Resource-holding Potential Research Articles

The role of skill in animal contests: a neglected component of fighting ability.

What attributes make some individuals more likely to win a fight than others? A range of morphological and physiological traits have been studied intensely but far less focus has been placed on the actual agonistic behaviours used. Current studies of agonistic behaviour focus on contest duration and the vigour of fighting. It also seems obvious that individuals that fight more skilfully should have a greater chance of winning a fight. Here, we discuss the meaning of skill in animal fights. As the activities of each opponent can be disrupted by the behaviour of their rival, we differentiate among ability, technique and skill itself. In addition to efficient, accurate and sometimes precise movement, skilful fighting also requires rapid decision-making, so that appropriate tactics and strategies are selected. We consider how these different components of skill could be acquired, through genes, experiences of play-fighting and of real fights. Skilful fighting can enhance resource holding potential (RHP) by allowing for sustained vigour, by inflicting greater costs on opponents and by minimizing the chance of damage. Therefore, we argue that skill is a neglected but important component of RHP that could be readily studied to provide new insights into the evolution of agonistic behaviour.

Boldness is for rookies: prefight boldness and fighting success in a sea anemone

Fighting experience (specifically winning or losing a fight) can significantly alter boldness, a component of resource-holding potential (RHP). Previous studies have shown that both the repeatability of boldness and mean-level boldness can be affected by fighting experience and that these effects are strongest in the recipients of agonistic behaviour. However, whether these postfight changes in boldness impact future contest success and whether subsequent contests further affect boldness remain unknown. Furthermore, little is known about the effects of the specific tactics used within a fight (within-fight experience) and how these might influence future fight performance and boldness. Here, we investigated the relationship between fighting success and boldness (measured as recovery time when startled) across repeated contests in the beadlet sea anemone, Actinia equina , measuring boldness on five occasions before, between and after two contests. We found that boldness (both repeatability and mean-level) was generally robust to the effects of fighting experience, apart from a decrease in the immediate boldness of losers after their second fight. Furthermore, we found that while prefight boldness significantly predicted fighting success and the level of aggression used in an individual's first fight, it did not predict victory or aggression in the second fight. Our findings thus indicate that different traits may be important in determining fighting success in consecutive fights and, moreover, that fighting experience may alter which traits contribute to an individual's RHP.

Differential dispersal costs and sex-biased dispersal distance in a cooperatively breeding bird

In most bird species, dispersal distance from the natal territory to a breeding territory is greater for females than for males. Two main hypotheses have been proposed to explain sex-biased dispersal: 1) it serves as an inbreeding-avoidance mechanism or 2) it is linked to a sex difference in resource-holding potential and territory establishment. Additionally, in species where individuals delay dispersal and become subordinates in a natal territory, differences in benefits of philopatry (e.g. territory inheritance, own reproduction) may also affect sex-biased dispersal. We show that in the group-living Seychelles warbler, Acrocephalus sechellensis, females disperse further to obtain a breeding position than males do. However, we found no evidence that female-biased dispersal distance can be explained by the above-mentioned hypotheses: further dispersal does not lead to less-related partners, both sexes defend and can inherit a territory, and subordinate females are more likely to obtain some reproduction than subordinate males. Instead, we provide evidence for a little-explored hypothesis based on sex differences in dispersal costs: namely that extra-territorial forays, pursued to search for limited vacancies, are more costly for males in terms of increased mortality, although the exact mechanism for this is unclear. In line with differential dispersal costs, males foray less far than females and often wait for local dispersal opportunities, ultimately resulting in a shorter average dispersal distance. Our results may help future studies in explaining sex-biased dispersal in social and perhaps also non-social species, and we suggest some mechanisms that may explain why sex-biased dispersal differs between species.

Aggressiveness compensates for low muscle strength and metabolic disadvantages in shell fighting: an outcome of the individual’s past

An individual’s metabolic competence is important when escalating to costly behaviours in agonistic encounters. The use of broken shells in the wild induces hermit crabs to reduce their overall metabolic rate; however, these crabs perform better in size-symmetric encounters than crabs that used intact shells in the wild. Given this surprising finding, we explored whether carrying a broken shell increases the resource holding potential (RHP) of hermit crabs by building up their muscle strength. These shells are very heavy, with an unusable portion due to being broken; however, the crabs have to carry the complete structure. Additionally, we explored whether the use of broken shells induces long-lasting consequences in motivation (aggressiveness). We conducted body size asymmetric contests to decrease the relative effect of aggressiveness by increasing the effect of RHP. We predicted a decrease of the agonistic behaviours of crab that occupied broken shells in the wild (CBS) relative to those that occupied intact shells (CIS). Symmetric and asymmetric contests were conducted in pairs formed of a CBS and a CIS, both forced to abandon them and occupy a Nerita shell. The CBS had lower muscle strength, but fought at higher intensity in symmetric contests than CIS. The differences in body mass decreased the expression of agonistic behaviours of CBS relative to CIS. Prolonged poor conditions following the use of a broken shell seem to increase aggressiveness by affecting the long-term subjective resource value. Our findings highlight the role of the recent past associated with shell used on fighting performance. Hermit crabs commonly fight to exchange their inadequate shell for a new one. Although high metabolic rates favour the fighting ability, crabs that occupied broken shells in the wild have low metabolism and perform better in shell fighting than crabs that used intact shells. Broken shells are heavy and larger due to having an unusable portion, but the crab has to carry the complete structure. We explored whether carrying these shells increases muscle strength and/or the aggressiveness of crabs, which might explain their fighting dynamic. Unexpectedly, crabs with broken shells were found to be weaker than those with intact ones. Instead, the use of a broken shell in the wild enhances individual aggressiveness. The results highlight that a previous history under adverse conditions can increase the likelihood of animals with functional disadvantages acquiring better resources.

Accurate resource assessment requires experience in a territorial fish

Although the relationship between resource-holding potential and contest dynamics is well studied, how the value of a contested resource influences aggressive interactions has received far less attention. Questions about how animals assess a contested resource, and whether they can update their assessments of resource value during a contest require additional testing. To address this issue, we conducted a series of experiments using an invasive, territorial fish, the round goby, Neogobius melanostomus . We used this species to investigate the impact of resource quality on contest dynamics, and to test how animals gather information on resource value. First, we found that fish preferred an enclosed shelter (‘high quality’) to an open shelter (‘low quality’). Despite this preference for high-quality shelter, fish fought equally hard for both high- and low-quality shelters in staged resource contests when they had no prior experience with the resource. However, when fish were given prior experience, contests over high-quality shelters began faster and had more aggressive acts than contests over low-quality shelters. Interestingly, when the value of the resource in the contest was switched from their prior experience, the fish seemed unable to fully update their appraisal of resource value, and contest dynamics were not strictly driven by the previous or current resource value. Round goby may therefore have a limited ability to update their appraisal of resource value when engaged in a contest. Together, our findings demonstrate that fish adjust their aggressive effort to reflect resource value, but previous experience with the resource is required to assess the resource efficiently.

Importance of weapon size in all stages of male–male contests in the hermit crab Pagurus minutus

Physical traits such as body size and weapon size typically reflect an individual’s resource holding potential (RHP). During male–male contests, contestants use these traits to assess their own and their opponent’s RHP. However, the advertisement of RHP does not always predict contest outcome. Here, we examined whether assessment index (body size or weapon size [major cheliped size]) and assessment tactics (self or mutual) are predictors of outcome in male–male contests of the hermit crab Pagurus minutus. In experimental contests over guarded females, intruders did not escalate the contest when their major cheliped was smaller than their opponent’s, implying that intruders use mutual assessment based on weapon size when deciding whether to escalate a contest. After escalation, intruders succeeded in taking over females within a shorter period of time with increasing major cheliped size relative to their opponent’s. Overall, males with a major cheliped that was larger than their opponent’s were more likely to win the contest, although some intruders later stopped guarding the female they had taken over. The importance of relative weapon size after escalation indicates that mutual assessment was also used in this phase of male–male contests. Together, these results suggest that males of P. minutus use mutual assessment based on weapon size throughout male–male contests, and that weapon size is an honest index of RHP. We examined whether assessment index (body or weapon size) and tactics (self or mutual) are predictors of outcome in male–male contests of the hermit crab Pagurus minutus. Intruders did not escalate contests when their major cheliped was smaller than their opponent’s, implying that mutual assessment based on weapon size was used to decide whether to escalate contests. After escalation, intruders succeeded in taking over females within a shorter period of time and were more likely to win with increasing weapon size relative to their opponent’s. The importance of relative weapon size after escalation indicated that mutual assessment was also used in this phase of contests. Together, these results suggest that males of P. minutus use mutual assessment based on weapon size throughout male–male contests, and that weapon size is an honest index of actual strength.

Complex contests and the influence of aggressiveness in pigs

Animal contests vary greatly in behavioural tactics used and intensity reached, with some encounters resolved without physical contact while others escalate to damaging fighting. However, the reasons for such variation remains to be fully explained. Aggressiveness, in terms of a personality trait, offers a potentially important source of variation that has typically been overlooked. Therefore, we studied how aggressiveness as a personality trait influenced escalation between contestants matched for resource-holding potential (RHP), using detailed observations of the contest behaviour, contest dynamics and escalation levels. We predicted that winner and loser behaviour would differ depending on personality. This was tested by examining 52 dyadic contests between pigs, Sus scrofa. Aggressiveness was assayed in resident–intruder tests prior to the contest. Contests were then staged between pigs matched for RHP in terms of body weight but differing in their aggressiveness. In 27% of the contests a winner emerged without escalated physical fighting, demonstrating that a fight is not a prerequisite between RHP-matched contestants. However, the duration of contests with or without fighting was the same. In contests without a fight, opponents spent more time on mutual investigation and noncontact displays such as parallel walking, which suggests that ritualized display may facilitate assessment and decision making. Winners low in aggressiveness invested more time in opponent investigation and display and showed substantially less aggression towards the loser after its retreat compared to aggressive winners. Aggressiveness influenced contest dynamics but did not predict the level of escalation. Prominent behavioural differences were found for the interaction between personality and outcome and we therefore recommend including this interaction in models where personality is considered. Analyses based on contest duration only would miss many of the subtleties shown here and we therefore encourage more detailed analyses of animal contests, irrespective of the level of contest escalation.

Age-dependent male mating tactics in a spider mite-A life-history perspective.

Males often fight with rival males for access to females. However, some males display nonfighting tactics such as sneaking, satellite behavior, or female mimicking. When these mating tactics comprise a conditional strategy, they are often thought to be explained by resource holding potential (RHP), that is, nonfighting tactics are displayed by less competitive males who are more likely to lose a fight. The alternative mating tactics, however, can also be explained by life‐history theory, which predicts that young males avoid fighting, regardless of their RHP, if it pays off to wait for future reproduction. Here, we test whether the sneaking tactic displayed by young males of the two‐spotted spider mite can be explained by life‐history theory. We tested whether young sneaker males survive longer than young fighter males after a bout of mild or strong competition with old fighter males. We also investigated whether old males have a more protective outer skin—a possible proxy for RHP—by measuring cuticle hardness and elasticity using nanoindentation. We found that young sneaker males survived longer than young fighter males after mild male competition. This difference was not found after strong male competition, which suggests that induction of sneaking tactic is affected by male density. Hardness and elasticity of the skin did not vary with male age. Given that earlier work could also not detect morphometric differences between fighter and sneaker males, we conclude that there is no apparent increase in RHP with age in the mite and age‐dependent male mating tactics in the mite can be explained only by life‐history theory. Because it is likely that fighting incurs a survival cost, age‐dependent alternative mating tactics may be explained by life‐history theory in many species when reproduction of old males is a significant factor in fitness.

The importance of motivation, weapons, and foul odors in driving encounter competition in carnivores.

Encounter competition is interference competition in which animals directly contend for resources. Ecological theory predicts the trait that determines the resource holding potential (RHP), and hence the winner of encounter competition, is most often body size or mass. The difficulties of observing encounter competition in complex organisms in natural environments, however, has limited opportunities to test this theory across diverse species. We studied the outcome of encounter competition contests among mesocarnivores at deer carcasses in California to determine the most important variables for winning these contests. We found some support for current theory in that body mass is important in determining the winner of encounter competition, but we found that other factors including hunger and species-specific traits were also important. In particular, our top models were "strength and hunger" and "size and hunger," with models emphasizing the complexity of variables influencing outcomes of encounter competition. In addition, our wins above predicted (WAP) statistic suggests that an important aspect that determines the winner of encounter competition is species-specific advantages that increase their RHP, as bobcats (Lynx rufus) and spotted skunks (Spilogale gracilis) won more often than predicted based on mass. In complex organisms, such as mesocarnivores, species-specific adaptations, including strategic behaviors, aggressiveness, and weapons, contribute to competitive advantages and may allow certain species to take control or defend resources better than others. Our results help explain how interspecific competition shapes the occurrence patterns of species in ecological communities.

Interspecific competition for nests: Prior ownership trumps resource holding potential for Mountain Bluebird competing with Tree Swallow

ABSTRACT Interspecific competition over nest sites is common among cavity-nesting birds, but little is known about what determines the outcome of such contests, particularly whether or not prior ownership plays a role. Using a box removal and replacement experiment, I tested whether Mountain Bluebird (Sialia currucoides) or Tree Swallow (Tachycineta bicolor) had the higher resource holding potential (RHP). A different box-blocking experiment with paired boxes on territories measured the extent to which prior ownership influenced contest outcomes for both species. Behavioral observations in the pre-laying period showed more physical aggression by Mountain Bluebird against Tree Swallow. Nevertheless, Tree Swallow won 70% of boxes when neither species had prior ownership, suggesting Tree Swallow had a higher RHP. When their boxes were blocked, 24% of Tree Swallow usurped boxes from Mountain Bluebird, which did not differ statistically from the 33% of boxes usurped by bluebirds from swallows; thus, prior owne...

Age and reproductive status influence dominance in wild female Phayre's leaf monkeys

In group-living mammals, social dominance can be achieved and maintained via kin support, winner–loser effects and individual differences in resource-holding potential (RHP). When dominance is based on RHP, the likelihood of winning is also influenced by the incentive to compete. For females, this equation can be quite complex, as both age and reproductive state can alter the relative value of resources and the risks associated with fighting. For example, females that are young, pregnant or lactating may have high nutritional demands, while lactating females also face risks associated with offspring survival. To date, however, there have been few studies investigating how such factors influence female agonistic relationships. Here, we use 2 years of data to evaluate how age and reproductive state influence the probability of winning, focusing on two groups (5–9 and 10–12 females) of wild Phayre's leaf monkeys, Trachypithecus phayrei crepusculus, at Phu Khieo Wildlife Sanctuary, Thailand. Consistent with previous studies, we found that young females and pregnant females were more likely to win dyadic interactions in the smaller group, PA. By contrast, the likelihood of winning was unrelated to age in the larger group, PB. Moreover, differences between reproductive states were less pronounced in PB, with females that were pregnant or in early lactation being more likely to win compared to females that were cycling. The deviating results for PB were likely associated with a greater number of competitors and small age differences intensifying intrasexual competition. These results highlight the importance of individual as well as demographic factors in female dominance relationships. In this population, females with high nutritional demands are more likely to win agonistic encounters, suggesting that female–female competition occurs primarily over access to resources.

Evolutionary routes to stable ownership.

Ownership can evolve in potentially any species. Drawing on insights from across disciplines, we distinguish between possession and ownership and present species-neutral criteria for ownership, defined as respect for possession. We use a variant of the tug-of-war evolutionary game to demonstrate how ownership can evolve in the form of a new, biologically realistic strategy, Restraint With Retaliation (RWR). In our game, resource holding potential (RHP) is assumed to be equal between interactants, and resource holding asymmetry determines whether ownership is adaptive. RWR will be evolutionarily stable when the ratio of resource holdings between interactants is relatively low, but not when this ratio is sufficiently high. We offer RWR as one evolutionary route to ownership among many, and discuss how ownership unites previously described behavioural phenomena across taxa. We propose that some but not all mechanisms of territory formation and maintenance can be considered ownership, and show that territories are not the only resources that can be owned. We argue that ownership can be a powerful cooperative solution to tragedies of the commons and problems of collective action throughout the biological world. We advance recent scholarship that has begun to investigate the biological importance of ownership, and we call for a comprehensive account of its evolutionary logic and taxonomic distribution. We propose that ownership should be considered a fundamental, unifying biological phenomenon.

Assessment strategies and fighting patterns in animal contests: a role for serotonin?

Accurate assessment of the probability of success in an aggressive confrontation with a conspecific is critical to the survival and fitness of the individuals. Various game theory models have examined these assessment strategies under the assumption that contests should favor the animal with the greater resource-holding potential (RHP), body size typically being the proxy. Mutual assessment asserts that an individual can assess their own RHP relative to their opponent, allowing the inferior animal the chance to flee before incurring unnecessary costs. The model of self-determined persistence, however, assumes that an individual will fight to a set personal threshold, independent of their opponent’s RHP. Both models have been repeatedly tested using size as a proxy for RHP, with neither receiving unambiguous support. Here we present both morphological and neurophysiological data from size-matched and mismatched stalk-eyed fly fights. We discovered differing fighting strategies between winners and losers. Winners readily escalated encounters to higher intensity and physical contact and engaged in less low-intensity, posturing behaviors compared with losers. Although these fighting strategies were largely independent of size, they were associated with elevated levels of 5-HT. Understanding the neurophysiological factors responsible for mediating the motivational state of opponents could help resolve the inconsistencies seen in current game theory models. Therefore, we contend that current studies using only size as a proxy for RHP may be inadequate in determining the intricacies of fighting ability and that future studies investigating assessment strategies and contest outcome should include neurophysiological data.

Fighting for mates: the importance of individual size in mating contests in rocky shore littorinids

Studies of mating contests have reported how traits (e.g. body size) related to resource-holding potential (RHP) and strategies to assess RHP and resource value influence contest outcome in many taxa but are rare in the Gastropoda. The influence of male size (as an index of RHP) and female size (as a measure of resource value) on contest outcome was investigated in two littorinid snails, Echinolittorina malaccana and E. radiata, in Hong Kong during May–June 2013. In these snails, contests between males take the form of a ‘challenger’ attempting to take over the copulation position occupied by a ‘defender’. Both challengers and defenders were, generally, smaller than the females in both species. In both species, the larger the challenger relative to the defender, the more likely he would replace the defender in the copulation position. The challengers were, however, more successful in E. radiata, as they generally challenged defenders that were smaller than themselves, suggesting an ability to detect rival size before entering into a contest in this species. When sizes of the contestants were similar, defenders were more likely to win contests in E. malaccana but not in E. radiata. Evidence for pure self-assessment of RHP and the ability to assess resource value in challengers was found in E. malaccana. Different fighting strategies appear to have evolved in these congeneric marine snail species, and decisions based on male and female sizes play an important role in determining male reproductive success.

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.

Individual participation in intergroup contests is mediated by numerical assessment strategies in black howler and tufted capuchin monkeys.

Asymmetries in resource-holding potential between opposing groups frequently determine outcomes of intergroup contests. Since both numerical superiority and high intergroup dominance rank may confer competitive advantages, group members should benefit from assessing the relative strength of rivals prior to engaging in defensive displays. However, differences in individual assessment may emerge when cost-benefit trade-offs differ among group members. We examine the influence of numerical superiority and intergroup dominance relationships on individual participation in intergroup encounters in black howler monkeys (Alouatta pigra) and tufted capuchin monkeys (Sapajus nigritus). Black howlers responded with longer vocal displays during encounters with neighbours with an equal number of resident males, while tufted capuchins increased their participation with increasing relative male group size. Within each species, males and females responded similarly to varying numerical odds, suggesting that despite pay-off asymmetries between males and females, both sexes were similarly influenced by numerical asymmetries in deciding to participate in collective group defence. Whereas the outcome of contests among tufted capuchins was determined by relative male group size, reflected in a pronounced intergroup dominance hierarchy, the absence of dominance relationships among black howler groups may have provoked prolonged vocal displays in order to assess rival groups with matching competitive abilities.

Willingness to provide is more important than ability to provide: women’s choice of a long-term male partner

According to evolutionary theory, women select men who have the ability and willingness to provide for their offspring. However, a man with an excellent resource-holding potential might distribute his resources to another woman or pursue short-term sexual opportunities with a variety of women. Indeed, the ability of a woman to identify a man’s ability to provide is useless if his resources are distributed to another woman or to his own mating efforts. Therefore, the ability to ascertain the willingness of men to provide for long-term partners is important to women. Although such willingness is not directly related to genetic quality, the ability to provide might be based on genetic factors and function as an indicator of “good genes.” We asked women during either their high- or low-fertility period to rate the desirability of six fictitious men described in a vignette that addressed their ability and willingness to gather and share resources. Ability and willingness to provide were less important when women considered short-term relationships, but these two factors affected mate preference for long-term relationships. Women did not value the absolute value of their mates’ long-term ability to provide, and they placed more importance on their willingness to share than on their ability to accumulate resources. Women’s menstrual cycle did not affect this pattern of preference.

Aggressiveness as a component of fighting ability in pigs using a game-theoretical framework

Understanding animal contests has benefited greatly from employing the concept of fighting ability, termed resource-holding potential (RHP), with body size/weight typically used as a proxy. However, victory does not always go to the larger/heavier contestant and the existing RHP approach thereby fails to accurately predict contest outcome. Aggressiveness, typically studied as a personality trait, might explain part of this discrepancy. We investigated whether aggressiveness forms a component of RHP, examining effects on contest outcome, duration and phases, plus physiological measures of costs (lactate and glucose). Furthermore, using the correct theoretical framework, we provide the first study to investigate whether individuals gather and use information on aggressiveness as part of an assessment strategy. Pigs, Sus scrofa, were assessed for aggressiveness in resident–intruder tests whereby attack latency reflects aggressiveness. Contests were then staged between size-matched animals diverging in aggressiveness. Individuals with a short attack latency in the resident–intruder test almost always initiated the first bite and fight in the subsequent contest. However, aggressiveness had no direct effect on contest outcome, whereas bite initiation did lead to winning in contests without an escalated fight. This indirect effect suggests that aggressiveness is not a component of RHP, but rather reflects a signal of intent. Winner and loser aggressiveness did not affect contest duration or its separate phases, suggesting aggressiveness is not part of an assessment strategy. A greater asymmetry in aggressiveness prolonged contest duration and the duration of displaying, which is in a direction contrary to assessment models based on morphological traits. Blood lactate and glucose increased with contest duration and peaked during escalated fights, highlighting the utility of physiological measures as proxies for fight cost. Integrating personality traits into the study of contest behaviour, as illustrated here, will enhance our understanding of the subtleties of agonistic interactions.

Nest size preferences and aggression in sand gobies (Pomatoschistus minutus)

In animal competition, resource holding potential (RHP) and resource value are two important factors determining the level of aggression and the outcome of contests. One valuable resource among nest-brooding animals that is subject to intense competition is a suitable nest substrate. Sand goby males (Pomatoschistus minutus) rely on finding good nest substrates, but the strategies vary between regions. We first investigated the nest size preferences in sand gobies from Kalmar Sound, a brackish area of the Baltic Sea with a shortage of suitable shells for nest construction and few invertebrate nest predators. Males expressed clear preference for larger nest substrates regardless of the male’s own size. To manipulate resource value, we provided males with large or small nests and tested if this and/or RHP affected aggression during nest defence. Resource value (a preferred large nest vs an unpreferred small nest) had no effect on aggression. However, RHP (total length of the resident male) had a significant effect. Larger males were more aggressive than smaller ones when matched against an opponent of the same size, suggesting that resident males acted according to own RHP.

Giant Australian cuttlefish use mutual assessment to resolve male-male contests

Game theory models provide a useful framework for investigating strategies of conflict resolution in animal contests. Model predictions are based on estimates of resource-holding potential (RHP) and vary in their assumptions about how opponents gather information about RHP. Models can be divided into self-assessment strategies (energetic war-of-attrition, E-WOA; cumulative assessment model, CAM) and mutual assessment strategies (sequential assessment model, SAM). We used laboratory-staged contests between male giant Australian cuttlefish, Sepia apama, to evaluate RHP traits and to test game theory models. Mantle length was a key indicator of RHP because it predicted contest outcome, whereby larger individuals were more likely to win a contest. Winners and losers did not match behaviours, ruling out the E-WOA. There was no relationship between contest outcome, duration and escalation rates, arguing against the CAM. Persistence to continue a contest was based on RHP asymmetry, rather than loser and/or winner RHP, providing support for the SAM. Motivation to fight was determined from a male's latency to resume a contest following the introduction of a female during a contest. The latency to resume a contest was negatively related to the size of the focal male and positively related to the size of their opponent. These results show that competing males are able to gather information concerning RHP asymmetries, providing support for mutual assessment. Furthermore, males showed significant behavioural differences in their responses to relatively larger than to relatively smaller opponents. Using an integrative approach, our study provides a well-substantiated example of mutual assessment.