Initiation and Resolution of Fights between Swimming Crabs (Liocarcinus depurator)

Fights between male swimming crabs (Liocarcinus depurator) were studied in the laboratory and in the field. These crabs fight readily in the laboratory, interactions being initiated equally often by the larger and the smaller of the two opponents, but usually being won by the larger. Many different combinations of cheliped and swimming leg postures are seen during fights, which fell into 4 categories: 13% involved only stationary display, 38% were resolved by a single approach and retreat by displaying crabs, 9% were resolved by multiple approaches and retreats and 39% involved physical contact between the crabs. Fight length was variable, and depended both on the absolute size and on the relative size of the participants. During the course of the fights, few behavioural differences were observed between the eventual winners and losers. Fights were less common in the field, but the same rules determined their initiation, content and outcome. The results are discussed in the context of game theory.     

Stickleback fights: why do winners win? Influence of metabolic and morphometric parameters

Pairs of reproductively mature male three-spined stickleback (Gasterosteus aculeatus) were introduced into unfamiliar aquaria and observed until one male became dominant. Skin carotenoid content, morphometric indexes, and metabolic capacities of the axial and pectoral muscles were examined to establish whether morphological or physiological parameters differentiated winners and losers. Stickleback that initiated fights typically won. Quick initiation led to quick victory. Overall, winners and losers differed in few morphological or metabolic characteristics, but these properties and the differences between these attributes for losers and winners of specific fights were linked with initiation time and fight duration. Morphometric indexes of losers were the primary determinants of initiation time and fight duration, whereas for winners muscle metabolic capacities were linked to these fight characteristics. The greater the hepatosomatic index (HSI) of losers, the longer the fight initiation times. Similarly, losers with high HSI and carotenoid levels resisted defeat longer. In winners, initiation time decreased as axial muscle phosphofructokinase levels increased and citrate synthase levels decreased, whereas the metabolic capacities of the pectoral muscle were linked with time to achieve victory. When losers had greater HSI values than the winners of a specific fight, fight initiation was delayed and fights lasted longer. When losers had higher carotenoid levels than winners, fights also lasted longer. On the other hand, when losers had more visceral fat (fat body mass over somatic mass) than winners, both initiation time and combat duration were reduced. These results suggest that male stickleback assess their physiological status and that of their opponents, in particular the HSI, and adjust their combat strategies accordingly.     

Prior residence, body size and the dynamics of territorial disputes between male freshwater angelfish

Territorial interactions between pairs of size mismatched, sexually mature male angelfish Pterophyllum scalare were investigated in three different conditions: with the larger fish resident (the large resident condition), with the smaller fish resident (the small resident condition) and in a neutral territory (the neutral condition). In the two resident conditions, approximately half of the intruders had previously held territories and half had not. In all categories of fight, one fish showed submissive postures and lost the fight; eventual losers performed both attack and threat at a lower rate than eventual winners. Attack rate declined as the encounter progressed, while rate of performance of threat postures increased. In fights on neutral territories, the larger fish won all fights. In all fights with a resident-intruder asymmetry, the resident fish won the encounter, regardless of relative size. In eventual winners but not in eventual losers, levels of attack were lowest in the neutral encounters. In the small resident condition, levels of attack (corrected for activity of the resident) were lower in intruders that had previously held a breeding territory. Relative size influenced behaviour shown during fights, in that overall intensity was correlated negatively with size differential in all conditions. Thus although prior residence is the primary determinant of the outcome of territorial encounters in this species, both relative body size and prior possession of territory also influence the nature of the interaction.     

Why do winners keep winning? Androgen mediation of winner but not loser effects in cichlid fish

Animal conflicts are influenced by social experience such that a previous winning experience increases the probability of winning the next agonistic interaction, whereas a previous losing experience has the opposite effect. Since androgens respond to social interactions, increasing in winners and decreasing in losers, we hypothesized that socially induced transient changes in androgen levels could be a causal mediator of winner/loser effects. To test this hypothesis, we staged fights between dyads of size-matched males of the Mozambique tilapia (Oreochromis mossambicus). After the first contest, winners were treated with the anti-androgen cyproterone acetate and losers were supplemented with 11-ketotestosterone. Two hours after the end of the first fight, two contests were staged simultaneously between the winner of the first fight and a naive male and between the loser of first fight and another naive male. The majority (88%) of control winners also won the second interaction, whereas the majority of control losers (87%) lost their second fight, thus confirming the presence of winner/loser effects in this species. As predicted, the success of anti-androgen-treated winners in the second fight decreased significantly to chance levels (44%), but the success of androgenized losers (19%) did not show a significant increase. In summary, the treatment with anti-androgen blocks the winner effect, whereas androgen administration fails to reverse the loser effect, suggesting an involvement of androgens on the winner but not on the loser effect.     

Vocal rate as an assessment process during fallow deer contests

Two types of model propose that strategic decisions during contests are determined either by (i) a mutual-assessment process or (ii) a self-assessment process. Vocal signals are thought to convey information about the competitive abilities of individuals, the ultimate function of which is a reduction in costs associated with fighting consistent with the principle of mutual assessment. Nevertheless, the limited evidence that male ungulates engage in mutual assessment of vocal rates during dyadic contests has been questioned. Therefore, we examined the vocal rates of winners and losers during escalated dyadic contests between male fallow deer in order to further inform on this issue. Our results showed that winners and losers did not differ in vocal rate. The best model fit that accounted for individual vocal rates included a preponderance of factors related to the opponent indicating that contestants were attending to their opponent during fights. Vocal rate was, therefore, dependent on estimates of opponent quality without reference to self, supporting an 'opponent-only' rather than a mutual assessment process.     

Post‐Contest Stridulation Used Exclusively as a Victory Display in Mangrove Crabs

Victory or triumph display is a post‐contest signal, performed only by winners and not by losers. While much is unknown about its function, there is mounting evidence that victory displays are widespread among animals. However, evidence remains anecdotal in crabs. Sesarmid crabs belonging to the genera Parasesarma and Perisesarma are known to have characteristic stridulatory structures on their chelipeds. In Perisesarma eumolpe, a mangrove crab, stridulation has been anecdotally purported as a triumph display. We examined whether stridulation in P. eumolpe is a victory display and the factors affecting it by staging 17 contest trials among males and investigating the factors influencing stridulations and fight outcome in 55 fights. Using generalised linear mixed‐effects models, we find that stridulations were generally performed by winners and after fights, especially when the fights were intense. In addition, stridulation was only observed in the context of a contest, never before or outside of it. Stridulation in P. eumolpe is likely a victory display, and, unlike other forms of victory display described for other species, it appears exclusively used for asserting victory.     

Mangrove crab uses victory display to “browbeat” losers from re‐initiating a new fight

Signalling behaviour is integral to animal contests. However, post‐contest signals, such as victory displays, have received relatively little attention. One hypothesised function of victory displays is to ensure a more lasting dominance by reducing the risk of losers re‐initiating a new contest with winners. Despite several theoretical studies using game theory that support this hypothesis, empirical support for the understanding of when and why victory displays are used with respect to browbeating is lacking. We use a common South‐East Asian mangrove crab, Perisesarma eumolpe, to examine whether the performance of victory displays by winners, among other factors, affects the time of fight re‐initiation by losers, if at all re‐initiated. Using mixed‐effects survival analysis models, we analysed 77 fights from 27 staged contest trials between randomly paired males. We found losers that experienced victory display performed by winners, presented a decreased instantaneous hazard rate of re‐initiating a new fight than losers that did not. These results corroborate previous game theoretical models indicating that victory displays may function to reduce the chances of losers re‐initiating another fight. In discouraging losers from restarting a fight, winners reduce the potential costs of a future contest.     

Fighting dynamics of male copperheads,Agkistrodon contortrix (Serpentes,Viperidae): Stress-induced inhibition of sexual behavior in losers

Adult male copperheads (Agkistrodon contortrix) fight for priority of access to females during the mating periods in spring and late summer. During fights, one male abruptly quits and retreats, and the other chases in pursuit. One male thus emerges as the winner and the other as the loser. Reversal of this outcome does not occur during the time of observation (30 min) nor in 24 hr postfight trials. In all cases, winners gain priority of access to females. Losers, in contrast, do not pursue females nor gain access to them, even when winners are removed from the arena. In this study, courtship performance of male A. contortrix was studied in the laboratory using subjects with either winning or losing experience from staged fights. All males used first were tested with a single female to determine courtship performance prior to the agonistic trials. From these tests, each male was given a single courtship score of 0 (no courtship) to 3 (most intense courtship). Only males receiving a score of 2–3 were used in the initial agonistic trials. All staged fights were conducted in a large arena and involved two males and one female. Following fights, winners and losers were tested again for courtship performance. In trials conducted at 24 hr and 7 days postfight, only losers were tested. It was found that prefight courtship scores were not significantly different between winners and losers. At 30 min postfight, most losers showed complete suppression of courtship behavior (score 0). Winners, in contrast, showed equivalent or an increase in their courtship scores. At 24 hr postfight, courtship scores of losers remained significantly lower than their prefight scores. At 7 days postfight, courtship scores of losers were not significantly difference from their original prefight scores. Fighting behavior in free-ranging A. contortrix represents a potentially significant cost to losers if it is associated with loss of reproductive opportunities. Recent evidence from hormonal studies indicates that inhibition of courtship and fighting behavior in male A. contortrix is stress-induced. © 1996 Wiley-Liss, Inc.     

Recognition of Dominance in the Big-Clawed Snapping Shrimp ( Alpheus Heterochaelis Say 1818) Part I: Individual or Group Recognition?

The snapping shrimp Alpheus heterochaelis uses its snapper claw to produce fast water jets in fights. Here we investigate whether these shrimp are able to recognise their opponents (individually or on a group level) in order to reduce fighting costs and risk of injury. Losers meeting familiar or unfamiliar winners differ from those meeting inexperienced opponents by showing immediate escapes after a contact as well as hardly any aggressive behaviours (e.g. water jets). There is a significant decrease in aggressiveness in these losers and this is maintained for days. In contrast, losers meeting inexperienced opponents show a slow stepwise decrease in aggressiveness after losing on several consecutive days. Thus, snapping shrimp can recognise the dominance status of the opponent. The lack of behavioural differences in losers meeting familiar or unfamiliar winners favours recognition on a group level rather than individual recognition.     

Imperfect assessment and limited information preclude optimal strategies in male-male fights in the orb-weaving spider Metellina mengei

Agonistic behaviour between male orb-web spiders Metellina mengei competing for access to female webs was examined in field experiments to test the major predictions of game theory. Winners of fights were significantly larger than losers, particularly with respect to the length of the first pair of legs, which are sexually dimorphic in this species and used extensively in agonistic encounters. The size of the winning male had no influence on contest intensity or duration, and neither did relative size. However, fight intensity and duration were both positively correlated with the size of the losing male. Resident males won significantly more contests than intruders. Winning intruders were significantly larger than winning residents and it was these winning intruders that tended to produce the longer fights. Female weight and hence reproductive value had a marked influence on fight intensity and duration of fights won by the intruder but not those won by the resident. This indicates that only the resident obtains information about the female. These data are discussed with reference to the discrepancy with theory and a failure of some contestants to obtain information on resource value and relative contestant size necessary to optimize fight strategy.     

The Napoleon Complex: why smaller males pick fights

Does it ever pay for smaller animals to initiate fights even when they are likely to lose? Asymmetry in payoffs between opponents or a suboptimal strategy resulting from likely losers misperceiving themselves as likely winners have both been proposed as possible explanations for the aggressive behavior of smaller males. The model presented here suggests that in some cases, even without a payoff asymmetry and allowing for only a small error in perception, likely losers are expected to attack first. If the value of the resource exceeds the cost of losing a fight, the cost of displaying is sufficiently small, and assessment of resource holding power is reasonably accurate but not perfect, the evolutionarily stable strategy (ESS) prompts those contestants who perceive themselves as the likely losers to initiate fights, while it prompts those contestants who perceive themselves as the likely winners to wait for the adversary to attack or retreat.     

Winning, losing, mood, and testosterone.

In two experiments, male college students either won or lost $5 on a task controlled entirely by chance. In both studies, winners reported a more positive mood change than did losers and, in Experiment 2, winners reported a more positive mood change than a neutral group that did not win or lose money. After the task was completed, winners exhibited significantly higher testosterone levels than losers. Levels of cortisol, a hormone associated with stress and arousal, did not differ among the groups, suggesting that a hormone-behavior response pattern for winning and losing is specific to testosterone. These data suggest that winning can alter testosterone levels in men and that mood may mediate such changes.     

Experimental evidence that winning or losing a fight does not affect sperm quality in a field cricket

Fighting is a powerful social experience that can affect male reproductive behavior, including ejaculatory strategies. Whereas winners may monopolize females, losers may instead perceive high sperm competition and limited future mating opportunities, and accordingly enhance ejaculate quality to maximize their reproductive success. In male field crickets Gryllus bimaculatus that fight aggressively for control of breeding territories, winners are known to possess sperm of lower quality (viability) compared to losers, but it remains unclear whether this is due to short‐term fighting consequences. To test if the fighting experience per se (winning or losing) affects male adjustment of sperm viability, we subjected males to winning and losing experiences by staging fights against size‐matched rivals of known fighting ability. These rivals were males that previously won or lost a fight and, due to “winner‐loser effects” kept winning or losing subsequent contests. We sampled sperm prior and after the fight and twice in control males with no fighting experience and found no differences in sperm viability across measures. We conclude that males do not tailor their ejaculate quality following a single fight, or based on its outcome. Intrinsic differences in other attributes between winners and loser phenotypes may explain differences in sperm quality previously described in this system.     

Changes in Heart Rate Associated with Contest Outcome in Agonistic Encounters in Lobsters

Agonistic contests between lobsters housed together in a confined space progress through encounters of increasing intensity until a dominance relationship is established. Once this relationship is established, losing animals continually retreat from the advances of winners.These encounters are likely to consume much energy in both winning and losing animals. Therefore, one might expect involvement of many physiological systems before, during and after fights. Here, we report effects of agonistic encounters on cardiac frequency in winning and losing adult lobsters involved in dyadic interactions.The results show that: (i) small but significant increases in heart rate are observed upon chemical detection of a conspecific; (ii) during agonistic interactions, further increases in heart rate are seen; and (iii) ultimate winners exhibit greater increases in heart rate lasting longer periods of time compared to ultimate losers. Heart rate in winners remains elevated for at least 15 min after the contests have ended and animals have been returned to their home tanks. Reduced effects are seen in second and third pairings between familiar opponents.The sustained changes in heart rate that we observe in winning lobsters may result from hormonal modulation of cardiac function related to the change in social status brought about by contest outcome.     

Demonstration of Strength and Concealment of Weakness in Escalating Fights of Male Swordtails (Xiphophorus helleri)

In the green swordtail (Xiphophorus helleri) confrontations between strange males regularly escalate to high levels of mutual Bites and Fin Grips, even between males differing greatly in size. The original expectation of early game theory models that the behaviours of the ultimate winners and losers are indistinguishable until shortly before the end of the fight could not be confirmed. A significant characteristic of loser behaviour is that the Biting rates are higher before and after escalation. Conversely, Fin Grips are more frequent in the ultimate winners than the losers. However, such behavioural differences are very poor predictors of the outcome of the fight from the viewpoint of a single fighting individual during the contest. Correct forecasts did not exceed 67%. The escalating fights of swordtails are considered as trials of strength in which the stronger male tries to demonstrate strength by the most costly behaviour pattern available, namely Fin Grips, and the weaker male conceals weakness quite successfully by countering with the same tactic and suppressing signs of weakness such as Avoidance behaviour.     

Does being paired give male and female convict cichlids (Amatitlania nigrofasciata) an advantage when competing against same-sex individuals?

Fight theory predicts that asymmetries between contestants can be used to predict the winners and losers in fights. Using the monogamous convict cichlid (Amatitlania nigrofasciata), we examined whether being in a pair bond has an advantage in defeating a single same-sex individual. We hypothesize that the male and female members of a pair bond would defeat a same-sex single intruder because it is beneficial to form a pair bond prior to competing for mutual resources, such as a breeding site. To test our hypotheses, we allowed paired males to engage in contests with single males with and without the interaction of their mate. In addition, we allowed paired females to engage in contests with single females with and without the interaction of their mate. Our results indicate that the paired male gained no advantage in being paired; however, paired females seem to have an advantage over single females because they typically defeated them. To reduce the influence of the other pair member on the fight, we restrained one member and allowed the other pair member to confront the same-sex individual. The paired male was frequently defeated while the paired female typically won. These results suggest that forming a pair bond gives females, but not males an advantage in fights with same-sex competitors.     

Social network analysis in pigs: impacts of significant dyads on general network and centrality parameters

In general, one animal is considered dominant over another animal if it has won more fights than its opponent. Whether this difference in won and lost fights is significant is neglected in most studies. Thus, the present study evaluates the impact of two different calculation methods for dyadic interactions with a significant asymmetric outcome on the results of social network analysis regarding agonistic interactions of pigs in three different mixing events (weaned piglets, fattening pigs and gilts). Directly after mixing, all animals were video recorded for 17 (fattening pigs, gilts) and 28 h (weaned piglets), documenting agonistic interactions. Two calculation methods for significant dyads, that is, dyadic interactions with a clear dominant subordinate relationship in which one animal has won significantly more fights than its encounter, were proposed: pen individual limits were calculated by a sign test considering the differences of won and lost fights of all dyadic interactions in each pen; dyad individual limits were determined by a one-sided sign test for each individual dyad. For all data sets (ALL, including all dyadic interactions; PEN or DYAD, including only significant dyads according to pen or dyad individual limits), networks were built based on the information of initiator and receiver with the pigs as nodes and the edges between them illustrating attacks. General network parameters describing the whole network structure and centrality parameters describing the position of each animal in the network were calculated. Both pen and dyad individual limits revealed only a small percentage of significant dyads for weaned piglets (12.4% or 8.8%), fattening pigs (4.2% or 0.6%) and gilts (3.6% or 0.4%). The comparison between the data sets revealed only high Spearman’s rank correlation coefficients (r_S) for the density, that is, percentage of possible edges that were actually present in the network, whereas the centrality parameters showed only moderate r_S values (0.37 to 0.75). Thus, the rank order of the animals changed due to the exclusion of insignificant dyads, which shows that the results obtained from social network analysis are clearly influenced if insignificant dyads are excluded from the analyses. Due to the fact that the pen individual limits consider the overall level of agonistic interactions within each pen, this calculation method should be preferred over the dyad individual limits. Otherwise, too many animals in the group became isolated nodes with zero centrality for which no statement about their position within the network can be made.     

Reciprocity between endocrine state and contest behavior in the killifish, Kryptolebias marmoratus

Given the dramatic behavioral effects of winning and losing contests, and pronounced changes in stress and sex steroid hormones post-fight, it is reasonable to suppose that these hormones also dictate future behavior. We sampled water-borne cortisol, testosterone (T), and 11-ketotestosterone (KT) before and after contests in the mangrove killifish, Kryptolebias marmoratus, to determine how endogenous steroid hormone levels might predict and respond to contest dynamics or success. Pre-fight cortisol related negatively, and pre-fight T related positively to contest initiation and winning, particularly in the smaller opponent. In the pairs where a larger fish won the contest, winners with higher pre-fight T and lower pre-fight cortisol delivered more attacks to the losers. Contest duration and escalation influenced post-fight hormone concentrations primarily in losers. Escalation significantly increased post-fight cortisol, T, and KT for losers but not for winners. However, winners that attacked losers at higher rates had higher levels of post-fight cortisol. Losers also demonstrate the most consistent post-fight hormone responses, particularly to contest escalation and duration. Despite the bidirectional relationship between hormones and contest behavior, we found no overall mean differences in pre- or post-fight cortisol, T, or KT between eventual winners and losers. Thus, it is evident that the categorical states of winner and loser cannot alone reveal the complex, reciprocal associations between endocrine systems and social behavior.     

Fighting the odds in the UK.

Caroline Richmond reports on miscellaneous winners and losers from the health care scene in the United Kingdom. The winners include a young patient who is holding her own against formidable medical odds after receiving heroic treatment for leukemia, and the country''s osteopaths, who have won the right to compile a statutory register. The losers are the venerable St. Bartholomew''s Hospital, which appears to have lost its battle to stay open, and a 32-year-old man who almost made it to medical school by posing as a teenager.     

Territorial interactions between larvae of the dragonfly Pyrrhosoma nymphula: outcome of encounters

The behaviour of final-instar larvae of the aquatic predator Pyrrhosoma nymphula (Odonata: Coenagrionidae) during laboratory-staged territorial interactions is described. Occupants, as distinct from intruders, won 72% of encounters. The behaviour of occupants during contests won by intruders was more like that of intruders during all contests than that of occupants during contests won by occupants. Contest outcome was little affected by either size differences between the contestants or the use of the Labial strike. Contest duration was not correlated with outcome, with size differences between contestants or with the use of the Labial strike. Winners and losers differed significantly in the number of acts used during encounters won by occupants (losers using more acts), but not during encounters won by intruders. Winners and losers also differed in their use of the behavioural acts Slow wave, Lateral display and Lamellae swipe during contests won by occupants, but not during contests won by intruders. The results are discussed in terms of the asymmetric war of attrition.