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.     

Estimating the energetic cost of fighting in shore crabs by noninvasive monitoring of heartbeat rate

After establishing shore crabs, Carcinus maenas, individually in separate aquaria, we used a noninvasive infrared phototransducer to monitor their heartbeat rate continously before, during and after fights with intruder crabs. We confirmed that heartbeat rate is a reliable indicator of oxygen consumption and then used it to estimate indirectly the energetic cost of fights differing in duration and intensity, and its dependence on prior residence and relative size of opponent. Prior residence in aquaria significantly increased the probability that crabs would initiate fights against intruders. The majority of fights were resolved by aggressive contacts, display being used extensively only against smaller intruders. Fights between evenly sized opponents and between residents and larger intruders involved almost continuous aggression, whereas fights with smaller intruders involved several shorter bouts of aggression. Fight duration was weakly correlated with the relative size of opponents. Heartbeat rate, measured only in residents, was elevated above resting levels throughout fights, hence energy expenditure during fighting increased linearly with fight duration. Contrary to expectation, heartbeat rate was not significantly influenced by relative size of the opponent or by the intensity of aggression. After fighting, heartbeat rate usually returned to resting levels within 30-60 min, recovery taking longer in fights against larger intruders, when the fight was always lost. We propose that prolonged elevation of heartbeat rate in residents that had lost to larger intruders represented a state of alertness, adaptive against impending risks of resource loss or injury. Copyright 2000 The Association for the Study of Animal Behaviour.     

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.     

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.     

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.     

Winning and losing: causes for variability in outcome of fights in male Magellanic penguins (Spheniscus magellanicus)

Game theory models predict that fighting ability should be moreimportant in contest outcome when the payoffs of winning arehigh for both contestants, and ownership should be more importantwhen payoffs are low. Male Magellanic penguins (Spheniscusmagellanicus) provide an opportunity to test these predictionsin a natural setting because payoffs of winning are higher for penguins fighting before egg laying and lower for penguinsfighting after egg laying, allowing the prediction of differencesin who should win and lose. We watched an area of approximately2000 Magellanic penguin nests from 1992 to 1996 at Punta Tombobreeding colony, Argentina; we quantified fighting behavior,banded contestants, measured their body size (here used as anindex of fighting ability), determined ownership status whenpossible, and monitored their reproductive success. We determinedthat male Magellanic penguins fought for nests and mates. Astheory predicts, before egg laying, body size difference wasmore important than ownership as a predictor of contest outcome and fight duration. After egg laying, owners won fights, andsize did not predict who won or how long they fought. Our comparisonsof nest ownership, nest quality, and chicks fledged by winnersand losers suggested that our predictions on the change inbenefits of winning before and after egg laying were correct.We conclude that game theory models are useful in predictingwho won or lost fights in male Magellanic penguins and thatultimate benefits of winning fights are related to fitness.     

Winning fights elevates testosterone levels in California mice and enhances future ability to win fights

The 'winner effect' has been studied in a variety of species, but only rarely in mammals. We compared effects of winning three, two, one, or zero resident-intruder encounters on the likelihood of winning a subsequent aggressive encounter in the California mouse (Peromyscus californicus). During the training phase, we ensured that resident males won all encounters by staging contests with mildly sedated, smaller intruders. During the test phase, the resident male encountered an unfamiliar, more evenly matched intruder that had experience winning an encounter and was larger than the resident. Testosterone (T) plasma levels significantly increased after the final test when they had experienced two prior winning encounters, and the probability of winning a future encounter increased significantly after three prior wins independent of intrinsic fighting ability. We hypothesize a 'winner-challenge' effect in which increased T levels serve to reinforce the winner effect in male California mice.     

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.     

Resource Holding Potential and the Outcome of Aggressive Interactions between Paired Male <Emphasis Type="Italic">Aegus chelifer chelifer</Emphasis> (Coleoptera: Lucanidae) Stag Beetles

Interactions between male stag beetles usually involve aggressive behavior using their long mandibles as weapons to compete with rival males over females. Considerable variation exists within populations in male body size, and may affect their behavior and the outcome of male-male contests. We investigated the aggressive interactions between male Aegus chelifer chelifer, a small tropical stag beetle species. Morphological traits in relation to aggressiveness and the outcome of fights were examined in laboratory-reared beetles. The fight-engagement ratios of major and minor morph males were not significantly different and analyses revealed that the size of body parts had more effect on the fighting success than the weapon part (mandibles). The probability of winning a contest was higher in males with a larger head width (HW), and so HW was considered as the resource holding potential (RHP). No effects of the trait size on the initiation of fights or aggressive intensity was found. Relationships between the fight duration and RHP were not significantly consistent with any assessment strategies, but were close to the mutual assessment model.     

Male contest investment changes with male body size but not female quality in the spider Nephila clavipes

Animals use rules to adjust their level of investment in a contest. We evaluate male strategies during contests over females in the golden orb-web spider Nephila clavipes. We tested whether male behaviour changes with female value, and found that contests were similar in intensity and outcome whether the female was a juvenile or adult, virgin or non-virgin, or whether one male had invested sperm in the female. We found evidence that males use a self-assessment strategy when deciding to withdraw from a contest. Loser body size and contestant size difference were correlated with a higher frequency of contest escalation, and fights involving two large males were more likely to escalate than a fight in which one male was small. A multiple regression showed that loser body size had a stronger effect on contest escalation than contestant body size difference. More importantly, the size of the winning male had no effect on contest escalation, a key prediction of a self-assessment strategy. In N. clavipes, body size is the primary factor that determines the outcome of male contests, and males do not appear to assess their opponent or the quality of the resource when deciding to withdraw from the fight.     

Fighting behaviour in territorial male roe deer <Emphasis Type="Italic">Capreolus capreolus</Emphasis>: the effects of antler size and residence

In all areas where they have been studied, male roe deer are believed to have a territorial mating system, although few quantitative studies have been conducted and there remains considerable debate about the function of male roe deer territories. We observed 139 aggressive interactions between male roe deer in Storfosna Island (Norway) during one territorial season (March–August). We recognised seven rank levels of escalation according to the potential danger of the behaviour. On the basis of the number of escalation levels included in the interactions, the complexity of the fights was also scored. We recorded the presence of other individuals during the interaction, the age, the antler size, the territorial status and the residency status of the two contestants and tested how these variables affected escalation, complexity and outcome of the fights. Most of the interactions ended with low levels of escalation, and physical contact occurred only in fights between two territorial bucks. The escalation was also affected by the difference in antler size index (the bucks escalated more when the difference in antler size was smaller) and increased with an increasing number of female deer present during the interaction. The resident buck won in 81% of the fights. When it drew or lost, it was generally both inferior in age and antler size, and the duration and escalation of the interactions were higher. However, even when a fight was lost, no territory loss occurred. These results are consistent with the evolutionary game theory and the proposed low risk–low gain strategy of roe deer bucks.     

Male attractiveness covaries with fighting ability but not with prior fight outcome in house crickets

In many species males that tend to win fights against othermales are more attractive to females. There are three ways inwhich male fighting ability and attractiveness may be associated:(1) attractiveness and fighting ability are influenced by thesame underlying traits (e.g., body size), (2) females prefermales that have directly observed winning fights, or (3) winningprevious fights indirectly improves a male's chance of beingpreferred by females. The last possibility may arise as a consequenceof the "loser effect"; in many species when a male loses a fighthis probability of losing subsequent fights increases. Thereare, however, no studies testing whether such a "loser effect"also influences male attractiveness. Here we show that maleattractiveness and fighting ability are positively correlatedin the house cricket, Acheta domesticus. Our experiment wasdesigned so that females could not directly observe the outcomeof fights, thus eliminating possibility (2) above. We then testedbetween possibilities (1) and (3) by making use of the factthat in some cricket species the "loser effect" can be eliminatedexperimentally by ‘shaking’ a male and stimulatingthe motor program for flying. We showed that in A. domesticus‘shaking’ does affect the outcome of subsequentfights. Males that had won two previous fights were less likelyto win a fight after being ‘shaken’ than when subjectto a control treatment. In contrast, males that had lost twoprevious fights were more likely to win a fight after being‘shaken’ than when they were not shaken. There was,however, no effect of ‘shaking’ on male attractiveness.We conclude that the "loser effect" does not alter the tendencyfor large, dominant males to be attractive to females. Instead,it appears that there are traits correlated with both fightingability and attractiveness. One such trait is body size. Fightwinners were significantly larger than losers and attractivenesswas positively correlated with male body size.     

Aggression and RHP in the Northern Swordtail Fish, Xiphophorus cortezi: The Relationship Between Size and Contest Dynamics in Male–Male Competition

Current theory predicts that contest outcome, as well as decisions on whether to initiate a contest, escalate during a contest or retreat are decided by asymmetries in resource holding potential (RHP) and/or expected payoffs between contestants. In this investigation, dyadic contests were staged between male swordtail fish (Xiphophorus cortezi) where individuals were paired based on cumulative fight records and were ranked at the end of the trials in order to approximate RHP. Size was the only asymmetry that I did not attempt to control for and as a result, I was able to determine the relationships between size, contest initiation, escalation and outcome. Individuals changed their contest initiation strategy based on their size relative to that of their opponents, and contrary to predictions, the smaller of the two males in each contest was more likely to initiate the conflict than was the larger male. However, the larger of the two males was more likely to win and standard length proved to be a moderate predictor of an individual's final rank. Regardless of size, initiators fared poorly, winning only 31% of the contests. In instances where the smaller males won the contests, they were no more likely to initiate the encounter than was the larger male. However, when small males did win, fights lasted longer, suggesting that in some cases smaller males may be able to outlast their opponents.     

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.     

Repeated Recent Aggressive Encounters Do Not Affect Behavioral Consistency in Male Siamese Fighting Fish

Consistent individual differences in behavior suggest that individuals respond in a predictable and repeatable manner in a specific situation while differing from other individuals. Male Siamese fighting fish exhibit consistent individual differences in decision‐making strategies when they encounter a receptive female and a rival male simultaneously. However, whether these differences are altered by recent experience is unknown. We examined the influence of repeated aggressive encounters on behavioral consistency and decision‐making. Males were presented with paired female–male dummies prior to any aggressive experiences to obtain a baseline measure. Next, males either won or lost three consecutive contests against rivals and then received the paired female–male dummies after each of these encounters. Overall levels of highly aggressive behaviors were affected by contest outcome, while levels of female‐directed were not. Not surprisingly, winning a fight led to an increase in male‐directed bites, an overtly aggressive behavior that only occurs after fights have escalated. Fighting a male before encountering the dummies caused males to perform more tail beats to the dummy male, perhaps as a result of increased motivation. Males exhibited similar levels of repeatability and used the same strategies when faced with conflicting stimuli regardless of fighting experience. Thus, while winning or losing a fight impacts overall aggression, it does not influence behavioral consistency. This study demonstrates that consistent individual differences and decision‐making strategies may be resistant to recent aggressive experiences, even over a period of days.     

Effect of body weight, antler length, resource value and experience on fight duration and intensity in fallow deer

We tested predictions of evolutionary game theory focusing on fight duration and intensity during contests between European fallow deer, Dama dama L. We examined the relation between contest duration and intensity and resource-holding potential (RHP; body weight and antler size), in an effort to reveal the assessment rules used by competing males. We examined other potential determinants of duration and intensity: resource value (the oestrous female) and experience of agonistic interactions. Asymmetry in body weight or antler length of contestants was not correlated with fight duration. Body weight and antler length of the fight winner or loser were also not correlated with fight duration. Neither were the body weight of the heavier or lighter animal or the antler length of the animal that had longer or shorter antlers. A measure of intensity (the jump clash) was positively related to the body weight of the losing animal and the lighter member of the dyad. These results are consistent with the hypothesis that opponents escalate contest intensity based on assessment of their own ability rather than through mutual assessment. There was no evidence that resource value is an important factor in either fight duration or intensity in this population. As the number of fights between pairs of males increased, there was a decrease in fight duration. Fights were longer when at least one member of a competing pair of males had previously experienced a victory.     

Ownership,size and reproductive status affect the outcome of food ball contests in a dung roller beetle: when do enemies share?

Theory predicts that asymmetry between contenders influences their ability to defend resources. More recently, some theoretical approaches have also examined the circumstances that might promote sharing of the disputed resources. We tested these hypotheses in males of the ball roller beetle Canthon cyanellus cyanellus. Males fight for possession of a food ball, which is a vital resource used for nesting. We evaluated the role of food resource ownership, body size and reproductive status on the outcome of contests (win, lose or share) between males that rolled a food ball (owners or finders) either alone or with a female partner, when faced with male intruders (or joiners). Large owners of a food ball had a higher probability of victory than small intruders, and small owners had a high probability of losing when faced with large intruders. The reproductive status of both contenders also influenced their chances of winning: previously mated owners of a food ball had a higher probability of winning than virgin owners. Males of a similar size tended to split the food ball, thereby sharing the resource. Our results suggest that competitors may adjust the intensity of their aggression depending at least on their own resource holding power (RHP), the value of the resource in dispute and perhaps even the RHP of their opponents. Sharing the food ball emerges as a fresh solution between similarly matched contestants.     

Male Defense of the Breeding Cavity and Factors Affecting the Persistence of Breeding Pairs in the Stomatopod,Gonodactylus bredini (Manning) (Crustacea: Hoplocarida)

In Caribbean Panama, nonreproductive male and female stomatopods are solitary and defend their own coral-rubble cavities. When breeding pairs form, however, males assume all responsibility for cavity defense. To compare success in cavity defense and defensive tactics among paired and unpaired males, and to examine the tendency for paired stomatopods to exchange their present mates for larger (higher quality) individuals, we introduced same-sized and 15% larger male, and same-sized and 15% larger reproductive female intruders to paired and unpaired male residents in a balanced design. Paired males were more successful at cavity defense than unpaired males, evidently because paired males strike intruders more than unpaired males, and because intruders fight less intensely against paired males than against unpaired males. Paired males occasionally attempted extrapair copulations, but showed little tendency to abandon their mates in favor of larger females. Paired females, however, mated readily with intruder males that evicted resident males. Populationwide female breeding synchrony and prolonged female receptivity before oviposition reduce variance in male mating success and may force males to guard the breeding cavity to assure their paternity. Uncertainty about the reproductive condition of intruder females may prevent males from exchanging mates.     

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     

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.