Resource-holding Potential Research Articles

Recognizing interspecific dominance signals? Blue tits adjust nest defence based on great tit's black bib size

AbstractAnimals use colours, morphological structures and behaviour to advertise their dominance status and ability to obtain resources (Resource Holding Potential, RHP) in agonistic contexts with conspecifics. Dominance relationships are also known between species, although the interactions and the information used to assess the other species' RHP remain obscure and empirical evidence of interspecific recognition of status is hard to obtain. Using behavioural inference is particularly important when a species needs to assess the potential loss of fitness in terms of reproduction or survival (e.g., risk of damage or predation) that could be inflicted by another species acting as a predator, parasite or competitor. Our study shows for the first time the existence of interspecific recognition of status signals: Blue tits Cyanistes caeruleus (subordinate species) perceive Great tits Parus major (dominant species) as threats as hole‐nesting competitors, and respond differently based on the size of the great tit's black tie stripe. Blue tits seemed to recognize the meaning of great tits' black ties because they were bolder when defending their nests against small‐tie (less dominant) great tits than when repelling attacks by large‐tie (more dominant) great tit males. Our results stress that behavioural inference can potentially be used to assess the meaning of status signals that presumably evolved in an intraspecific signalling context.

Male starling floaters preferentially visit nests of males with reduced resource holding potential.

Floaters are sexually mature individuals that are not able to reproduce by defending breeding resources. Floaters often visit active nests, probably to gather public information or to compete for a nesting site. We tested the hypothesis that floaters preferentially prospect nests in which they have a better chance of taking over, and that they do so by assessing the owners' resource holding potential (RHP). We manipulated the flight capacity of male and female breeders in a population of spotless starlings (Sturnus unicolor) by clipping two flight feathers per wing before egg laying, thus increasing their wing-load and likely impairing their condition. We subsequently monitored breeder and floater activity by means of transponder readers during the nestling period. We found that nests owned by wing-clipped males were visited by a greater number of male floaters than control nests. This effect was absent in the case of wing-clipped females. The number of male floaters also increased with increasing nestling age and number of parental visits. The experiment shows that male floaters preferentially prospect nests in which the owner shows a reduced RHP, a strategy that likely allows them to evict weak owners and take over their nests for future reproductive attempts.

Choosing a bigger opponent: the path to victory and greater gains for the small contestant

Animals often engage in contests over limited resources. The probability of winning a contest is primarily determined by the individual's fighting ability relative to its opponent and the perceived value of the disputed resource. Individuals of the hermit crab Calcinus californiensis frequently fight over gastropod shells. We conducted a free-choice experiment to assess the factors that determine individuals’ choice of opponent, contest initiation, and contest resolution. We placed hermit crabs occupying two shell species into a large container and monitored agonistic interactions between crabs. We assessed the asymmetries in fighting ability based on the differences in body mass between the opponents. The shell species and fit (i.e., shell size relative to crab body size) were used as measures of the objective and subjective resource value, respectively. Motivation influenced contest initiation; the crabs occupying too-tight shells were more likely to initiate a contest than the ones in looser-fitting shells. In most cases, the attackers fought for a shell with a looser fit, even if that meant losing a tighter-fitting shell of the preferred shell species. The fighting success for attackers was positively associated with the number of bouts of rapping and the shell size improvement. However, success was negatively correlated with body size asymmetry; attackers that chose opponents larger than themselves were more likely to evict their opponent than the attackers that chose opponents that were smaller. Experimental designs that allow animals to select their own opponents, rather than assigning specific opponents, can strongly contribute to knowledge of agonistic interactions.Significance statementFighting dynamics are commonly assessed by estimating the influence of the resource-holding potential and resource value in pair-matched opponents. Here, however, we examined the influence of asymmetries in resource-holding potential and the objective and subjective value of gastropod shells on the choice of a contender and contest resolution through a free-choice opponent experiment in hermit crabs. The contest initiation was driven by the motivation to obtain a better gastropod shell species or one with a better size fit—factors which are known to improve individual fitness. Furthermore, fighting success was associated with an individual's persistence in displaying aggressive behaviors and its motivation to obtain a better resource. However, contrary to the predictions of game theoretical models, fighting success was higher when attackers chose opponents larger than themselves. Our results highlight the relevance of assessing fighting under more natural conditions by allowing animals to select their opponents.

Bile acids as putative social signals in Mozambique tilapia (Oreochromis mossambicus)

Chemical cues provide potential mates with information about reproductive status and resource-holding potential. In the Mozambique tilapia (Oreochromis mossambicus), males can distinguish female reproductive status through chemical cues, and accessibility of males to females depends on their position in the hierarchy, determined in part by chemical cues. Here, we hypothesized that tilapia faecal cues are attractive to conspecifics once released into the water. C18 solid-phase extracts of faeces from dominant males and pre-ovulatory females evoked stronger olfactory epithelium electrical responses (EOG) than, respectively, subordinate males and post-spawning females. Mass spectrometry of the reverse-phase C18 high-performance liquid chromatography fractions of these extracts with highest EOG, identified by amino acids and bile acids. Faeces from pre-ovulatory females contain significantly higher concentrations of cholic acid (CA) and taurocholic acid (TCH) than both post-spawning females and males. A pool of amino acids had no effect on aggression or attraction in males. However, males were attracted to the scent of pre-ovulatory female faeces, as well as CA and TCH, when applied separately. This attraction was accompanied by increased digging behaviour compared to the odour of post-spawning females. CA and TCH exert their action through separate receptor mechanisms. These findings are consistent with a role for faeces – and bile acids therein – in chemical communication in this species, acting as an attractant for males to reproductive females.

Sequential analysis reveals use of mutual assessment in contests between wild New Zealand giraffe weevils

ABSTRACT When resources such as mates or mating sites are limited, selection drives the evolution of complex and frequently violent fighting behaviour. Contest outcome is determined by an individual’s resource holding potential (RHP) in comparison to that of their opponent. During contests individuals may assess only their own RHP, or they may mutually assess both their own and their opponent’s RHP to determine the effort they allocate to a contest. Male giraffe weevils (Lasiorhynchus barbicornis) bear an elongated rostrum used as a weapon during intense fights over access to females. We used sequential analysis to target the fine-scale structure of contests and phases of contest escalation to determine the assessment strategy used by rival male giraffe weevils in the wild. We found significant non-random temporal structure in behavioural transitions in all transition matrices, and winner and loser transition matrices were significantly different. Contest de-escalation was extremely rare compared to escalation and winners and losers used very different behaviours during contests overall. This study provides support for the sequential assessment model of mutual assessment by male giraffe weevils during competitive interactions. It also demonstrates the utility of sequential analysis in making sense of the often complex interactions occurring in wild insect populations.

Mating status, independent of size, influences lethal fighting in an entomopathogenic nematode

Males of many species compete over access to females by physical contests. Previous experience of mating and the opportunity to mate with a female may influence the motivation of males to engage in contests and the outcome of such contests. Often, prior mating results in increased aggression and probability of success. This is mediated by the effects on the male's subjective evaluation of both the resource value (RV) and his own ability to acquire the resource (resource-holding potential, RHP). Moreover, having mated may also affect a male's actual fighting ability. In Steinernema nematodes, mated males paired with naïve males are more likely to win contests. Here we show that this advantage in mated males of Steinernema carpocapsae cannot be explained solely by the physical changes brought about by prior female contact, since males exposed to female pheromone alone developed sperm and increased in size like mated males but did not have the same advantage as them in contests with naïve males. Effects of mating on other components of RHP, such as skill or motivation, or on RV may explain the greater probability of mated males winning. We also show that mating had differential effects on the probability of a male initiating attack, depending on whether the opponent was a mated male (and thus ready to mate again) or naïve, consistent with the relative threat of the opponent as a competitor for copulations.

Group resource-holding potential: worker size, colony size and the outcome of contests in ants

Group resource-holding potential: worker size, colony size and the outcome of contests in ants

Doors to the Homes: Signal Potential of Red Coloration of Claws in Social Hermit Crabs.

Red coloration on a signaler's body may be an informative signal in many animals. For species that inhabit architecture (e.g., burrows, nests, or other structures), certain parts of the body are more exposed than others, potentially serving as superior platforms for signaling via coloration. Yet whether animals differentially advertise red coloration on body parts that are more versus less exposed from their architecture remains to be tested. Here, we systematically quantified red coloration in social hermit crabs (Coenobita compressus). These crabs inhabit architecturally remodeled shells and have claws that visibly block the shell entrance, like doors to their homes. We hypothesized that red coloration of claws may be a signal of resource-holding potential (RHP). Consistent with this RHP signaling hypothesis, we found that within the same individuals' bodies, exposed claws showed significantly greater red coloration than unexposed carapaces. Furthermore, larger body size predicted greater red coloration of claws. Competing hypotheses (e.g., interspecific signaling, camouflage, and UV protection), while not explicitly tested, nevertheless appear unlikely based on natural history. Red claw coloration may therefore function as a signal to conspecifics, and experiments are now needed to test recipient responses. Broadly, relative to surrounding architecture, exposed body surfaces offer rich potential as signaling platforms for coloration.

Sex differences in cooperative coalitions: a mammalian perspective.

In group-living species, cooperative tactics can offset asymmetries in resource-holding potential between individuals and alter the outcome of intragroup conflicts. Differences in the kinds of competitive pressures that males and females face might influence the benefits they gain from forming intragroup coalitions. We predicted that there would be a female bias in intragroup coalitions because females (1) are more like to live with kin than males are, and (2) compete over resources that are more readily shared than resources males compete over. We tested this main prediction using information about coalition formation across mammalian species and phylogenetic comparative analyses. We found that for nearly all species in which intragroup coalitions occur, members of both sexes participate, making this the typical mammalian pattern. The presence and frequency of female or male coalitions were not strongly associated with key socio-ecological factors like resource defensibility, sexual dimorphism or philopatry. This suggests that once the ability to form intragroup coalitions emerges in one sex, it is likely to emerge in the other sex as well and that there is no strong phylogenetic legacy of sex differences in this form of cooperation. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.

Intersexual social dominance mimicry drives female hummingbird polymorphism.

Female-limited polymorphisms, where females have multiple forms but males have only one, have been described in a variety of animals, yet are difficult to explain because selection typically is expected to decrease rather than maintain diversity. In the white-necked jacobin (Florisuga mellivora), all males and approximately 20% of females express an ornamented plumage type (androchromic), while other females are non-ornamented (heterochromic). Androchrome females benefit from reduced social harassment, but it remains unclear why both morphs persist. Female morphs may represent balanced alternative behavioural strategies, but an alternative hypothesis is that androchrome females are mimicking males. Here, we test a critical prediction of these hypotheses by measuring morphological, physiological and behavioural traits that relate to resource-holding potential (RHP), or competitive ability. In all these traits, we find little difference between female types, but higher RHP in males. These results, together with previous findings in this species, indicate that androchrome females increase access to food resources through mimicry of more aggressive males. Importantly, the mimicry hypothesis provides a clear theoretical pathway for polymorphism maintenance through frequency-dependent selection. Social dominance mimicry, long suspected to operate between species, can therefore also operate within species, leading to polymorphism and perhaps similarities between sexes more generally.

Bystander fallow deer engage in third-party behaviour based on similarities in contestant resource-holding potential

Competitive dyadic interactions frequently attract the attention of bystanders that follow and disrupt the ongoing contest. The motivation for bystanders to engage in such third-party behaviour is considered by several different theoretical approaches; one such model argues that bystanders intervene to prevent subordinates from gaining a winner effect, thereby becoming a threat to the individual's dominant status within the group. This study investigates the role of contestant morphology as a motivating factor in initiating third-party behaviour. We investigated whether two correlates of resource-holding potential, prerut body weight and antler weight, were associated with third-party behaviour in rutting male fallow deer, Dama dama . In addition, we examined whether a third factor, reproductive effort (weight loss during the rut) was associated with third-party behaviour. There was a positive relationship between antler weight and the number of times individual males experienced third-party behaviour during contests. This relationship was not evident for either prerut weight or weight loss. An analysis of third-party behaviour showed that as the difference in both prerut and antler weight between the competing males declined, there was an increase in the probability that the dyad would experience third-party behaviour. However, there was no such association between the difference in weight loss between contestants and third-party behaviour. Thus, dyads of males closely matched in terms of individual quality were likely to experience third-party behaviour. We show for the first time that morphological traits associated with resource-holding potential are important cues used by rivals as a basis for engaging in third-party behaviour. • Dyadic fights are often disrupted by third-party group members. • Larger weapons were associated with experiencing more third-party behaviour. • Dyads similar in body and antler weight experienced more third-party behaviour. • Bystander males gather information about fighting rivals' size and quality. • This information is used to inform decisions to engage in third-party behaviour.

Do male panther chameleons use different aspects of color change to settle disputes?

In many animals, males engage in agonistic interactions. Color signals are commonly used to mitigate these potentially harmful interactions. Both pigment-based color and structural color, notably ultraviolet coloration, are used in this context to convey information, including an animal's resource holding potential (RHP) or social status. Despite extensive previous work on this topic, the ability to change color in this context has received relatively little attention. Moreover, no studies have considered the visible and the ultraviolet components of this ability. Thus, whether changes in ultraviolet play a role in settling intraspecific disputes remains unknown. Here, we investigate the role of color change during intrasexual agonistic interactions in male panther chameleons (Furcifer pardalis). To do so, we combined behavioral experiments and color analysis. Our results show that the outcome of male intrasexual agonistic interactions depends on particular aspects of color change in the visible spectrum. Dominant males exhibit more brightness changes and Euclidian distance changes within the HSV color space at the level of the bands and interbands, suggesting a prominent role of these patterns in panther chameleon communication. Our results also align with previous studies in another chameleon species, thus supporting the key role of brightness changes in chameleon communication, at least in a competitive context. Interestingly, although our species did exhibit UV coloration, neither this coloration nor its changes seem to be involved in intrasexual agonistic interactions among males, possibly because those signals may be used for other purposes like attracting mates, repelling predators, or deception.

‘Hangry’ Drosophila: food deprivation increases male aggression

Aggressive interactions are costly, such that individuals should display modified aggression in response to environmental stress. Many organisms experience frequent periods of food deprivation, which can influence an individual's capacity and motivation to engage in aggression. However, because food deprivation can simultaneously decrease an individual's resource-holding potential and increase its valuation of food resources, its net impact on aggression is unclear. Here, we tested the influence of increasingly prolonged periods of adult food deprivation on intermale aggression in pairs of fruit flies, Drosophila melanogaster. We found that males displayed increased aggression following periods of food deprivation longer than a day. Increased aggression in food-deprived flies occurred despite their reduced mass. This result is probably explained by an increased attraction to food resources, as food deprivation increased male occupancy of central food patches, and food patch occupancy was positively associated with aggression. Our findings demonstrate that aggressive strategies in male D. melanogaster are influenced by nutritional experience, highlighting the need to consider past nutritional stresses to understand variation in aggression.

Contests between male New Zealand sheet-web spiders, Cambridgea plagiata (Araneae: Desidae)

ABSTRACT Male competition for females can often take the form of direct physical contests. The outcome of a given contest or the decision to persist is determined by the resource holding potential (RHP) of rivals, which often corresponds to body size or weapon size. Males of the endemic New Zealand sheet-web spider Cambridgea plagiata Forster & Wilton 1973 have exaggerated chelicerae that are used in contests to gain access to females. We staged male–male contests in the field to determine the factors contributing to contest duration and outcome. The current models which describe how individuals make decisions to persist in a contest fall broadly into (i) energetic war of attrition or pure self-assessment, (ii) mutual assessment, and (iii) cumulative assessment. Our results showed that male body size was the key predictor in determining the winner of a given contest. The durations of contests were more consistent with predictions from either mutual or cumulative assessment models. We highlight that staging contests in the field may result in more realistic results and natural behaviours. Similar to the congener C. foliata, it appears that further development of current contest models may be required to understand male contests in sheet-web spiders.

Differential effects of aerobic capacities on fight outcome in giant hissing cockroaches

When animals engage in contests, ‘fights’ are usually noninjurious, involving either signals or trials of strength. Such fights end once an individual assesses that it is the weaker opponent, or it has reached the threshold level of costs it is prepared to pay. We investigated the agonistic behaviours performed and the relative costs paid by winners and losers during aggressive interactions in two species of Madagascan hissing cockroaches (the wide-horned cockroach, Gromphadorhina oblongonota , and the flat-horned cockroach , Aeluropoda insignis ). By combining contest observations with measures of energetic expenditure and using X-ray computed tomography to compare the internal structure of the respiratory systems of the competitors, we revealed the differential physiological investment associated with resource-holding potential in these two species. Winners in G. oblongonota had larger respiratory volumes than predicted for their size compared to losers. Gromphadorhina oblongonota fought more aggressively and had larger respiratory systems overall than A. insignis , which engaged in less physical fighting. This indicates differential investment in fight tactics, and associated anatomy that may promote contest success. Invertebrate species at the upper limits of body size need to maintain efficient respiratory systems to support their size while also remaining subject to the influence of sexual selection. • Male hissing cockroaches compete over territories and access to fertilizations. • Weaponry and contest dynamics vary between species in this tribe. • X-ray CT scanning was used to compare the respiratory structures of competitors. • Respiratory volumes were higher in dominants of the more competitive species. • Sexual selection may act on respiratory anatomy that can promote contest success.

Effect of diet and rearing density on contest outcome and settlement in a field cricket

The ability to win fights is expected to be influenced by the rearing and nutritional conditions experienced by individuals. We hypothesized that crowded rearing conditions would foreshadow intense competition for resources in adult male Gryllus firmus (Scudder) field crickets and thus favour greater investment in mandibular weaponry. In line with prediction, males developed relatively larger weapons in crowded rearing conditions but this investment did not translate into greater success in contests against size-matched males that were reared singly. Rather, we found that low-density males were more likely to defeat high-density males under some experimental conditions, possibly because low-density males are more aggressive. Overall, our strongest observed effect was that males with larger weaponry were more likely to win contests, independent of rearing density. We also manipulated the adult diet of males to test the hypothesis that greater fat loads, and thus potentially greater stamina, would improve success in contests. Contrary to prediction, increased fat load did not increase a male’s probability of winning a contest possibly because fights in field crickets are too short to invoke stamina. Broadly speaking, animals decide whether to give up in a fight by assessing either their own (self-assessment) resource-holding potential (RHP) or by assessing a combination of their own and their opponent’s RHP (mutual assessment). Our study lends some support to the hypothesis that male G. firmus crickets decide to persist in a fight by assessing their own RHP rather than via mutual assessment. Animals fight each other for access to, and control of, resources that they require for survival and reproduction (e.g. food, shelter, and mates). Although considerable empirical research has shown that individuals having a larger body size or weapons generally possess greater fighting ability—resource-holding potential (RHP)—and are thus typically more successful in combat, the factors contributing to the development of an individual’s RHP have received less attention. One potential environmental factor dictating RHP is population density; however, the effect of density on RHP is difficult to predict. Developing under high density could cause individuals to invest more in RHP-related traits because these conditions might signal intense competition for mates in the near future. However, individuals reared under high density are often less aggressive than their low-density counterparts. The food available to an adult could also be important because the consumption of fat could improve an individual’s stamina, an RHP-related trait important in combat. Our study testing the impact of these two factors on male fighting ability in the sand field cricket (Gryllus firmus) found limited support for the hypothesis that rearing density and diet significantly influence a male’s ability to win a fight against another male. Instead we found stronger support for the notion that, all else being equal, males with larger mandibles, or weapons, than their opponent were more likely to win a fight.

Subjective resource value affects aggressive behavior independently of resource-holding-potential and color morphs in male common wall lizard

Game theory models predict the outcome of a dyadic contest to depend on opponents’ asymmetries in three main traits: resource-holding potential (RHP), resource value (RV) and aggressiveness. Using male common wall lizards Podarcis muralis, a polymorphic species showing three discrete morphs (white, yellow, and red), we investigated how the aggressive behavior varies according to a change in subjective RV and color morphs, while controlling for the asymmetry in RHP (using mirrors). By comparing the aggression of the same individual towards its mirror image in two different arenas (familiar = high subjective RV; novel = low subjective RV), we showed that lizard aggressive behavior was more intense and prolonged in the familiar arena than in the new one, thus supporting the occurrence of a direct relationship between motivation and aggression in this species. We also found the overall aggressiveness to differ from individual to individual, supporting the general hypothesis that aggressiveness is a trait associated with personality. By contrast, no effect of morphs was detected, ruling out the occurrence of morph specific variation in the aggressiveness. Our results highlight that an individual’s motivation and personality might be as important as RHP and RV in the resolution of animal contests.

Winner effects and switching assessment strategies facilitate fast and frugal decisions in territorial contests

Animals compete in contests over limited resources, and contestants with greater fighting ability, or resource-holding potential (RHP), typically win contests. Contest strategies have evolved to balance contest costs with the benefit of winning resources. Sometimes, contestants decide to leave by estimating their opponent's relative RHP. This strategy (mutual assessment) is cost-effective because it allows weaker opponents to leave contests against formidable opponents before accruing higher costs. However, acquiring reliable information can be costly. Here, we showed that in snapping shrimp ( Alpheus angulosus ) contests, contestants assessed relative RHP quickly and cost-effectively by assessing their opponent's recent contest success. By staging 26 contests between randomly matched individuals and 24 contests between RHP-matched individuals, we determined that snapping shrimp assessed their opponent's RHP during initial contest phases but no longer assessed relative RHP during escalated phases. Then, after staging 24 contests between individuals with contest experience the day prior, we found that snapping shrimp integrated RHP and recent contest success to make contest decisions. This strategy facilitated fast and accurate judgments when the recent winner was also larger but often resulted in the larger individual retreating when facing a small recent winner. Notably, these systematic biases were corrected when RHP differences were stark. Taken together, our findings demonstrate that by assessing recent contest success early in a contest, snapping shrimp can avoid risky contests. Furthermore, by integrating recent contest success with direct observations of RHP, contestants avoid losing contests prematurely. Similar assessment strategies may be widespread, because they circumvent risky contests while minimizing premature defeats from weaker recent winners. • Snapping shrimp switched from mutual assessment to cumulative assessment. • Snapping shrimp assessed their opponent's recent contest success. • Winner effects facilitated early and accurate contest decisions.

The Influence of Gender and Resource Holding Potential on Aggressive and Prosocial Resource Control Strategy Choice in Early Childhood

Through the lens of resource control and resource holding potential theory, an investigation was conducted into the effect of resource opponent characteristics on frequency of aggressive and prosocial resource control strategy selection in 4-5-year-old boys and girls. Children (N = 92; 4-5 years old) were asked how they would respond to 12 hypothetical resource holding potential (RHP) vignettes, in which resource control opponents varied in ‘toughness’, ‘physical size’ and whether or not they were accompanied by friends. Girls gave significantly more prosocial responses to the vignettes than boys, and boys provided significantly more coercive responses compared to girls with some differences with age. Prosocial vignette responses were given significantly more frequently when the opponent was ‘not very tough’ as opposed to when they were ‘very tough’. Findings suggest that both boys and girls utilise some form of discrimination when deciding on how to respond to resource competition scenarios and that there are some age and gender differences in their reported response strategies. Findings are discussed in terms of resource control and RHP theory. Future study should investigate whether such differences translate into real-world observed resource control behaviour.

Perceived and actual fighting ability: determinants of success by decision, knockout or submission in human combat sports.

Animal contest theory assumes individuals to possess accurate information about their own fighting ability or resource-holding potential (RHP) and, under some models, that of their opponent. However, owing to the difficulty of disentangling perceived and actual RHP in animals, how accurately individuals are able to assess RHP remains relatively unknown. Furthermore, it is not just individuals within a fight that evaluate RHP. Third-party observers evaluate the fight performance of conspecifics in order to make behavioural decisions. In human combat sports, when fights remain unresolved at the end of the allotted time, bystanders take a more active role, with judges assigning victory based on their assessment of each fighter's performance. Here, we use fight data from mixed martial arts in order to investigate whether perceived fighting performance (judges' decisions) and actual fighting success (fights ending in knockout or submission) are based on the same performance traits, specifically striking skill and vigour. Our results indicate that both performance traits are important for victory, but that vigour is more important for fights resolved via decision, even though the effect of vigour is enhanced by skill. These results suggest that while similar traits are important for fighting success across the board, vigour is overvalued in judges' perceptions of RHP.