. The results indicate that angelfish are capable of distinguishing the social status of conspecifics and can discriminate between shoals composed of dominants and subordinates on the basis of previous interactions. It is suggested that the tendency to avoid shoals of dominant companions may be due to the disadvantage of enhanced competition, subordinates being more affected.]