Do female great tits (Parus major) assess males by eavesdropping? A field study using interactive song playback

Male singing behaviour correlates with extra-pair success in several passerine birds. Singing interactions during territorial contests provide relative information on the males involved. Such information may be important in female extra-pair behaviour and eavesdropping on singing interactions among males may allow females to make such relative assessments. We used interactive playback to instigate singing contests with male great tits during the peak fertile period of their mate in an attempt to alter females'' assessment of mates'' quality relative to neighbours (potential extra-pair partners). We escalated a contest to one male (by overlapping his songs) and then subsequently de-escalated a contest (by alternating) to a neighbour. Intrusions onto neighbouring territories by females mated to either treatment male were then monitored. Females mated to escalation treatment males were more likely to intrude following playbacks than females mated to de-escalation treatment males. Although the absolute song output of males did not differ between treatments, males produced more song relative to playback in de-escalation treatments and relative song output was positively correlated with female intrusions. Therefore, female great tits eavesdrop on singing interactions and change their visitation rates to neighbouring territories according to their mate''s singing performance relative to neighbours.     

Contests with deadly weapons: telson sparring in mantis shrimp (Stomatopoda)

Mantis shrimp strike with extreme impact forces that are deadly to prey. They also strike conspecifics during territorial contests, yet theoretical and empirical findings in aggressive behaviour research suggest competitors should resolve conflicts using signals before escalating to dangerous combat. We tested how Neogonodactylus bredini uses two ritualized behaviours to resolve size-matched contests: meral spread visual displays and telson (tailplate) strikes. We predicted that (i) most contests would be resolved by meral spreads, (ii) meral spreads would reliably signal strike force and (iii) strike force would predict contest success. The results were unexpected for each prediction. Contests were not resolved by meral spreads, instead escalating to striking in 33 of 34 experiments. The size of meral spread components did not strongly correlate with strike force. Strike force did not predict contest success; instead, winners delivered more strikes. Size-matched N. bredini avoid deadly combat not by visual displays, but by ritualistically and repeatedly striking each other''s telsons until the loser retreats. We term this behaviour ‘telson sparring'', analogous to sparring in other weapon systems. We present an alternative framework for mantis shrimp contests in which the fight itself is the signal, serving as a non-lethal indicator of aggressive persistence or endurance.     

Preference for Male Traits Differ in Two Female Morphs of the Tree Lizard,Urosaurus ornatus

Non-random female mating preferences may contribute to the maintenance of phenotypic variation in color polymorphic species. However, the effect of female preference depends on the types of male traits used as signals by receptive females. If preference signals derive from discrete male traits (i.e., morph-specific), female preferences may rapidly fix to a morph. However, female preference signals may also include condition-dependent male traits. In this scenario, female preference may differ depending on the social context (i.e., male morph availability). Male tree lizards (Urosaurus ornatus) exhibit a dewlap color polymorphism that covaries with mating behavior. Blue morph males are aggressive and defend territories, yellow males are less aggressive and defend smaller territories, and orange males are typically nomadic. Female U. ornatus are also polymorphic in dewlap color, but the covariation between dewlap color and female behavior is unknown. We performed an experiment to determine how female mate choice depends on the visual and chemical signals produced by males. We also tested whether female morphs differ in their preferences for these signals. Female preferences involved both male dewlap color and size of the ventral color patch. However, the female morphs responded to these signals differently and depended on the choice between the types of male morphs. Our experiment revealed that females may be capable of distinguishing among the male morphs using chemical signals alone. Yellow females exhibit preferences based on both chemical and visual signals, which may be a strategy to avoid ultra-dominant males. In contrast, orange females may prefer dominant males. We conclude that female U. ornatus morphs differ in mating behavior. Our findings also provide evidence for a chemical polymorphism among male lizards in femoral pore secretions.     

Male collared lizards,Crotaphytus collaris (Sauria: Crotaphytidae), signal females by broadcasting visual displays

The signalling function of displays broadcast when animals are distant from conspecifics can be difficult to determine. I tested the extent to which visually transmitted broadcast displays given by free‐ranging territorial male collared lizards signalled same‐sex rivals or females. One test involved recording the frequency of broadcast displays, aggressive contests with rivals, and courtship encounters with females during ten reproductive seasons when local sex ratios varied markedly. The frequency of broadcast displays decreased as the ratio of male competitors to females increased. The frequency with which males initiated contests with rivals was not related to the ratio of competitors to females, whereas the frequency of courtship interactions decreased with sex ratio because there were fewer females to court. The behaviour of males that defended territories during two successive seasons showed a similar pattern. Broadcast display frequency was positively correlated with courtship frequency, but not with the frequency of contests with rivals. Lastly, individual males gave more broadcast displays during focal observations when they also engaged in courtship encounters with females than other observations when they engaged in aggressive conflicts with rival males. Although these results do not reject the possibility that broadcast displays may also signal male rivals, they support a major role of these displays in advertisement to females. © 2013 The Linnean Society of London     

Partitioning the Components of Sexual Selection: Attractiveness and Agonistic Behaviour in Male Wax Moths,Achroia grisella (Lepidoptera: Pyralidae)

Two components of sexual selection in the lesser wax moth, Achroia grisella, are clearly defined: females choose males based on characters of their ultrasonic advertisement signals, and males display agonistic behaviour patterns in contests over signalling stations. We conducted a series of laboratory trials to determine whether successes in these two sexual selection arenas were related. Our trials showed that winners in contests over signalling stations were characterized by earlier initiation of both signalling and aggression. These characteristics may indicate higher levels of ‘motivation,’ but it is unclear whether this level is a fixed trait. There was no relationship, however, between any measure of a male's attractiveness to females and his success in winning competition trials. Thus, inter- and intra-sexual selection may be acting on different, uncorrelated traits in A. grisella.     

Impaired sperm quality,delayed mating but no costs for offspring fitness in crickets winning a fight

The outcome of male–male contest competition is known to affect male mating success and is believed to confer fitness benefits to females through preference for dominant males. However, by mating with contest winners, females can incur significant costs spanning from decreased fecundity to negative effects on offspring. Hence, identifying costs and benefits of male dominance on female fitness is crucial to unravel the potential for a conflict of interests between the sexes. Here, we investigated males' pre‐ and post‐copulatory reproductive investment and its effect on female fitness after a single contest a using the field cricket Gryllus bimaculatus. We allowed males to fight and immediately measured their mating behaviour, sperm quality and offspring viability. We found that males experiencing a fight, independently of the outcome, delayed matings, but their courtship effort was not affected. However, winners produced sperm of lower quality (viability) compared to losers and to males that did not experience fighting. Results suggest a trade‐off in resource allocation between pre‐ and post‐mating episodes of sexual selection. Despite lower ejaculate quality, we found no fitness costs (fecundity and viability of offspring) for females mated to winners. Overall, our findings highlight the importance of considering fighting ability when assessing male reproductive success, as winners may be impaired in their competitiveness at a post‐mating level.     

Carotenoid-based epaulettes reveal male competitive ability: experiments with resident and floater red-shouldered widowbirds

Many birds display carotenoid-based ornaments, which are typically considered to be honest indicators of individual health and condition. Experimental work on male red-shouldered widowbirds, Euplectes axillaris, has demonstrated a function of the carotenoid-based epaulettes in male contests and territory acquisition. Using two experiments, we investigated whether the natural variation in this colour signal reveals male competitive ability. Males with larger and redder (more longwave) epaulettes established territories to the exclusion of males with smaller and less red signals, which formed a large population of ‘floaters’. In an experiment in which we removed 42 resident males, these floaters rapidly filled up vacant territories. Among removed birds held in captivity, residents strongly dominated floaters in dyadic contests over access to an easily monopolized feeder (i.e. outside the context of territory defence). Only epaulette size predicted the outcome of these male contests. In addition, when competitors were experimentally given similar epaulette signals (removed or painted red to the average population size), the males were involved in more aggressive interactions than during unmanipulated contests, but residents continued to outcompete floaters. On release (after 8 days) to the breeding grounds, most residents (88%) rapidly reclaimed their territories from replacements. Combined, these results suggest that some intrinsic ‘resource-holding potential’, associated with the variation in epaulette signal, is primarily responsible for residents dominating nonresidents. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Mangrove crab uses victory display to “browbeat” losers from re‐initiating a new fight

Signalling behaviour is integral to animal contests. However, post‐contest signals, such as victory displays, have received relatively little attention. One hypothesised function of victory displays is to ensure a more lasting dominance by reducing the risk of losers re‐initiating a new contest with winners. Despite several theoretical studies using game theory that support this hypothesis, empirical support for the understanding of when and why victory displays are used with respect to browbeating is lacking. We use a common South‐East Asian mangrove crab, Perisesarma eumolpe, to examine whether the performance of victory displays by winners, among other factors, affects the time of fight re‐initiation by losers, if at all re‐initiated. Using mixed‐effects survival analysis models, we analysed 77 fights from 27 staged contest trials between randomly paired males. We found losers that experienced victory display performed by winners, presented a decreased instantaneous hazard rate of re‐initiating a new fight than losers that did not. These results corroborate previous game theoretical models indicating that victory displays may function to reduce the chances of losers re‐initiating another fight. In discouraging losers from restarting a fight, winners reduce the potential costs of a future contest.     

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.     

Chameleons communicate with complex colour changes during contests: different body regions convey different information

Many animals display static coloration (e.g. of feathers or fur) that can serve as a reliable sexual or social signal, but the communication function of rapidly changing colours (as in chameleons and cephalopods) is poorly understood. We used recently developed photographic and mathematical modelling tools to examine how rapid colour changes of veiled chameleons Chamaeleo calyptratus predict aggressive behaviour during male–male competitions. Males that achieved brighter stripe coloration were more likely to approach their opponent, and those that attained brighter head coloration were more likely to win fights; speed of head colour change was also an important predictor of contest outcome. This correlative study represents the first quantification of rapid colour change using organism-specific visual models and provides evidence that the rate of colour change, in addition to maximum display coloration, can be an important component of communication. Interestingly, the body and head locations of the relevant colour signals map onto the behavioural displays given during specific contest stages, with lateral displays from a distance followed by directed, head-on approaches prior to combat, suggesting that different colour change signals may evolve to communicate different information (motivation and fighting ability, respectively).     

Fighting in Males of the Autumn Spider,Metellina segmentata: Effects of Relative Body Size,Prior Residency and Female Value on Contest Outcome and Duration

Males of the autumn spider, Metellina segmentata (***Araneac: Metidae), compete for access to mates by guarding the orb webs of mature females. We investigated the influences of relative male righting ability and resource value on fighting behaviour by staging interactions in the field on webs occupied by females. In these contests, the larger male nearly always defeated its opponent when it was at least 10% greater in size. For smaller size asymmetries between opponents, the male previously resident on the female's web usually won the contest. Contest duration decreased exponentially with increasing size asymmetry between opponents, as predicted if each male assessed its relative size and adjusted its fighting strategy according to its likelihood of winning. Contest duration was also greater when the prior resident was the lighter opponent, or when size and residency asymmetries favoured different opponents as winners. Prior residents fought longer over larger, more fecund females, indicating an adjustment of fighting effort according to assessments of resource value. In contrast, intruders did not increase their fighting effort over larger females, suggesting an inability to assess female size quickly and accurately. Assessment appears to reduce the costs of settling conflicts, but imperfect information can result in inaccurate assessments and unexpected outcomes. Assessment strategies are used by other types of spiders to resolve contests, but this appears to be the first evidence for such strategies among orb-web-building spiders.     

Overt and covert competition in a promiscuous mammal: the importance of weaponry and testes size to male reproductive success

Male contests for access to receptive females are thought to have selected for the larger male body size and conspicuous weaponry frequently observed in mammalian species. However, when females copulate with multiple males within an oestrus, male reproductive success is a function of both pre- and postcopulatory strategies. The relative importance of these overt and covert forms of sexual competition has rarely been assessed in wild populations. The Soay sheep mating system is characterized by male contests for mating opportunities and high female promiscuity. We find that greater horn length, body size and good condition each independently influence a male's ability to monopolize receptive females. For males with large horns at least, this behavioural success translates into greater siring success. Consistent with sperm-competition theory, we also find that larger testes are independently associated with both higher copulation rates and increased siring success. This advantage of larger testes emerges, and strengthens, as the number of oestrous females increases, as dominant males can no longer control access to them all. Our results thus provide direct quantitative evidence that male reproductive success in wild populations of mammals is dependent upon the relative magnitude of both overt contest competition and covert sperm competition.     

Weaponry, color, and contest success in the jumping spider Lyssomanes viridis

Weaponry and color badges are commonly theorized to function as visual signals of aggressiveness or fighting ability. However, few studies have supported a signaling function of weaponry, and the role of color in invertebrate competitive interactions remains virtually unexplored. Jumping spiders (Salticidae) make excellent invertebrate models for studying weaponry and color because males of many species are colorful and possess exaggerated chelicerae, which are used as weapons in escalated contests. To determine whether color or weaponry might function as visual signals in male-male competitions, we investigated relationships between contest success, cheliceral length, and red coloration in Lyssomanes viridis. Males having longer chelicerae than their opponents were significantly more likely to win (p=0.0008). Males who won, despite being smaller than their opponents, had significantly less red chelicerae than their opponents (p=0.01). Male and female cheliceral length, as well as foreleg length, correlated tightly with body size. Cheliceral and foreleg length showed significantly stronger positive allometry in males than in females. We conclude that male chelicerae and forelegs are under strong positive selection for their use in physical fights and/or as visual signals of fighting ability.     

Reciprocity between endocrine state and contest behavior in the killifish, Kryptolebias marmoratus

Given the dramatic behavioral effects of winning and losing contests, and pronounced changes in stress and sex steroid hormones post-fight, it is reasonable to suppose that these hormones also dictate future behavior. We sampled water-borne cortisol, testosterone (T), and 11-ketotestosterone (KT) before and after contests in the mangrove killifish, Kryptolebias marmoratus, to determine how endogenous steroid hormone levels might predict and respond to contest dynamics or success. Pre-fight cortisol related negatively, and pre-fight T related positively to contest initiation and winning, particularly in the smaller opponent. In the pairs where a larger fish won the contest, winners with higher pre-fight T and lower pre-fight cortisol delivered more attacks to the losers. Contest duration and escalation influenced post-fight hormone concentrations primarily in losers. Escalation significantly increased post-fight cortisol, T, and KT for losers but not for winners. However, winners that attacked losers at higher rates had higher levels of post-fight cortisol. Losers also demonstrate the most consistent post-fight hormone responses, particularly to contest escalation and duration. Despite the bidirectional relationship between hormones and contest behavior, we found no overall mean differences in pre- or post-fight cortisol, T, or KT between eventual winners and losers. Thus, it is evident that the categorical states of winner and loser cannot alone reveal the complex, reciprocal associations between endocrine systems and social behavior.     

Agonistic Behavior in the Squid Loligo plei (Loliginidae,Teuthoidea): Fighting Tactics and the Effects of Size and Resource Value

Observations of small schools of squids in captivity suggested that dominance relationships among males were based upon major differences in the frequency or duration of their agonistic behavior, but staged contests showed few differences. During staged contests, squids exhibited up to 21 separate behaviors. Some contests included a complex array of visual signals and side-by-side posturing (Lateral Display) followed by physical contact during Fin beating. There was behavioral variability and step-wise escalation during the contests: squids performed either 1. long sequences of visual signaling followed by Chasing and Fleeing; or 2. short sequences of visual signaling followed by physical Fin beating and ending with Chasing and Fleeing. Size influenced outcome in all contests; larger males were more likely to win the contest. Size had no effect on contest duration, but contest duration was shorter when resource value was high, especially when a male established temporary ownership of a female. We speculate that when the perceived resource value is high, male squids are more likely to engage in a shorter yet riskier fighting tactic.     

The role of pigment based plumage traits in resolving conflicts

The role of melanin ‘badges of status’, in male–male competition has been well‐studied, in contrast, carotenoid based plumage has largely been examined in the context of female mate choice. Recent work has shown that carotenoid signals can also function in male–male competition, although the functions of the two types of signals is currently unclear. Here, we examine the relationships between colouration, dominance and aggression in the crimson finch Neochmia phaeton, a species where males have both conspicuous red carotenoid plumage and a black melanin patch. We examined the importance of carotenoid and melanin based signals in three contexts: 1) among free‐living birds interacting at a feeding station: we found that neither colour signal influenced the outcome of interactions; 2) in staged dyadic contest in captivity: we found that coloration from carotenoid pigments was positively related to the probability of winning a contest, while the size of the melanin plumage patch was not related to winning; and 3) in staged dyadic contests where male plumage colour had been masked: we found that the number of interactions required to determine dominance increased. While the underlying natural plumage colour was still important in these contests, birds with more intense carotenoid colouration were now more likely to lose. These results confirm carotenoid‐based signalling in male–male contests. However this signal is used in conjunction with other factors such as self‐assessment and body condition. Contrary to traditional expectations, the black melanin patch was not found to be important in this context.     

Prior residence effect determines success of male–male territorial competition in a color polymorphic poison frog

Male–male competition shapes resource distributions and reproductive success among individuals, and can drive trait evolution when phenotypes differ in competitive abilities and/or strategies. Divergence of populations, regardless of the cause, is often accompanied by divergence in male competitive ability, and such asymmetries can play an important role in mediating the interactions and evolutionary trajectory of the nascent lineages. Here, we designed a field experiment to examine the importance of color, a divergent trait, in determining territorial contest outcomes in the poison frog Oophaga pumilio. Males of different O. pumilio color morphs differ in aggression level, suggesting a potential dominance hierarchy between these divergent phenotypes. In a contact zone between red and blue-color morphs, we first removed territorial males from their calling sites, and examined whether certain color morph(s) were better at establishing in these now-vacant territories. We then staged a territorial contest by simultaneously releasing the original and the new occupant to their point of capture. Surprisingly, we found no significant effect of color on acquiring territories or winning staged contests. However, the original occupants won against the new occupant in 84% of the staged contests, revealing a strong prior residence effect. This suggests that asymmetries that stem from prior residency override coloration in predicting contest outcomes of male–male territorial contests in wild O. pumilio. Thus, contradicting our hypothesis, male–male territorial competition alone seems unlikely to exert selection on coloration in this contact zone.     

Territory acquisition in a polymorphic lizard: An experimental approach

Males of the colour polymorphic Australian painted dragon lizard Ctenophorus pictus occur in red or yellow head colouration. In a previous experiment, we showed that red is associated with a higher probability of winning staged contests for resources (females or space) and that manipulation of male colouration by painting males in the opposing morph changed the dynamics of staged interactions by prolonging them 30‐fold. Thus, colour is linked to behavioural differences between males and is involved in information transfer between competing males. This inherent red dominance could result in yellow males being marginalized to poorer quality territories in terms of access to females, food, perch sites or shade. With an experiment in the wild, we test to what extent this prediction is upheld, and how colour manipulation affects morph‐specific success in territory acquisition when male body size, territory quality and emergence time from hibernation are controlled through manipulation or randomization. There was no significant effect of colour category per se, although on average red males remained closer to the release sites (our proxy for territory acquisition ability) than yellow males and artificially altered morphs moved the furthest away. There was a significant interaction effect between colour category and experimental release position, which may be linked to differences in how exposed (or not) these positions were and morph‐specific ability to cope with such exposure (e.g. ‘boldness’). Our data show that territory acquisition success is not merely a function of competitive ability but a composite outcome of a suite of factors, including signal perception.     

Temporal and Spatial Distribution of Male Scent Marks in the Polygynous Greater Sac-Winged Bat

Scent marks are relatively long-lived signals that can be perceived by conspecifics when the producer is absent. Therefore, it is often not obvious to whom the signal is directed. In daytime roosts of the polygynous greater sac-winged bat, males scent mark territories with facial gland secretions. Territories are a valuable resource for males, as they offer exclusive courtship opportunities, which results in increased male reproductive success and, consequently, increased male–male competition over territories. The information encoded in male scent marks could, therefore, be either directed at females as part of an olfactory courtship display or at male competitors as part of territorial behaviour. We expected territorial males to scent mark in the morning, shortly before females return to the territory and close to female roosting sites, if scent marks are directed at females as part of the courtship display. And we expected harem males to scent mark at the territory boundaries, where male–male encounters are most likely to occur, if scent marks are directed at male competitors. We found that males marked more frequently in the afternoon, at a time when all females have already left the territory, and harem males marked at the territory boundaries and not inside their territory in the area where females roost. At boundaries males fan volatiles from specialised wing sacs towards competitors outside the territory. Scent marking of male Saccopteryx bilineata might therefore be congruent with the assessment-hypothesis, which states that scent marks offer intruders the possibility to make an olfactory assessment of the territory owner without direct physical interaction. Thus, scent marks of male S. bilineata are most likely influenced by male–male competition and not by female choice.     

The flexible lek: Phymatopus hecta the gold swift demonstrates the evolution of leking and male swarming via a hotspot (Lepidoptera: Hepialidae)

Leking moths present an evolutionary problem in their apparently simultaneous reversal of male–female attraction. The mating system of Phymatopus (or Hepialus) hecta embraces an unusually wide range of procedures. Both males and females use medium‐range olfactory attractants (also probably visual signals), and both sexes will lure, and both will approach, the other, either when flying or perched. This produces an ‘infinite variety’ which includes the classic moth mating procedure (males fly to sessile female); a typical lek procedure (female flies to sessile male); a mating swarm (hovering male follows passing female); and intermediates such as a mutual courtship dance. Male behaviour includes a flying display, two sessile displays, and an escalating war of attrition. The system is versatile, persistent, and probably evolutionarily stable. The lek site has a high density of perches suitable for copulation which facilitate predator‐escape by means of a dead drop. The whole supports a model for the evolution of resource‐based leks which commence with a concentration of females on a hotspot, leading to a concentration of males; and then an escalating process of sexual selection as males become increasingly attractive over a distance to females, and females use the males as a way of locating the resource. The main stabilizing pressure may be selection for efficient mate acquisition, and as with grouse leking systems, the precondition for evolution was probably having travelling females that actively sought a reproductive resource or a predator free space. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114 , 184–201.