Outcome Of Fights Research Articles

Weapon Performance, Not Size, Determines Mating Success and Potential Reproductive Output in the Collared Lizard (Crotaphytus collaris)

In territorial polygynous taxa, reproductive success reflects phenotypic variation. Using Crotaphytus collaris, a sexually dimorphic lizard in which males use the head (i.e., jaws and associated musculature) as a weapon when territorial interactions escalate to fights, we tested the hypothesis that weapon performance (i.e., bite force) is a better predictor of fitness than body or weapon size. Bite-force performance predicted the number of female home ranges overlapped, estimated mating success, and potential reproductive output. However, no body or weapon size measure correlated with these estimates of fitness, and only one weapon dimension (head width) correlated with bite force. These results indicate that weapon performance has far stronger effects on fitness than body or weapon size, likely because it directly influences fight outcomes. As such, it is desirable that the use of morphology as a proxy for performance and its presumed extensions to fitness be based on empirical morphology-performance relationships.

Alternative Male Mating Behaviors Dependent on Relative Body Size in Captive Oval Squid Sepioteuthis lessoniana (Cephalopoda, Loliginidae)

We observed the reproductive behavior of the oval squid Sepioteuthis lessoniana in captivity. The male used three different mating behaviors: male-parallel (MP), male-upturned (MU) and sneaking. Male competition over females frequently occurred before and during the female egg-laying period, and the outcome of most fights depended on male body size. Larger males guarded their partners from other males and performed MP mating during the egg-laying period of the paired females. In contrast, there was no pairing and mate guarding in MU mating and sneaking, which were adopted by smaller subordinate males as alternative tactics outside female egg-laying period and during the period, respectively. MP matings were 95% successful, but more than half of MU matings were unsuccessful. Higher mating success in MP mating was achieved through pairing, whereas males in MU mating were less successful because mating attempts without pair formation were often foiled by escape of the female. Sneaking was successful in all cases but occurred less frequently. Spermatophores were attached at the opening of the oviduct in MP mating, whereas they were attached around the female buccal membrane in MU mating and sneaking. Considering the route of egg transportation, higher fertilization success can be expected in MP mating because of the advantageous location of the attached spermatophores. Our results suggest that MP mating is used by larger, paired males during the female egg-laying period, and that MU mating and sneaking are alternative tactics adopted by smaller, subordinate males. These alternative mating behaviors would be conditional strategy dependent on relative body size, because some individual males displayed both MP and MU mating behaviors.

Weapon Performance, Not Size, Determines Mating Success and Potential Reproductive Output in the Collared Lizard (Crotaphytus collaris)

In territorial polygynous taxa, reproductive success reflects phenotypic variation. Using Crotaphytus collaris, a sexually dimorphic lizard in which males use the head (i.e., jaws and associated musculature) as a weapon when territorial interactions escalate to fights, we tested the hypothesis that weapon performance (i.e., bite force) is a better predictor of fitness than body or weapon size. Bite‐force performance predicted the number of female home ranges overlapped, estimated mating success, and potential reproductive output. However, no body or weapon size measure correlated with these estimates of fitness, and only one weapon dimension (head width) correlated with bite force. These results indicate that weapon performance has far stronger effects on fitness than body or weapon size, likely because it directly influences fight outcomes. As such, it is desirable that the use of morphology as a proxy for performance and its presumed extensions to fitness be based on empirical morphology‐performance relationships.

Bridging the gap between mechanistic and adaptive explanations of territory formation

How animals divide space can have fundamental implications for the population dynamics of territorial species. It has recently been proposed that space can be divided if animals tend to avoid fight locations, rather than the winner of fights gaining access to exclusive resources, behaviour that generates exclusive territories in two-dimensional space. A game-theory model has shown that this avoidance behaviour can be adaptive, but the adaptiveness has not been investigated in a spatially realistic context. We present a model that investigates potential strategies for the acquisition of territories when two-dimensional space must be divided between individuals. We examine whether exclusive territories form when animals avoid all encounters with others, or only those encounters that have led to losing fights, under different fighting costs and population densities. Our model suggests that when fighting costs are high, and the population density is low, the most adaptive behaviour is to avoid fight locations, which generates well-defined, exclusive territories in a population that is able to resist invasion by more aggressive strategies. Low fighting costs and high population densities lead to the break-down of territoriality and the formation of large, overlapping home ranges. We also provide a novel reason as to why so-called paradoxical strategies do not exist in nature: if we define a paradoxical strategy as an exact mirror-image of a common-sense one, it must respond in the opposite way to a draw as well as to wins and losses. When this is the case, and draws are common (fight outcomes are often not clear-cut in nature), the common-sense strategy is more often adaptive than a paradoxical alternative.

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

In many species males that tend to win fights against other males are more attractive to females. There are three ways in which male fighting ability and attractiveness may be associated: (1) attractiveness and fighting ability are influenced by the same underlying traits (e.g., body size), (2) females prefer males that have directly observed winning fights, or (3) winning previous fights indirectly improves a male's chance of being preferred by females. The last possibility may arise as a consequence of the “loser effect”; in many species when a male loses a fight his probability of losing subsequent fights increases. There are, however, no studies testing whether such a “loser effect” also influences male attractiveness. Here we show that male attractiveness and fighting ability are positively correlated in the house cricket, Acheta domesticus. Our experiment was designed so that females could not directly observe the outcome of fights, thus eliminating possibility (2) above. We then tested between possibilities (1) and (3) by making use of the fact that in some cricket species the “loser effect” can be eliminated experimentally by ‘shaking’ a male and stimulating the motor program for flying. We showed that in A. domesticus ‘shaking’ does affect the outcome of subsequent fights. Males that had won two previous fights were less likely to win a fight after being ‘shaken’ than when subject to a control treatment. In contrast, males that had lost two previous fights were more likely to win a fight after being ‘shaken’ than when they were not shaken. There was, however, no effect of ‘shaking’ on male attractiveness. We conclude that the “loser effect” does not alter the tendency for large, dominant males to be attractive to females. Instead, it appears that there are traits correlated with both fighting ability and attractiveness. One such trait is body size. Fight winners were significantly larger than losers and attractiveness was positively correlated with male body size.

The influence of weaning age on post-mixing agonistic interactions in growing pigs

The effects of differences in weaning age on agonistic interactions between pigs after regrouping were investigated, studying 47 piglets from six litters weaned either between 9 and 12 days of age (EW, n=24) or between 21 and 23 days of age (CW, n=23). At 9 weeks of age, both EW and CW animals were regrouped into four pens based on their weight (six EW, six CW/pen) and all agonistic interactions within EW pairs and within CW pairs were monitored until 3 days post-mixing. Results indicate that EW animals fought longer than CW pigs on day 1, while no effect of weaning age was found on subsequent days. Furthermore, whereas no significant effects of weaning age were found on the outcome of fights, on day 1, the number of fights not won by the initiator was greater for EW pigs. It is concluded that early weaning of piglets leads to a short-lasting increase in aggression after mixing. Possible mechanisms are discussed.

Housing immature domestic pigs in large social groups: implications for social organisation in a hierarchical society

Immature domestic pigs are increasingly housed in large social groups (>50 pigs) without an understanding of how they adapt to these conditions. At a conventional group size (typically 10–30 animals), pigs exhibit dominance relationships which are frequently established using physical assessments of strength and fighting ability and may include the use of aggressive behaviour. The relationships also rely on individual identification of group members and the recall and reinforcement of previous fight outcomes. This paper reviews the implications of a large group size for the establishment and long-term maintenance of dominance relationships in immature pigs. Evidence suggests that, in large groups, less reliance is placed on aggression during the immediate post-mixing phase than would be expected if the same proportion of dominance relationships are established using aggression in both large and small groups. This occurred despite an ability to distinguish between pen mates and non-pen mates. The energetic costs to a pig of establishing dominance relationships with a given proportion of group members is likely to increase with group size. It is considered whether these elevated costs place a ceiling on the number of fights a pig can engage in or whether they are able to assess dominance ability using passive means and thereby reduce the proportion of group members with which they fight. It is probable that a combination of these two routes is responsible for the limitation of aggression observed. Sub-grouping behaviour, investigated in large poultry groups, appears not to be adopted by pigs in response to a large group size. There is a need for further fundamental research to investigate the way in which pigs adapt behaviourally to a large group size at the level of the individual pig and several potentially fruitful investigations are suggested.

A 16 year study of injuries to professional kickboxers in the state of Victoria, Australia

Objectives: To determine the rate and type of injuries occurring to registered professional kickboxers in Victoria, Australia over a 16 year period. Methods: Data describing all fight outcomes and injuries...

A 16 year study of injuries to professional boxers in the state of Victoria, Australia

Objectives: Concerns about the significant injury risks in boxers have been well documented. To inform the continuing debate, updated information about the risk of injury for participants, and suitable means...

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

Game theory models predict that fighting ability should be 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)]

Stress Responsiveness Affects Dominant–Subordinate Relationships in Rainbow Trout

The magnitude by which plasma cortisol levels increase following exposure to a stressor is a heritable trait in rainbow trout. The relative growth in coculture of F1 lines selected for high responsiveness (HR) and low responsiveness (LR) to a confinement stressor suggested that behavioral characteristics related to food acquisition, aggression, or competitive ability might differ between the two lines. This hypothesis was tested using the F2 generation of the selected lines. The F2 lines clearly exhibited the characteristics of the F1 parents, displaying significantly divergent plasma cortisol responses to a 1-h confinement stressor and a high heritability for the trait. Behavioral differences between the lines were assessed by observing the outcome of staged fights for dominance in size-matched pairs of HR and LR fish. The identification of dominant and subordinate fish within each pair on the basis of their behavior was supported by the levels of blood cortisol in the fish attributed to each group (dominant ⪡ subordinate). Fish from the LR line were identified as dominant in significantly more trials than were HR individuals. The results suggest that behavioral attributes that affect the outcome of rank-order fights are closely linked to the magnitude of the plasma cortisol response to stress in rainbow trout. Whether the link is causal or circumstantial is not yet evident.

Body Size, Leg Autotomy, and Prior Experience as Factors in the Fighting Success of Male Crab Spiders, Misumenoides formosipes

Game theory predicts which characteristics of male crab spiders should affect their success in mate-guarding contests. Previous data on Misumenoides formosipes suggested that body size and leg number influenced fight outcome, but the study had methodological problems. Using improved methods, we corroborated the size advantage but refuted the disadvantage of leg reduction. We also conducted the first test for an invertebrate on the effect that a single contest has on the outcome of subsequent contests. When size and residency status were controlled, prior winners defeated prior losers after only one contest experience. We discuss the importance of controlling for previous experiences in studies of contest resolution and the ramifications for both past and future studies.

Power Struggles, Dominance Testing, and Reproductive Skew.

Models of reproductive skew are concerned with the partitioning of reproduction between dominant and subordinate members of a group. In an interesting extension of these models, Reeve and Ratnieks briefly considered whether it might benefit subordinates to engage in aggressive behavior to test the fighting ability of a dominant. Their analysis suggested that such testing should be more probable in groups that feature high skew and, hence, perhaps among closer relatives (because high relatedness favors high skew). Here we explore in more detail the possibility of dominance testing. Three models that differ in the outcome of fights over dominance are presented: in the first model, the loser of the challenge is killed; in the second model, the loser is evicted from the nest; and, in the third model, the loser becomes (or remains) subordinate. In each case we consider the independent effects of the parameters that determine skew (namely, relatedness, group productivity, and ecological constraints) on the predicted level of dominance testing. We then construct an amalgamated model to examine situations where fights may lead to any one of the three outcomes. Our analysis reveals that, in the majority of cases, higher relatedness will in fact lead to lower levels of aggression. Moreover, dominance testing need not be associated with high skew. Rather, the relationship between skew and dominance testing will depend on which factor (relatedness, group productivity, or level of ecological constraints) is principally responsible for variation in the distribution of reproduction.

Asymmetry and fighting performance in the shore crab Carcinus maenas

Fluctuating asymmetries (left–right differences in symmetric traits) can be negatively related to fitness parameters in a number of biological systems. Hence, it has been suggested that symmetric individuals should outcompete asymmetric individuals during intraspecific agonistic encounters. However, there is a lack of experimental evidence for such a relationship. We investigated the relationship between trait asymmetry (both directional and fluctuating asymmetry) and the outcome of agonistic encounters among size-matched male shore crabs. Our findings indicate that cheliped (‘weapon claw’) directional asymmetry is not related to the outcome of fights, whereas fluctuating asymmetry in the fifth pereiopod, but not the second pereiopod, is negatively related to the likelihood of winning conspecific aggressive encounters. This relationship is most readily explained by a biomechanical advantage in symmetric individuals, as the fifth pereiopod is likely to be mechanically important in maintaining stability and balance during fighting. There is no evidence that asymmetry (in traits that display fluctuating asymmetry) is related to an intrinsic individual quality factor. None the less, the relative mechanical advantage of low asymmetry may give rise to fitness benefits in symmetric crabs that may have evolutionary consequences.

When size is not everything: determining the relative importance of two asymmetries influencing contest outcome

Correspondence: Y. Brandt, Department of Biology, Indiana University, Bloomington, IN 47405, U.S.A. (email: ybrandt@indiana.edu). Studies of fighting behaviour in fish have repeatedly shown that the larger contestant in pairwise contests is much more likely to win than is the smaller contestant, even when the difference in size is subtle (Turner & Huntingford 1986; Enquist et al. 1990; Ribowski & Franck 1993). Body size is an important asymmetry in determining contest outcome across a wide range of taxa, because larger contestants are physically stronger and thus can inflict more damage upon their opponents (Maynard Smith 1982; Riechert 1998). Yet in a study of contests staged between male cichlid fish Tilapia zillii, Neat et al. (1998) found that larger contestants won only 58% of all contests. They found a much better predictor of contest outcome: contestants with relatively larger testes won 88% of all contests. Based on P values obtained from a multiple logistic regression analysis, they concluded that relative testes weight was a good predictor of fight outcome while relative body weight was not. Here I argue three points. (1) Neat et al. have misinterpreted the results of their experiment, having based their conclusion upon statistical significance (P values). In contrast, comparing the regression coefficients reveals that, compared with testes weight, relative body weight may be less important, as important, or even many times more important in predicting contest outcome. Thus, while Neat et al. have demonstrated that relative testes weight plays a role in determining contest outcome, their data do not support the conclusion that relative body weight bears little influence on contest outcome. (2) Neat et al.’s experiment was predisposed to reveal an effect of testes size, but far less likely to reveal an effect of body size, on contest outcome. Their study had very low statistical power for detecting the effect of body size, because contestants were paired such that their body size

Mouth morphology, testes size and body size in male Tilapia zillii: implications for fighting and assessment

In Tilapia zillii, the outcome of fights is closely related to difference in testis weight between opponents rather than differences in body weight. Testes size was predictable statistically on the basis of the size of the mouth in relation to body size, suggesting that among other functions mouth morphology may have evolved to facilitate assessment during fighting.

Illegality, Enlightenment and Ambiguity: A Hot Italian Recipe

Studying Italian immigration policy gives the author a chance to reconsider public policy making patterns, particularly ones concerning social issues. Innovative measures addressed to low social strata – at least in Italy – often originate in benevolent illegal practices introduced by sympathetic civil servants and social workers, pressed and supported by voluntary sector associations, charities and unions. Practices promoted by lobbying are, step by step, embodied in local administration and social services directives and circulars, and then diffused and standardized over the national territory by central government circulars. Senior public administrators and expert committees eventually filter and integrate these practices in the light of comparative policy studies and with a view to possible political outcomes; also they polish, adapt, and correct the practices to translate them into bills of law. Parliament will discuss and amend them according to party and intra-party alignments. The actual legislation will be the outcome of fights and compromises; even so, a good share of enlightment (expert committees) and benevolence (low strata lobbying) will still be present in the final product. Legislation originating from benevolent illegal practice will in turn be partially eroded by malevolent illegal practice, by circulars and decrees illegally used in fields constitutionally protected by law. A remarkable share of the decision making process takes place sheltered from party conflicts, from parliamentary action or from public opinion. This sort of ‘extra-political’ policy tends to greater significance when new party elites come to power, and to lesser when the new elite becomes established.

Elevated predation risk changes mating behaviour and courtship in a fiddler crab

The fiddler crab, Uca beebei, lives in individually defended burrows, in mixed-sex colonies on intertidal mud flats. Avian predation is common, especially of crabs unable to escape into burrows. Mating pairs form in two ways. Females either mate on the surface at their burrow entrance ('surface mating') or leave their own burrow and sequentially enter and leave ('sample') courting males' burrows, before staying in one to mate underground ('burrow mating'). We tested whether perceived predation risk affects the relative frequency of these mating modes. We first observed mating under natural levels of predation during one biweekly, semi-lunar cycle. We then experimentally increased the perceived predation risk by attracting grackles (Quiscalus mexicanus) to each half of the study site in two successive biweekly cycles. In each experimental cycle, crabs were significantly less likely to mate on the side with more birds. Moreover, on the side with elevated predation risk, the number of females leaving burrows to sample was greatly reduced relative to the number of females that surface-mated. Males waved less and built fewer mud pillars, which attract females, when birds were present. We discuss several plausible proximate explanations for these results and the effect of changes in predation regime on sexual selection.

Fighting and assessment in male cichlid fish: the effects of asymmetries in gonadal state and body size

In fights between animals over limited resources, the larger contestant often wins. Game theoretical models of animal fighting predict that relative body size is assessed during the fight and thus determines fight duration and intensity. In addition, if the contestants differ in the value they place on the disputed resource, this can also influence the outcome, duration and intensity of the fight. We studied territorial fighting in a cichlid fish,Tilapia zillii, in relation to relative body size and gonad weight. Relative gonad weight was a much stronger predictor of fight outcome than relative body size, even when body weight asymmetries were as large as 30%. This suggested that males with large gonads were fighting harder to defend their territory, perhaps because the value of a territory correlates with the gonadal state of the individual. A detailed analysis of mouth wrestling observed during fighting suggested that relative body size is assessed. However, contestants smaller than their opponent often continued to fight in spite of their size disadvantage. Weight disadvantaged winners appeared to fight more fiercely as suggested by a negative correlation between weight asymmetry and the proportion of bites inflicted by the winner. During escalated fighting, winners and losers differed consistently with regard to a behaviour termed mouth locking. Although neither biting nor persistence in mouth locking was related to gonad weight, we propose that the fish may have been assessing asymmetries unrelated to relative body size and possibly more related to levels of cost and the motivation to persist.

Alternative reproductive tactics and male-dimorphism in the horned beetle Onthophagus acuminatus (Coleoptera: Scarabaeidae)

Adult dung beetles (Onthophagus acuminatus) exhibit continuous variation in body size resulting from differential nutritional conditions experienced during larval development. Males of this species have a pair of horns that protrude from the base of the head, and the lengths of these horns are bimodally distributed in natural populations. Males growing larger than a threshold body size develop long horns, and males that do not achieve this size grow only rudimentary horns or no horns at all. Previous studies of other horned beetle species have shown that horned and hornless males often have different types of reproductive behavior. Here I describe the mating behaviors of the two male morphs of O. acuminatus during encounters with females. Females excavate tunnels beneath dung, where they feed, mate and provision eggs. Large, horned males were found to guard entrances to tunnels containing females. These males fought with all other males that attempted to enter these tunnels. In contrast, small, hornless males encountered females by sneaking into tunnels guarded by other males. In many instances, this was accomplished by digging new tunnels that intercepted the guarded tunnels below ground. Side-tunneling behavior allowed sneaking males to enter tunnels beneath the guarding male, and mate with females undetected. Both overall body size and relative horn length significantly affected the outcome of fights over tunnel ownership. These results suggest that alternative reproductive tactics may favor divergence in male horn morphology, with long horns favored in males large enough to guard tunnels, and hornlessness favored in smaller males that adopt the “sneaking” behavioral alternative.