Direct benefits of social dominance in juvenile crayfish

Effects of Cheliped Amputation on the Personality of Crayfish

Animal personality, which describes inter-individual differences and intra-individual consistency in behaviors across time and contexts, has been widely observed and has significance for both ecology and evolution. Morphological modifications, particularly during early life stages, may highly influence animal behavior in adulthood; thus, exploring this relationship can elucidate personality development throughout ontogeny. In this study, we reared juvenile crayfish (Procambarus clarkii) with different degrees of cheliped mutilation and explored their personality patterns, including exploration and aggression, when they reached sexual maturity. Male crayfish showed repeatability in exploration, and both sexes showed repeatability in aggression. We observed no significant correlation between the two behavioral traits, indicating the absence of behavioral syndromes. Moreover, exploration did not differ according to the type of mutilation, but crayfish with more intact chelipeds were more aggressive, and males were more aggressive than females. These results indicate that cheliped mutilation may modify the average levels of personality traits associated with competition or self-defense. Our study provides insights into how morphological modifications may shape animal personalities in adulthood.

Winner and loser effects influence subsequent mating interactions in crayfish

In species whose social structure includes dominance relationships, individuals are likely to engage in frequent agonistic interactions with conspecifics, and these interactions can have substantial effects on participants. For example, 'winner' and 'loser' effects, whereby winning or losing a contest increases the probability of winning or losing subsequent encounters, have been described in many species. However, a smaller body of research has shown that winning or losing a contest can lead to additional behavioral changes that affect other domains of an individual's social experiences. Here, we report on an experiment designed to evaluate the effects of prior contests on subsequent mating interactions in the crayfish (Faxonius virilis). We presented males with mating opportunities either immediately following or 7 days after a contest with a conspecific male. We predicted that winners would be more likely to mate than losers, because of either or both winner/loser effects and differences in male competitiveness. We found that, when presented with a mating opportunity immediately following a contest, winning males were more likely to mate than were losing males. We also found that these differences had eroded within 7 days, such that there was no significant difference in the proportions of winners and losers that mated after that period. We concluded that the changes in mating behavior that we observed immediately after a contest were likely due to relatively short-term winner and loser effects, rather than any differences in the males' competitiveness, which would presumably be of longer duration.

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. The number of spikes increased as did a sustained membrane depolarizations. Regardless of social status, the output effects on the uropod motor neurones of all interneurones except VE-1 remained unchanged. VE-1 mainly inhibited the uropod opener motor neurones in naive animals, but tended to excite them in dominant animals. Synaptic enhancement of the sensory response of ascending interneurones was also observed in naive animals treated with bath-applied serotonin. However, subordinate animals or naive animals treated with octopamine had no noticeable effect on the synaptic response of their ascending interneurones to sensory stimulation. Thus, enhancement of the synaptic response is a specific neural event that occurs when crayfish attain social dominance and it is mediated by serotonin.

Cellular interactions between social experience, alcohol sensitivity, and GABAergic inhibition in a crayfish neural circuit

We report here that prior social experience modified the behavioral responses of adult crayfish to acute alcohol exposure. Animals housed individually for 1 wk before alcohol exposure were less sensitive to the intoxicating effects of alcohol than animals housed in groups, and these differences are based on changes in the nervous system rather than differences in alcohol uptake. To elucidate the underlying neural mechanisms, we investigated the neurophysiological responses of the lateral giant (LG) interneurons after alcohol exposure. Specifically, we measured the interactions between alcohol and different GABA_A-receptor antagonists and agonists in reduced crayfish preparations devoid of brain-derived tonic GABAergic inhibition. We found that alcohol significantly increased the postsynaptic potential of the LG neurons, but contrary to our behavioral observations, the results were similar for isolated and communal animals. The GABA_A-receptor antagonist picrotoxin, however, facilitated LG postsynaptic potentials more strongly in communal crayfish, which altered the neurocellular interactions with alcohol, whereas TPMPA [(1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid], an antagonist directed against GABA_A-receptors with ρ subunits, did not produce any effects. Muscimol, an agonist for GABA_A-receptors, blocked the stimulating effects of alcohol, but this was independent of prior social history. THIP [4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol], an agonist directed against GABA_A-receptors with δ subunits, which were not previously known to exist in the LG circuit, replicated the suppressing effects of muscimol. Together, our findings provide strong evidence that alcohol interacts with the crayfish GABAergic system, and the interplay between prior social experience and acute alcohol intoxication might be linked to changes in the expression and function of specific GABA_A-receptor subtypes.NEW & NOTEWORTHY The complex interactions between alcohol and prior social experience are still poorly understood. Our work demonstrates that socially isolated crayfish exhibit lower neurobehavioral sensitivity to acute ethanol compared with communally housed animals, and this socially mediated effect is based on changes in the nervous systems rather than on differences in uptake or metabolism. By combining intracellular neurophysiology and neuropharmacology, we investigated the role of the main inhibitory neurotransmitter GABA, and its receptor subtypes, in shaping this process.

Morphology, performance and fluid dynamics of the crayfish escape response

Sexual selection can result in an exaggerated morphology that constrains locomotor performance. We studied the relationship between morphology and the tail-flip escape response in male and female rusty crayfish (Faxonius rusticus), a species in which males have enlarged claws (chelae). We found that females had wider abdomens and longer uropods (terminal appendage of the tail fan) than males, while males possessed deeper abdomens and larger chelae, relative to total length. Chelae size was negatively associated with escape velocity, whereas longer abdomens and uropods were positively associated with escape velocity. We found no sex-specific differences in maximum force generated during the tail flip, but uropod length was strongly, positively correlated with tail-flip force in males. Particle image velocimetry (PIV) revealed that the formation of a vortex, rather than the expulsion of fluid between two closing body surfaces, generates propulsion in rusty crayfish. PIV also revealed that the pleopods (ventral abdominal appendages) contribute to the momentum generated by the tail. To our knowledge, this is the first confirmation of vortex formation in a decapod crustacean.

Discrete modulation of anti-predatory and agonistic behaviors by sensory communication signals in juvenile crayfish

We investigated how the exchange of sensory signals modulates the individual behaviors of juvenile crayfish in an anti-predatory context as well as during intraspecific agonistic encounters. We first compared crayfish housed in total sensory isolation or in pairs with access to chemical and visual cues. After 1 week of housing, we analysed their individual responses to a visual danger signal while they were foraging. We found that crayfish previously housed in pairs with exchange of sensory signals responded to a simulated predator attack predominantly with freezing behavior, whereas animals deprived of all sensory communication mostly responded by performing escape tail-flips. Next, we used the same housing conditions in between repeated fights in pairs of crayfish. Aggressive and submissive behaviors increased in subsequent fights both after total isolation and after exchange of olfactory and visual signals. Thus, unlike responses to simulated predator attacks, intraspecific agonistic behavior was not modulated by exposure to the same sensory signals. However, when we tested the effects of olfactory or visual communication independently, aggression increased dramatically after the exchange of olfactory signals, which also led to a high number of rank reversals in second fights, suggesting a destabilization of the original dominance relationship. Exposure to visual cues during the 1-week separation, however, produced the opposite effect, reducing agonistic behaviors and rank reversals. These findings demonstrate that exchange of sensory signals modulates future anti-predatory decision-making and intraspecific agonistic behaviors discretely, suggesting that the effect of these signals on shared neural circuitry is context dependent.

Bioluminescent backlighting illuminates the complex visual signals of a social squid in the deep sea

Visual signals rapidly relay information, facilitating behaviors and ecological interactions that shape ecosystems. However, most known signaling systems can be restricted by low light levels-a pervasive condition in the deep ocean, the largest inhabitable space on the planet. Resident visually cued animals have therefore been hypothesized to have simple signals with limited information-carrying capacity. We used cameras mounted on remotely operated vehicles to study the behavior of the Humboldt squid, Dosidicus gigas, in its natural deep-sea habitat. We show that specific pigmentation patterns from its diverse repertoire are selectively displayed during foraging and in social scenarios, and we investigate how these behaviors may be used syntactically for communication. We additionally identify the probable mechanism by which D. gigas, and related squids, illuminate these patterns to create visual signals that can be readily perceived in the deep, dark ocean. Numerous small subcutaneous (s.c.) photophores (bioluminescent organs) embedded throughout the muscle tissue make the entire body glow, thereby backlighting the pigmentation patterns. Equipped with a mechanism by which complex information can be rapidly relayed through a visual pathway under low-light conditions, our data suggest that the visual signals displayed by D. gigas could share design features with advanced forms of animal communication. Visual signaling by deep-living cephalopods will likely be critical in understanding how, and how much, information can be shared in one of the planet's most challenging environments for visual communication.

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. More than 2 h of residency in a shelter was sufficient for small owners to defeat large intruders. Small animals that stayed in a shelter for 24 h still tended to win following removal of the shelter 10 min before pairing with large intruders, but 2 h residents were occasionally beaten by large intruders without the support of shelters during pairings. The prior residence effect thus developed depending on the duration of residency. To clarify whether the strength of the prior residence effect was affected by the quality of a shelter, large and small owners with different combinations of high- and low-quality shelters were paired. When both large and small owners possessed a high-quality shelter, the frequency of agonistic bouts was reduced. Even if agonistic bouts occurred, the win frequency of small owners was almost equal to that of large owners. Thus, the residence effect on small owners was sufficiently strong to overcome the physical disadvantage of small animals to large opponents. By contrast, small owners of low--quality shelters were frequently beaten by large owners with the shelters of same or better quality. We conclude that the outcome of fights over the resource shelter is highly dependent on both the perception of shelter quality and body size differences.

Foraging dynamics are associated with social status and context in mouse social hierarchies

Living in social hierarchies requires individuals to adapt their behavior and physiology. We have previously shown that male mice living in groups of 12 form linear and stable hierarchies with alpha males producing the highest daily level of major urinary proteins and urine. These findings suggest that maintaining alpha status in a social group requires higher food and water intake to generate energetic resources and produce more urine. To investigate whether social status affects eating and drinking behaviors, we measured the frequency of these behaviors in each individual mouse living in a social hierarchy with non-stop video recording for 24 h following the initiation of group housing and after social ranks were stabilized. We show alpha males eat and drink most frequently among all individuals in the hierarchy and had reduced quiescence of foraging both at the start of social housing and after hierarchies were established. Subdominants displayed a similar pattern of behavior following hierarchy formation relative to subordinates. The association strength of foraging behavior was negatively associated with that of agonistic behavior corrected for gregariousness (HWIG), suggesting animals modify foraging behavior to avoid others they engaged with aggressively. Overall, this study provides evidence that animals with different social status adapt their eating and drinking behaviors according to their physiological needs and current social environment.

Fighting over burrows: the emergence of dominance hierarchies in the Norway lobster (Nephrops norvegicus)

Animals fight over resources such as mating partners, territory, food or shelter and repeated contests lead to stable social hierarchies in different phyla. The group dynamics of hierarchy formation are not characterized in the Norway lobster (Nephrops norvegicus). Lobsters spend most of the day in burrows and forage outside of them according to a diel (i.e. 24 h-based) activity rhythm. Here, we use a linear and generalized mixed model approach to analyse, in seven groups of four male lobsters, the formation of dominance hierarchies and rank-related changes in burrowing behaviour. We show that hierarchies emerge within 1-3 days and increase in steepness over a period of 5 days, while rank changes and number of fights gradually decrease over a 5-day period. The rank position determined by open area fights predicts the outcome of fights over burrows, the time spent in burrows, and the locomotor activity levels. Dominant lobsters are more likely to evict subordinate lobsters from their burrows and are more successful in defending their own burrows. They spend more time in burrows and display lower levels of locomotor activity outside the burrow. Lobsters do not change their diel activity rhythms as a result of a change in rank, and all tested individuals showed higher activity at night and dusk compared with dawn and daytime. We discuss how behavioural changes in burrowing behaviour could lead to rank-related benefits such as reduced exposure to predators and energy savings.

Prior social experience affects the behavioral and neural responses to acute alcohol in juvenile crayfish

The effects of alcohol on society can be devastating, both as an immediate consequence of acute intoxication and as a powerful drug of abuse. However, the neurocellular mechanisms of alcohol intoxication are still elusive, partly because of the complex interactions between alcohol and nervous system function. We found that juvenile crayfish are behaviorally sensitive to acute alcohol exposure and progress through stages that are strikingly similar to those of most other intoxicated organisms. Most surprisingly, we found that the social history of the animals significantly modified the acute effects of alcohol. Crayfish taken from a rich social environment became intoxicated more rapidly than animals that were socially isolated before alcohol exposure. In addition, we found that the modulation of intoxicated behaviors by prior social experience was paralleled on the level of individual neurons. These results significantly improve our understanding of the mechanisms underlying the interplay between social experience, alcohol intoxication and nervous system function.

Social Interactions and Indirect Genetic Effects on Complex Juvenile and Adult Traits

Most animal species are social in one form or another, yet many studies in rodent model systems use either individually housed animals or ignore potential confounds caused by group housing. While such social interaction effects on developmental and behavioral traits are well established, the genetic basis of social interactions has not been researched in as much detail. Specifically, the effects of genetic variation in social partners on the phenotype of a focal individual have mostly been studied at the phenotypic level. Such indirect genetic effects (IGEs), where the genotype of one individual influences the phenotype of a second individual, can have important evolutionary and medically relevant consequences. In this chapter, we give a brief outline of social interaction effects, and how systems genetics approaches using recombinant inbred populations can be used to investigate indirect genetic effects specifically, including maternal genetic effects. We discuss experimental designs for the study of IGEs and show how indirect genetic loci can be identified that underlie social interaction effects, their mechanisms, and consequences for trait variation in focal individuals.

Effects of sertraline on behavioral indices of crayfish Orconectes virilis

Sertraline, a selective serotonin re-uptake inhibitor, is a widely prescribed antidepressant in North America. Though sertraline is continuously released from wastewater treatment plant discharge to surface water, effects of aqueous exposure of sertraline on behavioral responses of aquatic animals are largely unknown. Our study explored the effects of aqueous exposures of sertraline on antagonistic bouts and predator response behavior of virile crayfish (Orconectes virilis). Crayfish were either exposed or not exposed to waterborne sertraline and then size-matched for paired antagonistic bouts to determine if sertraline affects the aggression of each crayfish. We investigated the effect of sertraline on responses to visual predator cues and determined whether sertraline acts as an olfactory cue. Our results demonstrate that crayfish exposed to sertraline are more aggressive when paired with control crayfish but, when sertraline crayfish are paired, there is no change in aggression. Attraction response to sertraline in behavioral mazes was also observed, which may represent a maladaptive behavior, and in an ecological context may result in crayfish moving to areas with elevated levels of sertraline. However, aqueous exposure to sertraline had no effect on predator responses of crayfish. Future research is warranted to determine whether such medicine released in wastewater treatment plant effluents produces long-term ecologically important consequences for aquatic animals residing in urbanized aquatic ecosystems.

Effects of Different Social and Environmental Conditions on Established Dominance Relationships in Crayfish

Like most social animals, crayfish readily form dominance relationships and linear social hierarchies when competing for limited resources. Competition often entails dyadic aggressive interactions, from which one animal emerges as the dominant and one as the subordinate. Once dominance relationships are formed, they typically remain stable for extended periods of time; thus, access to future resources is divided unequally among conspecifics. We previously showed that firmly established dominance relationships in juvenile crayfish can be disrupted by briefly adding a larger conspecific to the original pair. This finding suggested that the stability of social relationships in crayfish was highly context-dependent and more transient than previously assumed. We now report results that further identify the mechanisms underlying the destabilization of crayfish dominance relationships. We found that rank orders remained stable when conspecifics of smaller or equal size were added to the original pair, suggesting that both dominant and subordinate must be defeated by a larger crayfish in order to destabilize dominance relationships. We also found that dominance relationships remained stable when both members of the original pair were defeated by larger conspecifics in the absence of their original opponent. This showed that dominance relationships are not destabilized unless both animals experience defeat together. Lastly, we found that dominance relationships of pairs were successfully disrupted by larger intruders, although with reduced magnitude, after all chemical cues associated with earlier agonistic experiences were eliminated. These findings provide important new insights into the contextual features that regulate the stability of social dominance relationships in crayfish and probably in other species as well.

Flexibility in metabolic rate confers a growth advantage under changing food availability

Phenotypic flexibility in physiological, morphological and behavioural traits can allow organisms to cope with environmental challenges. Given recent climate change and the degree of habitat modification currently experienced by many organisms, it is therefore critical to quantify the degree of phenotypic variation present within populations, individual capacities to change and what their consequences are for fitness.

Flexibility in standard metabolic rate (SMR) may be particularly important since SMR reflects the minimal energetic cost of living and is one of the primary traits underlying organismal performance. SMR can increase or decrease in response to food availability, but the consequences of these changes for growth rates and other fitness components are not well known.

We examined individual variation in metabolic flexibility in response to changing food levels and its consequences for somatic growth in juvenile brown trout (Salmo trutta).

SMR increased when individuals were switched to a high food ration and decreased when they were switched to a low food regime. These shifts in SMR, in turn, were linked with individual differences in somatic growth; those individuals that increased their SMR more in response to elevated food levels grew fastest, while growth at the low food level was fastest in those individuals that depressed their SMR most.

Flexibility in energy metabolism is therefore a key mechanism to maximize growth rates under the challenges imposed by variability in food availability and is likely to be an important determinant of species’ resilience in the face of global change.

Intensive removal of signal crayfish (Pacifastacus leniusculus) from rivers increases numbers and taxon richness of macroinvertebrate species

Invasive species are a major cause of species extinction in freshwater ecosystems, and crayfish species are particularly pervasive. The invasive American signal crayfish Pacifastacus leniusculus has impacts over a range of trophic levels, but particularly on benthic aquatic macroinvertebrates. Our study examined the effect on the macroinvertebrate community of removal trapping of signal crayfish from UK rivers. Crayfish were intensively trapped and removed from two tributaries of the River Thames to test the hypothesis that lowering signal crayfish densities would result in increases in macroinvertebrate numbers and taxon richness. We removed 6181 crayfish over four sessions, resulting in crayfish densities that decreased toward the center of the removal sections. Conversely in control sections (where crayfish were trapped and returned), crayfish density increased toward the center of the section. Macroinvertebrate numbers and taxon richness were inversely correlated with crayfish densities. Multivariate analysis of the abundance of each taxon yielded similar results and indicated that crayfish removals had positive impacts on macroinvertebrate numbers and taxon richness but did not alter the composition of the wider macroinvertebrate community. Synthesis and applications: Our results demonstrate that non-eradication-oriented crayfish removal programmes may lead to increases in the total number of macroinvertebrates living in the benthos. This represents the first evidence that removing signal crayfish from riparian systems, at intensities feasible during control attempts or commercial crayfishing, may be beneficial for a range of sympatric aquatic macroinvertebrates.

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%). These winner and loser effects were mimicked by injection of serotonin and octopamine. Serotonin-injected naive small crayfish were more likely to win in pairings with untreated larger naive crayfish (winning probability of over 60%), while octopamine-injected naive large animals were beaten by untreated smaller naive animals (winning probability of 20%). Furthermore, the winner effects of dominant crayfish were cancelled by the injection of mianserin, an antagonist of serotonin receptors and were reinforced by the injection of fluoxetin, serotonin reuptake inhibitor, just after the establishment of social order of the first pairings. Injection of octopamine channel blockers, phentolamine and epinastine, by contrast, cancelled the loser effects. These results strongly suggested that serotonin and octopamine were responsible for winner and loser effects, respectively.

Neural circuit reconfiguration by social status

The social rank of an animal is distinguished by its behavior relative to others in its community. Although social-status-dependent differences in behavior must arise because of differences in neural function, status-dependent differences in the underlying neural circuitry have only begun to be described. We report that dominant and subordinate crayfish differ in their behavioral orienting response to an unexpected unilateral touch, and that these differences correlate with functional differences in local neural circuits that mediate the responses. The behavioral differences correlate with simultaneously recorded differences in leg depressor muscle EMGs and with differences in the responses of depressor motor neurons recorded in reduced, in vitro preparations from the same animals. The responses of local serotonergic interneurons to unilateral stimuli displayed the same status-dependent differences as the depressor motor neurons. These results indicate that the circuits and their intrinsic serotonergic modulatory components are configured differently according to social status, and that these differences do not depend on a continuous descending signal from higher centers.

Thermal games in crayfish depend on establishment of social hierarchies

An unequal resource distribution is commonly seen in dominance hierarchies, in which the individual with the higher status is more successful in obtaining the resource. One possible resource is preferred temperature. When situations allow, ectotherms regulate their body temperature by behaviourally selecting different environmental conditions, achieving, when possible, a preferred temperature. Using a shuttlebox, the preferred temperature for Procambarus clarkii was determined to be 23.9°C with upper and lower voluntary escape temperatures of 25.9 and 21.8°C, respectively. If this preferred temperature zone (21.8–25.9°C) was valued as a resource, given the choice between a preferred temperature and a non-preferred temperature, crayfish should compete over the preferred temperature, with the dominant individual of dyadic pairs achieving the preferred temperature more often than the subordinate. Using a dual-choice experimental tank, competition over a binary temperature choice between rank-established paired crayfish was determined under both warm and cold challenge conditions (warm vs preferred temperature and cold vs preferred temperature, respectively). In naive pairings, similar levels of competition over the preferred temperature occurred in both warm and cold challenge trials, as predicted by game theory. In established pairings, however, dominant crayfish gained significantly greater access to preferred temperature in both warm and cold challenge conditions. These results demonstrate that crayfish engage in a cost–benefit assessment during their initial agonistic contests over temperature, but as hierarchies mature, these thermal games are decided by the dominant animal gaining primary access to the temperature resource.

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. Dominant–subordinate relationships were formed between juvenile crayfish as early as the third stage of development. Patterns of agonistic bouts to determine social hierarchy became more aggressive during development. The dominant–subordinate relationship was usually determined after contact in crayfish of less than 20 mm and 20–32 mm in length, while several bouts of fights were necessary for crayfish of 41–48 and 69–75 mm in length. Furthermore, social hierarchy was formed more rapidly in small crayfish. In larger animals, the number of approaches by dominant animals that promoted retreat in subordinate animals increased after the establishment of the winner–loser relationship. In smaller crayfish, in contrast, no measurable changes in these behaviour patterns were observed before and after the establishment of the winner–loser relationship. With increasing body size, the probability of tailflips decreased while that of retreats increased as the submissive behavioural act of subordinate animals.

Aggression and welfare in a common aquarium fish, the Midas cichlid

Many species of fishes are aggressive when placed in small aquaria. Aggression can negatively affect the welfare of those individuals toward whom it is directed. Animals may behave aggressively in order to defend resources such as food, shelter, mates, and offspring. The decision to defend depends on the distribution of resources and on ecological factors such as number of competitors, amount of available space, and amount of habitat complexity. This study tested the effects of these factors on aggression in a common aquarium fish, the Midas cichlid (Amphilophus citrinellus). The study found that time spent behaving aggressively was not associated with small-scale differences in group size or available space. Aggression was significantly lower in a large aquarium with a complex habitat. Aquaria of sizes typically used in the companion animal (pet) hobby did not provide optimal welfare for cichlids housed with aggressive conspecifics. The public should be aware that this and similar species require larger aquaria with complex habitat, which elicit more natural behavior.

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. We show that the response pattern to the same sensory stimulus changed with social status in the small crayfish. Crayfish are territorial animals and a dominant–subordinate relationship was determined when two previously unacquainted animals were paired. This winner–loser hierarchy was observed in pairs of small crayfish. Before fighting, all crayfish showed a dart response following mechanical stimulation of the tailfan. However, the probability of occurrence of a turn response increased significantly in the crayfish that won a fight. This behavioural transition from dart to turn response occurred immediately and was maintained for at least 3 days even if a dominant crayfish was isolated again with no opponent.

Indirect genetics effects and evolutionary constraint: an analysis of social dominance in red deer, Cervus elaphus

By determining access to limited resources, social dominance is often an important determinant of fitness. Thus, if heritable, standard theory predicts mean dominance should evolve. However, dominance is usually inferred from the tendency to win contests, and given one winner and one loser in any dyadic contest, the mean proportion won will always equal 0.5. Here, we argue that the apparent conflict between quantitative genetic theory and common sense is resolved by recognition of indirect genetic effects (IGEs). We estimate selection on, and genetic (co)variance structures for, social dominance, in a wild population of red deer Cervus elaphus, on the Scottish island of Rum. While dominance is heritable and positively correlated with lifetime fitness, contest outcomes depend as much on the genes carried by an opponent as on the genotype of a focal individual. We show how this dependency imposes an absolute evolutionary constraint on the phenotypic mean, thus reconciling theoretical predictions with common sense. More generally, we argue that IGEs likely provide a widespread but poorly recognized source of evolutionary constraint for traits influenced by competition.

Neural control of behavioural choice in juvenile crayfish

Natural selection leads to behavioural choices that increase the animal's fitness. The neuronal mechanisms underlying behavioural choice are still elusive and empirical evidence connecting neural circuit activation to adaptive behavioural output is sparse. We exposed foraging juvenile crayfish to approaching shadows of different velocities and found that slow-moving shadows predominantly activated a pair of giant interneurons, which mediate tail-flips that thrust the animals backwards and away from the approaching threat. Tail-flips also moved the animals farther away from an expected food source, and crayfish defaulted to freezing behaviour when faced with fast-approaching shadows. Under these conditions, tail-flipping, an ineffective and costly escape strategy was suppressed in favour of freezing, a more beneficial choice. The decision to freeze also dominated in the presence of a more desirable resource; however, the increased incentive was less effective in suppressing tail-flipping when paired with slow-moving visual stimuli that reliably evoked tail-flips in most animals. Together this suggests that crayfish make value-based decisions by weighing the costs and benefits of different behavioural options, and they select adaptive behavioural output based on the activation patterns of identifiable neural circuits.

Spiny lobsters use urine-borne olfactory signaling and physical aggressive behaviors to influence social status of conspecifics

Decapod crustaceans, like many other animals, engage in agonistic behaviors that enhance their ability to compete for resources with conspecifics. These agonistic behaviors include the release of chemical signals as well as physical aggressive and submissive behaviors. In this study, we report that Caribbean spiny lobsters, Panulirus argus, use both urine-borne chemical signaling and physical aggressive behaviors during interactions with conspecifics, and that these agonistic behaviors can influence the behavior and eventual social status of the interactants. Spiny lobsters that engaged primarily in physical aggressive behaviors became dominant, whereas spiny lobsters that received these physical aggressive behaviors responded with avoidance behaviors and became subordinates. Dominant animals frequently released urine during social interactions, more than when they were not in contact with subordinates and more than when they were not paired with another animal. Subordinates released urine significantly less often than dominants, and no more than when not paired. Preventing release of urine by catheterizing the animals resulted in an increase in the number and duration of physical interactions, and this increase was primarily driven by dominants initiating interactions through physical aggressive behaviors. Introducing urine from one of the catheterized animals into an aquarium reduced physical aggressive behavior by dominant animals to normal levels. Urine-borne signals alone were capable of inducing avoidance behaviors from solitary spiny lobsters in both laboratory and field conditions. We conclude that urine serves as a chemical signal that communicates social status to the interactants. Ablation experiments showed that that these urine signals are detected primarily by aesthetasc sensilla of the olfactory pathway.

Circadian Regulation of Agonistic Behavior in Groups of Parthenogenetic Marbled Crayfish, Procambarus sp

Crustaceans have frequently been used to study the neuroethology of both agonistic behavior and circadian rhythms, but whether their highly stereotyped and quantifiable agonistic activity is controlled by circadian pacemakers has, so far, not been investigated. Isolated marbled crayfish ( Procambarus spec.) displayed rhythmic locomotor activity under 12-h light:12-h darkness (LD12:12) and rhythmicity persisted after switching to constant darkness (DD) for 8 days, suggesting the presence of endogenous circadian pacemakers. Isogenetic females of parthenogenetic marbled crayfish displayed all behavioral elements known from agonistic interactions of previously studied decapod species including the formation of hierarchies. Groups of marbled crafish displayed high frequencies of agonistic encounters during the 1st hour of their cohabitation, but with the formation of hierarchies agonistic activities were subsequently reduced to low levels. Group agonistic activity was entrained to periods of exactly 24 h under LD12:12, and peaks of agonistic activity coincided with light-to-dark and dark-to-light transitions. After switching to DD, enhanced agonistic activity was dispersed over periods of 8-to 10-h duration that were centered around the times corresponding with light-to-dark transitions during the preceding 3 days in LD12:12. During 4 days under DD agonistic activity remained rhythmic with an average circadian period of 24.83 ± 1.22 h in all crayfish groups tested. Only the most dominant crayfish that participated in more than half of all agonistic encounters within the group revealed clear endogenous rhythmicity in their agonistic behavior, whereas subordinate individuals, depending on their social rank, initiated only between 19.4% and 0.03% of all encounters in constant darkness and displayed no statistically significant rhythmicity. The results indicate that both locomotion and agonistic social interactions are rhythmic behaviors of marbled crayfish that are controlled by light-entrained endogenous pacemakers.