Courtship song, male agonistic encounters, and female mate choice in the house cricket,Acheta domesticus (Orthoptera: Gryllidae)

Whether female crickets choose among males based on characteristics of the courtship song is uncertain, but in many species, males not producing courtship song do not mate. In the house cricket,Acheta domesticus, we examined whether a female chose or rejected a male based on his size, latency to chirp, latency to produce courtship song, or rate of the high-frequency pulse of courtship song (“court rate”). We confirmed that females mated only with males that produced courtship song, but we found no evidence that the other factors we measured affected a female’s decision to mate. In addition, we investigated whether the outcome of male agonistic encounters affected the subsequent production of courtship song. In one experiment, we observed courtship and mating behavior when a single female was placed with a pair of males following a 10-min interaction period between the two males. Winners of male agonistic encounters had higher mating success. However, winners and losers of agonistic encounters were not different in their likelihood or latency to produce courtship song or in the number of times they were disrupted by the other male in the pair. In a second experiment, we allowed two males to interact for a 10-min period, but following this interaction period, we placed a female with each male separately and observed courtship and mating behavior. The mating success of winners and losers was not different under these circumstances, and we found no differences between winners and losers in any subsequent courtship or mating behavior examined. We conclude that winning agonistic encounters influences a male’s mating success in ways other than his production of courtship song and this effect is lost when winning and losing males are separated and each is given an opportunity to mate.     

Male—male aggression in the plethodontid salamander Desmognathus ochrophaeus

Aggressive encounters between pairs of male mountain dusky salamanders (Desmognathus ochrophaeus) were staged in the laboratory in the absence of any obvious limited resource. We observed aggressive interactions which sometimes escalated to biting. Physical injuries were inflicted during some aggressive encounters; however, the consequences of injury for future fitness are uncertain. Several behaviour patterns used in contests apparently functioned as threat displays, and these sometimes ended contests before they escalated to biting. We could detect no significant influences of three types of asymmetries among males in determining the winners and losers of contests (body size, recent mating experience and familiarity with the testing arena). Three cases of 'homosexual' courtship were observed. Both intermale aggression and intermale courtship may be interpreted as forms of competition for mates.     

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.     

Male Competition in a Wandering Spider (Cupiennius getazi,Ctenidae)

We describe male-male competition in a wandering spider living on plants (Cupiennius getazi, Ctenidae) and discuss it within the general context of the mating system. 1. Males produce vibratory courtship signals (duration about 20 s) and competition signals (2 s). Upon exposure to female silk, males produce almost exclusively courtship signals (98%) if alone or in the presence of a female. In the presence of a rival alone, an average of 25% of a male's vibratory signals are courtship signals and 75% competition signals. In the presence of both a rival and a female, an average of 50% are courtship and 50% competition signals. Females respond to both male courtship and/or competition signals with vibratory courtship whereas males react by vibratory competition. The intensity of the reaction of both males and females is independent of the signal type. 2. Males displaying vibratory signals move slowly over the plant and repel attacks from rivals and females with extended front legs. Pairs of males interact in three ways. (i) Both males produce vibratory signals; one of them leaves the plant (53% of 90 trials). (ii) Both males vibrate, approach and touch (20%) or pounce on each other (20%). (iii) A male approaches the signalling opponent without producing vibrations and attacks him (7%). This is a conditional vibrocryptic tactic. The presence of a female incites male competition. Males do not interact with the female but approach each other (in 24% of the 26 trials “vibrocryptically”) and escalate more often (88%) and more quickly to overt fight than in the absence of a female. The male remaining on the plant approaches the female. 3. Male-male fights are ritualized. During 64 bodily contacts no male was injured. Males exposed to female silk and males using the vibrocryptic tactic were more often the winners of an interaction than males not exposed to female silk and than males vibrating while approaching their rival. The outcome of fights is not correlated with age, leg length, body weight and rate of signalling when no female is present. In contrast, body weight and leg length determine the outcome when a responding female is present, the larger male being the winner. 4. Intrasexual and intersexual interactions suggest that both male competition and female choice mechanisms may regulate sexual selection in this species.     

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.     

Experimental evidence that winning or losing a fight does not affect sperm quality in a field cricket

Fighting is a powerful social experience that can affect male reproductive behavior, including ejaculatory strategies. Whereas winners may monopolize females, losers may instead perceive high sperm competition and limited future mating opportunities, and accordingly enhance ejaculate quality to maximize their reproductive success. In male field crickets Gryllus bimaculatus that fight aggressively for control of breeding territories, winners are known to possess sperm of lower quality (viability) compared to losers, but it remains unclear whether this is due to short‐term fighting consequences. To test if the fighting experience per se (winning or losing) affects male adjustment of sperm viability, we subjected males to winning and losing experiences by staging fights against size‐matched rivals of known fighting ability. These rivals were males that previously won or lost a fight and, due to “winner‐loser effects” kept winning or losing subsequent contests. We sampled sperm prior and after the fight and twice in control males with no fighting experience and found no differences in sperm viability across measures. We conclude that males do not tailor their ejaculate quality following a single fight, or based on its outcome. Intrinsic differences in other attributes between winners and loser phenotypes may explain differences in sperm quality previously described in this system.     

Demonstration of Strength and Concealment of Weakness in Escalating Fights of Male Swordtails (Xiphophorus helleri)

In the green swordtail (Xiphophorus helleri) confrontations between strange males regularly escalate to high levels of mutual Bites and Fin Grips, even between males differing greatly in size. The original expectation of early game theory models that the behaviours of the ultimate winners and losers are indistinguishable until shortly before the end of the fight could not be confirmed. A significant characteristic of loser behaviour is that the Biting rates are higher before and after escalation. Conversely, Fin Grips are more frequent in the ultimate winners than the losers. However, such behavioural differences are very poor predictors of the outcome of the fight from the viewpoint of a single fighting individual during the contest. Correct forecasts did not exceed 67%. The escalating fights of swordtails are considered as trials of strength in which the stronger male tries to demonstrate strength by the most costly behaviour pattern available, namely Fin Grips, and the weaker male conceals weakness quite successfully by countering with the same tactic and suppressing signs of weakness such as Avoidance behaviour.     

Why do winners keep winning? Androgen mediation of winner but not loser effects in cichlid fish

Animal conflicts are influenced by social experience such that a previous winning experience increases the probability of winning the next agonistic interaction, whereas a previous losing experience has the opposite effect. Since androgens respond to social interactions, increasing in winners and decreasing in losers, we hypothesized that socially induced transient changes in androgen levels could be a causal mediator of winner/loser effects. To test this hypothesis, we staged fights between dyads of size-matched males of the Mozambique tilapia (Oreochromis mossambicus). After the first contest, winners were treated with the anti-androgen cyproterone acetate and losers were supplemented with 11-ketotestosterone. Two hours after the end of the first fight, two contests were staged simultaneously between the winner of the first fight and a naive male and between the loser of first fight and another naive male. The majority (88%) of control winners also won the second interaction, whereas the majority of control losers (87%) lost their second fight, thus confirming the presence of winner/loser effects in this species. As predicted, the success of anti-androgen-treated winners in the second fight decreased significantly to chance levels (44%), but the success of androgenized losers (19%) did not show a significant increase. In summary, the treatment with anti-androgen blocks the winner effect, whereas androgen administration fails to reverse the loser effect, suggesting an involvement of androgens on the winner but not on the loser effect.     

Stickleback fights: why do winners win? Influence of metabolic and morphometric parameters

Pairs of reproductively mature male three-spined stickleback (Gasterosteus aculeatus) were introduced into unfamiliar aquaria and observed until one male became dominant. Skin carotenoid content, morphometric indexes, and metabolic capacities of the axial and pectoral muscles were examined to establish whether morphological or physiological parameters differentiated winners and losers. Stickleback that initiated fights typically won. Quick initiation led to quick victory. Overall, winners and losers differed in few morphological or metabolic characteristics, but these properties and the differences between these attributes for losers and winners of specific fights were linked with initiation time and fight duration. Morphometric indexes of losers were the primary determinants of initiation time and fight duration, whereas for winners muscle metabolic capacities were linked to these fight characteristics. The greater the hepatosomatic index (HSI) of losers, the longer the fight initiation times. Similarly, losers with high HSI and carotenoid levels resisted defeat longer. In winners, initiation time decreased as axial muscle phosphofructokinase levels increased and citrate synthase levels decreased, whereas the metabolic capacities of the pectoral muscle were linked with time to achieve victory. When losers had greater HSI values than the winners of a specific fight, fight initiation was delayed and fights lasted longer. When losers had higher carotenoid levels than winners, fights also lasted longer. On the other hand, when losers had more visceral fat (fat body mass over somatic mass) than winners, both initiation time and combat duration were reduced. These results suggest that male stickleback assess their physiological status and that of their opponents, in particular the HSI, and adjust their combat strategies accordingly.     

Does being paired give male and female convict cichlids (Amatitlania nigrofasciata) an advantage when competing against same-sex individuals?

Fight theory predicts that asymmetries between contestants can be used to predict the winners and losers in fights. Using the monogamous convict cichlid (Amatitlania nigrofasciata), we examined whether being in a pair bond has an advantage in defeating a single same-sex individual. We hypothesize that the male and female members of a pair bond would defeat a same-sex single intruder because it is beneficial to form a pair bond prior to competing for mutual resources, such as a breeding site. To test our hypotheses, we allowed paired males to engage in contests with single males with and without the interaction of their mate. In addition, we allowed paired females to engage in contests with single females with and without the interaction of their mate. Our results indicate that the paired male gained no advantage in being paired; however, paired females seem to have an advantage over single females because they typically defeated them. To reduce the influence of the other pair member on the fight, we restrained one member and allowed the other pair member to confront the same-sex individual. The paired male was frequently defeated while the paired female typically won. These results suggest that forming a pair bond gives females, but not males an advantage in fights with same-sex competitors.     

Patterns of information flow in the hermit crab Calcinus tibicen

The rate of information transfer, as estimated by changes in the probabilities of execution of visual displays during agonistic interactions, was measured for individual hermit crabs. Using aggregate data it was demonstrated that winners gained more information from losers than losers from winners. Examination of the won and lost fights of individual crabs failed to show any consistent differences in the rate of information transfer. However, crabs that had higher rates of transfer (both in their won and lost fights) won significantly more interactions. Based upon the information transfer values observed, a mixed-strategy model of communication is outlined.     

Display behaviour and dewlap colour as predictors of contest success in brown anoles

Many animals display visual signals in male contests for access to females and territories. These visual signals can be multimodal and stimulate different aspects of a signal receiver's visual system. Over two summers, we tested whether aspects of behaviour and dewlap colour might function as signals that predict contest success when males compete for access to either mates or territories in male brown anole lizards. We found that behaviour (PC1, a correlated composite of head‐bob, push‐up, and dewlap extension frequency) and an aspect of dewlap colour (PC3, the relative amounts of ultraviolet, yellow, orange, and red of the dewlap margin) were retained in the minimum adequate model predicting contest success across years and social contexts. Winners showed significant differences in behaviour (winners displayed more) and dewlap margin PC3 (winners had lower PC3 scores) compared to contest losers. These findings suggest that display behaviour and dewlap colour might serve as signals indicating a male's ability to win contests for access to females and territories. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 646–655.     

Deferred agonistic behavior in a long-lived scincid lizard Eumeces laticeps

Summary A laboratory experiment with the broad-headed skink (Eumeces laticeps) involving staged agonistic encounters demonstrates that larger males have an advantage over smaller ones in agonistic bouts. Field data on head wounds produced by intraspecific fighting during the breeding season show a much higher frequency of new wounds among males over 100 mm in snout-vent-length than in smaller males. The significant difference in new-wound frequency strongly suggests avoidance of fights by the small males, which is corroborated by laboratory and field observations. Access by males to reproductively active females depends on the ability to defeat other males in aggressive contests virtually always involving head biting if the males are of nearly equal size. Because the probability of winning agonistic encounters increases with size, young males avoid fights with older males. Aggressive contests with larger males and reproductive attempts other than courtship in the absence of larger males are deferred.Aggressive behavior in E. laticeps may be employed in direct defense of females, but might also be expressed in defense of specific sites and/or territories. In the laboratory, males in their home cages were significantly more likely to win encounters with males of similar size than were males fighting in the home cages of opponents. This suggests that encounter site could be important in determining encounter outcome and that field study of possible site defense or territoriality is needed.     

Temporal Pattern of Agonistic Interaction in Two Gerbil Species (Rhombomys opimus and Gerbillus perpallidus) Differing in Resistance to Social Pressure

This study compares temporal patterns of intraspecific agonistic interactions in two gerbil species in order to indicate interspecific differences in levels of social resistance. Both cross-sex and same-sex pairs of great gerbils (Rhombomys opimus Licht., 1823), and only same-sex male pairs of pallid gerbils (Gerbillus perpallidus Setzer 1958) were observed during staged encounters on a neutral arena. Analysis of three latency measures—latency to first agonistic interaction; latency to overt aggression (attack and/or ‘arrested’ fight); and latency to establishment of a stable winner-loser asymmetry among opponents—revealed both similarities and differences among the species. Latencies to first agonistic interaction were similar (did not differ significantly) among species and sexes. However, great gerbil males showed significantly more long latencies to establishment of a stable asymmetry among opponents, than great gerbil females or pallid gerbil males. So, the periods of symmetrical struggle in agonistic conflict last longer in great gerbil males, than in great gerbil females or pallid gerbil males. These differences in temporal pattern of agonistic interaction may reflect sex and species differences in resistance to social stress.     

Male Mating Success in the Presence of a Conspecific Opponent in a Madagascar Hissing Cockroach,Gromphadorhina portentosa (Dictyoptera: Blaberidae)

The influence of a conspecific competitor on male mating behavior was examined in a Madagascar hissing cockroach, Gromphadorhina portentosa. Previous studies have suggested that both male-male competition and female discrimination during courtship interactions may influence male mating success. Familiar pairs of males with a known social association were placed in an arena with a single virgin female and observed. As expected, subordinate males mated significantly less often than their dominant opponents. In pairs in which one male mated, dominant individuals limited the access of subordinates to females. Dominant males displayed an increased frequency and duration of interaction with the female. However, in pairs where both males remained unmated, the mating behavior of dominant and subordinate males did not differ significantly. As interactions progressed, as in the case of males that remained unmated, subordinate males gained increased access to the female. Mated males tended to be larger than their opponent although within a rank, males that mated were no larger than those that remained unmated. These results are discussed in light of the possible roles of male-male competition and female discrimination during courtship interactions.     

The Outcome of a Previous Social Interaction with a Same‐sex Conspecific Affects the Behavior of Meadow Voles,Microtus pennsylvanicus

In species where conspecifics compete for resources such as territories, remembering where a neighbor was previously encountered and the outcome of that interaction may give individuals advantages over nearby conspecifics. We used a two‐phase experiment to test the hypothesis that female meadow voles, Microtus pennsylvanicus, who during the breeding season are territorial and agonistic toward one another, can use details of an encounter with another female in one location to later navigate nearby areas. During the encounter phase, pairs of females interacted for two minutes in one isolated section of a Y‐maze; control females were placed in alone. Females were scored as either winners or losers. Winners displayed twice as many agonistic acts against their opponent. The test phase took place after a retention interval of one hour, 1 d, or 1 wk. Single females were returned to a clean and empty Y‐maze and allowed to explore the entire apparatus for 15 min. We recorded the amount of time spent in each section of the maze. After retention intervals of one hour and 7 d winners, losers, and controls spent similar amounts of time in each section. However, after 24 h, winners spent more time in the encounter section; losers and control females spent similar amounts of time in each section. The results suggest that meadow voles' memory of the details of a single encounter is influenced by the emotional valence attached to that event. The duration of memory may be associated with the establishment of territories by female meadow voles.     

Dominant-subordinate relationships in hamsters: sex differences in reactions to familiar opponents

In the majority of mammalian species, males are dominant over and more aggressive than females. In contrast, some reports suggest that female golden hamsters are more aggressive than males but systematic comparisons using the same methods for both sexes are rare. We observed same-sexed pairs of hamsters over repeated trials to assess whether sex differences existed in the level of agonistic behavior and in the development and maintenance of dominant-subordinate relationships with familiar partners. There were no sex differences in measures of agonistic behavior or fear responses (fleeing) during the initial series of three trials on the first day of testing. Following a four-day interval, males that had lost in session 1 showed fearful responses to a familiar dominant male and were not likely to engage in a fight with him. In contrast, females that lost the initial fights were not fearful and fought vigorously with the familiar winner in subsequent encounters. Although the amount of agonistic behavior engaged in by females did decrease over the course of the three sessions, females that lost did not demonstrate an increase in fear, as measured by the latency to flee. Males that lost fights did show increased fear during later trials and sessions. These results suggest that female hamsters are less affected by losing fights than males are and thus that females are less likely than males to develop highly polarized dominant-subordinate relationships. Further work is needed to understand the mechanisms underlying these sex differences.     

Exposure to the steroid hormone 20-hydroxyecdysone modulates agonistic interactions in male Homarus americanus

In this study we present evidence that 20-hydroxyecdysone (20E) affects agonistic behavior in male American lobsters and that male and female animals differ in their response to the hormone. Thirty-minute staged fights were conducted between large males exposed either to artificial seawater (ASW) or 20E and small, anosmic opponents. The nephropores of both combatants were blocked. Fights were videotaped and quantitatively analyzed for aggressive, defensive and avoidance behaviors using an ethogram in which behaviors are ranked according to aggressiveness. Unlike female lobsters, exposing male lobsters to 20E did not increase their aggressive behavior; however, there was a marginally significant trend toward an increase in defensive behaviors with a lower aggressive content than in their ASW-exposed counterparts. The opponents of 20E-exposed animals performed significantly more aggressive behaviors than their counterparts. In fights with 20E-exposed animals, the overall aggressive intensity of the fight was increased and the animals performed a greater number of avoidance behaviors. Unlike the effects of 20E on females, where exposure to 20E caused an increase in overall agonistic arousal, males only exhibited a change in frequency of their behaviors. These findings suggest that while 20E affects both males and females in agonistic encounters, the nature of the effect is different for the two sexes.     

Agonistic interactions with asymmetric body size in two adult-age groups of the annual killifish Millerichthys robustus (Miller & Hubbs, 1974)

In this study, the author evaluated two adult age groups of the Mexican rivulus Millerichthys robustus with body size asymmetries to determine the strategies used by an annual killifish during agonistic interactions of different ontogenetic stages. To achieve this goal, the author first characterized the ethogram of agonistic interactions of M. robustus composed of seven behavioural units in males and five behavioural units in females. The author then analysed agonistic interaction strategies used by males and females with body size asymmetries in two groups of different adult ages that represent different ontogenetic stages: (a) just after sexual maturity was reached, at 5 weeks of age, and (b) near natural death, at 24 weeks of age. The agonistic behaviour patterns of M. robustus were compatible with the logic of mutual assessment. Large males had an advantage during their interactions in both age groups, winning all of the encounters. Nonetheless, there was more aggression in 5-week-old fish encounters. In addition, small 24-week-old fish were more aggressive than small 5-week-old fish. These changing strategies may be because of the cost–benefits required during a fight at each ontogenetic stage. In the female encounters, size did not predict winners, as both small and large fish won a similar number of encounters, and some contests remained unresolved regardless of age group. There was a tendency for small females of any age to risk more than males in fights to maintain reproductive fitness.     

Hormonal and behavioral responses of starlings during a confrontation with males or females at nest boxes during the reproductive season

We investigated in an aviary experiment the behavioral and hormonal responses of European starlings (Sturnus vulgaris) that were moved from a same sex group to an aviary containing either a nest box alone, a nest box and another male, or a nest box and a female. Luteinizing hormone (LH) and testosterone (T) levels increased significantly and independently of the situation, suggesting that nest boxes were the most important stimulus affecting the levels of these hormones. Some birds occupied more than two boxes (winners), and others a single or no box (losers). Levels of T increased less in males that did not acquire a nest box. However, the increase in LH was similar in all males after the test. Singing was positively correlated with T levels. Winners started singing earlier and sang more during a contest than losers. In the presence of females LH increased more in winners than in losers, while the increase in T was similar in both groups. In females, there was no increase in T but LH increased in the presence of males. Levels were higher in females paired with winners than in females paired with losers. Finally, winners advertised their nest boxes more frequently than losers. These results indicate that within a relatively short time frame levels of LH and T increase following the transfer from a flock to a territorial situation and can react independently from each other depending on reproductive circumstances. For males, the possession of a nest box and, for females, the qualities of the male seemed to be the most important factors stimulating reproduction.