Changes in minnow, Pimephales promelas Rafinesque, schooling behaviour associated with infections of brainencysted larvae of the fluke, Ornithodiplostomum ptychocheilus

The schooling behaviour of unparasitized fathead minnows, Pimephales promelus Rafinesque, was compared to that of minnows infected with brain-dwelling metacercariae of the fluke, Ornithodiplostomum ptychocheilus (Faust). Laboratory results showed that schools of infected fish divided more frequently, were less compact, and occupied positions closer to the water surface than control schools. These results are discussed with reference to the possibility that this larval parasite manipulates minnow behaviour to increase host vulnerability to predation.     

Predator attack motivation influences the inspection behaviour of European minnows

Predator inspection behaviour at different levels of attack motivation (attack status of the predator) was investigated in European minnows Phoxinus phoxinus from a population sympatric with pike Esox lucius , during controlled laboratory experiments. Shoals of minnows performed more predator inspections and formed larger inspection group sizes shortly after an attack by a pike. After inspection, minnows returned to the safety of the main shoal, regardless of predator motivation. Minnows which inspected last-before and first-after a strike by a pike modified their behaviour after inspection; they reduced feeding, increased shoaling, flicked their dorsal and pectoral fins and skittered. This behaviour signified alarm and appeared to reflect the severity of the threat posed by the predator at the time of inspection. Fish that had inspected when the pike displayed low attack motivation did not modify their behaviour after inspection to reflect alarm. Information concerning the attack motivation of the predator is probably transferred passively throughout the shoal by changed inspector behaviour and by inspection rate. These data demonstrate that: (1) minnows modified their behaviour after inspection to reflect a predator's attack motivation; and (2) minnows which inspected immediately before a strike appeared to anticipate the future attack and modified their behaviour accordingly.     

Predator-prey behaviour of fathead minnows, Pimephales promelas and largemouth bass, Micropterus salmoides in a model ecosystem

The predator-prey behaviours displayed by largemouth bass, Micropterus salmoides and fathead minnows, Pimephales promelas , were investigated. Fathead PRMOWS were subjected to predation by largemouth bass and observed in a model system that was designed to mimic a natural ecosystem. Anti-predator devices utilized by fathead minnows include schooling, surface swimming, formation of a circular aggregation, and seeking refuge under vegetation.     

The ontogeny of schooling behaviour in the striped jack

The ontogeny of schooling behaviour was investigated in laboratory-reared striped jack Pseudocaranx dentex larvae and juveniles. Mean separation angle between nearest individuals averaged 78 and 82° in 10- and 12-mm fish, respectively, and decreased to 57° in 16-mm fish. In addition, interindividual distance decreased from three times body length in 12-mm fish to twice the body length in 16-mm individuals; this value continued to decrease gradually to 1·3 at 19 mm to 0·79 at 30 mm. Mutual attraction due to visual recognition was observed in 12-mm fish and increased with total length. The optokinetic response ( R_o , the ability of a fish to keep station with moving patterns) first appeared in 4–6-mm larvae. In spite of the traditional emphasis of the importance of R_o in schooling behaviour, the onset of R_o was insufficient to result in school formation. The emergence of mutual attraction seems essential for the ontogeny of schooling.     

Behavioural responses of fathead minnows to hypoxanthine-3-N-oxide at varying concentrations

Antipredator behaviour of fathead minnows Pimephales promelas increased significantly on exposure to hypoxanthine-3-N-oxide at concentrations as low as 0·4 n with no further increase in response at concentrations up to 6·7.     

Size-segregative behaviour in minnow shoals

Shoals composed of equal numbers of two size-classes of European minnows were observed undisturbed, feeding and after threat from a pike in a large arena tank.
The time/frequency budget and analysed sequences of behaviour of the two size-classes were very similar. Irrespective of size, for standard behaviour measures, fish in the shoal behaved similarly under the same external influences, including predator threat.
In contrast, however, the distribution of the two size-classes provided evidence of size segregation within the shoal. This was brought about by individual minnows making shoaling responses preferentially to their own size-class. After exposure to the predator, shoaling responses changed and differed between small and large minnows.
The outcomes of contests at foraging patches were governed primarily by fish size and information asymmetry rather than by occupation of a feeding site.
The experiment shows that asymmetrical pay-offs in foraging and in response to predator threat are the probable reasons for size-segregation behaviours. This conclusion supports the views of earlier workers that mechanical sorting by swimming speed is not an important factor in size segregation in shoals.     

Photosynthesis and transpiration of the flag leaf in four spring-wheat cultivars

Co₂ exchange and transpiration rates of the flag leaves of four spring wheat (Triticum aestivum L.) cultivars, namely Glenlea, Neepawa, Opal and Kolibri, were compared using infra-red gas-analysis technique. The plants were grown in a controlled environment under an 18-h photoperiod, with day and night temperatures of 20 and 15° C, respectively. The time course of the CO₂-exchange rate (CER) of the flag leaf differed among cultivars. CER began to decrease rapidly some 2 weeks after ear emergence in Glenlea, Neepawa and Kolibri, but only after 4 weeks in Opal. The decline in CER of Glenlea, Neepawa and Opal was continuous throughout the period of grain development whereas in Kolibri CER was maintained at a constant level between the 4th and 6th weeks after ear emergence. The transpiration rates of the flag leaves of the 4 cultivars did not change markedly until 6–7 weeks after ear emergence, indicating that the reduction in CER was not primarily a response to increased stomatal resistance to the diffusion of CO₂. Removing the ear of the main shoot of intact plants failed to depress CER of the subtending flag leaf until 5 weeks after ear removal. Removing the ears of all the tillers of plants in which all but 3 tillers had been removed at ear emergence did not depress CER until 4 weeks after ear emergence, but removal of the ear of the main shoot of plants where all the tillers had been removed at ear emergence reduced the CER of the flag leaf 2 weeks after ear removal. Removal of tillers at ear emergence had a marked effect on the time course of CER and transpiration rates of the flag leaf. Both CER and transpiration rates of a 4-tiller plant were maintained at a higher level throughout ear development as compared to those of a one-tiller plant. The transpiration rate of the flag leaf of Glenlea increased during the later part of the life of the leaf even for one-tiller plants with no ear, indicating that such a stomatal response may be part of the normal course of leaf aging and not a response to a feedback stimulus from the ear.     

Chronological observations of primary somatosensory cortical maps in kittens following low thoracic (T12) spinal cord transection at 2 weeks of age.

The present study investigated the reorganization of the somatosensory cortex in kittens following T12 spinal cord transection at 2 weeks of age. Multiunit electrophysiological methods were used to map the somatosensory cortex of kittens at 3, 6, and 9 weeks after the transection. The entire reorganized cortical region was driven by substitute cutaneous inputs, primarily from the trunk, at 3 weeks after spinal cord transection. Although the level of cortical responsiveness remained the same throughout the 9 weeks studied, internal trunk representation changed, and there was an increase in shoulder girdle representation and emergence of forelimb representation. Poor somatotopic and topographic order was observed in the reorganized cortex, regardless of time posttransection. Finally, trunk receptive fields displayed a wide variety of shapes, sizes, and orientations not seen in the normal cortex.     

Predation by brown trout: a major mortality factor for sexually mature European minnows

Brown trout Salmo trutta in the subalpine lake, Øvre Heimdalsvatn, showed large temporal variation in the rate of predation on the introduced minnow Phoxinus phoxinus population. Minnows were found in the stomachs of brown trout between 16 and 38 cm L _T. Significantly greater predation was recorded shortly after ice break at the end of June 1999, with frequencies of 9 and 20% within the L _T classes 16–29·9 cm and  ≥30 cm, respectively. Predation on minnows was only occasionally detected during July, August and September. The high level of predation coincided with minnow spawning, and lengths of consumed minnows were equal to those of sexually mature individuals. Accepting a causal link between minnow spawning, which lasted c . 3 weeks, and the contemporary high rate of predation, the estimated annual consumption of minnows by the brown trout population would be 138 kg wet mass. Although most of the annual consumption of minnows by brown trout (90%) occurred within a very short period (3 weeks), it accounted for a significant proportion (60%) of the annual loss in biomass of the sexually mature part of the population.     

Chronological Observations of Primary Somatosensory Cortical Maps in Kittens following Low Thoracic (T12) Spinal Cord Transection at 2 Weeks of Age

The present study investigated the reorganization of the somatosensory cortex in kittens following T₁₂ spinal cord transection at 2 weeks of age. Multiunit electrophysiological methods were used to map the somatosensory cortex of kittens at 3, 6, and 9 weeks after the transection. The entire reorganized cortical region was driven by substitute cutaneous inputs, primarily from the trunk, at 3 weeks after spinal cord transection. Although the level of cortical responsiveness remained the same throughout the 9 weeks studied, internal trunk representation changed, and there was an increase in shoulder girdle representation and emergence of forelimb representation. Poor somatotopic and topographic order was observed in the reorganized cortex, regardless of time posttransection. Finally, trunk receptive fields displayed a wide variety of shapes, sizes, and orientations not seen in the normal cortex.     

Preferences for familiar fish do not vary with predation risk in the European minnow

In the near-natural conditions of a fluvarium in the River Frome, U.K., European minnows Phoxinus phoxinus displayed schooling preferences for familiar conspecifics. Schools were composed of 75% familiar fish. The minnows in this river co-occur with many piscivores, the most notable being the pike Esox Iucius . The preference for familiar shoalmates was not increased by the threat of predatory attack from a model pike, despite the antipredator benefits afforded to individual members of schools of familiar fish.     

Effects of exposure to predatory cues on territorial behaviour of male fathead minnows

We conducted a laboratory study to determine if male fathead minnows, Pimephales promelas, altered their territorial behaviour associated with reproduction in response to combinations of visual and chemical cues from northern pike, Esox lucius. We introduced the following stimuli to a territorial male: a brick (control), fathead minnow alarm pheromone, a pike fed brook stickleback, Culea inconstans, or a pike fed fathead minnow. The territorial behaviour of males did not change when the control was added. Male minnows experiencing threat from pike fed stickleback significantly reduced the frequency at which they performed three territorial behaviours, but, within 12 h, had returned to pre-exposure activity levels. Male minnows subjected to alarm pheromone alone and to pike fed fathead minnow significantly reduced their territorial behaviour, abandoned their nests, and did not return to pre-exposure levels of activity after 24 h. We suggest that because risk of predation triggers prolonged decreases in territorial defense, it may affect competition between nesting males and female mate choice. We conclude that fathead minnows can assess the severity of predatory threat and adjust their reproductive behaviour accordingly.     

Swarming and mating of Aedes communis mosquitoes in nature

The date of the beginning of mating behaviour in males and females, the rate of insemination and the increasing of bloodsucking activity of females were studied in natural environments. Over 80% of females mated on the 3-4th day after emergence; after fertilization their behaviour changed from looking for males for coupling to looking for ones for a prey. The male swarming began on the 5th day after emergence and simultaneously the appearance of inseminated females was observed. The places of mating of males and females were investigated. It was established that coupling took place in swarms with swarming males and out of swarms with freely flying males.     

Forms of goal-directed behavior as affected by induced changes in the level of endogenous beta-endorphin in rats

Marked alterations in feeding and defense behaviour and motor activity partly resembling the effects of exogenous beta-endorphin administration were demonstrated in the experiments on rats. These alterations were observed after immunization with beta-endorphin--bovine serum albumin conjugate (two subcutaneous injections at a 7-day interval at a dose of 75 micrograms, 1 mole BSA/6 moles beta-endorphin mixed with complete Freund's adjuvant). A decrease in beta-endorphin content in some brain structures was noted. Unlike control animals, the immunized rats revealed within 3-4 weeks an increase in food intake without any rise in body weight and practically no response to handling.     

The development of spatial behaviour and the hippocampal neural representation of space

The role of the hippocampal formation in spatial cognition is thought to be supported by distinct classes of neurons whose firing is tuned to an organism''s position and orientation in space. In this article, we review recent research focused on how and when this neural representation of space emerges during development: each class of spatially tuned neurons appears at a different age, and matures at a different rate, but all the main spatial responses tested so far are present by three weeks of age in the rat. We also summarize the development of spatial behaviour in the rat, describing how active exploration of space emerges during the third week of life, the first evidence of learning in formal tests of hippocampus-dependent spatial cognition is observed in the fourth week, whereas fully adult-like spatial cognitive abilities require another few weeks to be achieved. We argue that the development of spatially tuned neurons needs to be considered within the context of the development of spatial behaviour in order to achieve an integrated understanding of the emergence of hippocampal function and spatial cognition.     

Prey selection by juvenile cyprinids from running water

SUMMARY. 1. The juveniles of dace ( Leuciscus leuciscus (L.)) and roach ( Rtuihts rtuihis (L.)) and yearling minnows ( Phoxtnus phoxinus (L.)) exhibited generally similar patterns of feeding behaviour and preferences for particular prey types.
2. Factors affecting prey selection included predator and prey size, prey activity and environmental conditions.
3. All three species preferred prey sizes approximately 0.6x their maximum gape.
4. Prey motion was essential to induce attack, and prey were usually selected in proportion to their relative activities.
5. Specialization on one prey type was observed in still water, and was always directed at the most active prey type. In flowing water no specialization was observed, and size selection was suppressed in the juvenile fish. Yearling minnows, however, were size selective in both still and flowing water.
6. The presence of macrophyte cover did not significantly change the pattern of prey selection, but did reduce the predation rale.
7. These results are discussed in the context of previous studies of prey selection and optimal foraging.     

Density and maturation of rodlet cells in brain tissue of fathead minnows (Pimephales promelas) exposed to trematode cercariae

Evidence for the presumed linkage between the enigmatic rodlet cells of fish and exposure to helminths is anecdotal and indirect. We evaluated the proliferation and development of rodlet cells in the optic lobes of fathead minnows exposed to cercariae of Ornithodiplostomum ptychocheilus. Mean rodlet cell densities (ca. 10/mm²) in the optic lobes were similar between unexposed controls and minnows with 1- and 2-week old infections. Rodlet cell densities increased at 4 weeks p.i., reaching maxima (ca. 200/mm²) at 6 weeks p.i., followed by a decline at 9 weeks. This temporal pattern of proliferation and maturation paralleled the development of metacercariae within the optic lobes. Unencysted metacercariae develop rapidly within tissues of the optic lobes for approximately 4 weeks after penetration by cercariae, then shift to the adjacent meninges to encyst. The former stage is associated with tissue damage, the latter with massive inflammation of the meninges. Thus, peak densities and maturation of rodlet cells correspond to the period when inflammation of the meninges caused by the large metacercarial cysts is at a maximum. Our results support recent contentions that rodlet cells comprise part of the host inflammatory defence response.     

Social interactions of juvenile Collared peccaries, Tayassu tajacu (Mammalia: Artiodactyla)

Is there a predictable relationship between species-typical behavioural development and social organization in mammals? Earlier work on canids and rodents suggested that adult sociality is associated with a developmental schedule in which juveniles showed, among themselves: (1) frequent social play; (2) frequent amicable contact; (3) frequent olfactory contact; (4) a delay in the emergence of agonistic behaviour. In the highly social Collared peccary (Tayassu tajacu) the behaviour of juveniles conformed only partially to this scheme. Juveniles engaged in social play with each other at an early age, but showed no other observable amicable or olfactory contact until eight to twelve weeks of age and showed no delay in the emergence of agonistic behaviour among themselves. Adults, in contrast, were conspicuously tolerant of juveniles, and 86% of juvenile social interactions in the first year took place with adults.     

Free—living fathead minnows rapidly learn to recognize pike as predators

Individuals from a natural population of approximately 20 000 fathead minnows from a pike–free pond did not respond with appropriate anti–predator behaviour upon encountering pike odour in laboratory tests. However, 14 days after 10 pike were stocked into the pond, minnows had acquired recognition of pike odour. Laboratory studies have indicated several possible mechanisms for acquiring predator recognition in fathead minnows. This study indicates that these, or similar processes, can produce major changes in predator recognition in the wild.     

Information Transfer across Fish Shoals under Predator Threat

The hypothesis that shoaling fish can obtain information about a predator's approach from changes in the behaviour of other shoal members was tested in an experiment in which receiver minnows (Phoxinus phoxinus) behind a one-way-mirror could observe the reaction of transmitter minnows threatened by the stalk of a pike (Esox lucius) model. Although the receiver minnows were out of visual contact with the pike model they decreased their foraging behaviour and started hiding when the pike model came towards the feeding patch of the transmitter fish. The presence of skittering behaviour and inspection behaviour in the transmitter but not in the receiver fish suggests that individual confirmation of the predator does play a role in determining the nature of the anti-predator response. Nevertheless there is clear evidence that receiver fish modify their own behaviour on the basis of information obtained from individuals which have seen a predator.