Opposing effects of dopamine on agonistic behaviour in crayfish.

The effects of dopamine on the agonistic behaviour of crayfish were analysed. When dopamine concentrations of 1 μmol l-1 were injected into large crayfish, individuals were beaten by smaller opponents, despite their physical advantage. Injection of 10 μmol l-1 dopamine into small animals increased their rate of winning against larger opponents.

Anxiety induces long-term memory forgetting in the crayfish.

When two male crayfish encounter, agonistic bouts are initiated and a winner-loser relationship is established. Larger animals are more likely to win with their physical advantage, but they are frequently beaten by small dominant animals with previous winning experience. This winner effect remains for several days.

Enhancement of synaptic responses in ascending interneurones following acquisition of social dominance in crayfish.

When crayfish have attained dominant status after agonistic bouts, their avoidance reaction to mechanical stimulation of the tailfan changes from a dart to a turn response. Ascending interneurones originating in the terminal ganglion receive sensory inputs from the tailfan and they affect spike activity of both uropod and abdominal postural motor neurones, which coordinates the uropod and abdominal postural movements. Despite the varying output effects of ascending interneurones, the synaptic responses of all interneurones to sensory stimulation were enhanced when they acquired a dominant state.

Aversive operant conditioning alters the phototactic orientation of the marbled crayfish.

Aversive learning was applied to affect the phototactic behaviour of the marbled crayfish. Animals initially showed negative phototaxis to white light and positive taxis to blue light. Using an aversive learning paradigm, we investigated the plasticity of innate behaviour following operant conditioning.

The effects of shelter quality and prior residence on marmorkrebs (marbled crayfish).

Many animals fight over a limited valuable resource. In marmorkrebs (marbled crayfish), large animals usually defeat small opponents but they are frequently beaten by small opponents that are shelter owners. A prior residence effect of marbled crayfish was analysed quantitatively in the present study.

Enhancement of habituation during escape swimming in starved crayfish.

Feeding is important to supply the immediate energy needs of animals and starved animals must expend energy in attempting to acquire foods irrespective of the danger of predation risk. Crayfish escape from attack of predators by tailflipping and in response to rostral stimuli crayfish show backward escape swimming following an initial rapid flexion of the abdomen. Since the tailflip is an energetically costly behaviour, the occurrence of a tailflip diminishes if a stimulus is repeatedly applied through habituation.

Nitric oxide-mediated intersegmental modulation of cycle frequency in the crayfish swimmeret system.

Crayfish swimmerets are paired appendages located on the ventral side of each abdominal segment that show rhythmic beating during forward swimming produced by central pattern generators in most abdominal segments. For animals with multiple body segments and limbs, intersegmental coordination of central pattern generators in each segment is crucial for the production of effective movements. Here we develop a novel pharmacological approach to analyse intersegmental modulation of swimmeret rhythm by selectively elevating nitric oxide levels and reducing them with pharmacological agents, in specific ganglia.

Tyraminergic modulation of agonistic outcomes in crayfish.

Octopamine, a biogenic amine, modulates various behaviors, ranging from locomotion and aggression to learning and memory in invertebrates. Several studies recently demonstrated that tyramine, the biological precursor of octopamine, also affects behaviors independent of octopamine. Here we investigated the involvement of tyramine in agonistic interaction of the male crayfish Procambarus clarkii.

Cyclic AMP-regulated opposing and parallel effects of serotonin and dopamine on phototaxis in the Marmorkrebs (marbled crayfish).

Phototactic behaviours are observed from prokaryotes to amphibians and are a basic form of orientation. We showed that the marbled crayfish displays phototaxis in which the behavioural response reversed from negative to positive depending on external light conditions. Animals reared in a 12-L/12-D light cycle showed negative phototaxis during daytime and positive phototaxis during night-time.

Role of cAMP signalling in winner and loser effects in crayfish agonistic encounters.

For territorial animals, establishment of status-dependent dominance order is essential to maintain social stability. In agonistic encounters of the crayfish Procambarus clarkii, a difference of body length of 3-7% is enough for larger animals to become dominant. Despite a physical disadvantage, small winners of the first pairings were more likely to win subsequent conflicts with larger inexperienced animals.

Habituation of Backward Escape Swimming in the Marbled Crayfish.

In the present study, we performed behavioral analyses of the habituation of backward escape swimming in the marbled crayfish, Procambarus fallax. Application of rapid mechanical stimulation to the rostrum elicited backward swimming following rapid abdominal flexion of crayfish. Response latency was very short-tens of msec-suggesting that backward swimming is mediated by MG neurons.

Serotonergic modulation of social status-dependent behavioural plasticity of the crayfish avoidance reaction.

Small crayfish usually showed escape-like dart responses to mechanical stimulation of the tailfan. Following agonistic bouts with conspecifics, dominant crayfish showed a defensive-like turn response to the same sensory stimulus. During the dart response, both uropods closed and animals walked forwards with the abdomen extended, while during the turn response the uropod on the stimulated side opened and animals turned towards the stimulus source with the abdomen frequently flexed.

Habituation of LG-mediated tailflip in the crayfish.

Crayfish escape from threatening stimuli by tailflipping. If a stimulus is applied to the rear, crayfish escape up and forwards in a summersault maneuver that is mediated by the activation of lateral giant (LG) interneurons. The occurrence probability of LG-mediated tailflip, however, diminishes and habituates if a stimulus is repeatedly applied.

Nitric oxide modulates a swimmeret beating rhythm in the crayfish.

The modulatory effects of nitric oxide (NO) and cAMP on the rhythmic beating activity of the swimmeret motor neurones in the crayfish were examined. Swimmerets are paired appendages located on the ventral side of each abdominal segment that show rhythmic beating activity during forward swimming, postural righting behaviour and egg ventilation in gravid females. In isolated abdominal nerve cord preparations, swimmeret motor neurones are usually silent or show a continuous low-frequency spiking activity.

Aminergic control of social status in crayfish agonistic encounters.

Using pairings of male crayfish Procambarus clarkii with a 3-7% difference in size, we confirmed that physically larger crayfish were more likely to win encounters (winning probability of over 80%). Despite a physical disadvantage, small winners of the first pairings were more likely to win their subsequent conflicts with larger naive animals (winning probability was about 70%). By contrast, the losers of the first pairings rarely won their subsequent conflicts with smaller naive animals (winning probability of 6%).

Social status-dependent modulation of LG-flip habituation in the crayfish.

Strong stimuli applied to the tailfan of the crayfish Procambarus clarkii evoked lateral giant interneurone (LG)-mediated tailflips. When the sensory stimulus was applied repeatedly, the response of the LG habituated until it failed to give rise to a spike. We found that this LG-flip habituation was dependent on social status.

Interlocking of chelae is a key factor for dominance hierarchy formation in crayfish.

We characterized the role of chelae during agonistic encounters of the crayfish Procambarus clarkii. Physical asymmetries in body length, body mass and chelae size were directly related to dominance hierarchy formation. More than 80% of winning crayfish had longer body and chelae lengths, and winners were usually heavier in body mass, even if their differences were less than 3% compared with losing opponents.

IP3-mediated octopamine-induced synaptic enhancement of crayfish LG neurons.

The biogenic amines, octopamine and serotonin, modulate the synaptic activity of the lateral giant interneuron (LG) circuitry of the crayfish escape behavior. Bath application of both octopamine and serotonin enhances the synaptic responses of LG to sensory stimulation. We have shown previously (Araki et al.

Development of agonistic encounters in dominance hierarchy formation in juvenile crayfish.

We have characterized the behavioural patterns of crayfish during agonistic bouts between groups of crayfish of four different body lengths (9-19, 20-32, 41-48 and 69-75 mm) to characterize changes in the patterns of agonistic encounter during development. The behaviour of both dominant and subordinate animals was analysed by single frame measurement of video recordings. Behavioural acts that occurred during agonistic bouts were categorized as one of seven types: capture, fight, contact, approach, retreat, tailflip and neutral.

Dominance hierarchy-dependent behavioural plasticity of crayfish avoidance reactions.

Crayfish showed avoidance reactions when mechanical stimulation was applied to their tailfan. The response pattern of the avoidance reaction was dependent on crayfish size. Small crayfish showed an escape-like dart response while larger crayfish displayed a defensive-like turn response.

Temperature dependent plasticity of habituation in the crayfish.

To determine the effects of thermal preconditioning on a simple form of learning and memory, habituation, we preconditioned crayfish with extreme temperatures and subsequently analysed their effects on mechanosensory input that evokes a response in the lateral giant interneurons, within the normal temperature range of the animal. We found that repetitive stimulation with a 1 s interstimulus interval led to habituation of the response the lateral giant in control animals at 22°C. Neither heat nor cold preconditioning had any effect on the probability of evoking a response in the lateral giant nor on the rate at which habituation occurred.

Cyclic AMP mediates serotonin-induced synaptic enhancement of lateral giant interneuron of the crayfish.

The lateral giant (LG)-mediated escape behavior of the crayfish habituates readily on repetitive sensory stimulation. Recent studies suggested that the biogenic amines serotonin and octopamine modulate the time course of recovery and/or re-depression of the LG response after habituation. However, little is known of how serotonin and octopamine effect LG habituation and what second-messenger cascades they may activate.

Decrease in excitability of LG following habituation of the crayfish escape reaction.

Crayfish escapes from threatening stimuli to the abdomen by tailflipping upwards and forwards. This lateral giant (LG)-mediated escape reaction habituates readily upon repetitive sensory stimulation. Using an isolated abdominal nerve cord preparation, we have analyzed the change in LG activity by applying additional sensory stimulation after different periods following habituation to characterize the retention of LG habituation.

Behavioral and electrophysiological experiments suggest that the antennular outer flagellum is the site of pheromone reception in the male helmet crab Telmessus cheiragonus.

Sexually competent females of Telmessus cheiragonus (helmet crab) release two pheromones that elicit grasping and copulation behaviors in males (Kamio et al., 2000, 2002, 2003). Our study aimed to use behavioral and electrophysiological techniques to identify the site of reception of these sex pheromones.