Agonistic Encounters Research Articles

Dishonest Signals of Strength in Male Slender Crayfish (Cherax dispar) during Agonistic Encounters

Many animals resolve disputes without combat by displaying signals of potential strength during threatening displays. Presumably, competitors use each other's displays to assess their relative strengths, and current theory predicts that these signals of strength should generally be honest. We tested this prediction by investigating the relationships among morphology, performance, and social dominance in males of the slender crayfish Cherax dispar. Crayfish routinely use their enlarged front claws (chelae) for both intimidation and fighting, making this species ideal for studying the honesty of weapon size. We evaluated five competing models relating morphological and physiological traits to dominance during paired competitive bouts. Based on the best model, larger chelae clearly resulted in greater dominance; however, chela strength had no bearing on dominance. Thus, displays of chela size were dishonest signals of strength, and the enlarged chelae of males seemingly function more for intimidation than for fighting. In addition, an analysis of the performance of isolated chela muscle showed that muscle from male crayfish produced only half the force that muscle from female crayfish produced (236.6+/-26.4 vs. 459.5+/-71.6 kN m(-2)), suggesting that males invest more in developing larger chelae than they do in producing high-quality chela muscle. From our studies of crayfish, we believe dishonest signaling could play a greater role in territorial disputes than previously imagined.

Dyadic social behaviour in the hamster: Evidence for contextual mediation

Dyadic social interactions among 34 adult male golden hamsters reared in either standard wire cages (Experiment 1) or cages with sandy substrates (Experiment 2) were observed for 15 min on consecutive days in two neutral arenas with either a bare Plexiglas or a sandy substrate. The tests showed that in the arena with the sandy substrate the hamsters spent less time engaged in agonistic encounters, initiated fewer agonistic encounters of all kinds and engaged in fewer agonistic encounters of a potentially physically damaging nature (i.e. violent encounters) than they did in the arena with the Plexiglas substrate. These effects were the same in animals reared under either condition. This finding argues against the behavioural effects being due to the novelty of a sand substrate to laboratory-reared hamsters. Consequently, the social behaviour of hamsters in laboratory settings is highly labile across various contexts. Therefore, it is necessary to examine the behavioural effects of contextual variables if g...

Agonistic behaviour of signal crayfish ( Pacifastacus leniusculus Dana) in different social environments: Effect of size heterogeneity on growth and food intake

The number and duration of agonistic encounters between signal crayfish Pacifastacus leniusculus individuals were monitored in two different social environments: a “stable” environment with large size variation and in an “unstable” environment with narrow size variation of conspecifics. The number of the agonistic interactions was higher in the “stable” environment. However, aggressive encounters lasted indicatively ( P = 0.098) longer in the “unstable” social environment. The number of encounters decreased significantly over the course of the communal rearing in both environments. The crayfish were kept individually before and after the communal rearing and growth and food consumption were measured. Both growth and food intake decreased when the animals were reared communally in comparison to the individual phases. The amount of cheliped, leg and antennal injuries did not differ between the two social environments, however, their occurrence increased during the communal rearing. These results suggest that the social environment of crayfish (the size variation of conspecifics) affects the number and the duration of agonistic encounters, while the absence of conspecifics (individual vs. communal) influences growth, food intake and the number of injuries. In a “stable” environment, fighting success was based on animal size. This was not the situation in an “unstable” environment, indicating the important role of behaviour on social hierarchy under conditions where size variation is limited, e.g. in restocked natural populations or aquaculture. Feeding success correlated poorly with fighting success and, therefore, feeding hierarchy does not reliably describe social hierarchy in crayfish populations.

The role of competitive dominance in the invasive ability of the Argentine ant (Linepithema humile)

To assess the importance of competi- tion in the advance of invasive species, bait stations have been used to determine the domi- nance hierarchy of a community of native ants in Donana National Park, southern Spain, and the status of the introduced species Linepithema humile (Argentine ant). Some native species, e.g. Cataglyphis floricola or Camponotus pilicor- nis, seem to be subordinate, i.e. occupy a low position in the competitive hierarchy; some are dominant (e.g. Pheidole pallidula), and others (e.g. Aphaenogaster senilis) occupy an intermedi- ate position in the hierarchy. The Argentine ant is a competitively dominant species, because of its aggressive behavior and relative abundance. Irre- spective of their position in the dominance hierarchy, L. humile and some native species adopt what games theory terms ''the bourgeois strategy'' during agonistic encounters with other species. Lone workers tend to be submissive in encounters whereas workers in the presence of other colony members are aggressive. L. humile was the only species which aggressively displaced large numbers of ants of other species from the bait. L. humile also expanded its range in the course of the experiment, displacing native spe- cies from parts of the study area.

Monoamines and decision making during contests in the hermit crab Pagurus bernhardus

During fights animals are expected to make a series of strategic decisions that involve interactions between information about the contest and the individual's nervous system that produce a change in behaviour. Biogenic monoamines such as serotonin (‘5-HT’) and dopamine are thought to prime decision-making centres for appropriate responses during aggressive interactions in crustaceans, and circulating levels vary both between individuals and during agonistic encounters. Aminergenic systems operate in diverse animal taxa and in this study we assayed circulating levels of 5-HT and dopamine following shell fights in the common European hermit crab, Pagurus bernhardus. The two roles in these fights, attacker and defender, perform different activities but, in both, 5-HT increased and dopamine declined in response to engaging in a fight. In defenders but not attackers, giving up was correlated with low 5-HT and dopamine. In attackers, motivation to initiate a fight was positively correlated with dopamine levels. Circulating monoamines are therefore involved in decision making during these aggressive encounters.

Tool-use in a display behaviour by Eurasian beavers (Castor fiber)

Tool use is rare amongst rodents and has never been recorded in connection with agonistic displays. We witnessed a behaviour, stick display (StD), involving tool use in free-living Eurasian beavers (Castor fiber) that we conclude is a display behaviour. Two beavers were the main performers of the signal that was observed in at least six beavers from three families. Beavers reacted to displays by increased evasive and agonistic behaviours compared with their usual behavioural patterns when at territory borders. The behaviour was almost exclusively seen between rivals at territory borders. We suggest that the display is used in agonistic encounters, mainly in a territorial context.

Activity patterns, behavioural repertoires, and agonistic interactions of crayfish: A non-manipulative field study

AbstractAgonistic behaviour of crayfish has been studied extensively in laboratory settings where pairs or groups of individuals are allowed to interact within an experimental arena. Crayfish agonistic behaviour within its natural context, however, has received little attention to date. The present, non-manipulative field study explored activity patterns, behavioural repertoires, and agonistic encounters of rusty crayfish (Orconectes rusticus) during the summer months using continuous, 24-hour, underwater video recording at a series of representative field sites. Following the filming, crayfish within the vicinity of the camera site were captured and measured. Individual densities were high, reaching a maximum of 68 individuals/m2 at some sites. Large crayfish predominantly inhabited deeper sections of the river and were mostly active at night, whereas small crayfish generally utilized the shallows and were active outside their burrows during day and dusk. Time outside their shelter was mainly used for feeding. Individuals frequently returned to the same shelter they had emerged from. Agonistic encounters were common events and generally occurred in the context of shelter acquisition or defense. Dyadic fighting progressed with escalating sequences of stereotyped aggressive acts. Furthermore, high intensities with unrestrained use of claws were seen in encounters between size-matched opponents. The results of this study allow us to root laboratory findings of crayfish aggression within a comprehensive, ethological framework and to consider ultimate consequences for individual fighting decisions and strategies.

Dishonest Signals of Strength in Male Slender Crayfish (Cherax dispar) during Agonistic Encounters

Dishonest Signals of Strength in Male Slender Crayfish (Cherax dispar) during Agonistic Encounters

Antiaggressive effects of topiramate in agonistic encounters between male mice

Topiramate, an antiepileptic drug, has been found to be useful for the treatment of aggression in clinical populations. However, no studies have explored the action of this compound on aggressive behavior in laboratory animals. This work examined the effects of topiramate (10, 20, 40 and 80 mg/kg, i.p.) on agonistic interactions between male mice, using an ethopharmacological approach. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration. Ten minutes of diadic interactions were staged between a singly housed and an anosmic mouse in a neutral area. The encounters were videotaped and the accumulated time allocated by subjects to 10 broad behavioral categories was estimated using an ethologically based analysis. Results showed that topiramate (20-80 mg/kg) produced a significant reduction of offensive behaviors (threat and attack), without affecting immobility. Digging behavior (all doses) was also significantly decreased. The antiaggressive effects of topiramate could be related to its ability for modulating positively GABA-A receptors and/or blocking AMPA subtype of glutamate receptors.

The Role of Cheliped Autotomy in the Territorial Behavior of the Freshwater Prawn Macrobrachium Lar

Abstract The role of cheliped autotomy in the territorial behavior of the freshwater prawn Macrobrachium lar was analyzed to determine whether or not prawns modified their defended territory size based on cheliped autotomy. Territory size measurements were recorded for captive prawns interacting in artificial tank habitats and were logged according to the locations where agonistic encounters occurred and aggressive pressures were equal. All prawns used in this study were mid-intermolt males in the size class 9.0 ± 1.5 cm, with staged encounters occurring under three treatment conditions in which fully intact prawns were matched against animals possessing no chelipeds, one cheliped, or two chelipeds (fully intact). Separate experiments for each condition were completed with four prawns per tank per 14-day trial and were run a total of three times each. The defended territory size mean for the Control prawns (matched only against other intact animals) did not differ significantly from one quarter of the tot...

Saccular potentials of the vocal plainfin midshipman fish, Porichthys notatus

The plainfin midshipman fish, Porichthys notatus, is a vocal species of teleost fish that generates acoustic signals for intraspecific communication during social and reproductive behaviors. All adult morphs (females and males) produce single short duration grunts important for agonistic encounters, but only nesting males produce trains of grunts and growls in agonistic contexts and long duration multiharmonic advertisement calls to attract gravid females for spawning. The midshipman fish uses the saccule as the main acoustic endorgan for hearing to detect and locate vocalizing conspecifics. Here, I examined the response properties of evoked potentials from the midshipman saccule to determine the frequency response and auditory threshold sensitivity of saccular hair cells to behaviorally-relevant single tone stimuli. Saccular potentials were recorded from the rostral, medial and caudal regions of the saccule while sound was presented by an underwater speaker. Saccular potentials of the midshipman, like other teleosts, were evoked greatest at a frequency that was twice the stimulus frequency. Results indicate that midshipman saccular hair cells of non-reproductive adults had a peak frequency sensitivity that ranged from 75 (lowest frequency tested) to 145 Hz and were best suited to detect the low frequency components (<or=105 Hz) of midshipman vocalizations.

Bioenergetics modeling to investigate habitat use by the nonindigenous crab,Carcinus maenas, in Willapa Bay, Washington

A bioenergetics model was developed and applied to questions of habitat use and migration behavior of nonindigenous European green crab (Carcinus maenas) in Willapa Bay, Washington, USA. The model was parameterized using existing data from published studies on the ecology and physiology ofC. maenas and allied brachyuran crabs., Simulations of the model were run describing four scenarios of habitat use and behavior during a 214-d simulation period (April–October) including crabs occupying mid littoral habitat, high littoral habitat, sublittoral habitat, and sublittoral habitat but undertaking intertidal migrations. Monthly trapping was done along an intertidal gradient in Willapa Bay to determine the actual distribution of crabs for the same time interval as the simulation period, and model results were compared to the observed pattern. Model estimates suggest no intrinsic energetic incentive for crabs to occupy littoral habitats since metabolic costs were c. 6% higher for these individuals than their sublittoral counterparts. Crabs in the littoral simulations were also less efficient than sublittoral crabs at converting consumed energy into growth. Monthly trapping revealed thatC. maenas are found predominantly in mid littoral habitats of Willapa Bay and there is no evidence of resident sublittoral populations. The discrepancy intimates the significance of other factors, including interspecific interactions, that are not incorporated into the model but nonetheless increase metabolic demand. Agonistic encounters with native Dungeness crabs (Cancer magister) may be chief among these additional costs, andC. maenas may largely avoid interactions by remaining in littoral habitats neglected by native crabs, such as meadows of nonindigenous smooth cordgrass (Spartina alterniflora). AdultC. maenas in Willapa Bay may occupy tidal elevations that minimize such encounters, and metabolic costs, while simultaneously maximizing submersion time and foraging opportunities.

Allopatric differentiation in the acoustic communication of a weakly electric fish from southern Africa, Marcusenius macrolepidotus (Mormyridae, Teleostei)

A few species of the weakly electric snoutfish, the African freshwater family Mormyridae, have been reported to vocalise. However, allopatric populations of a single species were never compared. Members of three allopatric Marcusenius macrolepidotus populations, originating from the Upper Zambezi River in Namibia, the Buzi River (Mozambique), and the Incomati River system in South Africa, vocalised with pulsatile growl- and tonal hoot sounds in dyadic confrontation experiments. A high rate of growling accompanied territorial and agonistic interactions and also non-threatening interactions between males and females, which in one pair appeared to be courtship. Growl sound characteristics of M. macrolepidotus from the Incomati system differed from those of the Upper Zambezi in a significantly higher frequency of the first harmonic (mean, 355 Hz vs 266 Hz). The two vocalising males from the Buzi River generated growls about twice as long as the other fish. Furthermore, the growl pulse period was about 4 ms in M. macrolepidotus from the Upper Zambezi River and from the Incomati system, but 6 ms in M. macrolepidotus from the Buzi River. Hoots were only observed in agonistic encounters. Hoot oscillograms showed a sinusoidal waveform, and the mean duration of this sound was similar in Incomati system fish (mean, 161 ms), Upper Zambezi fish (172 ms) and Buzi fish (103 and 145 ms for the two vocalising individuals). The mean frequency of the first hoot harmonic was higher in Incomati system fish (326 Hz) than in Upper Zambezi fish (245 Hz). Both growl and hoot occurred only in the presence of conspecifics, probably signalling the presence and condition of an opponent, territory owner or potential mate. This is the first evidence for (1) sound production and acoustical communication in another species and genus, M. macrolepidotus, from southern Africa to be (2) geographically differentiated.

Fighting fit: thermal plasticity of metabolic function and fighting success in the crayfishCherax destructor

1. We examined the effect of thermal acclimation on fighting success and underlying performance traits in the crayfish Cherax destructor. We tested the hypothesis that animals will be more successful when fighting at their acclimation temperature than at a colder or warmer temperature, and that changes in metabolic capacity underlie differences in behavioural performance. 2. Thermal acclimation (to 20 degrees C and to 30 degrees C) had a significant effect on behavioural contests, and the likelihood of winning was significantly greater when individuals fought at their acclimation temperature against an individual from an alternate acclimation temperature. 3. The ratio of ADP stimulated respiration to proton leak (respiratory control ratio) of isolated mitochondria increased significantly in chelae muscle of the cold-acclimated group, and differences in respiratory control ratio between winners and losers were significantly correlated with the outcome of agonistic encounters. However, acclimation did not affect tall muscle mitochondria or the activity of pyruvate kinase in either chelae or tail muscle. 4. The force produced by closing chelae was thermally insensitive within acclimation groups, and there were no significant differences between acclimation treatments. None the less, differences in chelae width between contestants were significantly correlated with the outcome of agonistic encounters, but this perceived resource holding power did not reflect the actual power of force production. 5. Thermal acclimation in C destructor has beneficial consequences for dominance and competitive ability, and the success of cold acclimated animals at the cold temperatures can be at least partly explained by concomitant up-regulation of oxidative ATP production capacity.

Rewarding effects of 3,4-methylenedioxymethamphetamine (“Ecstasy”) in dominant and subordinate OF-1 mice in the place preference conditioning paradigm

We tested the ability of 3,4-methylenedioxymethamphetamine (MDMA) to induce conditioned place preference (CPP) in dominant and subordinate OF-1 mice subjected to cohabitation and repeated sessions of agonistic confrontation, as well as in non-confronted mice. We selected doses of MDMA (2, 6, 10 mg/kg) previously reported to induce CPP in mice and we measured expression of c-Fos evoked by the treatments in non-confronted mice. MDMA induced c-Fos protein in several corticolimbic regions involved in drug-induced reward. Mice were exposed to brief sessions of agonistic confrontation on 5 consecutive days. Determinations of circulating hormones and drug conditioning tests were carried out on completion of the encounters. The results of hormone assays indicated that dominant mice had higher serum concentrations of testosterone, but lower levels of corticosterone, than submissive mice. Post-conditioning tests after drug conditioning (4 injections of MDMA or saline on alternate days) showed that MDMA significantly produced CPP at doses of 2 and 6 mg/kg, but not at 10 mg/kg, an inverted U-shaped pattern of conditioning that was invariable in non-confronted, dominant and subordinate mice. These results demonstrate that the endocrine and behavioural correlates linked to social status and social stress in mice are not paralleled by significant changes in the rewarding efficacy of MDMA in the CPP paradigm under the specific conditions tested.

Effects of Previous Experience on the Agonistic Behaviour of Male Crickets, Gryllus bimaculatus

Male solitary animals frequently enter aggressive interactions with conspecific individuals to protect their territory or to gain access to females. After an agonistic encounter, the loser (subordinate individual) changes its behaviour from aggression to avoidance. We investigated agonistic interactions between pairs of male crickets to understand how dominance is established and maintained. Two naïve males readily entered into agonistic interactions. Fights escalated in a stereotyped manner and were concluded with the establishment of dominance. If individuals were isolated after the first encounter and placed together 15 minutes later, subordinate crickets tended to avoid any further contact with the former dominant opponent. Moreover, subordinate males also avoided unfamiliar dominant and naïve opponents. They displayed aggressive behaviour only towards unfamiliar subordinate opponents. This suggests that the subordinate male change their behaviour depending on the dominance status of the opponent. Dominant crickets, in contrast, displayed aggressive behaviour towards familiar as well as unfamiliar opponents. If the interval between the first and second encounter was longer than 30 minutes, the former subordinate male showed aggressive behaviour again. However, if the subordinate cricket was paired with the same opponent three consecutive times within 45 minutes, it avoided the former dominant opponent for up to 6 hours following the third encounter. Our results suggest that the maintenance of dominance in male crickets depends largely on the behavioural change of subordinate individuals. Possible mechanisms to maintain dominance are discussed.

Aggressiveness and memory: Subordinate crabs present higher memory ability than dominants after an agonistic experience

A relationship between aggressiveness and memory has been proposed in several studies with different animal species. Here, we study this possibility in the crab Chasmagnathus granulatus, using the context-signal memory model (CSM) that involves an association between the learning context and a visual danger stimulus. Each experiment consisted of an agonistic phase and a memory one. During the former, matched pairs of male crabs were staged in two 10-min encounters and the dominant or subordinate condition of each member of the dyad was determined. During the memory phase, crabs were trained to acquire CSM and tested 24 h later. Results showed that the agonistic encounter, staged 48 h before the acquisition of CSM, can modulate memory according to the dominance condition of the fighter; in such a way that memory retention of subordinates results higher than that of dominants. By contrast, when the memory phase preceded the agonist one, forthcoming dominants and subordinates did not differ in their memory ability. The memory modulation would not be linked to a dominance status but to a persistent dominance relationship fully reconstructed in each encounter between the same opponents. Therefore, the crab’s CSM would not depend directly on predetermined intrinsic properties, but on the outcome of the fight, which would be determined in turn by the relative aggressiveness of the fighters. The finding that the agonistic episode modulates memory opens the possibility of using this episodic interference to probe the function of diverse phases of CSM.

Social defeat and footshock increase body mass and adiposity in male Syrian hamsters

Obesity is a world-wide epidemic, and many factors, including stress, have been linked to this growing trend. After social stress (i.e., defeat), subordinate laboratory rats and most laboratory mice become hypophagic and, subsequently, lose body mass; the opposite is true of subordinate Syrian hamsters. After social defeat, Syrian hamsters become hyperphagic and gain body mass compared with nonstressed controls. It is unknown whether this increase in body mass and food intake is limited to subordinate hamsters. In experiment 1, we asked, do dominant hamsters increase food intake, body mass, and adiposity after an agonistic encounter? Subordinate hamsters increased food intake and body mass compared with nonstressed controls. Although there was no difference in food intake or absolute body mass between dominant and nonstressed control animals, cumulative body mass gain was significantly higher in dominant than in nonstressed control animals. Total carcass lipid and white adipose tissue (WAT) (i.e., retroperitoneal and epididymal WAT) masses were significantly increased in subordinate, but not dominant, hamsters compared with nonstressed controls. In experiment 2, we asked, does footshock stress increase food intake, body mass, and adiposity. Hamsters exposed to defeat, but not footshock stress, increased food intake relative to nonstressed controls. In animals exposed to defeat or footshock stress, body mass, as well as mesenteric WAT mass, increased compared with nonstressed controls. Collectively, these data demonstrate that social and nonsocial stressors increase body and lipid mass in male hamsters, suggesting that this species may prove useful for studying the physiology of stress-induced obesity in some humans.

AN EXAMINATION OF AGONISTIC INTERACTIONS IN THE WHIP SPIDER PHRYNUS MARGINEMACULATUS (ARACHNIDA, AMBLYPYGI)

Abstract Intraspecific interactions in adult whip spiders (Phrynus marginemaculatus) were investigated in a laboratory setting to quantify agonistic interactions and to determine predictors of contest outcome. Males were initially paired with size-symmetric or size-asymmetric opponents to assess the effect of size symmetry on contests. Three weeks later, the same males were paired with either the same opponent, or a different opponent to determine whether or not individuals remember earlier encounters. Finally, we quantified aspects of female-female contests. Agonistic encounters between males are characterized by varying degrees of pedipalpal opening, elevation displays, and rapid flicking (∼ 29 Hz) of the antenniform leg. Duration of elevation displays was a predictor of contest outcome, with individuals being more likely to win if they held an elevated posture for longer than their opponent during the contest. Relative size influenced both contest duration and weight loss, with contests between size-sy...

Effects of surgical castration on the behavioural and physiological responses of weaned pigs

Surgical castration is an acute stressor that can affect the behaviour, endocrine and immune responses of pigs [1,2]. Therefore, it may impair the health and welfare of these animals. This could be of particular concern at weaning, which constitutes a severe nutritional, physical and psychological stressor often associated with increased disease susceptibility [3]. Thus, an experiment was carried out to evaluate the effect of surgical castration on postweaning behaviour and on the behavioural, endocrine and immune responses elicited by a low-dose lipopolysaccharide (LPS) challenge after weaning. At 5 days-ofage, 64 male piglets were randomly assigned to undergo surgical castration or were left untreated. Pigs were weaned at 28 days-of-age. Behaviour post-weaning and mixing was assessed during a 1-h period, during which agonistic interactions were recorded. One day post-weaning, pigs were injected with a single dose of 0 or 5 μg/kg of body weight (BW) of LPS from Escherichia coli. Sickness behaviour was studied by scan sampling every 5 minutes for 45 minutes at 0, 1, 2, 3, 4, 6 and 8 h after the challenge was initiated. Blood samples were taken at 0, 2, 12 and 24 h after injection and were analysed for plasma concentrations of tumor necrosis factor-alpha (TNF-α), interleukin 1-beta (IL-1β), C-reactive protein (CRP), serum amyloid A (SAA) and cortisol. Saliva samples were also taken when pigs were 3, 4, 5, 6 and 8 weeks-of-age for subsequent determination of salivary testosterone concentrations. Results showed that entire males were more aggressive than castrated pigs immediately after weaning (P < 0.05). Administration of LPS provoked behaviours characteristic of sickness including a reduction in general activity, as well as decreased eating and exploratory behaviours (P < 0.05). Significant treatment by challenge interactions showed that castration reduced the occurrence of sickness behaviours induced by LPS, such as depressed general activity (P < 0.01), anorexia (P < 0.01) and reduced exploratory behaviours (P < 0.05). LPS administration increased TNF-α levels (P < 0.05), with peak concentrations 2 h after injection (P < 0.01). CRP levels of LPStreated pigs were higher that saline-treated animals at 12 h (P < 0.05). LPS administration tended to increase plasma SAA levels (P < 0.1), but did not increase cortisol levels. Nonetheless, castration did not affect the response of pro-inflammatory cytokines, acute phase proteins and cortisol to the challenge. Concentrations of testosterone in saliva were higher in entire males (P < 0.001). Furthermore, salivary testosterone levels in entire males varied with age and were markedly elevated at 4 weeks-of-age (P < 0.001), which coincided with weaning. These results show that surgical castration reduces aggressiveness at weaning. It is likely that peak levels of testosterone are in part responsible for the higher frequency of agonistic encounters among entire male pigs [4]. In addition, castration affects the coping mechanisms of weaned pigs against a low-dose LPS challenge. It is also possible that entire males may be more efficient in overcoming the bacterial endotoxin challenge, taking into consideration the beneficial effects of sickness behaviour in the recovery from infection [5]. In conclusion, surgical castration reduces aggressiveness at weaning and also impairs the behavioural, but not the endocrine and immune responses elicited by low-dose LPS challenge in pigs. from Prevention of Boar Taint in Pig Production: The 19th Symposium of the Nordic Committee for Veterinary Scientific Cooperation Gardermoen, Norway. 21–22 November 2005