Fighting in Males of the Autumn Spider,Metellina segmentata: Effects of Relative Body Size,Prior Residency and Female Value on Contest Outcome and Duration

Males of the autumn spider, Metellina segmentata (***Araneac: Metidae), compete for access to mates by guarding the orb webs of mature females. We investigated the influences of relative male righting ability and resource value on fighting behaviour by staging interactions in the field on webs occupied by females. In these contests, the larger male nearly always defeated its opponent when it was at least 10% greater in size. For smaller size asymmetries between opponents, the male previously resident on the female's web usually won the contest. Contest duration decreased exponentially with increasing size asymmetry between opponents, as predicted if each male assessed its relative size and adjusted its fighting strategy according to its likelihood of winning. Contest duration was also greater when the prior resident was the lighter opponent, or when size and residency asymmetries favoured different opponents as winners. Prior residents fought longer over larger, more fecund females, indicating an adjustment of fighting effort according to assessments of resource value. In contrast, intruders did not increase their fighting effort over larger females, suggesting an inability to assess female size quickly and accurately. Assessment appears to reduce the costs of settling conflicts, but imperfect information can result in inaccurate assessments and unexpected outcomes. Assessment strategies are used by other types of spiders to resolve contests, but this appears to be the first evidence for such strategies among orb-web-building spiders.     

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.     

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.     

What are the consequences of being left-clawed in a predominantly right-clawed fiddler crab?

Male fiddler crabs (genus Uca) have an enlarged major claw that is used during fights. In most species, 50% of males have a major claw on the left and 50% on the right. In Uca vocans vomeris, however, less than 1.4% of males are left-clawed. Fights between opponents with claws on the same or opposite side result in different physical alignment of claws, which affects fighting tactics. Left-clawed males mainly fight opposite-clawed opponents, so we predicted that they would be better fighters due to their relatively greater experience in fighting opposite-clawed opponents. We found, however, that (i) a left-clawed male retains a burrow for a significantly shorter period than a size-matched right-clawed male, (ii) when experimentally displaced from their burrow, there is no difference in the tactics used by left- and right-clawed males to obtain a new burrow; however, right-clawed males are significantly more likely to initiate fights with resident males, and (iii) right-clawed residents engage in significantly more fights than left-clawed residents. It appears that left-clawed males are actually less likely to fight, and when they do fight they are less likely to win, than right-clawed males. The low-level persistence of left-clawed males is therefore unlikely to involve a frequency-dependent advantage associated with fighting experience.     

The assessment game in sand fiddler crab contests for breeding burrows

The single enlarged claw of male sand fiddler crabs, Uca pugilator, is used in contests for control of breeding burrows. The larger of the two contestants has the larger claw and usually wins. Males use one or more of 10 agonistic elements that vary in intensity from a no-contact extension of the claw to the flip of an opponent. We used the sequence of elements employed and the duration of unstaged, naturally occurring contests in a South Carolina salt marsh to evaluate three models of extended contests: (1) energetic war of attrition, (2) cumulative assessment and (3) sequential assessment. Contests usually began with elements of low action intensity and often proceeded to elements of high intensity. Elements of higher intensity were correlated with both contest duration and the number of contest elements. Contest duration increased as opponents became more evenly matched in size, a result consistent with both cumulative and sequential assessment models. Variation in duration increased as the relative sizes of opponents increased, also in accordance with sequential assessment. The absolute size of the smaller contestant had no effect on contest duration, in contrast to predictions based on cumulative assessment or energetic war of attrition models. Contestants that lost a fight were more likely to engage immediately in another fight without loss of contest intensity, if their previous fight had been long and intense. This result is inconsistent with contests of endurance, such as the energetic war of attrition or the cumulative assessment game, but it is consistent with the ritualized display of strength and fighting skill. Thus, sequential assessment appears to best explain ritualized fiddler crab contests. Cumulative assessment, however, may be the appropriate model for extended, nonritualized, all-out fights. Cumulative assessment may also explain the tenure of individuals on breeding grounds where multiple engagements are likely to test endurance and tolerance to damage over a period of days. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Negotiation or aggression during shell fights of the hermit crab Pagurus bernhardus?

Shell fighting behaviour of the hermit crab Pagurus bernhardus was investigated. Analysis of fights between crabs in which there was little or no asymmetry in potential benefit for the two crabs from a shell exchange suggested that the duration of the fight increased as the potential benefit increased. Further experiments indicated that a naked crab was capable of evicting a housed crab by a process of direct aggression. Analysis of fights in which there was a slight asymmetry in potential gains from shell exchange indicated that the result of the fight was primarily determined by the large of the two crabs. These results are contrary to the proposal of Hazlett (1978) that the interactions represent a process of negotiation rather than aggression.     

Residency and size affect fight duration and outcome in the fiddler crab Uca annulipes

We performed a field experiment to investigate the effect of carapace width, major cheliped length and burrow ownership on the righting success of male fiddler crabs (Uca annulipes) . We removed males from their burrows and released them back into the colony ( n = 82). Released males tended to initiate encounters with burrow owners slightly smaller than themselves. Several general predictions of Sequential Assessment Game models of contest behaviour were supported: (1) residents won more encounters; (2) intruders were more likely to win when larger than residents. When body size (carapace width) was controlled for, intruders with relatively large claws for their body size were more likely to win contests; (3) the duration of encounters was related to the size difference between males; (4) encounters won by the larger male were of shorter duration than those won by the smaller male; (5) encounters won by the resident tended to be of shorter duration than those won by intruders ( P = 0.07); (6) on average, encounter duration was longer when the intruder was larger than the resident. However, the encounters we documented began with seemingly costly behaviour such as pushing and the inter-locking of claws and did not unambiguously escalate from initial low cost behaviours. Sequential assessment of relative fighting ability may therefore not have been occurring. Prior visual assessment of opponents' fighting ability, followed by 'all-out fights' during physical encounters may also provide a plausible explanation for our results.     

Sexual dominance in hermit crab shell fights: asymmetries in owner–intruder status,crab size,and resource value between sexes

We studied sexual dominance and seasonal differences in aggressiveness of individuals in intraspecific competition for shells of the hermit crab Pagurus filholi in terms of size of contestants and duration of the attempt to deprive other crabs of their shell. Experiments were conducted using paired intrasexual and intersexual contests in the pre-breeding and post-breeding seasons. Size ratios between contestants were systematically varied to assess the sexual difference in size and owner advantages. In both intrasexual and intersexual contests intruder crabs tended to win the contests more often as their size increased, that is, size advantage overcame owner advantage. Although we did not recognize a sexual difference in size and owner advantages in contest outcomes, male intruder crabs took a shorter time to deprive female owners of a shell than to deprive male owners. Furthermore, male individuals in the pre-breeding season had significantly longer fight durations. Fighting is costly. Thus males can afford to expend more energy and time fighting, indicating that males are dominant over females in shell fights as both intruders and owners. Electronic Publication     

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.     

Aggression among Lekking Male Fallow Deer (Dama dama): Territory Effects and Relationship with Copulatory Success

We studied the aggressive behavior of territorial male fallow deer (Dama dama) at two leks. Daily number of escalated fights was not correlated with number of matings. A dominance index including all agonistic interactions was weakly correlated with copulatory success; the correlation was stronger when each half of the rut was considered separately. Dominance likely changed over the rut due to fatigue. We ranked lek territories by the number of copulations seen in each. Males that won fights were likely to take over the loser's territory only if it ranked higher than the one they held. Winners were more likely to fight with a third male after defeating an opponent that held a higher-ranking territory than one from a lower-ranking territory. Exposure to attacks by third-party males may be a major cost of fighting. Males appear aware of the relative value of different lek territories, but the frequency of aggression was not scaled to potential fitness benefits, possibly because males seldom fought with opponents they were unlikely to beat. The outcome of interactions on the lek may not always reflect the relative dominance rank of the contestants. Females are unlikely to use the outcome of fights as a direct criterion for mate selection.     

Does Lateral Presentation of the Palmate Antlers During Fights by Fallow Deer (Dama dama L.) Signify Dominance or Submission?

A central aim of the study of animal communication is to identify the mode and content of information transferred between individuals. The lateral presentation of the antler palm between male fallow deer has been described as either a signal of individual quality or an attempt to avoid fighting. In the first case two phenotypic features have been proposed by which transmission of individual quality may be facilitated. These are antler size and antler symmetry. The alternative hypothesis proposes that the lateral presentation of antlers occurs as a consequence of averting a threatening posture and may signify a reluctance to fight. We examined whether mature fallow deer use lateral palm presentation as a display during fights to indicate antler size and symmetry. We found no relationship between presentation rate of the antler and antler size and symmetry. Furthermore, males did not preferentially present their larger antler to their opponent. We also investigated whether the rate at which males presented antlers laterally during a fight was related to their ability to win the fight. Our results show that the male who performed more presentations during a fight was more likely to lose it. There were behavioural differences in the way in which a bout of presentation ended; subsequent losers tended to turn their body away from their opponent and subsequent winners tended to lower their antlers to an opponent which we interpret as an invitation to continue fighting. We conclude that the lateral palm presentation serves to de-escalate fighting between mature fallow deer. It is not a mechanism by which to communicate individual quality but rather an indication that a male is less committed to continuing investment in the current contest.     

A high aggression strategy for smaller males

Male-male conflict is common among animals, but questions remain as to when, how and by whom aggression should be initiated. Factors that affect agonistic strategies include residency, the value of the contested resource and the fighting ability of the two contestants. We quantified initiation of aggression in a fish, the desert goby, Chlamydogobius eremius, by exposing nest-holding males to a male intruder. The perceived value of the resource (the nest) was manipulated by exposing half of the residents to sexually receptive females for two days before the trial. Resident male aggression, however, was unaffected by perceived mating opportunities. It was also unaffected by the absolute and relative size of the intruder. Instead resident aggression was negatively related to resident male size. In particular, smaller residents attacked sooner and with greater intensity compared to larger residents. These results suggest that resident desert goby males used set, rather than conditional, strategies for initiating aggression. If intruders are more likely to flee than retaliate, small males may benefit from attacking intruders before these have had an opportunity to assess the resident and/or the resource.     

A TEST OF THE SEQUENTIAL ASSESSMENT GAME: FIGHTING IN THE BOWL AND DOILY SPIDER FRONTINELLA PYRAMITELA

Male bowl and doily spiders (Frontinella pyramitela: Linyphiidae) engage in dangerous fights over access to females. Relatively smaller individuals are more at risk of fatal injury than their larger opponents. Males assess relative fighting ability during contests: smaller individuals tend to give up quickly. Fights occur between a male with information about the value of the contested female (number of fertilizable eggs) and an intruding male with less information. In this paper, a sequential assessment game (a game theory model of fighting behavior) is adapted to male combat in the bowl and doily spider to attempt a quantitative test. The model makes predictions about fight duration, probability of winning, and the occurrence of fatalities as a function of resource value and size asymmetry. Comparison with empirical data from staged contests yields a generally good quantitative agreement with the predictions. A few deviations are also noted.     

Use of energy reserves in fighting hermit crabs

When animals engage in fights they face a series of decisions, which are based on the value of the contested resource and either their relative or their absolute fighting ability. Certain correlates of fighting ability or 'resource holding potential' such as body size are fixed but physiological correlates are expected to vary during the encounter. We examine the role of energy reserves in determining fight outcomes and parameters during 'shell fighting' in hermit crabs. During these fights, the two contestants perform very different roles of attacker and defender. We show that the balance of the total energy pool, in the form of glucose and glycogen, determines the ability of defenders to resist eviction from their shells. Low glucose in evicted defenders is not caused by depletion of energy reserves, rather mobilization of glycogen appears to be the result of a strategic decision about whether to resist effectively, based on the perceived fighting ability of the attacker. Attackers, however, always initiate the fight so such a decision for this role appears unlikely. In addition to influencing decisions and ability during fights, physiological correlates of fighting ability can in turn be influenced by strategic decisions.     

Effect of environmental enrichment upon resource holding power in fish in prior residence situations

Resource holding power (RHP), as expressed by gaining dominance, can be affected by extrinsic and intrinsic factors. Extrinsic factors that increase the RHP include e.g. prior exposure to the contest area. The pay-off asymmetry hypothesis was tested according to which there is an asymmetry in the value the resident's territory has for the resident and intruders, i.e. the resident loses more than intruder opponents when losing the contest over a territory in which it has invested much energy during the exploration of food and shelter resources, during the settlement of conflicts with territorial neighbours, etc. This asymmetry will increase the resident's chance to win the fight over intruders. If the resident-intruder asymmetry is enhanced by presenting resource-rich territories to e.g. fish (structurally diverse or 'rich' aquariums), the hypothesis predicts that the resident's dominance chance (probability to win the fight) will be higher than in structurally 'poor' aquariums. It was found that residents were proportionately more often dominant (fight winners) than intruders in the rich compared to the poor aquariums in all seven tested fish species. This demonstrates that a high territory resource value (aquarium enrichment) significantly facilitates the expression of the resident's dominance advantage (prior residence effect). In contrast to dominance, aggressive behaviour before the dominance settlement did not generally differ between residents and intruders when compared in rich and poor aquariums. This suggests that dominance in itself and aggression prior to dominance settlement are at least partially guided by different motivational systems.     

Agonistic behavior in wild male Magellanic penguins: when and how do they interact?

Game-theory models predict that the frequency and type of agonistic interactions should vary with the value of the resource being contested. We describe bill duels and overt fighting in male Magellanic penguins (Spheniscus magellanicus) at a breeding colony and determine whether these behaviors change with the value of the nests over which they interact. Bill duels represent low levels of aggression while overt fighting high levels of aggression. Consistent with predictions, overt fighting was more common before egg laying when nests have the highest potential value while bill duels were more common at failed nests later in the season when nests are less valuable as they could not be used for reproduction until the next season. Contrary to expectations, overt fights were shorter and resulted in fewer cuts before egg laying than after egg laying. Large size asymmetries between opponents before egg laying may enable losers to quickly assess their opponents and leave before they are hurt. As predicted, the duration and damage occurring during overt fights were positively correlated with nest cover, which is correlated with higher reproductive success. We conclude that male Magellanic penguins have rules of engagement that in the most cases follow game-theory predictions on when and how to interact.     

Detailed analysis of fighting in polecats (Mustelidae) using ciné film

The phenomenon of fighting was investigated under laboratory conditions using polecats ( Mustela putorius, M. furo and interspecific hybrids). Diadic interactions between male polecats were recorded on 16 mm cine film in an unfamiliar area of 16 m², one individual having been introduced ten minutes before its opponent.
The behaviour patterns involved in fighting are described and their frequencies of occurrence, duration and average bout lengths specified. Biting, which occupied 41% of the animal's time in fighting, and attacking, which made up 27% of the bouts of behaviour, were the most important actions involved in fighting. Polecats most commonly bite their opponent's neck and bites in this region were the longest in duration. Success in gaining a bite was influenced by the opponent's behaviour at the time of the attack.
Polecats fight when one individual bites its opponent and the opponent retaliates by biting; bite was shown to be the commonest response to being bitten. The length of a fight appears to be determined by the levels of motivation to bite of the two opponents, while biting and being bitten operate as a positive feed back mechanism. The fight terminates when the more aggressive opponent ceases to make spontaneous attacks. The reasons why one individual wins a fight are that it consistently spends more time than its opponent in biting, it persists for longer in making spontaneous attacks and its method of attacking is more efficient.     

Resource value differentially affects fighting success between reproductive and non-reproductive seasons

Inter-male competition for resources is usually studied during species’ reproductive seasons because fighting is common and conspicuous, but how this competition compares with that during the non-reproductive season is rarely investigated. Here, we compared competition for burrows between the reproductive and non-reproductive seasons in a mud crab. We conducted two natural and three experimental observations: Under natural conditions, we observed fights between residents and intruders in (1) reproductive and (2) non-reproductive seasons, and found similar results in both seasons; two factors, body size difference and residency, contributed equally to fight outcomes; (3) During the reproductive season we created an intruder by capturing a resident male and placing him in the burrow of another resident to induce a fight; (4) We repeated this but first placed a female in the burrow before introducing the intruder; findings for both experiments were similar to those for natural fights; (5) During the non-reproductive season, we repeated the third experiment and found a different result: fight outcome was determined by the difference in body size, not residency. This is the first study to show that differing subjective value of a resource between the reproductive and non-reproductive seasons affects fight outcomes.     

Effects of residence,aggressive experience and intruder familiarity on attack shown by male mice

Two groups of 12 mature male Swiss Morini strain mice were matched for aggressiveness on the basis of their response to anosmic docile male intruders after 24 h individual housing in a large defensible cage. One group was subsequently individually housed without disturbance for a further 12 days whereas the second group was exposed to a new anosmic intruder every 3 days over this same period. All mice were subsequently retested against anosmic intruders for a 10 min period. Animals which had had the opportunity to fight repeatedly showed more attack than individuals lacking such experience. A second experiment contrasted the responses of dominant isolates to the same or a different anosmic intruder, 10 min after a successful attack. Familiar intruders were attacked less vigorously than unfamiliar mice. It seems likely that the defeated mouse becomes less potent as a stimulus eliciting attack as the resident becomes habituated to it. Conversely, unfamiliar intruders evoke aggressive reactions by residents despite the prolonged fights they had had before final testing. These experiments provide little support for the appetence view of aggression in mice (i.e. the view that aggressiveness is augmented by depriving the animal of the opportunity to fight) or the view that this phenomenon is simply a consequence of “social deprivation”.     

Startle durations reveal visual assessment abilities during contests between convict cichlids

In animal contests, the widespread ability of contestants to assess their opponents’ resource holding potential (RHP) relative to their own, termed mutual assessment, has recently been questioned. It is possible that each contestant may only have information about its own abilities or state, incurring costs up to a particular threshold then giving up, termed self-assessment. We used a technique that provides a measure of fight motivation to discriminate between different assessment models during aggressive encounters between male convict cichlids, Amatitlania nigrofasciata. A novel stimulus was applied to cause a startle response in one contestant of an aggressively interacting, size mis-matched pair, whereby the animal temporarily stops fighting. The time taken to resume the contest has been verified to provide a measure of the motivation to fight, from which it is possible to infer if any visual information concerning opponent asymmetries has been gathered. The data showed support for two differing types of assessment. There was some support for self-assessment, with startle duration being negatively related to own size, and, in a later trial series some support for an opponent only assessment strategy, with startle duration being positively related to opponent size. These results are consistent with individuals learning to use visual information about opponents when deprived of other sensory cues. Evidence within a trial supporting visual mutual assessment was lacking and possible reasons for this are discussed.