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Codivergence of sexual traits and mate preferences can lead to assortative mating and subsequently reproductive isolation. However, mate choice rarely operates without intrasexual competition, and the effects of the latter on speciation are often overlooked. Maintaining trait polymorphisms despite gene flow and limiting assortative female preferences for less-competitive male phenotypes are two important roles that male–male competition may play in the speciation process. Both roles rely on the assumption that male–male competition limits the expression of divergent female preferences. We tested this assumption in the highly color-polymorphic strawberry poison frog (Oophaga pumilio). Females prefer males of the local color, suggesting that reproductive isolation may be evolving among color morphs. However, this inference does not account for male–male competition, which is also color-mediated. We housed females with two differently colored males, and compared reproductive patterns when the more attractive male was the territory holder versus when he was the nonterritorial male. Females mated primarily with the territory winner, regardless of coloration, suggesting that when a choice must be made between the two, male territoriality overrides female preferences for male coloration. Our results highlight the importance of considering the combined effects of mate choice and intrasexual competition in shaping phenotypic divergence and speciation.

Population-level trait variation within species plays an often-overlooked role in interspecific interactions. In this study, we compared among-individual variation in web phenotype and foraging behavior between native black widows (Latrodectus hesperus) and invasive brown widows (Latrodectus geometricus). We staged repeated contests whereby native widows defended their webs against intruders of both species to 1) investigate how trait variation mediates web contest outcome among native widows and 2) see whether widow behavior differs in response to an invasive spider. In only one trait, the average number of foraging lines, did black widows differ from brown widows. Black widow residents that built more structural lines were more likely to successfully defend their webs from conspecific intruders (i.e., be the sole spider remaining on the web postinteraction). This association between web structure and contest outcome did not exist in trials between black widows and invasive brown widows; however, in interspecific interactions, these same residents were more likely to have intruders remain on the web rather than drive them away. Surprisingly, brown widows did not usurp black widows. Brown widows were never observed signaling, yet black widow residents signaled equally to intruders of both species. Our results suggest that among-individual variation among native species can influence the response toward invasive competitors and outcome of these interactions.

How animals decide to withdraw from contests is central to understand the evolution of fighting behavior. Game theory models suggest 2 major types of decision criteria: 1) self-assessment, where individuals withdraw when they reach a cost-threshold determined by their own fighting ability that may or may not be affected by injuries, or 2) mutual assessment, where the decision is based on information about the relative fighting ability of the opponents. Many empirical studies have assumed that opponents use a single strategy throughout the whole fight. However, they often find partial support for a specific model. This might be due to individuals changing their strategy between phases of a contest. In this work, we addressed this issue by evaluating if males of the cricket Melanotes ornata switch their assessment strategy between phases. We used hind femur length as a proxy for fighting ability, as it was the attribute most strongly associated with contest outcome. Overall fight duration was positively associated with the loser’s femur length and negatively associated with the winner’s femur length, while the probability of escalation to physical aggression was negatively related to the difference in femur between opponents. However, such relationships held only at the first contest phase. During the escalated phase, fight duration was only correlated (although weakly) with femur length of losers. These results indicate that M. ornata males perform mutual assessment in the initial phase but switch their assessment strategy when fights escalate, suggesting a single strategy does not correctly explain how contests are settled.

Lay Summary How do animals decide to give up on a fight? Fighting ability is central to the answer, and we may be assuming that it increases linearly with body size, when that may not be entirely true. Here, we adapt a framework for analyzing fights to allow fighting ability to increase exponentially with body size. We show that when that assumption is considered, the answer may differ.

Intraspecific variation in behavior has largely been neglected by community ecologists to date. Recently, however, a number of studies demonstrated that intraspecific variation can have profound consequences for species interactions and thereby alter community dynamics in solitary organisms. Here, we study how intraspecific variation in collective behaviors (also called "collective personalities") affects the outcome of resource contests between 2 co-occurring species of ants, Temnothorax longispinosus and T. curvispinosus. Our results revealed that intraspecific variation in colonies’ exploration behavior and aggressiveness predicts the outcome of interspecific contests for food and nest sites. How exploratory behavior affected the outcome of the foraging and nest site contests depended on the species: exploratory behavior seemed to enhance performance in foraging contests in T. curvispinosus but diminish it in T. longispinosus. More interestingly, whether a species was successful in nest site contests depended not only on its collective personality but also on the personality of its opponent colony. Temnothorax longispinosus experienced greater success if its opponent colony had similar exploratory tendencies to its own. In contrast, T. curvispinosus performed best when its opponent colony exhibited a contrasting exploratory tendency to its own. Our data demonstrate that intraspecific variation in colony behavior can have consequences for contest outcomes and ensure that no one species or behavioral strategy consistently experiences superior success. This, in turn, might help to maintain variation in collective behavior in multiple interacting populations and prevent competitive exclusion of one of the species.

During agonistic contests, males may assess the relative differences between their own and their opponent’s resource-holding potential or simply persist in a contest according to an internal threshold. Game theory models such as the sequential assessment model, energetic war of attrition, and the cumulative assessment model were developed to place assessment strategy in an evolutionary framework. Distinguishing between these models requires one to document contest structure and test predictions of the relationship between the size of the contestants and contest duration and probability of escalation. This study focused on the escalating fighting behavior and competitive assessment strategy of the New Zealand giraffe weevil (Lasiorhynchus barbicornis). Aggressive fighting occurred frequently between males of all sizes, and body length (which included rostrum length) was an important predictor of contest outcome. Contest duration was negatively related to body length difference and the size of the winning male and showed a nonsignificant positive relationship with loser size. The probability of fight escalation showed a significant negative relationship with body length difference, a positive relationship with loser size, and a nonsignificant negative relationship with winner size. Contests were also found to escalate, but not de-escalate, and behavioral matching did not occur during all phases. Male behavior during contests was therefore most consistent with mutual assessment under the sequential assessment model.

Contest behavior forms an important part of reproductive investment. Life-history theory predicts that as individuals age and their residual reproductive value decreases, they should increase investment in contest behavior. However, other factors such as social experience may also be important in determining age-related variation in contest behavior. To understand how selection acts on contest behavior over an individual’s lifetime, it is therefore important to tease apart the effects of age per se from other factors that may vary with age. Here, we independently manipulate male age and social experience to examine their effects on male contest behavior in the burying beetle Nicrophorus vespilloides. We found that social experience, but not age, influenced male contest behavior but that these changes in behavior did not alter contest outcomes. Male size (relative to his opponent) was overwhelmingly the most important factor determining contest outcome. Our results suggest that in systems with high variation in fighting ability among males, there may be little opportunity for selection to act on factors that influence contest outcomes by altering motivation to win.

Conspicuous color signals are commonly used by a wide diversity of animals to advertise some specific aspect of their competitive ability. In particular, orange and red colors are often used as an aggressive signal to potential rivals. The iconic Australian frillneck lizard (Chlamydosaurus kingii) has a large and extensible frill that varies geographically in the extent of yellow, orange, and red present. Focusing on the red-orange lizards found in Western Australia, we first established that, in contrast to most lizards studied to date, the red-orange–colored frill is carotenoid rather than pterin based. Second, we measured chromatic and achromatic aspects of male frills before staging dyadic contests between males to determine whether color is used to signal fighting ability. Both chromatic and achromatic measures of the red-orange patches on the lizard’s frills, as well as similarly colored patches on their throats, were reliable predictors of competitive ability; males possessing more colorful displays dominated size-matched competitors in dyadic contests. Apart from large differences in body size and mass (>10%), no other colorimetrics (e.g., white patches), frill traits (e.g., size, relative and absolute patch sizes), or morphological measures (e.g., head size, bite force) were found to predict the outcome of contests. To the best of our knowledge, this is the first example of carotenoid-based patches signaling male fighting ability in a lizard.

Adult animals can eavesdrop on behavioral interactions between potential opponents to assess their competitive ability and motivation to contest resources without interacting directly with them. Surprisingly, eavesdropping is not yet considered as an important factor used to resolve conflicts between family members. In this study, we show that nestling barn owls (Tyto alba) competing for food eavesdrop on nestmates' vocal interactions to assess the dominance status and food needs of opponents. During a first training playback session, we broadcasted to singleton bystander nestlings a simulated vocal interaction between 2 prerecorded individuals, 1 relatively old (i.e., senior) and 1 younger nestling (i.e., junior). One playback individual, the "responder," called systematically just after the "initiator" playback individual, hence displaying a higher hunger level. To test whether nestlings have eavesdropped on this interaction, we broadcasted the same prerecorded individuals separately in a subsequent playback test session. Nestlings vocalized more rapidly after former initiators' than responders' calls and they produced more calls when the broadcasted individual was formerly a junior initiator. They chiefly challenged vocally juniors and initiators against whom the likelihood of winning a vocal contest is higher. Owlets, therefore, identified the age hierarchy between 2 competitors based on their vocalizations. They also memorized the dynamics of competitors' previous vocal interactions, and used this information to optimally adjust signaling level once interacting with only 1 of the competitor. We conclude that siblings eavesdrop on one another to resolve conflicts over parental resources.

It has recently been proposed that dominance perceptions in men function, at least in part, to reduce the potential costs of within-sex competition for resources, and that sensitivity to cues of men’s dominance is greatest among men who would incur the largest costs if they engaged in competition with rivals indiscriminately (i.e., low-dominance men). Consistent with these proposals, we found that men randomly allocated to priming conditions in which they imagined losing confrontations with other men subsequently demonstrated greater sensitivity to dominance cues when assessing the dominance of men’s faces than did men randomly allocated to priming conditions in which they imagined winning confrontations. No equivalent effect occurred for perceptions of men’s trustworthiness, suggesting that the priming effect observed for dominance judgments may be somewhat specific to competition-related perceptions. Collectively, these findings suggest that men’s perceptions of other men’s dominance are facultative, changing in response to contextual cues, such as the outcomes of recent confrontations. Such responses could play a critical role in calibrating men’s dominance sensitivity according to their recent experiences and are consistent with findings from experiments with other species in which the outcome of prior confrontations modulated competition-related behaviors. Key words: aggression, dominance, fighting experience, within-sex competition. [Behav Ecol]

In animal contests, opponents often perform repeated displays that are assumed to advertise their stamina and thereby fighting ability. However, given the severe time and energetic constraints imposed by such displays, we hypothesized that separate signals, performed early in a fight, may be used to reduce subsequent costs. We investigated whether the amount of cheliped flicks performed by a defending hermit crab during a prefight assessment period was indicative of the performance capacity of the defender and whether the frequency of flicks predicted the subsequent outcome of contests. Defenders that won fights by retaining their shells produced more vigorous flicking than those that were evicted. There was a strong trend between the rate of flicking performed by the defender and the maximum speed attained in performance capacity trials. Further, the rate of flicking was positively correlated with the duration of pauses that attackers left between bouts of shell-rapping, an indicator of attacker fatigue. Thus, these displays might inform the attacker about the potential persistence of the defender and therefore about the likely costs that the attacker will incur. Indeed, the rate of flicking performed by defenders early in the fight strongly predicts the eventual outcome of the contest. Key wor ds: contest, hermit crab, performance, resource-holding potential, signal. [Behav Ecol]

International audience; Contests for indivisible resources are often settled on the basis of the asymmetry that exists between contestants in their ownership status: Owners (i.e., individuals already possessing a resource) usually retain the resource when facing intruder competitors. This owner advantage is predicted to be more pronounced as the asymmetry in ownership status accentuates: when the residency period increases, the probability of owners keeping their resource should increase and contestant aggressiveness should be reduced. In the present study, we tested this prediction in a parasitoid wasp, Eupelmus vuilleti, where females fight for hosts, larvae of Callosobruchus maculatus, on which to lay their eggs. To do so, we experimentally varied the arrival times of 2 conspecific females on a host, generating different asymmetries in ownership status between them. We further explored the strategies adopted by intruder females according to the stage reached by the owners in their host exploitation sequence. When the residency period was short, both females fought and contests were won by the female valuing more greatly the host, rather than by the owner per se. The loser left the host vicinity and the winner exploited the host alone. In contrast, when the residency period was long (the owners were ready to parasitize the host), the intruders did not leave but instead waited for the departure of the resident female in order to superparasitize the host. This "waiting strategy" seems particularly adaptive in this species, in which females tend to prefer already parasitized hosts to healthy hosts. Key words: contest resolution, Eupelmus vuilleti, female egg load, ownership status, resource value. [

Contest behavior, where individuals compete directly against one another for access to limited resources, is widespread across animal taxa. In many cases, contests are settled though the use of noninjurious behavior such as agonistic signals and even fights that involve weapons are often resolved through processes of assessment and strategic decision making. Here, we determine the role of these "decision rules" during staged contests in a simple animal, the beadlet sea anemone Actinia equina using a recently suggested approach of analyzing 1) traits linked to resource holding potential (RHP), 2) relationships between RHP and contest duration, and 3) contest dynamics. Depending on the activities used in the encounter, RHP, is linked to overall body size, the size of stinging nematocyst weapons, or by the ability to land blows on the opponent. Furthermore, changes in the intensity of aggression as the contest progresses indicate the use of 2 distinct types of self-assessment-based decision rules, which differ according to whether weapons are used in the contest. Therefore, these fights in animals that lack a centralized nervous system appear to involve the use of logical decision rules similar to those observed in contests in animals that are often assumed to be more "complex" in their behavior. Indeed, anemones appear to use different sources of information about incurred costs, depending on the intensity of the contest. Copyright 2011, Oxford University Press.

In social species that cooperatively defend territories the decision to retreat or attack in contests between groups is likely to depend on ecological and social factors. Previous studies have emphasized the importance of the encounter location or the size of competing groups on the outcome. In addition, the identity of the intruder, whether familiar or stranger, may also play a role. To test whether the same factors affect the resident group’s decisions already at the beginning of contests, we simulated intergroup encounters in banded mongooses (Mungos mungo). When spotting rival groups banded mongooses emit ‘‘screeching calls’’ which lead group members to bunch up. With playbacks of these calls, we tested how the groups’ response was affected by the following factors: 1) the location of the playback in relation to their territory (exclusive use vs. overlap); 2) the number of resident individuals; and 3) the origin of calls (neighbor vs. stranger) used. Subjects were more likely to approach the loudspeakers and arrive within 1 m of the speakers in the exclusive use zone than in the overlap zone. Moreover, larger groups tended to be more likely to move toward the loudspeakers and were also more likely to arrive there. The origin of calls used in the playbacks did not affect the groups’ responses. These findings exemplify the importance of the combined effect of location and group size on group decisions during impending intergroup contest. Key words: banded mongooses, group decision, group size, intergroup encounter, Mungos mungo, territory. [Behav Ecol]

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. Copyright 2010, Oxford University Press.

Winning aggressive social encounters can enhance the probability of future victories. This so-called winner effect occurs in diverse species and is thought to be an intrinsic phenomenon mediated by postencounter hormone release. Yet, recent evidence suggests the possibility that certain extrinsic factors also influence the winner effect’s formation within an individual, possibly by affecting the expression of hormone titers that follow a fight. We first investigated in the monogamous and territorial male California mouse (Peromyscus californicus) whether the effect of residency, an extrinsic factor, influences the winner effect’s formation and the endogenous secretion of testosterone and/or progesterone after a dispute. We found that California mice that acquire winning experience in unfamiliar physical locations do not form a full winner effect. Furthermore, this species does not experience a testosterone pulse after a fight in an unfamiliar cage. These findings indicate that environmental context can mediate the winner effect’s formation, possibly by affecting the expression of postencounter testosterone pulses. Second, we compared the winner effect of the California mouse to that of the white-footed mouse (Peromyscus leucopus), a close relative that is promiscuous and less-territorial. We found that, compared with California mice, white-footed mice exhibit neither a full winner effect, despite similar past winning experiences, nor a postencounter surge in testosterone. This finding suggests that these behavioral and physiological phenomena vary among even closely related species and are possibly linked to aspects of social biology, including the degree to which individuals of each species are territorial. Key words: aggression, Peromyscus, residency, social behavior, testosterone, winner effect. [Behav Ecol]

Models of dyadic contests for indivisible resources have predicted that the owner–intruder role distinction can suffice as a cue for evolutionarily stable resolution. This outcome may be ‘‘common sense’’ (prior owners retain the resource) or counterintuitively ‘‘paradoxical’’ (the intruder takes over), but the most recent models predict paradoxes to be an infrequent result, and there are also very few candidate examples provided by empirical study. Possible paradoxical outcomes were recently reported from the parasitoid wasp Goniozus legneri in which adult females compete directly for hosts. Here we provide further investigation, taking into account influences of contest ability (body size) and the value of the host to each contestant (correlated with the developmental stage of the owner’s brood). We additionally evaluate contest strategies in terms of respect for ownership as evidenced by attack behavior during contests. Goniozus legneri shows weak, and thus only partial, respect for role asymmetries: such mixed strategies are predicted by recent models that assume population-level feedback on resource value parameters. Contest outcomes are influenced by asymmetries in resource value and body size and are generally common sense. Instances of paradoxical contests remain predictably elusive. Key words: antibourgeois strategy, Goniozus legneri, maternal investment, paradoxical strategy, partial respect, resource value asymmetry. [Behav Ecol]

During conflict, males often assess their opponent’s fighting ability and motivation via dynamic signals. We conducted an interactive video playback study using male Jacky dragons, Amphibolurus muricatus, to determine which signalling strategy was the most effective at deterring aggression and eliciting submission. A 3D computer-animated lizard was used to present aggressive signals (push-up displays) and submissive ones (slow arm-waves). This approach reproduced natural display motor patterns precisely while controlling variation in morphology. Treatments all commenced with the stimulus lizard producing bouts of push-ups, but then diverged after the subject lizard’s responses, according to predetermined rules. Lizards attacked the stimulus more frequently when it responded to submission with slow arm-waves, revealing that their behavior during a contest is sensitive to social contingencies. Individuals that signal submission without retreating are likely to incur a receiver retaliation cost. In addition, assessment processes are surprisingly sophisticated, involving the monitoring of both an index signal (push-ups) and a conventional one (slow arm-waves) during a single interaction. Key words: Amphibolurus, interactive playback, signalling, submissive display, threat display. [Behav Ecol]

There are many examples of individuals forming coalitions to obtain or protect a valuable resource. We present an analytical model of coalition formation in which individuals seek alliances if they judge themselves too weak to secure the resource alone. We allow coalition seeking to carry an investment cost (θ) and let contest outcomes depend probabilistically on the relative fighting strengths of contesting parties, with effective coalition strength directly proportional to combined partner strength. We identify the evolutionarily stable strength thresholds, below which individuals within triads should seek a coalition. We show that if θ exceeds a critical value, then unilateral fighting over resources is an evolutionarily stable strategy (ESS). Universal (3-way) coalitions are also an ESS outcome if θ is less than a second critical value. Both of these extreme solutions are less likely to arise, the greater the variance in fighting strengths and the greater the benefit from dominating opponents. Our analysis also identifies intermediate solutions in which only the weaker individuals seek coalitions: only then can a true coalition (2 vs. 1) form. We characterize these ESSs and show that true coalitions are more likely to arise when the effective strength of a coalition is less than the sum of its individual strengths (antergy). Alliances in primates are characterized by antergy, high reliability of strength as a predictor of contest outcome, and high variability in strengths. These are precisely the conditions in which in our model most favors true coalition formation. Copyright 2007, Oxford University Press.

Animals advertise aspects of individual quality in a range of situations including during agonistic contests over access to resources. The advertisement can be produced by different types of signal, which can be broadly classified into ‘‘conventional signals’’ and ‘‘costly signals.’’ In both cases, the signals are thought to be honest such that any benefits to cheating are very limited due to prohibitive costs of advertising an inaccurately high level of quality. However, some individuals may benefit by low-level cheating in systems that are otherwise honest. Here, I test this possibility for a costly signal by analyzing residuals from relationships between a key parameter of signal magnitude and two measures of fighting ability from ‘‘shell fights’’ in hermit crabs. Contrary to the expectations for significant use of bluffing, individuals that performed at a greater magnitude than expected for their ability were more likely to win the encounter but used fewer repetitions than those that performed below the level expected for their ability. This indicates that the level of performance is primarily driven by the cost and that the functional significance of signal residuals in this case is that they provide information on several measures of fighting ability. Key words: contest, cost, deception, hermit crab, honesty, signal. [Behav Ecol]

Two rationales have been proposed verbally for the function of victory displays, which are performed by the winners of contests but not by the losers. The ‘‘advertising’’ rationale is that victory displays are attempts to communicate victory to other members of a social group that do not pay attention to contests or cannot otherwise identify the winner. The ‘‘browbeating’’ rationale is that victory displays are attempts to decrease the probability that the loser of a contest will initiate a future contest with the same individual. We formally explore the logic of these rationales with game-theoretic models. The models show that both rationales are logically sound; however, all other things being equal, the intensity of victory displays will be highest through advertising in groups where the reproductive advantage of dominance is low and highest through browbeating in groups where the reproductive advantage of dominance is high. Key words: bystander effects, game theory, signaling, victory displays. [Behav Ecol]

In males that compete aggressively for females, size and age may determine which males obtain access to these females. In the present study, we use the crab spider, Misumena vatia, a species with males that do not grow after becoming sexually mature adults, to test the hypothesis that age affects the success of males competing for access to females. M. vatia is an excellent species to test this hypothesis because it is possible to disentangle age from size, characters that typically vary together in the species usually tested. We staged encounters between similar-sized older and younger adult male M. vatia in the presence of a female to determine the role of age in male access to females. Encounters between the males occurred during 63.3% of these pairings. Younger males won significantly more (70.2%) of the encounters than did older ones, but did not initiate significantly more encounters than did older ones (62.5%). Although older males won only 29.8% of these encounters, they initiated significantly more (76.5%) of them than predicted by chance. This design also allowed us to test Parker’s hypothesis that older individuals should exhibit a higher level of aggression than younger ones. However, attacks by younger males were most likely to include extensive bodily contact, whereas attacks by older males involved significantly less contact. These results counter the frequent assertion that older individuals usually prevail over younger ones in contests for access to females, and that older males are more likely to engage in highly overt aggression than are younger ones. Aging may decrease reproductive opportunities and success rates of male M. vatia, affecting as many as nearly one-fourth of their encounters. Key words: age, crab spider, male contest, Misumena, size. [Behav Ecol 15:883–888 (2004)]

Selection usually acts differently on males and females during intrasexual competition for resources and/or mates. Nevertheless, agonistic behavior has been examined both theoretically and empirically mostly in males. Our research questions whether males and females follow the same rules of engagement in intrasexual contests as predicted by the sequential assessment model (SAM). The SAM predicts negative correlations between contest intensity and duration and the magnitude of asymmetry in resource holding power (RHP) between the contestants, such that the most escalated contests are those between similarly endowed individuals. We staged male and female intrasexual contests with varying degrees of body size asymmetry under a round robin design using the monogamous Texas cichlid fish (Herichthys cyanoguttatum) as a study case. We used Mantel's matrix analysis to compare how the behavioral content, duration, structure, and outcome of male and female contests were affected by the relative body size of the contestants. In the case of males, relative size in each contest predicted outcome, duration, and frequency of conventional and escalated behaviors according to prevailing theory. Female contest structure and outcome, however, were not predicted by the relative size of contestants. We discuss our results in terms of other asymmetries that might be important in structuring female contests, and we propose potential approaches to study female--female aggression. Copyright 2004.

When foraging in groups, animals frequently use either scramble or contest tactics to obtain food at clumps found by others. The question of which competitive tactic should be used has been addressed from two different perspectives: a simple optimality approach and a game theoretic approach. Surprisingly, both approaches make strikingly different predictions about how percapita frequency of aggression within groups should change as a function of food abundance and competitor density. Resource defense theory typically predicts dome-shaped relationships between the per-capita frequency of aggression and both food abundance and competitor density, whereas game theoretic models predict an increase in aggression with competitor density and a decline in aggression with increased food abundance. We developed a game theoretic model to explore whether the predictions of resource defense theory and the game theoretic approach can be reconciled. Our model assumes that players have different competitive abilities and can adopt roles of either finder or joiner that affect the quantity of food that can be gained from a food clump. In accordance with earlier game theoretic models, we predict an increase in aggression with competitor density when animals compete by pair-wise contests. However, when food clumps can be challenged by more than one competitor, both the costs and benefits of defending increase with competitor density, which results in a dome-shaped relationship between the two variables. Our model predicts that aggression should always decrease as the density of food clumps increases. Key words: aggression, competitor asymmetry, evolutionarily stable strategy model, finder’s advantage, foraging groups, resource defense. [Behav Ecol 14:2‐9 (2003)]

Game theory models predict that fighting ability should be more important in contest outcome when the payoffs of winning are high for both contestants, and ownership should be more important when payoffs are low. Male Magellanic penguins (Spheniscus magellanicus) provide an opportunity to test these predictions in a natural setting because payoffs of winning are higher for penguins fighting before egg laying and lower for penguins fighting after egg laying, allowing the prediction of differences in who should win and lose. We watched an area of approximately 2000 Magellanic penguin nests from 1992 to 1996 at Punta Tombo breeding colony, Argentina; we quantified fighting behavior, banded contestants, measured their body size (here used as an index of fighting ability), determined ownership status when possible, and monitored their reproductive success. We determined that male Magellanic penguins fought for nests and mates. As theory predicts, before egg laying, body size difference was more important than ownership as a predictor of contest outcome and fight duration. After egg laying, owners won fights, and size did not predict who won or how long they fought. Our comparisons of nest ownership, nest quality, and chicks fledged by winners and losers suggested that our predictions on the change in benefits of winning before and after egg laying were correct. We conclude that game theory models are useful in predicting who won or lost fights in male Magellanic penguins and that ultimate benefits of winning fights are related to fitness. Key words: aggression, fight outcome, fighting, game theory, penguins, Spheniscus magellanicus. [Behav Ecol 13:462–466 (2002)]

Although intrasexual contests generally favor bigger or stronger individuals, the relevance of body size to war of attrition-type disputes between weaponless animals such as butterflies is unclear. In this study I aimed to investigate the significance of size in this context by studying territorial contests in Hypolimnas bolina (L.), a species that exhibits consistent seasonal plasticity in body size. In this species adult age is positively correlated with large size in spring but with small size in autumn. This shift allowed independent evaluation of the relevance of each variable (size and age) to intrasexual contest success. Observation of a population of marked individuals indicated that only age appeared important, with the winners of pair-wise contests significantly older than losers in both seasons, and with contests lasting longer when the age difference between the combatants was small. Age was also linked to residency; residents won 99% of all contests. This study suggests that size does not matter in these aerial disputes, but age and residency do. It is not yet possible to determine whether older butterflies are intrinsically better competitors, or whether they simply have greater opportunity to find a vacant territory. Key words: aggression, war of attrition, nymphalid, Lepidoptera. [Behav Ecol 11:591–596 (2000)]

Although aggressive conflicts over hosts occur among females in many species of insect parasitoids, few studies have examined the mechanisms by which these contests are resolved. In Trissolcus basalis, a parasitoid of pentatomid bug egg masses, females co-exploiting an egg mass (patch) encounter one another repeatedly and fight for possession of the patch. We investigated the resolution of pairwise contests by experimentally varying the release time of females and the size of the patch. Logistic regression showed that the female arriving first on the patch was more likely to win both the first agonistic encounter and to retain overall possession of the patch. This advantage to the first female suggests a resource-correlated asymmetry in favor of the first female, due to her having invested more offspring in the patch. Although escalations were more common when the asymmetry in arrival times was small, the majority of encounters within all contests were nevertheless resolved without escalated fighting, with the resident attacking and the intruder backing down. Thus contest resolution basically followed a ‘‘bourgeois’’ rule. Residents tolerated intruders more frequently when the patch size was larger and the second female was released later, illustrating the trade-off faced by residents between defending the patch and continuing to exploit it. Key words: agonistic behavior, asymmetries, bourgeois strategy, egg parasitoid, Trissolcus basalis. [Behav Ecol 10:122‐127 (1999)]

Recent theoretical studies have drawn attention to the importance of understanding the costs females experience during mate choice and mating and how females resolve the trade-offs presented by such costs. In garibaldi damselnsh (Hypsypops rubicundus) females defend permanent feeding and shelter territories and must leave their territories to search for and spawn with nesting males. Both mate searching and spawning occur in bouts, separated by returns to the territory. I used focal female observations to test predictions of the hypothesis that such behavior is a means of minimizing the amount of food lost to competitors that enter the female's territory while she is searching for or spawning with males. Consistent with this hypothesis, there was a strong likelihood that the number of intruders entering the territory would increase linearly, and hence their total impact exponentially, with time away. In addition, the average duration of searching bouts and the duration of a spawning bout were significantly inversely related to a measure of territorial intruder pressure. Most intruders were heterospeedfic food competitors; incidence of intrusion by conspecifics was rare, and intruding conspecifics did not contest the owner upon her return. In addition, the time females spent in their territories before beginning another bout of searching was not positively related to the duration of the previous boutThus, there, is no support for the alternative hypotheses that returning to the territory is a means of preventing takeover of the territory by conspecifics or is the result of fatigue.

The cost of performing an agonistic behavior, or tactic, will have consequences for an individual's rate of cost accrual, the tactic's evolutionary stability if used as an assessment signal, and its pattern of use in the behavioral choreography of a contest. Few studies have attempted to quantify the costs of fighting, particularly with regard to energy expenditure. Flow-through respirometry revealed that house cricket males can expend energy at relatively high rates when fighting (more than eight times resting levels) depending on the particular tactic performed. Acoustic signalling (striduladon) constituted the least costly of seven measured agonistic tactics, while wrestling with an opponent, the most energetically costly tactic, consumed oxygen at a net rate more than 40 times that of striduladon. Low-cost tactics are used by opponents more frequently than more costly tactics, providing evidence for an escalating tactical convention based on energetic costs. The moderate energetic cost of some tactics suggests they may function as reliable signals in the assessment of wrestling ability. Net energy costs per contest increased linearly with contest duration for both contest winners and losers, but winners tended to expend more energy per contest than losers. The likely fitness effects of energy expended while fighting are discussed. The results of this study indicate that energy expenditure is an important cost shaping contest strategies in Achtta dtmtstxau.

it or find femininity attractive where women do not benefit from contest competition—and initial research suggests support for this hypothesis (Scott, Pound, Stephen, Clark, & Penton-Voak 2010; Snyder, Fessler, Tiokhin, Frederick, Lee, & Navarrete 2011; Stone 2011). The reflection prompted by this review presents an opportunity to clarify our questions— including explaining the trait before we explain preferences for it.

There are two distinct questions at the heart of the facial masculinity literature—the function of the trait, and women’s preferences for it. I argue that we should establish the former before we explain the latter. Women’s preferences for facial femininity indicate that we cannot presume attractiveness explains selection for secondary sexual traits like facial masculinity. A new direction in research on sexual selection in humans. This is a timely and much needed critical evaluation of the support for the immunocompetence hypothesis generally, and of the trade-off hypothesis specifically. There are 2 questions at the heart of this literature, and we have been led astray by asking only 1 of them. Facial masculinity is a secondary sexual trait, which means it evolved because it provided some advantage in mating competition (Andersson 1994). If we are to understand when and why women find masculinity attractive, our explanation ought to be informed by the function of the trait. Emphasizing the former question to answer the latter can lead to problems, as was made clear to me in the review article. In the section, “Female responses to masculinized stimuli may reflect preferences for competitive mates,” the authors must make their case for why an aggressiveness hypothesis can better account for women’s attraction to feminized faces than the trade-off hypothesis. And yet—men evolved masculine faces. Explaining women’s preferences for femininity cannot be the complete story, because they cannot explain selection for masculinity. This, of course, lends support for an aggressiveness hypothesis, which parsimoniously explains the existence of the trait as well as women’s aversion to it. Women’s preferences for facial femininity suggest that contest competition and female choice do not necessarily select for the same traits. Different sexual selection mechanisms indeed select for different kinds of traits, and can result in sexual selection for a variety of traits that are unattractive. Attractiveness research on secondary sexual traits should then begin not by explaining preferences, but by explaining the trait. To best understand when and why women find a secondary sexual trait attractive, we ought first to understand what the trait is for—because it may not be for attracting women. Accordingly, discovering which sexual selection mechanisms are responsible for men’s and women’s secondary sexual traits is of paramount importance for future research on sexual selection in humans (e.g., Puts 2010). This perspective predicts that if facial masculinity was selected for use in contest competition, women should find masculine mates attractive in contexts where contest competition predicts benefits to women, and either ignore it or find femininity attractive where women do not benefit from contest competition—and initial research suggests support for this hypothesis (Scott, Pound, Stephen, Clark, & Penton-Voak 2010; Snyder, Fessler, Tiokhin, Frederick, Lee, & Navarrete 2011; Stone 2011). The reflection prompted by this review presents an opportunity to clarify our questions— including explaining the trait before we explain preferences for it.