Aggressiveness as a component of fighting ability in pigs using a game-theoretical framework

Understanding animal contests has benefited greatly from employing the concept of fighting ability, termed resource-holding potential (RHP), with body size/weight typically used as a proxy. However, victory does not always go to the larger/heavier contestant and the existing RHP approach thereby fails to accurately predict contest outcome. Aggressiveness, typically studied as a personality trait, might explain part of this discrepancy. We investigated whether aggressiveness forms a component of RHP, examining effects on contest outcome, duration and phases, plus physiological measures of costs (lactate and glucose). Furthermore, using the correct theoretical framework, we provide the first study to investigate whether individuals gather and use information on aggressiveness as part of an assessment strategy. Pigs, Sus scrofa, were assessed for aggressiveness in resident-intruder tests whereby attack latency reflects aggressiveness. Contests were then staged between size-matched animals diverging in aggressiveness. Individuals with a short attack latency in the resident-intruder test almost always initiated the first bite and fight in the subsequent contest. However, aggressiveness had no direct effect on contest outcome, whereas bite initiation did lead to winning in contests without an escalated fight. This indirect effect suggests that aggressiveness is not a component of RHP, but rather reflects a signal of intent. Winner and loser aggressiveness did not affect contest duration or its separate phases, suggesting aggressiveness is not part of an assessment strategy. A greater asymmetry in aggressiveness prolonged contest duration and the duration of displaying, which is in a direction contrary to assessment models based on morphological traits. Blood lactate and glucose increased with contest duration and peaked during escalated fights, highlighting the utility of physiological measures as proxies for fight cost. Integrating personality traits into the study of contest behaviour, as illustrated here, will enhance our understanding of the subtleties of agonistic interactions.

To breathe or fight? Siamese fighting fish differ when facing a real opponent or mirror image.

Displays are a feature of animal contest behaviour and have been interpreted as a means of gathering information on opponent fighting ability, as well as signalling aggressive motivation. In fish, contest displays often include frontal and lateral elements, which in the latter involves contestants showing their flanks to an opponent. Previous work in a range of fish species has demonstrated population-level lateralization of these displays, preferentially showing one side to their opponent. Mirrors are commonly used in place of a real opponent to study aggression in fish, yet they may disrupt the normal pattern of display behaviour. Here, using Siamese fighting fish, Betta splendens, we compare the aggressive behaviour of males to a mirror image and real opponent behind a transparent barrier. As this species is a facultative air-breather, we also quantify surface breathing, providing insights into underlying fight motivation. Consistent with previous work, we found evidence of population-level
lateralization, with a bias to present the left side and use the left eye when facing a real opponent. Contrary to expectations, there were no differences in the aggressive displays to a mirror and real opponent, with positive correlations between the behaviour in the two scenarios. However, there were important differences in surface breathing, which was more frequent and of longer duration in the mirror treatment. The reasons for these differences are discussed in relation to the repertoire of contest behaviour and motivation when facing a real opponent.

To breathe or fight? Siamese fighting fish differ when facing a real opponent or mirror image

Displays are a feature of animal contest behaviour and have been interpreted as a means of gathering information on opponent fighting ability, as well as signalling aggressive motivation. In fish, contest displays often include frontal and lateral elements, which in the latter involves contestants showing their flanks to an opponent. Previous work in a range of fish species has demonstrated population-level lateralization of these displays, preferentially showing one side to their opponent. Mirrors are commonly used in place of a real opponent to study aggression in fish, yet they may disrupt the normal pattern of display behaviour. Here, using Siamese fighting fish, Betta splendens, we compare the aggressive behaviour of males to a mirror image and real opponent behind a transparent barrier. As this species is a facultative air-breather, we also quantify surface breathing, providing insights into underlying fight motivation. Consistent with previous work, we found evidence of population-level lateralization, with a bias to present the left side and use the left eye when facing a real opponent. Contrary to expectations, there were no differences in the aggressive displays to a mirror and real opponent, with positive correlations between the behaviour in the two scenarios. However, there were important differences in surface breathing, which was more frequent and of longer duration in the mirror treatment. The reasons for these differences are discussed in relation to the repertoire of contest behaviour and motivation when facing a real opponent.

The energy costs of sexual dimorphism in mole-rats are morphological not behavioural.

Different reproductive strategies of males and females may lead to the evolution of differences in their energetic costs of reproduction, overall energetic requirements and physiological performances. Sexual dimorphism is often associated with costly behaviours (e.g. large males might have a competitive advantage in fighting, which is energetically expensive). However, few studies of mammals have directly compared the energy costs of reproductive activities between sexes. We compared the daily energy expenditure (DEE) and resting metabolic rate (RMR) of males and females of two species of mole-rat, Bathyergus janetta and Georychus capensis (the former is sexually dimorphic in body size and the latter is not) during a period of intense digging when males seek females. We hypothesized that large body size might be indicative of greater digging or fighting capabilities, and hence greater mass-independent DEE values in males of the sexually dimorphic species. In contrast to this prediction, although absolute values of DEE were greater in B. janetta males, mass-independent values were not. No differences were apparent between sexes in G. capensis. By comparison, although RMR values were greater in B. janetta than G. capensis, no differences were apparent between the sexes for either species. The energy cost of dimorphism is most likely to be the cost of maintenance of a large body size, and not the cost of behaviours performed when an individual is large.

The Soviet Union and the International Brigades, 1936-1939

The International Brigades are typically viewed as a fighting force whose impetus came from the Comintern, and thus from within the walls of the Kremlin. If the assumption is essentially correct, the broader relation between Stalin’s USSR and the IB has received little attention. This chapter constitutes an empirically-based study of the Soviet role not only in the formation of the IB, but of the Red Army’s collaboration with IB units, and Moscow’s role in the climax and denouement of the brigadistas’ Spanish experience. This study’s principal conclusion is twofold: First, that the creation and sustenance of the IB was part of Stalin’s goal of linking the Loyalist cause with that of the Soviet Union and international communism, a component of a larger geo-strategic gamble which sought to create united opposition to the fascist menace, one which might eventually bring Moscow and the West into a closer alliance. The second conclusion is that the IB, like the broader projection of Soviet power and influence into the Spanish theater, was an overly ambitious operational failure whose abortive retreat is indicative of the basic weakness of the Stalinist regime in the years prior to the Second World War.

Self-assessment by males during energetically costly contests over precopula females in amphipods

In animal contests, individuals can either engage in mutual assessment of both their own and their opponent's resource-holding potential (RHP) and adjust their behaviour according to estimated differences, or instead persist in accordance with thresholds determined by assessment of just their own RHP. We examined the predictions of alternative mutual assessment and self-assessment models for decision rules in contest resolution during struggles between males over females in precopula in the amphipod Gammarus pulex. Contest duration was positively related to the weight of the loser but not the weight of the winner. Our results support the hypothesis that males rely on information about their own RHP in determining contest behaviour and do not use information about their opponent. Fighting was energetically costly, and energy reserves were depleted during contests. Contest duration was associated with the physiological state of the loser (but not the winner) at the end of the contest, and to a lesser extent his size, further supporting self-assessment. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Motivational change during shell fights in the hermit crab Pagurus bernhardus

During agonistic interactions the motivation of each contestant is expected to vary because of increased information and changes in fighting ability. In shell fights between hermit crabs over gastropod shells, attackers rap their shell in a series of bouts against that of the defender whereas defenders remain withdrawn into their shells until the encounter is resolved; either the defender is evicted from its shell or the attacker 'gives up' and the defender retains its shell. We assessed the motivational state of attackers for performing rapping by measuring the duration of startle responses elicited by a novel stimulus. We staged fights between pairs of crabs in six different groups defined by the potential gain in shell quality available to attackers (high or low) and by the point at which the novel stimulus was applied (prior to rapping, after one bout or after four bouts). Startle response duration decreased during the first four bouts of fighting and showed a U-shaped relationship with the relative difference in size between the crabs. There was, no difference in startle response duration between high- and low-gain groups. Individuals showing short startle responses were likely to be victorious and we conclude that the relationship between the relative size difference of the opponents and. startle duration reflects that between size difference and the cost of gaining an eviction. (C) 2001 The Association for the Study of Animal Behaviour.

Decision rules, energy metabolism and vigour of hermit-crab fights

Aggressive interactions between animals are often settled by the use of repeated signals that reduce the risk of injury from combat but are expected to be costly. The accumulation of lactic acid and the depletion of energy stores may constrain activity rates during and after fights and thus represent significant costs of signalling. We tested this by analysing the concentrations of lactate and glucose in the haemolymph of hermit crabs following agonistic interactions over the ownership of the gastropod shells that they inhabit. Attackers and defenders play distinct roles of sender and receiver that are fixed for the course of the encounter. Attackers perform bouts of 'shell rapping', which vary in vigour between attackers and during the course of the encounter, and are a key predictor of victory. In contrast to the agonistic behaviour of other species, we can quantify the vigour of fighting. We demonstrate, to our knowledge for the first time, an association between the vigour of aggressive activity and a proximate cost of signalling. We show that the lactate concentration in attackers increases with the amount of shell rapping, and that this appears to constrain the vigour of subsequent rapping. Furthermore, attackers, but not defenders, give up when the concentration of lactate is high. Glucose levels in attackers also increase with the amount of rapping they perform, but do not appear to influence their decision to give up. Defenders are more likely to lose when they have particularly low levels of glucose. We conclude that the two roles use different decision rules during these encounters.

Signal residuals and hermit crab displays: flaunt it if you have it!

In animal contests selection should favour information gathering regarding the likely costs and benefits of continued conflict, and displays may provide a means for contestants to gain information about the fighting ability or aggressive intent of competitors. However, there is debate over the reliability of such displays and low levels of deception may occur within otherwise honest signalling systems. Hermit crabs use displays involving the chelipeds during agonistic encounters. We examined how variation in chelae size in relation to body size, a determinant of fighting ability, affects their use in displays and the process and outcome of contests over gastropod shells. In accordance with deceptive use of an otherwise honest signal, we found that contestants with large chelipeds for their body size spent more time performing the cheliped presentation display. Moreover, cheliped residuals and displays influenced the escalation level of encounters. There was a positive association between cheliped displays and the occurrence of 'grappling', but a negative association between displays and the occurrence of shell fights, suggesting that displays may signal aggressive intent and a reluctance to back off or accept the more passive defender role in a fight. Furthermore, the smaller of the two contestants in shell fights had larger cheliped residuals compared to those smaller contestants not involved in shell fights, which is consistent with disrupted opponent assessment. This study adds to mounting evidence that when acting as a signaller, individuals for whom the display exaggerates competitive ability attempt to manipulate opponents, using the display more often. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Large body size for winning and large swords for winning quickly in swordtail males, Xiphophorus helleri

Contestants can either assess their own resource-holding potential relative to their opponent (mutual assessment) or rely solely on the assessment of their own fighting ability (self-assessment). To discriminate between these possibilities, we staged dyadic territorial contests between 'size-matched' male swordtails. These contests consist of a combination of ritualized displays and direct fighting. Although size differences were small, winners were larger than losers and smaller fish tended to be winners only when the size difference was negligible. Body size, however, did not influence contest duration and there was no increase in contest duration with mean body size; thus, there is no support for self-assessment in these animals. We also examined the effects of the sword, which comprises a sexually selected extension used in female choice that reduces swimming efficiency but increases acceleration. The length of the sword (adjusted for body size) did not differ between winners and losers; however, losers conceded earlier if the opponent had a large sword for its body size but this decision was independent of the loser's own sword length. Losers thus assessed the swords of winners, which precludes self-assessment; however, because winners appeared not to assess the swords of losers, this does not fully support the idea of mutual assessment. (c) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Cumulative or sequential assessment during hermit crab shell fights: effects of oxygen on decision rules

Agonistic interactions between animals are often settled by the use of repeated signals which advertise the resource-holding potential of the sender. According to the sequential assessment game this repetition increases the accuracy with which receivers may assess the signal, but under the cumulative assessment model the repeated performances accumulate to give a signal of stamina. These models may be distinguished by the temporal pattern of signalling they predict and by the decision rules used by the contestants. Hermit crabs engage in shell fights over possession of the gastropod shells that they inhabit. During these interactions the two roles of signaller and receiver may be examined separately because they are fixed for the duration of the encounter. Attackers rap their shell against that of the defender in a series of bouts whereas defenders remain tightly withdrawn into their shells for the duration of the contest. At the end of a fight the attacker may evict the defender from its shell or decide to give up without first effecting an eviction; the decision for defenders is either to maintain a grip on its shell or to release the shell and allow itself to be evicted. We manipulated fatigue levels separately for attackers and defenders, by varying the oxygen concentration of the water that they are held in prior to fighting, and examined the effects that this has on the likelihood of each decision and on the temporal pattern of rapping. We show that the vigour of rapping and the likelihood of eviction are reduced when the attacker is subjected to low oxygen but that this treatment has no effect on rates of eviction when applied to defenders. We conclude that defenders compare the vigour of rapping with an absolute threshold rather than with a relative threshold when making their decision. The data are compatible with the cumulative assessment model and with the idea that shell rapping signals the stamina of attackers, but do not fit the predictions of the sequential assessment game.

School-related predictors of smoking, drinking and drug use: Evidence from the Belfast Youth Development Study

Objective

To examine whether students’ school engagement, relationships with teachers, educational aspirations and involvement in fights at school are associated with various measures of subsequent substance use.
Methods

Data were drawn from the Belfast Youth Development Study (n = 2968). Multivariate logistic models examined associations between school-related factors (age 13/14) and substance use (age 15/16).
Results

The two factors which were consistently and independently associated with regular substance use among both males and females were student–teacher relationships and fighting at school: positive teacher-relationships reduced the risk of daily smoking by 48%, weekly drunkenness by 25%, and weekly cannabis use by 52%; being in a fight increased the risk of daily smoking by 54%, weekly drunkenness by 31%, and weekly cannabis use by 43%. School disengagement increased the likelihood of smoking and cannabis use among females only.
Conclusion

Further research should focus on public health interventions promoting positive relationships and safety at school.

So Why Did the Guns Fall Silent? How Interplay, not Stalemate, Explains the Northern Ireland Peace Process

The precise rationale for, and timing of, the Northern Ireland peace process of the 1990s and beyond, which developed after more than two decades of conflict, has yet to be fully explained. It has been a common assumption that it arose from a stalemate involving the Irish Republican Army (IRA), the 'regular' pro-state forces of the British Army and Royal Ulster Constabulary and the 'irregular/ultra' pro-state loyalist paramilitary groups of the Ulster Volunteer Force (UVF) and Ulster Defence Association (UDA). Under this interpretation, military/paramilitary deadlock led to ripeness for peace, amid reappraisals by all parties to the conflict of the utility of violence accompanied by reinterpretations of earlier political orthodoxies. The IRA could not remove the British sovereign claim to Northern Ireland; British forces could not militarily defeat the IRA and loyalists and republicans were engaged in a futile inter-communal sectarian war. This stalemate thesis has obvious attraction in explaining why a seemingly intractable war finally subsided, but is less convincing when subject to empirical testing among republican and loyalist participants in the conflict. This article moves away from 'top-down' generalist narratives of the onset of peace, which tend to argue the stalemate thesis, to assess 'bottom-up' interpretations from the actual combatants as to why they ceased fighting. It suggests an asymmetry, rather than mutuality, of perception that there was 'military' cessation by the armed non-state groups, with neither republican nor loyalist interpretations grounded in notions of stalemate. The article concludes by urging a wider consideration of the important and persistent interplay of the military and political in conflicts such as Northern Ireland.

Struggles against Injustice:: Contemporary Critical Theory and Political Violence

This article investigates a significant problem in contemporary critical theory, namely its failure to address effectively the possibility that a campaign of political violence may be a legitimate means of fighting grave injustice. Having offered a working definition of ‘political violence’, I argue that critical theory should be focused on experiences of injustice rather than on ideals of justice. I then explore the reasons as to why, save for some intriguing remarks on retrospective legitimation, Jürgen Habermas has not addressed this issue directly. While Axel Honneth's recognition theory may have greater potential here, the absence of explicit consideration of the matter by him leaves considerable work to do. I introduce five questions in the concluding section that provide a starting point in setting out an appropriately stringent, normative test for claims that support violent action against injustice.