Role of the olfactory pathway in agonistic behavior of crayfish, <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Crayfish establish social dominance hierarchies through agonistic interactions, and these hierarchies are maintained through assessment of social status. Chemical signals influence several aspects of fighting behavior, but the specific chemosensory sensilla involved in detecting these signals in crayfish are unknown. The goal of our study was to examine the importance of aesthetasc sensilla—olfactory sensors on the antennules of decapod crustaceans—in regulating changes in fighting behavior in crayfish, Procambarus clarkii, over the course of repeated pairings. We selectively ablated aesthetascs from pairs of crayfish after the first day of trials and compared the behavior of these ablated animals to that of pairs of intact controls. Results show that unablated crayfish significantly decreased the number and duration of fights over repeated pairings, whereas crayfish lacking aesthetascs continued to engage in similar amounts of fighting across all three trial days. This difference shows that aesthetascs regulate fighting behavior in P. clarkii.     

Morphological and Behavioural Traits Affecting the Intensity and Outcome of Male Contests in Gallotia galloti galloti (Family Lacertidae)

This study describes the sequence of behaviour during aggressive encounters between male ‘tizón’ lizards (G. galloti galloti) and assesses the effect of morphological and behavioural traits on the outcome and intensity of staged aggressive encounters between males. Aggressive encounters ranged from only throat extension to escalated fights with biting and rolling over. Winners were heavier, had longer heads, and performed tongue-flicking, throat extension and biting at a higher rate than losers. The rate of aggressive behaviour increased with decreasing difference in snout-to-vent length, head length and head width of the contestants. The results are in agreement with some predictions of the sequential assessment game model in that probability of victory increased with the difference in fighting ability and that the rate of aggressive behaviour was higher in contests between animals of similar size.     

Examination of prior contest experience and the retention of winner and loser effects

In many animal taxa, prior contest experience affects future performance such that winning increases the chances of winning in the future (winner effect) and losing increases the chances of losing in the future (loser effect). It is, however, not clear whether this pattern typically arises from experience effects on actual or perceived fighting ability (or both). In this study, we looked at winner and loser effects in the jumping spider Phidippus clarus. We assigned winning or losing experience to spiders and tested them against opponents of similar fighting ability in subsequent contests at 1-, 2-, 5-, and 24-h intervals. We examined the strength of winner and loser effects, how long effects persist, as well as how experience affected perceived and actual fighting ability. Our results demonstrate that winner and loser effects are of approximately the same magnitude, although loser effects last longer than winner effects. Our results also demonstrate that previous experience alters actual fighting ability because both the assessment and escalation periods were affected by experience. We suggest that the retention time of experience effects depends on expected encounter rates as well as other behavioral and ecological factors. In systems with short breeding seasons and/or rapidly fluctuating populations, context-dependent retention of experience effects may allow males to track their status relative to the fluctuating fighting ability of local competitors without paying the costs necessary to recall or assess individual competitors.     

Diurnal rhythm of male–male combat behavior in the bean bug Riptortus pedestris (Heteroptera: Alydidae)

In many insects, mating is affected by the day–night cycle, i.e., diurnal rhythm. Although there are many reports that mating and other reproductive behaviors are controlled by daily rhythms in various taxonomic insect species, little attention has been paid to the effect of daily rhythms on male fighting behavior. Here, we investigate whether the frequency and escalation of male–male aggressive interaction exhibit diurnal rhythms under a long‐day condition in the bean bug Riptortus pedestris. Despite the fact that male aggressive behaviors were most often observed in the middle of the later half of light periods, no interaction was found between escalation of fighting and the time period. The results, at least, suggest that male aggressive behaviors are influenced by diurnal rhythms like other reproductive behaviors in R. pedestris.     

Strong Competition Does Not Always Predict Play Asymmetry: The Case of South American Sea Lions (Otaria flavescens)

Although play fighting has been studied for over a century in both human and non‐human animals, quantitative data on marine mammals are still scarce. Here, we investigated play fighting in South American sea lions (Otaria flavescens), one of the most sexually dimorphic species with an extreme polygynous mating system, high levels of both intra‐ and inter‐sexual competition. All these features make South American sea lions a good model species to test some predictions on play fighting. Our results indicate play is restricted to juveniles, being inhibited among adults, and as to be expected in a species that shows a high degree of sexual dimorphism, it is mainly expressed in males. Even though playful interactions were punctuated by competitive behaviours, animals played in a highly symmetric way and were able to adjust their competitive playful interactions in a flexible manner and so reduce the risk of escalation to a minimum level. They were highly selective in their choice of playmates by limiting the number of players per session and playing more with age‐matched companions and friends. All these factors taken together are probably at the basis of the low risk of escalation recorded during the study. This result is predictive of a high ability and motivation of these animals to engage in play behaviour which can have a possible role not only in the acquisition of dominance status, but also in establishing and maintaining social relationships, an unexpected role in a so highly competitive species.     

Honesty of agonistic signalling and effects of size and motivation asymmetry in contests

Game theoretical models predict that the main function of fighting behaviour is to assess the relative fighting ability of opponents. The sequential assessment game has often been used to investigate contests, while honest signalling theory has received much less attention. With the wolf spider Hygrolycosa rubrofasciata we investigated whether male agonistic signalling can reveal honest information about fighting ability, and how size and motivation asymmetries affect male fighting behaviour. We also determined whether male–male competition affects the courtship behaviour of the males. We found that agonistic drumming activity is an honest indicator of male fighting ability, and that relative size asymmetry and motivation to fight both contribute to the fighting ability. We also found that male–male competition decreases the courtship drumming rate of subdominant males, suggesting that male–male competition limits the opportunities for female choice. We conclude that sequential assessment and honest signalling may both be used in settling contests, and that they may be used simultaneously. Received: 10 December 1998 / Received in revised form: 23 June 1999 / Accepted: 5 July 1999     

Assessment strategy and the evolution of fighting behaviour

The view is examined that the adaptive value of conventional aspects of fighting behaviour is for assessment of relative RHP (resource holding power) of the combatants. Outcomes of aggressive disputes should be decided by each individual's fitness budget available for expenditure during a fight (determined by the fitness difference between adoption of alternative strategies, escalation or withdrawal without escalation) and on the rate of expenditure of the fitness budget if escalation occurs (determined by the RHPs of the combatants). Thus response thresholds for alternative strategies (“assessments”) will be determined by natural selection on a basis of which opponent is likely to expend its fitness budget first, should escalation occur. This “loser” should retreat (before escalation) and the winner should stay in possession of the resource. Many aggressive decisions depend on whether one is a resource holder, or an attacker. Assuming the RHP of the combatants to be equal, there are many instances of fitness pay-off imbalances between holder and attacker which should weight the dispute outcome in favour of one or other opponent by allowing it a greater expendable fitness budget. Usually the weighting favours the holder; the attacker therefore needs a correspondingly higher RHP before it may be expected to win. This is not invariably the case, and much observed data fits the predictions of this sort of model. If assessments are perfect and budget expenditure rates exactly predictable, then there would never seem to be any case for escalation. Escalation can be explained in terms of injury inflictions (expenditures) occurring as discrete events; i.e. as “bouts” won or lost during fighting. Assessment can give only a probabilistic prediction of the outcome of a bout. A simple model is developed to investigate escalation situations. Each combatant assesses relative RHP; this correlates with an absolute probability of winning the next bout (c_abs). The stake played for is infliction of loss of RHP and is determined by the fitness budgets of the opponents. (Each individual plays for the withdrawal of its opponent.) This defines a critical probability of winning (c_crit) for each combatant, above which escalation is the favourable strategy (c_abs > c_crit) and below which withdrawal is favourable (c_abs < c_crit). Escalation should occur only where c_abs-c_crit is positive for both combatants. This model gives predictions compatible with the observations, indicating that RHP loss alone can be adequate to explain withdrawal: escalation behaviour. Withdrawal tendency will be increased by low searching costs. Escalations should be restricted to closely matched RHP opponents if RHP disparity is the major imbalance. Outside the “escalation range” of a given individual, the higher RHP individual wins and the lower one loses (i.e. it should withdraw after conventional display). RHP disparity and holder: attacker imbalance should both interact to shape the observed pattern, though their relative importances will depend on species and situation. In some instances selection may favour immediate withdrawal from an occupied territory even without assessment of RHP.     

Socially selected ornaments and fitness: Signals of fighting ability in paper wasps are positively associated with survival,reproductive success,and rank

Many animals have ornaments that mediate choice and competition in social and sexual contexts. Individuals with elaborate sexual ornaments typically have higher fitness than those with less elaborate ornaments, but less is known about whether socially selected ornaments are associated with fitness. Here, we test the relationship between fitness and facial patterns that are a socially selected signal of fighting ability in Polistes dominula wasps. We found wasps that signal higher fighting ability have larger nests, are more likely to survive harsh winters, and obtain higher dominance rank than wasps that signal lower fighting ability. In comparison, body weight was not associated with fitness. Larger wasps were dominant over smaller wasps, but showed no difference in nest size or survival. Overall, the positive relationship between wasp facial patterns and fitness indicates that receivers can obtain diverse information about a signaler's phenotypic quality by paying attention to socially selected ornaments. Therefore, there are surprisingly strong parallels between the information conveyed by socially and sexually selected signals. Similar fitness relationships in social and sexually selected signals may be one reason it can be difficult to distinguish the role of social versus sexual selection in ornament evolution.     

Contest competition and men's facial hair: beards may not provide advantages in combat

In contemporary human societies, where direct male-male competition is reduced compared to ancestral societies, sporting competitions remain an avenue for status acquisition via intra-sexual competition. Beards are the most visually salient and sexually dimorphic of men's secondary sexual traits and play a strong role in communicating masculinity, dominance and aggressiveness intra-sexually. Hypotheses have been advanced that beards provide advantages in intra-sexual combat, as protective organs and honest signals of fighting ability. Here we provide the first test of these hypotheses using data from professional mixed martial arts fighters competing in the Ultimate Fighting Championship. We explored whether secondary sexual traits (height, weight, beardedness), fighting stance (southpaw, orthodox), arm reach and past contest experiences impact on contest outcomes. If beards function as protective organs, bearded fighters should succumb to fewer knock-outs, and hence protection to injuries to the jaw, fewer abrasions and lacerations to the face and brain damage than clean-shaven fighters. Alternatively, if beards signal fighting ability then bearded fighters should win more fights. We found no evidence that beardedness was associated with fewer losses by knock-out or greater fighter ability. While fighters with longer reaches won more fights, neither stance nor past experience influenced fight outcomes. We suggest that beards represent dishonest signals of formidability that may serve to curtail the escalation of intra-sexual conflict through intimidation rather than providing advantages in direct combat.     

Chemoreception and the Assessment of Fighting Abilities in the Lizard Liolaemus monticola

When an individual faces the risk of a conflict, its ability to make ‘correct’ decisions is crucial to its fitness. Research on decision making has focused mainly on visual and acoustic signals, while chemical signals have received much less attention, despite their relevance for many species. Chemosignals can be detected in the absence of the signaller and, in the context of fighting risk, this property confers the advantage that the receiver can avoid agonistic interactions or, if they are unavoidable, that it can prepare itself for the conflict. I studied the behaviour of males of the lizard Liolaemus monticola in the laboratory when they were confronted with chemosignals of a potential opponent. During this ‘pre‐confrontation’ stage, I tested the following predictions: (1) lizards can derive precise information from chemosignals of conspecifics, and use this to respond with precision to the perceived risk and (2) the best predictor of the receiver behaviour, and therefore the best predictor of the risk involved in the fight, is the relative fighting ability of opponents. As a measure of fighting ability, I used body size. ‘Intruders’ were placed in the terrarium of unfamiliar ‘residents’ during the absence of the latter, and their behaviours were recorded. Simple regressions were performed between the different behavioural variables and with the body sizes of intruder and resident, and with the relative difference in body sizes of opponents. The latter was the best predictor of intruder behaviour: it was negatively correlated with behaviours associated with activity (i.e. motion time), chemoexploration (i.e. number of tongue flicks) and behaviours associated with social interactions (i.e. head bobs). These results suggest that males can process information from chemosignals and decisions made during the ‘pre‐confrontation’ stage are based on the assessment of the relative fighting abilities (i.e. relative body size) of opponents.     

Mutual assessment via visual status signals in Polistes dominulus wasps

Many animals use signals to assess the fighting ability of rivals and reduce the cost of aggressive competition. However, little is known about how an individual''s own quality influences their signal assessment decisions. Polistes dominulus wasps have visual signals of fighting ability that provide a good model for testing the dynamics of rival choice. We found that rival assessment behaviour was influenced by the advertised quality of the individual, their rivals, and the interaction between individual and rival quality. Individuals of high advertised quality were more likely to challenge rivals and individuals of low advertised quality were more likely to be challenged. However, when choosing among two rivals with different advertised quality, individuals did not simply choose the lower quality rival. Instead, they only preferred the lower quality rival when there was a small difference between their own advertised quality and that of their rivals. Individuals were not choosy when both rivals advertised relatively high or relatively low quality. Therefore, although P. dominulus facial patterns function as conventional signals of fighting ability that provide valuable information about their bearer''s behavioural strategy, there is substantial variation in signal responses based on the relative intensity of the senders'' and receivers'' signals.     

The effect of injury on the agonistic behavior of the Stomatopod,Gonodactylus Bredini (manning)

The stomatopod Gonodactylus bredini is a predatory, aggressive crustacean possessing powerful raptorial appendages capable of inflicting serious injury on conspecifics. These weapons are readily employed during contests for cavities in coral rubble. In this study, we document the incidence of wounds in a population of G. bredini from Panama, determine the influence such injuries have on the behavior and fighting ability of individuals when competing for cavities, and examine associated costs of injury. A major consequence of injury in G. bredini is a severe reduction in fighting ability which in turn can alter the outcome of contests for cavities and the behaviors used by injured animals during such contests. A less immediate, but potentially costly consequence of injury due to increased chances of cannibalism and predation and lost breeding opportunities, is an acceleration in the onset of molt cycles in animals missing raptorial appendages.     

Draglines and Assessment of Fighting Ability in Cannibalistic Jumping Spiders

The frequency of injury and death during female-female aggression varies in the jumping spider genus Portia, with interactions being more violent (likely to end in death or injury of one of the combatants) in P. labiata (from Sri Lanka) than in another two species (P. fimbriata from Australia and P. schultzi from Kenya). To investigate the role of draglines in the assessment of fighting ability, two types of tests were carried out: 1) dragline discrimination and 2) mirror image response (Portia's reaction to mirror images is comparable to interaction with conspecific rivals). For both types of testing, triplets of equal-size conspecific females were used: one female (the test spider) was exposed to draglines of two equal-size conspecific females they had not encountered before (donor spiders). The fighting abilities of donor spiders were determined directly by staging intraspecific contests between them. In dragline-discrimination tests (spider placed in petri dish containing draglines from two conspecific females with different fighting ability), females of P. labiata, but not the other two species, avoided draglines of the superior fighter (i.e., they spent the majority of their time on draglines of donor spiders with lesser fighting ability). For mirror-image testing, the test spider was placed in a petri dish containing a mirror and draglines. Each test spider was tested on two successive days, with donor draglines in the two tests coming from conspecific females with different fighting ability. In these tests, females of P. labiata (but not the other two species) spent less time embracing (each spider pressing its forelegs, palps and front of body against the other spider) and more time in a part of the petri dish where view of the mirror was obstructed when on the draglines of donor spiders with greater fighting ability than when on the other conspecific's draglines. Findings from this study suggest that P. labiata females use signpost cues associated with draglines to assess the relative fighting abilities of unknown opponents.     

Sound Characteristics and Outcome of Contests in Male Croaking Gouramis (Teleostei)

A correlative study using similar-sized males of the croaking gourami Trichopsis vittata was carried out to investigate whether sound characteristics influenced winning and if relative fighting ability was assessed by acoustic signals. Pair-wise contests between males were decided using lateral displays (LD) and vocalization in 26 cases, whereas 66 fights escalated to the frontal display (FD) phase. Physical fighting (mouth wrestling) and injuries were rarely observed in this species. Winners were generally larger than their opponents, and this effect was more pronounced in non-escalated than in escalated contests. Sounds of fight winners had a higher sound pressure level and also a lower dominant frequency. Neither number of acoustic signals nor duration of lateral and frontal displays were predictors of contest outcome. Acoustic measures were highly correlated to body weight. These results indicate that traits correlated with RHP (such as sound pressure level and dominant frequency) were predictors of the outcome, while traits not correlated with size (such as number and duration of displays) did not influence winning. In accordance with the main prediction of assessment models, the contest duration (cost) increased with the decrease in asymmetry of body length as well as sound pressure level. No such relationships were found for weight and dominant frequencies in LD- and FD-contests. The present study indicates that morphological and sound characteristics influence winning in fish. Moreover, the results suggest that croaking gouramis settle conflicts without damaging combats by assessing asymmetries in different components of RHP such as body weight and length, which may reliably be signalled by acoustic and visual assessment signals.     

Does prior residency interact with loss? A study of male–male contests in the hermit crab Pagurus minutus

Residency is an important predictor of success in contests with ownership asymmetries. Residency often can interact with a winning experience. However, given that some residents lose a contest even when showing an ownership advantage and that the process leading to loss often determines the loser's subsequent success, prior ownership might also interact with a loss. Here, we staged experimental contests between males of the hermit crab Pagurus minutus with a similar-sized weapon (i.e., cheliped) to examine this possibility. Male–male contests in this species occur between a solitary intruder and an owner guarding a mature female. We evaluated (a) whether resource ownership and female value affect the contest outcome and (b) whether the probability of winning after losing differs depending on the initial role of the loser (i.e., owner or intruder) by using precopulatory guarding pairs of P. minutus collected from the field. In the first fighting trial, we found an ownership advantage and increasing owner success as the body size of his partner increased. Although some owners lost the fight, in contrast to our prediction, the frequency of losing in the second fighting trial did not differ between prior owners and prior intruders. Because losers from the first fighting trial of male–male contests have no female regardless of their initial role, this shared solitary status might be related to the lack of difference in success in the second fighting trial. Moreover, unlike in other animals, resident status might not always assure greater fighting ability in P. minutus males because guarding Pagurus males can avoid male–male contests by climbing up objects in the field. Losers in the first trial, therefore, may have been weaker contestants based on traits other than size, regardless of whether they were owners or intruders.     

Visual Assessment of Relative Body Size in a Cichlid Fish,the Oscar,Astronotus ocellatus

In cichlid fishes, fighting ability, success at nest defense, and fecundity are all positively correlated with body size. Selection should therefore favor the evolution of strategies for the assessment of relative body size during intraspecific interactions. The effect of relative body size on agonistic behavior in the oscar (Astronotus ocellatus) was tested using dummies. As predicted by game theory models, attack was strongly correlated with the size of the dummy relative to the subject. The most intense aggression occurred when dummy size was approximately 75% of subject size. These data support the prediciton that perceived body size asymmetries are important determinants of agonistic behavior in these fishes. Further, the results suggest that oscars can visually assess relative body size, and may estimate relative fighting ability without tests of strength. Subject size was positively correlated with intensity of aggressive behavior. Attack and display frequencies were positively correlated with a subject's body size, while latencies to approach and attack dummies were negatively correlated with subject size.     

Do Blackbirds Signal Motivation to Fight with Their Song?

Conflicts about resources can be solved with physical fights, but animals will in general try to avoid them due to the costs and risks associated with fighting. Fight outcome depends on the fighting ability as well as the motivation to fight, which means that individuals should try to assess both during a pre‐escalation phase. In the present study, we investigated whether blackbirds (Turdus merula) acoustically signal their motivation to fight with their advertisement song, which consists of a motif part with pure‐toned low frequency elements followed by a twitter part with more complex and higher‐pitched elements. We tested (1) whether the temporal and spectral characteristics of spontaneous songs broadcasted by a territorial male could predict its subsequent aggressive behaviour to a playback and (2) if the song of territorial males changed in case they responded aggressively to the playback. We found no effects in the temporal song structure, which contradicts results from a previous study involving playback experiments with blackbirds. We did however find an interesting pattern in the spectral characteristics of the twitter, since aggressively responding males significantly increased the twitter frequency after the playback. The post‐playback songs of aggressive responders were nevertheless indistinguishable from spontaneous pre‐playback songs of non‐aggressive responders. Therefore, we conclude that changes in twitter frequency, rather than absolute twitter frequencies, are advertising information about motivation to fight.     

Influence of previous residency and body mass in the territorial contests of the butterfly Hermeuptychia fallax (Lepidoptera: Satyrinae)

Although many studies have evaluated the possible rules used by males to settle territorial contests, few have simultaneously considered the possibility of mutual or self-assessment of fighting ability and the effect of prior residence on the chances of winning. Here, we experimentally investigated the influence of previous residency on the development and outcome of contests between males of the butterfly Hermeuptychia fallax. By comparing the frequency of resident victories in nonmanipulated disputes versus interactions in which both rivals were induced to behave as residents, we showed that prior residency may interact with body mass in contest resolution. In nonmanipulated disputes, resident males showed high winning probabilities, although they were similar to losers in body mass. However, when both males behaved as residents, the disputes were longer and were settled in favor of the heavier male. This indicates that, although residency is an important component of male willingness to fight, it is not the only factor influencing conflict resolution. Despite the correlation between body mass and territorial success, the weight of neither winners nor losers correlated with fighting duration. We conclude that residence asymmetry may sometimes conceal male traits important to contest resolution and that it may obscure the identification of the assessment strategy used in contests.     

Effects of starvation on the fighting ability of invasive and autochthonous ants

Ants are widespread in all terrestrial habitats, and competitive interactions between species are common. Although redistribution of food within a colony may buffer the negative effects of temporary resource shortages, colony functionality can be compromised when famine is prolonged. One of the possible effects of famine is impairment of the fighting ability of species, with cascade effects on community. Here, we investigated whether food shortage alters the fighting ability of workers of three dominant species in the Mediterranean area: the invasive alien species, Lasius neglectus and Linepithema humile, and one highly polydomous autochthonous species belonging to the Tapinoma nigerrimum complex. We performed laboratory tests of interspecific one-on-one aggression and pairwise group contests between species, with all possible combinations of artificially satiated and starved groups. Results showed that starvation had a scarce effect on the individual aggressiveness in all three species. Similarly, the outcomes of the group fights were only lightly affected, but with an important exception. The positions of species in the fighting hierarchies were in most cases clear and linear, with L. neglectus at the top. However, we found that L. humile and L. neglectus showed equal mortality when one of the two species was starved and the other satiated. Although we investigated only one aspect of competition, that is, fighting ability, our results provide a piece of the complex jigsaw of competitive interactions of ants, and suggest that food deprivation can be a determinant that alters the relationships between ants and promotes or hampers the coexistence of dominant species.     

Mate choice in female convict cichlids (<Emphasis Type="Italic">Amatitlania nigrofasciata</Emphasis>) and the relationship between male size and dominance

We examined how male size and fighting ability influence a female’s mate assessment process and her eventual mate choice in the monogamous convict cichlid, Amatitlania nigrofasciata. Females always chose the larger of two males when they were allowed to see a larger male next to a smaller one and when a larger male defeated a smaller one in a fight. They did not differentiate between large and small males when they did not see the two males together nor did they choose a dominant over a subordinate male when both were the same size. We suggest that females select on the basis of male size because it is a better predictor of both direct and indirect benefits (i.e., future competitive interactions and foraging ability) than dominance behavior only. Despite selecting one male over the other early in the courtship period, females continued to visit both males until spawning. Our evidence suggests that this assessment behavior more closely resembles a bet-hedging tactic rather than the female’s indecision as to which male will be her mate.