Intensity Of Contests Research Articles

Behavioral threat and appeasement signals take precedence over static colors in lizard contests

Abstract The interplay between morphological (structures) and behavioral (acts) signals in contest assessment is still poorly understood. During contests, males of the common wall lizard (Podarcis muralis) display both morphological (i.e. static color patches) and behavioral (i.e. raised-body display, foot shakes) traits. We set out to evaluate the role of these putative signals in determining the outcome and intensity of contests by recording agonistic behavior in ten mesocosm enclosures. We find that contests are typically won by males with relatively more black coloration, which are also more aggressive. However, black coloration does not seem to play a role in rival assessment, and behavioral traits are stronger predictors of contest outcome and winner aggression than prior experience, morphology, and coloration. Contest intensity is mainly driven by resource- and self-assessment, with males probably using behavioral threat (raised-body displays) and de-escalation signals (foot shakes) to communicate their willingness to engage/persist in a fight. Our results agree with the view that agonistic signals used during contests are not associated with mutual evaluation of developmentally-fixed attributes, and instead animals monitor each other to ensure that their motivation is matched by their rival. We emphasize the importance of testing the effect of signals on receiver behavior and discuss that social recognition in territorial species may select receivers to neglect potential morphological signals conveying static information on sex, age, or intrinsic quality.

Effects of a past contest on the future winning probability in a hyper‐aggressive fruit fly

AbstractIn various animal taxa, prior experience of contests influences the consequences of subsequent contests. A well‐known example is the winner and loser effects, in which winners have a higher winning probability, whereas losers become more likely to lose in the subsequent contests. Previous studies have suggested that the intensity of past contests also affects the future winning probability in two ways: modulating the extent of the winner–loser effect or decreasing the winning probability of both winners and losers. However, the number of studies that investigated the effect of both the contest outcome and intensity has been limited. Here, we analyzed the effect of past fighting experience in a hyper‐aggressive fruit fly Drosophila prolongata to ask (1) whether the winner–loser effect exists in this species and (2) how the contest intensity influences the subsequent winning probability. To disentangle the multiple factors affecting the winning probability, we employed the experimental design involving both body size manipulation and the comparison of different intervals between the two contests. The results did not support the existence of the winner–loser effect: both winners and losers of the first contest showed decreased winning probability in the second contest. With a short interval (2 h), contest intensity negatively influenced the winning probability in winners, though the significance level of its effect was marginally above the statistical threshold. In contrast, contest intensity had no effect in losers. Notably, contest intensity positively correlated with the winning probability after the longer interval (1 d) in both winners and losers, suggesting that it reflects the intrinsic fighting potential of individuals. The possible mechanisms underlying the observed results were discussed. Our study illustrates the transient influence of past contests other than the winner–loser effect.

Sternal Punctures in Common Loons (Gavia immer): Gender and Territorial Aggression

Aggression between adult Common Loons (Gavia immer) occurs frequently during the breeding season. In the past, it was suspected that most instances of intraspecific aggression took place between adult males. However, recent reports from the field suggest that female adult loons also participate in these battles. Postmortem investigation has shown that the damage incurred during these battles can range from incidental to fatal injuries. Sternal punctures are the most lasting evidence of this trauma and can serve as long-term records. Nearly half (46%, n = 268/574) of the loons received at Tufts Wildlife Clinic for postmortem from 2007 to 2015 were found to have sternal punctures. We conducted a focused analysis of the sternal punctures of 102 of these adult loons (49 female and 53 male) and found no significant difference in the number, distribution, or severity of sternal punctures between male and female loons. This suggests that the frequency and intensity of aggressive physical contests are remarkably similar between sexes and that there is no gender difference in the severity of these battles. Female Common Loons participate in lethal combats as often as their male counterparts. These findings provide an opportunity to better understand and study the biological or behavioral drivers of this aggression that is prevalent among both male and female Common Loons.

Size, sex and social experience: Experimental tests of multiple factors mediating contest behaviour in a rockpool fish

AbstractAggressive contests amongst conspecifics are important to understand from an ecological and evolutionary perspective as contest dynamics can directly influence individual fitness. For some species, individual attributes such as relative body size closely predict the outcome, intensity and duration of contests, whereas for others, prior social experiences play a key role. However, disentangling the relative effects of individual attributes and social experiences is challenging from an experimental perspective, and because of this, few studies have investigated relative effects of multiple factors. Rockpool fishes have been well studied in terms of factors governing abundance, distribution and community structure, but much less so in terms of contest behaviour. This is surprising because contest dynamics are likely to directly affect the distribution of fishes along the rocky shore, and hence indirectly govern population and community composition. Here, we explored multiple factors potentially influencing contest behaviour in a numerically dominant, resident intertidal fish species, Bathygobius cocosensis (Gobiidae). Using a series of staged pairwise contest trials, we investigated the effect of size, sex and social experiences (namely prior residency and winner–loser experiences) on contest dynamics. We found no evidence that prior residency influenced contest outcome, suggesting social experiences play a minor role in contest dynamics. Previous winner/loser experience also did not influence contest outcome, although this is likely a product of low sample size. In addition, the likelihood of winning was unrelated to contestant sex, and the combination of sexes in paired contests did not influence contest intensity or duration. Instead, body size was related to contest outcome, intensity and duration in the majority of experimental trials. These results suggest that body size rather than sex or social experiences is the key determinant of contest dynamics in this species. We suggest that the dynamic biotic and abiotic environment inhabited by intertidal fish may reduce the influence of prior social experiences in modulating contest dynamics.

Comparative evidence supports a role for reproductive allocation in the evolution of female ornament diversity

1. Sexually selected ornaments are highly variable, even among closely related species, and the ultimate causes of variation in ornament evolution are unclear, including in rare cases of female ornament expression. One hypothesis is that differences across species in female reproductive allocation may help to explain patterns of female ornament expression among insects with nuptial gifts.2. Dance flies (Diptera: Empididae: Empidinae) vary considerably among species in the presence and extravagance of female ornaments, which probably evolved through female contests for mates. In most dance flies, adult females appear to acquire all their dietary protein from nuptial gifts provided by males during mating. The importance of nuptial feeding on egg development is not yet known.3. To test the prediction that the presence of female ornaments reflects differences in the degree to which females rely on nuptial feeding for egg development, egg development was examined in wild females of two species, one ornamented and the other unornamented. An ageing technique based on cuticular bands was validated, which permitted a regression of egg size on adult age.4. We found that egg development depended on mating status in the ornamented species alone, meaning the eggs of unmated females of the ornamented species did not develop. This contrast across species is consistent with expectations that females of different species vary in their dependence on nuptial gifts for egg development.5. These findings provide preliminary support for the hypothesis that differences in reproductive allocation mediate the intensity of female contests for nuptial gifts.

Workload of official contests, net cost of transport, and metabolic power of Mangalarga Marchador horses of marcha batida or picada gaits.

This study aimed to characterize the maximum heart rate (HR) and the intensity of official marcha contests (OMC) and to compare the cost of transport (COT) and metabolic power (Pmet) of Mangalarga Marchador (MM) horses of marcha batida (MB) and marcha picada (MP) gaits. Twenty-two MM horses participated in this study. The experiment was conducted in 3 phases: 1) maximum effort test (MET), 2) OMC, and 3) standardized marcha test (SMT). To characterize the HR, 19 horses (14 MB and 5 MP) underwent a MET. Of those, 13 (9 MB and 4 MP) were monitored during the OMC, which consisted of 4 stages: marcha, walk, functional trial, and rest. The average heart rate (HR) in each stage of the OMC was related to the HR to determine their relative intensity. The SMT was performed with 14 horses (9 MB and 5 MP), of which 11 had already participated in the previous stages. The COT and Pmet were calculated from the HR values obtained during the SMT. Blood samples were collected to analyze plasma lactate concentration ([Lac]). One-way ANOVA or 1-way repeated-measures ANOVA followed by the Tukey's test ( < 0.05) were used to analyze the results. The average HR was 211 ± 11 and 214 ± 11 beats/min (bpm) for the MB and MP groups, respectively, with no difference ( = 0.7066) between them. The [Lac] increased as a result of the MET ( < 0.05), with no difference between groups ( > 0.05). This indicated that horses of both groups had the same physical fitness levels. The OMC stages defined in our study differed ( < 0.05) regarding the relative intensity of the HR, except for the walk and standing stages, which were similar ( = 0.0875). The MP group presented greater COT ( = 0.0247) and Pmet ( = 0.0193). It can be concluded that the mean HR of MM horses (MB and MP) is 212 ± 11 bpm. The OMC of the MM breed can be characterized as an effort of intermittent and submaximal intensity. In addition, the locomotion of the MB horses is probably more energetically efficient than that of MP horses.

Effects of group size and contest location on the outcome and intensity of intergroup contests in wild blue monkeys

Intergroup contests determine access to resources and influence the evolution of group living in social species. Asymmetries in resource-holding potential and payoffs should influence the outcome and intensity of such contests. We evaluated predictors of contest outcome and intensity using data collected over 40 months from 6 groups of wild blue monkeys, Cercopithecus mitis. We found increased odds of winning when a group was larger and used the contest site more than its opponent, and when contests occurred closer to the group's home range centre while farther from the opponent's centre. However, a larger difference in group size (across five pairs of opposing groups) did not predict a greater proportion of contests won by the larger group. Some evidence suggested increased odds of a draw when group sizes were more similar. In addition, contests were longer and more aggressive when groups were more similar in size and when the contest site was similarly central in both groups' home ranges. Contests were also more aggressive when the opposing groups' use of the contest site was more similar. Overall, asymmetries in resource-holding potential (i.e. group size) and/or payoffs related to the contest's location influenced a group's competitive advantage, the likelihood of a draw and the intensity of intergroup contests. Although comparable data are limited, it seems clear that both types of asymmetries can play a role in determining the outcome and intensity of intergroup contests, and that the relative power of each may vary across species.

The role of male coloration in the outcome of staged contests in the European common wall lizard (Podarcis muralis)

Colour signals play a key role in regulating the intensity and outcome of animal contests. Males of the common wall lizard (Podarcis muralis) show conspicuous ventrolateral ultraviolet (UV)-blue and black patches. In addition, some populations express a striking ventral colour polymorphism (i.e., discrete orange, white and yellow morphs). In this study, we set out to evaluate the potential signalling function of these colour patches by staging pairwise combats between 60 size-matched adult lizards (20 per morph). Combats were held in a neutral arena, with each lizard facing rivals from the three morphs in a tournament with a balanced design. We then calculated a fighting ability ranking using the Bradley–Terry model, and used it to explore whether ventral colour morph, the size of UV-blue and black patches or the spectral characteristics of UV-blue patches (i.e., brightness, hue, chroma) are good predictors of fighting ability. We did not find an effect of the UV-blue patches on contest outcome, but the size of black patches emerged as a good predictor of fighting ability. We also found that winners were more aggressive when facing rivals with black patches of similar size, suggesting that black patches play a role in rival assessment and fighting rules. Finally, we found that orange males lost fights against heteromorphic males more often than yellow or white males. In light of these results, we discuss the potential signalling function of ventrolateral and ventral colour patches in mediating agonistic encounters in this species.

Do resource value and ownership status affect intensity and resolution of contests in a parasitoid wasp?

AbstractBiological control of bruchid beetles, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae), infesting cowpea seeds, Vigna unguiculata (L.) Walpers (Fabaceae), can be performed via augmentative releases of Dinarmus basalis Rondani (Hymenoptera: Pteromalidae) parasitoid wasps. Females of the latter species are therefore likely to experience intense intraspecific competition: they should encounter numerous previously parasitized hosts but also conspecific competitors, with which they may fight to secure hosts on which to lay their eggs. Such contests might therefore disrupt biological control programs. Here, we studied aggressive behavior that D. basalis females show toward conspecific competitors and subsequent host exploitation strategies. We further investigated factors that classically affect contest intensity and outcomes in animals, such as the effect of ownership status, by manipulating the residency period before the intruder's arrival. In addition, we tested the effect of the size of female reproductive tissue (measured in terms of egg load) and the quality of the habitat previously experienced by females (either rich or poor in hosts). These two factors are expected to influence the value that females place on the host and therefore the costs they are willing to pay to win it. Finally, we discussed the consequences of agonistic behaviors on females' host exploitation strategies. Our results suggest that contest competition may actually enhance host control by favoring parasitoid dispersion, rather than disrupting it.

How do fighting ability and nest value influence usurpation contests in Polistes wasps?

Most research on animal contests has focused on the factors that influence the intensity and outcome of aggressive contests within nonsocial species, while relatively little is known about contests in social taxa. Here, we examine contests among queens of the social paper wasp, Polistes dominulus. Queens use multiple reproductive strategies, including nesting alone, usurping established colonies, and cooperatively joining other queens. We stage contests between a nesting queen and a challenger to test how resource value (RV) and resource holding potential (RHP) influence (a) who occupies the nest at the end of the contest and (b) the extent of conflict between the queen and challenger. We found that RHP, as measured by individuals’ facial patterns and body size, influenced the outcome of the contest. Challengers with high RHP were more likely to successfully usurp the nest than challengers with low RHP. Interestingly, queens with relatively high RHP were more likely to form a cooperative association with the challenger than queens with lower RHP, suggesting that queens may evict individuals that are an aggressive threat. RV influenced the intensity of conflict. There was more aggressive conflict over large nests than over small nests. Overall, social taxa have complex contest dynamics with important parallels to contests in nonsocial taxa. Studying contests in social taxa provides an important perspective on the factors that influence individual decisions about conflict versus cooperation.

Increased risk and benefit simultaneously alter the outcome of territorial fights

AbstractCompetition for resource, including territories is seen in a broad range of taxa. There has been much research on factors that determine the intensity and outcome of competitions (e.g. resource holding potentials: RHP, and resource value: RV). No research, however, has shown how different factors can simultaneously alter the intensity and outcome of contests. We investigated the effects of RV on fighting behavior and success in inter-tidal, territorial male crabs. Under natural conditions the larger rival won contests irrespective of whether he was the resident or intruder (i.e. there was no residency effect). We then motivated intruders to fight hard by subjecting them to the threat of predation, and found that they were more likely to win contests. When we also motivated residents to fight hard by placing a female in his burrow (i.e. both rivals were simultaneously motivated to fight due to the perceived increase in resource value), we found that the contests escalated more and that resident males had a slightly increased chance of winning. This is the first report of two factors simultaneously affecting motivation and therefore altering the escalation and outcome of a contest.

How dear is my enemy: Intruder-resident and resident-resident encounters in male sand fiddler crabs (Uca pugilator)

AbstractMale sand fiddler crabs (Uca pugilator) defend territories that consist of a breeding burrow and a display area where they wave their claw to attract females. Burrow-holding males engage in agonistic contests with both intruding males that attempt burrow take-overs and with other territory-holding neighbors that apparently attempt to limit waving or other surface activities of rivals. Contests employ one or more behavioral elements that range from no claw contact to use of the claw to push, grip, or flip an opponent. We placed each observed element into one of six groups ranked by intensity, which was based on the degree of claw contact and apparent energy expenditure. In the field, contests with intruders began at higher intensity and escalated more rapidly than did those with neighbors. Thus, U. pugilator males exhibit a dear enemy response toward neighbors. However, resident-resident contests increased in intensity when burrows were close, neighbors faced each other when exiting burrows, and neighbors were of similar size. Proximity and orientation determine the ease with which a neighbor may be engaged. Also, neighbors that are close and of similar size pose a greater threat to mating opportunities, favoring heightened intensity of contests.

Female sex pheromone-mediated effects on behavior and consequences of male competition in the shore crab (Carcinus maenas).

Exposure to receptive female pheromone elicits guarding behavior in shore crab males (Carcinus maenas), but little is known about the effects of sex pheromone on male competition or if the female plays an active role in mate choice. This study examined whether female pheromone enhanced agonistic behavior between males and what effects visual and chemical cues had on the rules and costs of such contests. We also investigated whether females exhibit a preference for males in terms of size. Under laboratory conditions, solitary male shore crabs engaged males who already had possession of a female. The visual and chemical presence of a receptive female had an impact on contest rules and costs. Fights were costly in terms of duration and of sustaining injury with either one or both crabs incurring injury in 40% of fights. To investigate the metabolic consequences of fighting over a perceived sexual resource (chemical cue only), fights were staged between pairs of size-matched males in the presence of water containing the female sex pheromone, water in which males had been kept, and untreated seawater. The duration and intensity of contests were greater when staged in the presence of the female pheromone compared with the two other treatments. Crabs that fought in the presence of female sex pheromone also had a greater accumulation of L-lactate and a reduction of glycogen stores. Fights were less costly in terms of injury with a single chemical cue compared with enhanced costs with a multiple sexual cue. The importance of female choice was determined by presenting postmolt females with different sized males. Males were kept in a fixed position, and the majority of females approached and performed courtship behavior to the largest males, demonstrating that females may be selective in terms of size.

Dynamics of intersexual conflict over precopulatory mate guarding in two populations of the isopod Idotea baltica

Aggressiveness during intersexual conflicts is predicted to depend on its costs, the value of winning and the power asymmetry of the contestants, all of which may vary between populations. In the marine isopod Idotea baltica (Pallas) a conflict occurs as females resist the attempts by males to start precopulatory mate guarding. We analysed contest dynamics with respect to female maturity stage, that is, to time left to reproductive moult, with which the payoffs of guarding for males and females change. We did this in two populations that differ in synchrony of reproduction, sex ratio and the degree of sexual dimorphism. The intensity and dynamics of contests differed between populations: in the more size-dimorphic population, females, the smaller sex, resisted less by forceful flexing but more by hooking their body than in the other population. Male aggressiveness stayed at a constant level with respect to female maturity. In the less size-dimorphic population, female resistance by flexing was intense and it decreased, while male persistence increased, with the approaching reproductive moult. Contests were more intense with small than with large males. These results fit well with the predictions from models of conflict behaviour. Assessment of the payoffs of winning versus contest costs, coadaptation of the level of aggressiveness to the other traits affecting contest outcome, and counteradaptations by the sexes to each other largely explain the dynamics and between-population differences of these contests.

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

AbstractThis 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.

Positive allometry is likely with mate choice, competitive display and other functions

Petrie (1988) argued that structures important in displaying competitive ability between individuals should be developed in a positively allometric manner in species where large animals usually win fights, with larger animals developing relatively larger structures, as with the frontal shield of the moorhen, Gallinula chloropus. Petrie's reasoning is that animals of low competitive ability have little to gain from paying the costs of developing a large structure because any structure advertising low ability will do little to reduce the number and/ or intensity of contests. In contrast, characters important in mate choice are considered unlikely to be positively allometric. Referring to moorhen shields, Petrie said 'If shields were important in mate choice it is hard to see why they should be positively allometric, since it would pay all individuals to invest maximally in structures that advertise their quality as mates, and this would result in shields being isometric.' In my view, positive allometry will often occur in characters used in mate choice or with various other functions, and is therefore not evidence that a character is used to display competitive ability. As animals grow, they will partition investment into both bodies and characters so that bigger animals have bigger characters. How much bigger they are will depend on both the costs and benefits of a larger body size, and the costs and benefits of a larger character. The key question is, as an animal acquires more resources to invest in growth, how much should it invest in the character and how much in body size? Positive allometry will result if the net benefit of larger characters increases faster than the net benefit of larger bodies. Negative allometry will result if the net benefit of larger characters increases more slowly. In other words, if the same resource investment into a character or body size brings a greater net benefit from the former, that is where investment will be concentrated, resulting in positive allometry. If, however, a greater net benefit comes from the latter, negative allometry will result. This applies to characters with mate choice, competitive display or any other functions. A character developed for mate attraction may be positively allometric for at least two reasons. First, smaller animals may be less able to obtain mates and so have little to gain from paying the costs of developing a large character that does little to increase the number of matings. This logic is similar to that used by Petrie (1988) for characters displaying competitive ability, and will apply whether body size influences mating success through intersexual competition or mate choice. There may be cases where competition between males prevents small males from gaining access to females, while females choose males with larger characters (e.g. in the pinyon jay, Gymnorhinus