Search

Sociality beyond mated pairs, whether in the form of nesting colonies, clustered territories or leks, presents an evolutionary puzzle because densely packed individuals typically incur high fitness costs. One hypothesis to explain clustered distributions is that they overlie clumped distributions of resources. However, numerous studies have shown that resource distributions are often insufficient to explain individuals' settlement decisions, suggesting that clustered breeding distributions are driven by other types of benefits, possibly related to ecological, social and genetic factors. One can ask more specifically whether animals cluster because of some underlying ecological factor, or whether aspects of their reproductive behaviour and mating systems are more influential. Accordingly, evaluating the influence of sexual selection upon the evolution of mating systems can be crucial for understanding the underlying causes of animal aggregations. In this article, we review the behavioural ecology of three types of mating systems where breeding occurs in clusters: colonial, lekking and socially monogamous clustered territorial systems. We highlight sexual selection as a potential explanation for the emergence of aggregations in all three cases. In particular, we discuss the hidden lek hypothesis, which postulates that aggregations in colonial and territorial species can be driven by increased opportunities for extrapair copulations. Finally, we feature our work with the blue-black grassquit, Volatinia jacarina , which illustrates the complexity of selective mechanisms that may favour territorial aggregations. Highlights • Many species breed in clusters that do not reflect underlying resource distributions. • Colonial, lekking and socially monogamous territorial species form aggregations. • The hidden lek hypothesis attempts to explain these clusters through sexual selection. • We illustrate clustering behaviour and possible mechanisms using a Neotropical bird. [ABSTRACT FROM AUTHOR]

Leks are aggregations of sexually displaying males visited by receptive females and characterized by intense male–male competition to attract mates. Success in lekking species is often contingent upon male display output and/or lek attendance, with energetically costly displays functioning as an honest indicator of male quality. Furthermore, display spaces are vigorously defended by territorial males, and territory characteristics are often linked to male phenotype. Here we describe the courtship and territorial behaviour of lekking lesser short-tailed bats, Mystacina tuberculata , and both behaviours appear to be conditional on body size. During the breeding season, lekking males occupy and defend small tree hollows and sing for long periods of the night to attract females. Although some males sing alone, others form ‘timeshare’ singing roosts, where multiple males visit sequentially to sing each night. In our study, solitary males were significantly smaller than timeshare males and individually had both higher song outputs and higher roost occupancy rates, although timeshare roosts had higher overall occupancy rates. There appeared to be no fitness difference between the two male groups, and while one timeshare roost contained relatively closely related individuals (which roost settlement simulations indicate was not a chance event), four did not. We discuss factors that may promote timeshare formation, including competition for access to desired roosts and potential by-product mutualisms. Courtship and sexual selection in bats is largely undescribed, and thus our study provides a useful description of behaviour in a little-studied taxon. [ABSTRACT FROM AUTHOR]

In species with alternative reproductive tactics, territorial males (guarders) are usually vigilant against sneakers, and aggressively attempt to eliminate them, imposing serious costs (injuries, sometimes death). Here I examined how sneakers escape from territorial attack in the triplefin blenny, Enneapterygius etheostoma , in the field, with the help of economic flight theory developed for predator–prey interactions. Sneakers hide around spawning sites for sneaking, but they are often detected and attacked by territorial males. Fleeing soon after the initiation of attack could reduce the risk of injuries. However, fleeing may be the wrong decision, resulting in a loss of benefit that could have been obtained by not fleeing, because of uncertainty about whether the sneaker is targeted. As the guarder–sneaker distance decreases, the target would become clear, and uncertainty is reduced accordingly. Therefore, it is predicted that flight initiation distance (FID, the predator–prey distance when escape begins) is determined by the cost–benefit balance. Two types of territorial aggression were identified: the ‘direct approach’, where the territorial male directly approaches a given sneaker, and the ‘reoriented approach’, where the territorial male turns to reorient and approaches it following an attack against the first target. A field study showed that sneakers fled earlier in the reoriented approach than in the direct approach. Model selection showed that FID in the reoriented approach was predicted by the guarder–sneaker distance at attack initiation (starting distance) alone, whereas FID in the direct approach was predicted by starting distance, the interaction between the approach speed of territorial males and the duration for which the sneakers monitored them. These results suggest that sneakers adjust flight decision rules to attack episodes, i.e. the economic decision in the direct approach, but the flush early decision in the reoriented approach. This study provides a novel example of adaptation in sneakers. [ABSTRACT FROM AUTHOR]

As a textbook example of a sexually selected trait, song in male birds has been extensively examined in the context of female mate choice and male–male competition for access to mates. Female song is also phylogenetically widespread, and probably ancestral. However, we know relatively little about when and why females sing. Female song may be important for female–male communication, e.g. fertility advertisement, mate attraction or coordinating the care of young. Alternatively, female song may function in the context of female–female competition for reproductive resources, e.g. nest sites, year-round territories or parental assistance. We quantified spontaneous song, and song in response to playback of an unfamiliar female song, in female and male superb fairy-wrens, Malurus cyaneus , across breeding stages. We found that females and males sang with roughly equal frequency spontaneously; however, females sang much more frequently than males in response to playback of unfamiliar female song. We found no difference in song rates across breeding stage, and no effect of age or the presence of subordinates. In both sexes, song rates increased slightly across the breeding season. Female song rates were also repeatable across the season. Overall, the results suggest that although female song is likely to be a multipurpose trait, as in males, the primary function in superb fairy-wrens appears to be female–female competition. [ABSTRACT FROM AUTHOR]

Agonistic interactions between males for the ownership of mating territories are common among animal species. There are at least three theoretical models aimed to clarify the rules used by rivals to decide the contest winner: war of attrition model (WOA), sequential assessment model (SAM) and cumulative assessment model (CAM). However, few empirical investigations have simultaneously tested predictions from these three models, reducing our ability to infer each model''s explanatory power. In this study, we used males of the dragonfly Diastatops obscura to identify traits that affect individual fighting ability (resource-holding potential, RHP) and to test predictions derived from WOA, SAM and CAM models. For this, we identified morphological and physiological male traits related to chances of victory, timed contests between males and evaluated the relationship between male traits, contest duration and performance of costly behaviours. Individual body mass represented the main trait affecting RHP. Contest duration decreased with increasing winner body mass and increased with increasing loser body mass, rejecting the WOA model. The probability of physical contact increased with decreasing mass differences between rivals. Additionally, when considering pairs of rivals that showed similar mass differences, contest duration was unrelated to loser body mass. Since fights can lead to physical contact, body mass may affect the capacity to inflict costs on the rivals. Also, the relationships between contest duration and RHP and between the probability of physical contact and RHP difference between rivals indicate that males perform mutual assessment of fighting ability, as presumed by SAM. [Copyright &y& Elsevier]

Although testosterone (T) has well known organizational and activational effects on aggression, the relationship between the two is not always clear. The challenge hypothesis addresses this problem by proposing that T will affect aggression only in fitness-enhancing situations. One way to test the challenge hypothesis is to examine the relationship between T and different types of aggression. Chimpanzees, Pan troglodytes, show aggressive behaviours in several contexts and provide an opportunity for such a test. Here we show that urinary T influences a form of male chimpanzee reproductive aggression, territorial boundary patrols. In contrast, T does not affect predatory behaviour, a form of aggression that has no immediate link to male reproduction. While these results are consistent with the challenge hypothesis, our results indicate that male chimpanzees experience a significant drop in urinary T during hunts. Additional analyses reveal that males who share meat with others display this decrease. The reason for this decrement is unclear, but we hypothesize that the relative lack of aggression that results from voluntary sharing episodes and the tolerance engendered by such acts may be contributory factors. [Copyright &y& Elsevier]

Animals use a variety of aggressive signals to mediate territorial interactions. Often these signals can be sufficient to ward off potential rivals, thus minimizing the chance of injury due to physical encounters. Yet not all behaviours produced during territorial interactions are aggressive signals. In this investigation, we examined the aggressive signals of black-capped chickadees, Poecile atricapillus, by determining which signals predict attack on a competitor. We used a recently developed playback protocol involving a loudspeaker and a taxidermic mount to simulate an intruder on males'' breeding territories. We examined males'' behaviours prior to any physical attack on the mount, both in the minute before attack and the time period preceding this minute. In the minute before attack, we found that gargle calls consistently predicted attack. In the preceding time period, we found that high song rate predicted attack. Surprisingly, we found that attack and the behaviours associated with attack were not significantly correlated with male dominance status. We conclude that song rate and gargle calling behaviour communicate intent to attack during territorial interactions in black-capped chickadees. These results expand our knowledge of aggressive signals during territorial encounters by revealing novel vocalizations used to communicate an animal’s probability to attack an opponent. [Copyright &y& Elsevier]

Physical strength and resource value are two key determinants of fighting success in most species. We investigated the role that resource value plays in determining fight outcome for a territory centred on a burrow in a fiddler crab, Uca annulipes. Males fought harder (escalated fights) for a territory during the mating period (when the burrow is also used for mating and breeding) than in the nonmating period (when it has value as a shelter). In both periods, having a burrow also allows access to the surrounding mudflat surface, where crabs forage. We confirmed earlier studies showing that males with regenerated claws are weaker competitors that are disproportionately evicted from their burrow during the nonmating period. Unexpectedly, however, males with a regenerated claw were not disproportionately evicted during the mating period. Fights at this time were also more escalated. We suggest this is because, when the disputed resource is also required for breeding, even weak males need to obtain and defend a burrow if they are to accrue any fitness. During the mating period, individuals with low resource-holding potential can improve their chances of mating if they escalate fights for burrows. [ABSTRACT FROM AUTHOR]

Interpopulation variation in territorial aggression can reflect differences in life history or competitive environments. Life history theory predicts that males with more opportunities for future reproduction should avoid risk-taking behaviour to minimize the cost of current reproduction, whereas competitive environments should favour higher aggression to defend limited resources. Additionally, male aggression can be modulated by familiarity with competitors to be either lower (dear enemies) or higher (nasty neighbours) towards neighbours. We conducted a territory intrusion experiment using neighbour–stranger songs to examine how territorial aggression differed in two populations of orange-crowned warblers, Oreothlypis celata, breeding in California and Alaska. The California population breeds at very high densities and has a higher annual survival relative to the Alaska population, which breeds at significantly lower densities and has a lower annual survival rate. We found that California males showed higher amounts of territorial aggression in response to simulated territory intrusions than did Alaska males, supporting the hypothesis that competitive environments, as indicated by breeding density, rather than life history, shape geographical variation in levels of aggression. Both populations discriminated between song stimuli of neighbours and strangers, but California males responded more strongly towards neighbours, whereas Alaska males responded more strongly towards strangers. We discuss these results in light of the mechanisms for overall aggression and neighbour–stranger discrimination. [ABSTRACT FROM AUTHOR]

Social monogamy in vertebrates often involves the joint defence of an all-purpose territory by pair members. Although both sexes presumably benefit from holding a territory, sex-related variation is often observed in territory defence at the interspecific level, particularly in birds. Most studies of territorial defence in monogamous birds, however, have been conducted on songbirds or on bird species living in temperate areas. In contrast, data on nonoscine tropical bird species remain scarce. We experimentally studied territorial defence in 20 pairs of Zenaida doves, a tropical and territorial monogamous bird species that maintains year-round pair bonds. Overall, males responded to intrusions more frequently than females. However, sex of the intruder had no effect on the reactivity of male or female residents. The use of aggressive behaviours of various intensities did not differ between males and females, irrespective of the sex of intruder. Although the percentage of male responses was correlated significantly and negatively with that of the females, the observed percentage of joint defence was significantly lower than would have been expected if pair members were reacting independently of each other. Finally, variation in reactivity of females to intruders was positively related to variation in intrusion pressure between trials, whereas no such trend was observed in males. We discuss our results in relation to the mating system of Zenaida doves and previous studies of territorial defence in birds. [Copyright &y& Elsevier]

Many animals can recognize previously encountered individuals and modify their behaviour towards them. Individuals also can have increased growth or other fitness components when interacting with familiar compared to unfamiliar individuals. One hypothesis explaining fitness benefits is that animals forage less in the presence of unfamiliar conspecifics because they spend time avoiding or interacting with these potentially more aggressive individuals. We tested this hypothesis in a territorial salamander, Plethodon cinereus, which is active on the forest floor at night. In our first experiment, we tested whether nocturnal activity was a suitable quantitative reflection of foraging. Level of nocturnal activity had a significant positive effect on mass gain and a significant negative effect on prey abundance in enclosures. Adult P. cinereus are known to be less aggressive towards familiar juveniles, and juveniles grow more when cohabitating with familiar adults, so we tested whether a lack of familiarity between juveniles and adults decreases nocturnal foraging activity of juveniles or adults. Juveniles were less active in enclosures with unfamiliar females than with familiar females with whom they had cohabitated in the laboratory. There were no differences in juvenile foraging activity based on familiarity with males. Surprisingly, adult salamanders were more active in enclosures with familiar juveniles than in enclosures with unfamiliar juveniles, even though juveniles are much smaller and do not pose physical danger towards adults. We conclude that adults and juveniles forage more when they interact with familiar conspecifics and we discuss hypotheses that may explain why familiarity affects interactions in these contexts. [ABSTRACT FROM AUTHOR]

Sick animals may change their feeding behaviour to compensate for infections. However, there is little information regarding whether infection affects (1) feeding behaviour of predators, (2) feeding behaviour using an experimental approach in the wild, (3) other costly behaviours and/or (4) physiological components of condition. We experimentally infected males of the predatory damselfly Hetaerina americana in a field experiment. We hypothesized that infection would reduce feeding behaviour. We further predicted a reduction in territorial activity, an increase in immune response (measured by the activity of phenoloxidase, PO) and a reduction of fat reserves and flight-associated muscle mass (two traits usually traded off with immune ability and territorial behaviour). We also infected males in a laboratory experiment that controlled for food supply and territorial activity, and measured the same physiological characters. Immune challenges in the field experiment unexpectedly increased feeding rate but did not change territorial activities. Muscle mass was reduced in the field but not in the laboratory, probably because of differences in the presence of energetically expensive territorial activities. In the laboratory, starvation and infection reduced PO activity and fat stores but did not affect muscle mass. Thus, our field and laboratory results support the idea that increased feeding compensates for infections in predators. [Copyright &y& Elsevier]

Variation in maternal behaviour can have profound consequences on offspring phenotype, survival, reproductive success, as well as maternal fitness. Understanding the mechanisms that underlie variation in maternal care can provide us with a more thorough understanding of the evolution of parental care. In some taxa, the effects of steroid hormones such as testosterone on paternal care have been well studied. However, patterns of female androgens in natural populations are rarely documented and relationships between maternal androgens and behaviour remain poorly studied. In this study, we first validated an enzyme immunoassay to measure faecal androgen metabolites (FAM) in territorial North American red squirrels, Tamiasciurus hudsonicus. We validated this assay by demonstrating that (1) our antibody reacts with testosterone metabolites, (2) reproductive females have significantly higher FAM than nonreproductive females, and (3) patterns of FAM were largely mirrored in plasma androgen levels. Second, we tested the hypothesis that androgen concentrations drive behavioural trade-offs in free-ranging breeding female red squirrels during gestation and lactation using 3 years of FAM data and 10 years of behavioural observations. FAM increased after conception and parturition, peaked during mid-lactation around the time of juvenile emergence, and then declined during the remainder of lactation and after weaning. Around the peak of FAM during mid-lactation, nest use was lowest, while territory defence and time spent foraging were at their highest levels. These associations between maternal androgens and behaviour support the hypothesis that androgens may play an important role in mediating maternal behaviour in free-ranging animals. [ABSTRACT FROM AUTHOR]

In most species, female reproductive success is determined by realized fecundity, which depends on the amount of female reproductive reserves and the availability of time for oviposition. Consequently, selection is likely to favour behaviour in virgin females that increases the likelihood of encountering males and thereby minimizing time without sperm. We used the speckled wood butterfly, Pararge aegeria, to test the hypothesis that virgin females increase the probability of encountering males by behaving more conspicuously. We also tested for an effect of age on behaviour, with the prediction that females behave more conspicuously if they remain unmated for a longer period. To do this we conducted controlled behavioural studies in large outdoor cages, comparing the behaviour of young and old, virgin and mated, females. We also assessed the time it took for a male to discover virgin versus mated females. Our results show an effect of age and mating status: old virgin females behaved more conspicuously than young virgin females and mated females, and spent more time in flight and performed more individual flights. Males also discovered virgin females faster than mated females. Furthermore, virgin females did not specifically locate the large sunspot, where perching males are found. Hence, females of P. aegeria adjust their behaviour in accordance with mating status and age, making them more likely to encounter a male and thereby maximize their reproductive success. This study underlines the importance of taking the distribution and behaviour of receptive females into account when studying mate-locating behaviour. [Copyright &y& Elsevier]

Optimality models predict that territory size will decrease as the costs of defence increase. One poorly understood cost is predation risk, especially the relative influence of short- versus long-term increases in predation risk. Under natural conditions, we quantified the territorial behaviour of juvenile Atlantic salmon, Salmo salar, exposed to either acute or chronic increases in perceived predation risk. The effects of an acute increase in predation risk were assessed by exposing 18 young-of-the-year (YOY) Atlantic salmon to a control of stream water and to an alarm cue (i.e. conspecific skin extract) while monitoring their territorial behaviour. We investigated the effects of a chronic increase in perceived predation risk by quantifying the territorial behaviour of YOY salmon in control versus risky sections of seven sites, where we manipulated the perceived predation risk over a 4-week period by releasing stream water in control sections and alarm cue in risky sections. We found that salmon exposed to the alarm cue decreased the number of switches between foraging stations, but they did not change their territory size or foraging rate. As predicted, YOY salmon in risky sections had smaller territories than in control sections. However, their foraging rates and number of switches between foraging stations did not differ between treatments. Our study suggests that juvenile Atlantic salmon are sensitive to both acute and chronic increases in perceived predation risk under natural conditions, and support the predictions of optimality models that territory size decreases with increasing predation risk. [Copyright &y& Elsevier]

The evolution of cooperation between unrelated individuals has been a central issue in evolutionary biology. The main problem in most theories of cooperation is how a cooperative player selects individuals to ‘trust’ so that he does not get exploited by noncooperators. While early models emphasized the role of direct experience with individuals in deciding who to trust, more recent work has shown that individuals can eavesdrop on interactions between other individuals to identify cooperators and noncooperators. This second route to cooperation is called indirect reciprocity. In spatially structured populations with repeated interactions between players, both sources of information (direct experience and observed reputation) are readily available. Most models and empirical studies to date, however, have considered indirect reciprocity only in one-shot interactions when direct experience is not available. We examined the role of indirect reciprocity in the maintenance of mutual restraint in aggression (Dear Enemy cooperation) between territorial male song sparrows, Melospiza melodia. We found that territory owners eavesdropped on simulated defections by a neighbour (intrusions onto a third bird’s territory) and subsequently retaliated against these defecting neighbours. Taken together with our previous results, these results suggest that both direct and indirect reciprocity can be at work in repeated-interaction scenarios, and together lead to emergence of cooperation. [ABSTRACT FROM AUTHOR]

The ecological relevance of behavioural syndromes is little studied in cooperative breeding systems where it is assumed that the behavioural type might influence individual decisions on helping and dispersal (e.g. shy, nonaggressive and nonexplorative individuals remain philopatric and helpful, whereas bold, aggressive, explorative individuals compete for vacancies outside their group and disperse). We measured the behavioural type of 19 subordinates in the cooperatively breeding cichlid fish Neolamprologus pulcher in their natural environment by quantifying six behavioural traits up to four times (‘trials’) in three different contexts, by presenting them with a conspecific intruder, a predator or nothing inside a tube. We found only moderate within-context repeatability (intraclass correlation coefficients) of the focal individual’s behaviour, except for attacking either the conspecific or the predator inside the tube. The focal individual’s attack rate of the tube was also positively affected by its group size. Averaging traits per context removed the between-trial variation, and consequently the across-context repeatability was very high for all six traits, except for territory maintenance. Trait values depended significantly on the context, except for territory defence. Consequently, individuals could be classified into different behavioural types based on their reaction towards the tube, but surprisingly, and opposite to laboratory studies in this species, ranging propensity and territory maintenance were not included in this behavioural syndrome. We suggest that more studies are needed to compare standardized focal personality tests (e.g. exploration propensity) with actual behaviour observed in nature (e.g. ranging and dispersal). [Copyright &y& Elsevier]

A great deal of variation is known to underlie the vocalizations of animals. Calls can for example vary between individuals or between social and behavioural contexts. Calls also have the potential to vary between groups. Many group-living animals are known to produce stereotyped group-specific calls and such group signatures are thought to play a role in territory defence or indeed mate choice. Group signatures are generally found in long-distance call variants that work to maintain contact between group members, sometimes referred to as ‘contact calls’. Cooperatively breeding, territorial meerkats, Suricata suricatta, also use contact calls, potentially to maintain social organization during foraging. However, these contact calls are generally quieter than long-distance calls in other species, and better described as ‘close calls’. We investigated whether these similar call types also possess group-specific signatures and whether any such variation is used by receivers. We recorded close calls from 71 individuals belonging to 10 meerkat groups. We found that such close calls indeed possessed group signatures, but that this underlying variation did not appear to be used by receivers, possibly because meerkats use other sensory systems to identify nongroup members. We stress the importance of conducting playback experiments when investigating group-specific vocal signatures and use our results as a basis for predicting which animals may rely on group information encoded within close calls. [Copyright &y& Elsevier]

The ability to discriminate among signallers and to respond to them on an individual basis provides receivers with substantial benefits. For example, discriminating among signallers allows receivers to ignore unreliable individuals or to focus their territorial defence on unfamiliar intruders. Such discrimination requires signals to be individually distinctive; that is, signals must vary more among than within individuals. Furthermore, receivers must be able to discriminate among the signals of different individuals. In this study, we used fine structural analysis to show that the simple songs of male black-capped chickadees are individually distinctive, but that substantial variation exists both within and among recordings of the same individual. This finding emphasizes the need for multiple recordings of each individual in studies of individual distinctiveness, since failing to measure variation across recordings of the same individual can make it difficult to determine whether signals vary among individuals or whether they simply vary among different recording sessions. To test whether chickadees discriminate among the signals of different individuals, we used a playback experiment in which we broadcast priming and discrimination stimuli to 45 territorial males. When individuals heard the playback of two different males, they produced more songs and remained near the loudspeaker for a longer period than when they heard two different exemplars from the same male. Chickadees can therefore discriminate among singers based exclusively on their songs, which may help to explain how chickadees eavesdrop on singing contests and subsequently select extrapair mates on the basis of song contest performance. [Copyright &y& Elsevier]

Individual recognition is expected to enhance fitness by allowing animals to direct appropriate behaviours to specific individuals during interactions with conspecifics. Reduced aggression towards territorial neighbours (‘dear enemy phenomenon’) is based on the assumption that strangers lacking territories pose a greater threat than territory-holding neighbours. Based on the ability of the subterranean rodent Ctenomys talarum (tuco-tuco) to distinguish between familiar and unfamiliar conspecific odours, I assessed whether males, the more aggressive sex, show dear enemy relationships and whether social experience with odour donors affects the memory of conspecific odours. Male–male contests in the laboratory were used to compare the aggressive behaviour of pairs of males. Familiar male tuco-tucos responded less aggressively during contests than unfamiliar males, providing evidence of the dear enemy relationship in C. talarum. Memory for familiar odours was affected by social experience since discrimination of known from novel odours lasted longer when males encountered each other in dyadic contests following familiarization with odours. Familiarity by odour cues would represent an important mechanism mediating neighbour recognition and territorial behaviour for tuco-tucos in the wild; intruders may represent a threat of great consequence for territory-holding individuals since they represent the potential loss of their burrow system and their priority of access to neighbouring females. [Copyright &y& Elsevier]

In many territorial species males invest substantially in weapons, which they use in fights to acquire and maintain territories that ultimately give them access to females. Females often live within male territories or in female-only areas that are segregated from males. Under these circumstances, females do not have to compete directly with males for space, and in the context of territory acquisition and defence there is therefore no cost to being weaponless. In fiddler crabs, however, weaponless females hold territories among well-armed males. How do they do this? Observations and replacement experiments were carried out on Uca annulipes to determine how males and females acquire and defend territories. Weaponless females were as capable as well-armed males of both acquiring and defending a burrow. Females acquired burrows by seeking out empty ones, while males acquired them by evicting male and female burrow owners. After acquiring a burrow, males mainly fought with male neighbours and females with female neighbours. Both sexes were equally likely to be evicted from their burrow and the likelihood that they remained on their territory for 24h or more was the same. Males and females thus used different strategies of burrow acquisition and defence, and the male strategy appeared to be more costly. We discuss possible explanations for these differences. [Copyright &y& Elsevier]

Territory owners often respond with greater aggression to strangers than to neighbouring individuals, a phenomenon known as the ‘dear enemy’ effect. As strangers are usually ‘floating’ individuals seeking to acquire a territory they pose a relatively greater threat to a resident than do neighbours, who are already territory owners. This explains why residents are less aggressive towards neighbours but not how they distinguish neighbours from strangers: do residents recognize their neighbours or respond to differences in the behaviour of neighbours and strangers? Using measures of fighting intensity we investigated the dear enemy effect in a fiddler crab, Uca mjoebergi. We then experimentally manipulated the residency status of pairs of neighbours to distinguish between mechanisms enabling the dear enemy response. Fights between resident and nonterritory-owning individuals were longer and more escalated than fights between neighbouring residents, whether the nonterritory-owner was familiar (a former neighbour) or unfamiliar to the resident. Our results are consistent with the ‘relative threat’ hypothesis to explain the dear enemy effect, and support the suggestion that residents use cues in the behaviour of an intruder to determine the level of threat posed and distinguish between neighbours and strangers. However, we note that the observed patterns can occur even if residents do not differentiate between intruder types, and simply respond appropriately to the aggressiveness and persistence of an intruder. [Copyright &y& Elsevier]

Wild chimpanzees can be dangerously violent against individuals that do not belong to their community, indicating a strong selection pressure on decision-making abilities in this context. The presence of a neighbouring male indicates a serious threat, although encountering an unfamiliar male is potentially even more dangerous because it indicates the arrival of a new group with whom the subjects have no previous history of interaction. We conducted playback experiments with members of three chimpanzee, Pan troglodytes verus, communities in the Taï National Park, Côte d''Ivoire, in which we simulated the unexpected presence of another chimpanzee. We tested subjects'' responses to pant hoots of familiar group members, neighbouring individuals and unfamiliar strangers. We found that neighbours and strangers elicited a wider range of gestural signals than familiar group members. Vocal responses were common in all conditions. Familiar group members mainly triggered pant hoot replies, whereas neighbour and stranger trials caused screams. Across conditions, males responded more strongly than females. Male party size had an effect on subjects'' vocal responses to strangers but not to neighbours, although neighbours were approached more closely. Our results show that chimpanzees are able to identify different classes of individuals by their pant hoot vocalizations, as judged by their differential responses to the calls of familiar group members, neighbours or strangers. The overall response patterns suggest that chimpanzees are aware of the different social consequences associated with encountering a neighbouring group or a group of strangers. [Copyright &y& Elsevier]

To understand how sexual selection works, it is important to distinguish between the mechanisms underlying mating success. One of the basic questions is to differentiate between the importance of territory-related resources (gained through male–male competition) and male quality in female choice. Few studies, however, have tried to separate these two often intercorrelated variables. We randomized territory quality among male pied flycatchers, Ficedula hypoleuca, and studied which male traits were associated with their success in female mate choice. Females appeared to choose multiple male traits in the wild when the males were not allowed to choose territories before female choice for males. Males with a long tarsus, large white wing patch and versatile song were favoured by females. In addition, the contrast of ultraviolet (UV) reflectance in the white wing patch relative to its background, that is, the dorsal brown-black coloration of the males, appeared to be an important mate choice cue. The UV reflectance had a stronger effect on pairing success in dark males than in brown ones. An experimental manipulation of the UV reflectance revealed that the UV coloration of the males appeared to be used in female choice early but not late in the pairing season, which suggests time-dependent plasticity in female choice. Our study thus exemplifies the complexity of mate choice; it is both temporally constrained and dependent on multiple ornaments. [Copyright &y& Elsevier]

Mate location strategies vary between species. Among butterflies two strategies are recognized: ‘patrolling’ males spend their life on the wing searching for females and ‘perching’ males stay at a specific site waiting to intercept passing females. In the speckled wood butterfly, Pararge aegeria, two alternative male strategies have been described: dominant males adopt a perching strategy monopolizing large sunspots on the forest floor, and subdominant males adopt a patrolling strategy. However, comparative analyses have shown that body design differs between perching and patrolling species, hence constraining opportunity for within-species variation in mate location strategy. We tested whether males differ in their propensity to adopt perching or patrolling behaviour by recording time spent flying during 30min when alone in a large cage with only one large sunspot and many smaller ones, and whether subdominant males adopt a patrolling strategy by allowing dyads of males to interact in the cage for 60min and recording the same behaviours again. All males adopted perching behaviour when alone, and subdominant males in dyads spent only a short time in extended flights after losing contests over territory ownership, soon returning to a perching strategy and making the best of a bad job from the vantage point of a small sunspot. We argue that previous descriptions of subdominant male P. aegeria adopting a patrolling strategy are based on too short observation periods, and have mistaken males in temporary transit for males adopting patrolling behaviour. [Copyright &y& Elsevier]

Song learning in birds makes it possible for males to faithfully imitate tutors and also to generate novel improvisations. Within local dialects of the Puget Sound white-crowned sparrow, most males share the terminal trill phrase in their songs. In contrast, the introductory note complex is more variable within local populations and appears to encode individual identity. We studied the song-learning process during initial territory establishment in a wild population of white-crowned sparrows. Although most adult males sing a single song type, many yearling males overproduce song types early in their first singing season before deleting all but one song type from their repertoire. We asked whether this attrition process favours retention of a song with a note complex that resembles that of a male''s neighbour, as would be predicted by various hypotheses assuming a benefit to song sharing, or whether it favours retention of a distinctive note complex, which would produce individuality in song. We found that males that initially overproduced song types retained shared note complexes, and that these males were more likely to share their adult note complex with neighbours than were young males that did not overproduce. Only 51% of recruits overproduced, however, and we close by speculating that overproduction and close song sharing may be correlates of male quality and learning ability. [Copyright &y& Elsevier]

We analysed 38 years of data on 46 lion prides in the Serengeti National Park, Tanzania, and found that territorial competition directly affected critical components of female fitness and that larger prides gained and maintained access to the highest-quality habitat. Neighbours had a significant negative effect on female reproductive success and survival, and larger prides were significantly more likely to maintain control of disputed areas and to improve the quality of their territories. Adult females were significantly less likely to be alone when a pride had more neighbours, suggesting sensitivity to risk of encounter. In most cases, the effects of intergroup territorial competition were associated only with prides that had not recently split (i.e. that were not closely related). Overall, males were more important in group-territorial competition than expected, and female mortality and wounding rates were significantly associated with male neighbours, suggesting that males may use lethal aggression to tip the balance of power in favour of their prides. Within the Felidae, only lions are consistently gregarious, and our research illustrates that numerical advantage in territorial competition is a primary benefit of group living in lions and may have been important in the evolution of lion sociality. [Copyright &y& Elsevier]

Many territorial animals, despite being in direct competition for resources such as space, food and mates, show reduced aggression towards their neighbours. This situation is called the Dear Enemy effect. One explanation of the Dear Enemy effect is that it is due to a conditional strategy like Tit for Tat where territory holders cooperate by reducing aggression towards neighbours that also show reduced aggression, but retaliate against aggressive neighbours. Previous research found evidence for such a conditional strategy in migratory species but not in species with long-term association between neighbours, suggesting that long-term neighbours might be engaged in more ‘forgiving’ strategies. We tested this hypothesis in male song sparrows, Melodia melospiza, which are resident year-round in our population (leading to long-term associations between neighbouring birds) and display the Dear Enemy effect. We found that following a simulated intrusion by a neighbour, song sparrow males responded more strongly to playback of this neighbour than to playback of a neutral neighbour from their respective boundaries, consistent with a conditional retaliation strategy. We suggest that the primary effect of an intrusion by a neighbour might be to increase the perceived risk of cuckoldry by the intruding male, and increased aggression and vigilance towards this neighbour might be a strategy to prevent cuckoldry. [Copyright &y& Elsevier]

Spatial abilities have been associated with many ecologically relevant behaviours such as territoriality, mate choice, navigation and acquisition of food resources. Differential demands on spatial abilities in birds and mammals affect the hippocampus, the region of the brain responsible for spatial processing. In some bird and mammal species, higher demands on spatial abilities are associated with larger hippocampal volumes. The medial and dorsal cortices are the putative reptilian homologues of the mammalian hippocampus, yet few studies have examined the relationship between these brain areas and differential spatial use strategies in reptiles. Furthermore, many studies in birds and mammals compare hippocampal attributes between species that use space differently, potentially confounding species-specific effects with effects due to differential behaviours in spatial use. Here, we investigated the relationship between spatial use strategies and medial and dorsal cortical volumes in males of the side-blotched lizard. In this species, males occur in three different morphs, each morph using different spatial niches: large territory holders, small territory holders and nonterritory holders with home ranges smaller than the territories of small territory holders. We found that large territory holders had larger dorsal cortical volumes relative to the remainder of the telencephalon compared with nonterritorial males, and that small territory holders were intermediate. These results suggest that some aspect of holding a large territory may place demands on spatial abilities, which is reflected in a brain region thought partially responsible for spatial processing. [Copyright &y& Elsevier]

Territory residency is associated with considerable benefits. In the speckled wood butterfly, Pararge aegeria, males fight over ownership of large sunspots in open forest habitats; winners become sunspot residents, and losers become nonterritorial and sit and wait for females in small sunspots. A previous study has shown that residents have higher mating success than nonterritorial males, although females are not more attracted to territorial males or sunspot territories per se. Here we tested the hypotheses (1) that the higher success of resident males is caused by visual mate detection being more efficient in a large than in a small sunspot, and (2) that only sunspots above a certain size are defended as territories. Field assessment of territorial sunspot size showed that defended sunspots were significantly larger than ‘average sunspots’ on the forest floor. Experimental tests of male ability to detect visually a model butterfly passing through a sunspot showed that males were more successful in pursuing and intercepting a passing model when flown a longer distance in the sunspot. Hence, we conclude that light conditions and associated visual mate detection and ability to complete mate flight pursuit can explain why P. aegeria males defend territories in large sunspots in forest habitats. [Copyright &y& Elsevier]

We conducted experiments on the intersexual and intrasexual consequences of epaulet colour in male red-winged blackbirds, Agelaius phoeniceus. In the female choice experiment, we gave captive females a choice between males with normal or dulled epaulets, and between males with normal or reddened epaulets. Females tended to associate more with normal males than with dulled males, but were equally likely to perform precopulatory displays to the two types of males. Females associated significantly more with redder-than-normal males and were more likely to perform precopulatory displays to reddened males. In the male–male competition experiment, we presented free-living territorial males with a male model to which we could attach wings with dulled, normal or reddened epaulets. Presence of the model with reddened epaulets resulted in significant increases in display rates by territory owners, but the increase in display rates was probably in response to males other than the territory owner flying through and trespassing rather than to the reddened epaulet model per se. Normal epaulets produced a significant decrease in song rates and approach distances of owners. Responses of territorial and other males did not differ significantly during normal and dulled epaulet presentations. These results support the hypothesis that epaulets of male red-winged blackbirds are salient inter- and intrasexual signals: unusually red epaulets were attractive to females and attracted more attention and aggression from male conspecifics than normal epaulets. Epaulet colour may thus be an example of intrasexual selection opposing intersexual selection. [Copyright &y& Elsevier]

The function of wolf, Canis lupus, faeces in chemical communication and the selection of raised and conspicuous substrates to increase their effectiveness as visual scent marks are well documented. Therefore, I hypothesized that faecal marks are not placed randomly on plants, and that wolves will select specific plants according to characteristics that enhance faeces as visual scent marks and ensure greater support and persistence of these marks over time. Analysis of the physical properties of plants marked by Iberian wolves showed that the choice of plants was clearly not random. The factors that determined selection were plant diameter, height and species. The mean height and diameter of faeces-marked plants were significantly greater than those of unmarked plants. Furthermore, plant use in relation to size (diameter and height) and species did not depend on availability in the environment. Persistence time was independent of the substratum type, height and altitude, but did depend on the scat content, being longer when the scat contained bone than when it contained hair or undetermined matter. These results indicate that the physical appearance of the plant is important for the wolf when deciding where to deposit faecal marks. Thus, the use of standard species and sizes of plants maximizes visual localization of faecal marks deposited by intruder and resident wolves. [Copyright &y& Elsevier]

Many animals display multiple signals that can be used by conspecifics to gather information about the condition or quality of potential mates or competitors. Different signals can indicate different aspects of individual quality or function in spatially or temporally separated periods. However, for long-distance migratory birds, it is unclear if signals, such as plumage traits, function in different phases of the annual cycle. We investigated the potential role of carotenoid-based tail and flank plumage, and bib size, in relation to extrapair paternity and polygyny in the American redstart, Setophaga ruticilla. This work complements our previous research suggesting tail feather brightness acts as a status signal, mediating territory acquisition during the nonbreeding season in Jamaica. Here, we show that tail feather brightness also serves as an important signal during the breeding season. Specifically, our results indicate that polygyny, a behaviour highly dependent on obtaining and defending multiple territories, is significantly predicted by tail brightness. Interestingly, flank redness best predicted whether individuals secured paternity at their nest and the proportion of within-pair offspring sired. We suggest that by expanding the study of plumage function in long-distance migrants to events occurring throughout the annual cycle, we gain a critical perspective on the function and evolution of ornamental traits. [Copyright &y& Elsevier]

The study of breeding habitat selection has focused mainly on physical characteristics of the environment such as nest sites and food abundance, both of which are required for successful reproduction. However, individuals may have limited time to make settlement decisions, and thus, their knowledge of resource availability may be incomplete. Furthermore, food abundance during settlement may not reflect levels later in the breeding season. An alternative perspective is that the most direct measure of habitat suitability is derived from social information such as the presence of conspecifics (conspecific attraction) or their reproductive performance (habitat copying). We tested resource and socially based hypotheses of habitat selection in a population of eastern kingbirds, Tyrannus tyrannus, at Malheur National Wildlife Refuge in southeastern Oregon, U.S.A. Kingbirds nested in areas with a greater proportion of suitable nest trees than what was generally available, but many areas with suitable numbers of trees went unused. Kingbirds also settled in areas of relatively high insect abundance, but only in years when overall abundance was low. We also found support for the socially based hypotheses. Relative to where they nested previously, kingbirds tended to settle in areas of higher conspecific density. But, we found stronger evidence in favour of habitat copying, suggesting that dispersing individuals settled in areas that produced more fledglings in the previous year. Kingbirds thus appeared to select breeding habitat based, in part, on resource availability, but dispersal decisions may be influenced by social information, primarily past reproductive success of conspecifics. [Copyright &y& Elsevier]

Sexual selection may take place before or after mating and may involve a large number of different mechanisms, for example, overt male aggression, mate choice, sperm competition and cryptic female choice. In most species, males show similar reproductive tactics and, hence, achieve their reproductive success in the same or a similar way. Sometimes, however, males evolve alternative reproductive tactics. One such example is the polychromatic Australian painted dragon lizard, Ctenophorus pictus, in which red males beat yellow males in staged contests for females and show different emergence patterns posthibernation in the wild with red males emerging to establish territories before yellow males do (at least in some years). Here we show that yellow males have significantly larger testes in relation to body size and condition than red males and copulate for a shorter period of time. Our mating experiments further showed that sperm storage played a significant role in male reproductive success (i.e. males sired offspring in later ovarian cycles than the one in which they actually mated). Furthermore, yellow males had a three times higher probability of paternity in some situations of sperm competition than red males, suggesting that male polymorphism may be associated with different reproductive tactics. [Copyright &y& Elsevier]

Animals assess many factors when choosing how aggressively to behave during interspecific competitive interactions. Aggressive behaviour can help win resources, but it can also be costly. Here we tested how context such as competitor familiarity, habitat type and resource value affect competitive behaviour using two ant species, Formica xerophila and F. integroides. We found that competitive encounters within an individual''s territory yielded more aggressive interactions than encounters in a neutral arena, and aggression towards competitors increased with resource value. Using a recently developed design combining behaviour assays between live ant dyads and ants paired with glass beads chemically resembling competitors, we isolated an individual''s behaviour during an encounter to show that its behaviour can be significantly affected by the behaviour of its competitor during the interaction. Furthermore, we determined that context can affect each species differently, and that these differences are consistent with differences in overall fighting abilities. Formica integroides from trees (but not from nests) behaved differently towards live and artificial F. xerophila. Formica integroides are behaviourally dominant, which facilitates a strategy wherein individuals aggressively defend the nest but reciprocate the behaviours of their opponents (showing an interspecific Tit-for-Tat strategy) when defending less valuable locations. Formica xerophila are generally submissive, which favours a highly context-dependent strategy. In particular, F. xerophila discriminate between familiar and unfamiliar F. integroides, and behave more aggressively towards foreign competitors than towards neighbouring competitors. Differences between species’ behaviours suggest that these interspecific interactions are dynamic context-dependent associations that cannot be reduced to a static dominance hierarchy. [Copyright &y& Elsevier]

Dispersal is a common phenomenon in animals, with important consequences for individual fitness and the genetics and structure of populations. We studied the causes and consequences of breeding dispersal from an individual perspective using as a model organism the colonial lesser kestrel. For this purpose, we gathered information on 235 birds that attempted to breed in 2 consecutive years (2004–2006) in any of the 22 colonies monitored in the study area. Eighty-two per cent of kestrels returned to the same breeding colony where they had attempted to breed in the previous year. Probability of dispersal decreased with age and individual reproductive performance in the season previous to dispersal and females dispersed more frequently than males. Dispersers settled in colonies with a higher mean reproductive performance than other available colonies located around their colony of origin. However, the size of the colony selected did not differ between selected and surrounding colonies. Thus, dispersers selected highly productive rather than large colonies. Own body condition or the quality of the mates obtained (estimated by their pectoral thickness and size) did not change for individuals that dispersed or for philopatric individuals in subsequent seasons. Although dispersers greatly increased their own breeding performance after dispersal, it did not exceed that of their philopatric counterparts. These results help to explain the coexistence of dispersal and philopatric behaviours within a population and suggest that dispersal may be an adaptive behaviour that increases reproductive performance, particularly for individuals that have suffered a bad breeding experience. [Copyright &y& Elsevier]

We investigated the effects of male size and adult diet on male sexual competitiveness and lifetime reproductive success of female mates in two tephritid flies with contrasting natural histories, the Mexican fruit fly, Anastrepha ludens, and the guava fruit fly, A. striata. Small, medium and large males received either a low-quality diet (sucrose offered every third day) or a high-quality diet (sucrose and protein offered ad libitum). Regardless of size or species, males on the high-quality diet copulated significantly more often across the 4 observation days than males on the low-quality diet. For A. ludens, both size and diet influenced territory defence by resident males, but only size affected the likelihood of success by invading males. Females that copulated with a low-quality fed male had significantly shorter maximum longevity, although there was no effect of male diet on the proportion of eclosed eggs. For A. striata, diet, but not size, influenced territory defence by invading males. Females discriminated strongly against males fed a low-quality diet but not against smaller males. However, females that copulated with medium and small males had lower fecundities than those copulating with large males. We discuss the costs for females of mating with smaller males and their inability to distinguish between males of different conditions, as well as interspecific differences in mate choice and postcopulatory consequences for females in terms of the ecological differences that distinguish these two species. [Copyright &y& Elsevier]

Species that vary in social structure within and among populations can provide unparalleled insight into the evolution of sociality. The theridiid spider Anelosimus studiosus varies widely in its social structure at the northern edge of its range. Colony sizes range from the solitary/territorial female with her offspring to cooperative colonies of tens to hundreds of adult females. In previous work, we developed an assured fitness returns ‘brood-fostering model’ that predicts that in cooler environments mothers in multiple-female colonies will have a selective advantage over solitary female nests. According to the model, at cool sites the rate of juvenile maturation is slowed, increasing the probability that the mother will die before the brood reaches independence. In her absence, other females would foster her brood. We tested this hypothesis by manipulating colony size and by monitoring the reproductive success of naturally occurring solitary and multifemale colonies in cold and warm temperature environments. Our results indicate that while multiple-female colonies have higher fitness at cool sites, the solitary female nests achieve higher fitness at warmer sites. The higher reproductive success of multifemale colonies at cold sites further reflects the total failure of solitary female nests at these sites. Solitary female nests that survived generally had higher reproductive success than multifemale colonies at all temperatures. In natural colonies, fitness was highest for smaller multifemale colonies in the colder environments and decreased in the larger colonies. We use these data to refine the brood-fostering model and discuss the results with regard to the observed polymorphism in social structure. [Copyright &y& Elsevier]

Among social insects, awareness of the presence of queen(s) or reproductive individuals is crucial to the maintenance of group cohesion. Although it is fairly well established that information on the queen''s presence is chemical, little is known about how this information is transmitted among colony members. In Diacamma sp., direct physical contact informs nestmate workers of the presence of the gamergate. We investigated the pattern and efficiency of transmission of gamergate information to workers in Diacamma sp. Workers could sense the absence of a gamergate and switch their behaviour within 3h of being orphaned. However, even in colonies with gamergates present, some workers failed to encounter the gamergate within 3h of their last contact. This transmission inefficiency increased with increasing colony size. Nevertheless, workers in colonies of a natural size range usually refrained from reproducing in the presence of gamergates. This suggests that self-restraint by workers in response to the perception of queen presence alone does not explain the absence of worker reproduction. The gamergate increased her frequency and duration of walking around in the nest as the colony size increased, possibly to improve contact efficiency and police worker reproduction. Simultaneously, dominance and policing behaviours by workers occurred more frequently with increased colony size. Our study shows that multiple complementary mechanisms, such as policing, dominance and self-restraint, regulate the reproductive division of labour in Diacamma sp. We also report the novel finding that the relative importance of these mechanisms can change over time as the colony grows. [Copyright &y& Elsevier]

True individual recognition (TIR), the ability to recognize conspecific individuals on the basis of identity cues, is required for the evolution of several social traits (e.g. the maintenance of dominance hierarchies). However, knowledge about the distribution and functional significance of TIR is scant in some vertebrate groups, such as reptiles. In this study we used a functional modification of a habituation–dishabituation paradigm to investigate the existence and adaptive significance of TIR in a territorial lizard (Podarcis hispanica, Lacertidae). Males discriminated between individual rivals of similar characteristics (e.g. size, weight, familiarity) solely on the basis of their scent marks. Males also remembered the spatial location of scent marks and subsequently behaved more aggressively towards rival males that consistently marked in the core than on the periphery of their experimental terrarium. Together, these results suggest that, in this species, scent marks function to identify the potential threat posed by each individual neighbour, allowing resident males to allocate their aggressive behaviour accordingly. Our findings challenge the simplistic and commonly held view that ‘dear enemy’ phenomena in lizards are exclusively based on familiarity asymmetries, and support an alternative threat level hypothesis in which TIR may be more important than previously acknowledged. [Copyright &y& Elsevier]

Alternative male mating tactics in species with external fertilization are often viewed as coercive matings by low-quality males, when a male, unable to attract a female himself, steals fertilizations from a spawning pair by adopting ‘sneaky’ mating tactics, thereby eroding the interests of both the pair-mating male and female. Although a cost of sneaking to guarder males is inevitable, we highlight emerging evidence that females may actually seek and benefit from mating with sneaking males. Sneaking may thus be a means by which females gain access to resources critical for reproduction when these are defended by males adopting a guarder tactic, while maintaining some control over indirect (genetic) benefits through mate choice. We consider a range of potential costs and benefits that females may obtain from matings that involve sneakers and review empirical studies on female responses to sneaking. We show that the outcome of the trade-off between costs and benefits is context specific and may vary among mating systems, species, populations within species, and individual females within populations. This emerging evidence undermines the view that sneaking necessarily represents forced fertilizations and that sneakers are always low-quality males making ‘the best of a bad job’. When females prefer to spawn in the presence of sneaker males, the distinction between deliberate polyandry and sneaking becomes ambiguous and females may only be limited in the expression of their mating preferences by resource monopolization or mate guarding by dominant males, resulting in an intersexual conflict. [Copyright &y& Elsevier]

We investigated whether male-specific territorial ‘yodels’ communicate information about individual size and condition in the common loon. Individuals in better condition and of larger body mass, but not larger structural body size, produced lower-frequency yodels, and changes in dominant frequencies of yodels between years reflected changes in male body mass and condition. An acoustic playback experiment indicated that potential receivers vocalized sooner and more often in response to low-frequency yodels, a possible indication that dominant frequencies of the yodel may communicate condition-dependent fighting abilities. Physiological constraints associated with mass and/or condition may preserve honest signalling by preventing small individuals from producing low-frequency yodels. [Copyright &y& Elsevier]

Croaking gouramis, Trichopsis vittata (family Osphronemidae), possess enhanced pectoral fin muscles and tendons, enabling the fish to generate series of short or long broadband bursts while beating the fins. Agonistic disputes over territories result in lateral displays during which both sexes produce croaking sounds. During mating, a female approaches a male''s nest at the water surface and emits purring sounds in a vertical, head-up position. This behaviour is followed by spawning bouts. I investigated whether aggressive and prespawning sounds differ in acoustic characteristics and whether they might convey different information. Agonistic sounds of both sexes lasted longer than the females'' prespawning sounds, consisting of four or five bursts/sound compared to 2.4 bursts in purring sounds, and included a smaller percentage of short bursts. Sound pressure levels were higher in agonistic than in prespawning sounds. The dominant frequency of male agonistic signals was lower than that of female prespawning sounds. Both sexes produced long, high-intensity croaking sounds during agonistic disputes; these probably help them assess the fighting ability of opponents. On the other hand, only females emitted short, low-intensity purring sounds, which probably initiate and coordinate spawning behaviour. The low sound level and short duration of prespawning sounds indicate that they function as mating displays at very short distances; this probably reduces the chance of attracting competitors or predators. The croaking gourami is the only fish species in which females are known to initiate spawning acoustically. [Copyright &y& Elsevier]

Interspecific territoriality is usually interpreted to result from interspecific interference competition, although it may also originate from mistaken species recognition. In the latter case, it may be based on similarity of secondary sexual characters. In the damselfly Calopteryx splendens, males have pigmented wing spots as a sexual character, and males with the largest spots resemble males of another species, Calopteryx virgo. Probably because of this resemblance, C. virgo males are more aggressive towards large- than small-spotted C. splendens males. We examined whether wing spot size of C. splendens males affects territorial interactions between the species. In a removal experiment, the number of territorial C. splendens increased after C. virgo males were removed. However, interspecific territoriality was incomplete since before the removal the territories of the species partially overlapped. Wing spot size of C. splendens seemed to affect interspecific territoriality: before the removal territorial and nonterritorial C. splendens males had similar spot sizes and the distance to the nearest C. virgo territory increased with wing spot size of C. splendens. In addition, after the removal of C. virgo, the relation between wing spot size and the distance to the nearest old C. virgo territory disappeared. Our results suggest that mistaken species recognition may account for the interspecific territorial behaviour in the two species. Furthermore, interspecific territoriality may cause negative selection on wing spot size and thus may explain character displacement in wing spot size of C. splendens males. [Copyright &y& Elsevier]

Within a female-defence polygynous mating system, males of the lizard A. carolinensis use an array of stereotyped signals and aggressive tactics to acquire and defend long-term territories containing multiple, sedentary females. In competition, body size appears to be important because size of free-ranging males correlates positively with volume of male territories and number of patrolled females. Therefore, an ability to assess body size during territorial contests should be an adaptive attribute that would influence the tactics of intermale aggression. To examine this premise, we staged contests between 10 pairs of males matched for size (i.e. symmetric contests) and 10 pairs mismatched for size (i.e. asymmetric contests), while all 20 pairs of males were matched for habitat resources, a mate, and resident status. Overall, we found (1) contest profiles best fit the features of a ‘fixed-phase, sequential assessment’ model of game theory, (2) body size and mass were highly correlated with contest outcome, (3) none of 12 signal variables predicted contest outcome, and (4) paired males generally matched aggressive tactics and signalling behaviours. We also examined the asymmetric contest profiles for deviations from the profiles of symmetric contests. We tested the proposition that smaller males of size-mismatched contests would assess their disadvantage and choose a bluff strategy to mitigate risky behaviour and avoid fighting. We found, however, that the risk-mitigation hypotheses were unsupported. Smaller males were not playing a bluff strategy, but rather a hawk strategy. They initiated risky tactics by (1) invading the habitats of their larger opponents, an act that invited retaliation, (2) showing no tendency to stay away from larger opponents, (3) maintaining high levels of aggressive signalling as encounters intensified, and (4) engaging larger opponents in physical fighting, despite losing 90% of their encounters. These empirical results support a recent game theoretical construct (‘Napoleon complex’) that models size-asymmetric contests in which smaller males initiate fights that they usually lose. Our data suggest that, if smaller males of A. carolinensis have breeding territories, then they will engage in costly contests, despite a low probability of defeating larger and equally motivated opponents. [Copyright &y& Elsevier]

Skew in the operational sex ratio of a population can have important consequences for mating competition and typically results in differential mating success. Population density can also influence mating behaviour and may interact with the operational sex ratio. We investigated the effects of both density and operational sex ratio on male territoriality and female oviposition in the zebrafish. We manipulated the sex bias in favour of either males or females at two density levels and measured the impact on females of aggression and courtship behaviour by territorial males in terms of egg production. Total egg production increased as a function of the number of females in each of the four treatments. However, mean per capita egg production was lower at high densities. We propose that this effect was due to increased aggression at high densities by territorial males towards rivals, which interrupted female spawning attempts. At high densities, territorial males maintained high rates of aggression regardless of sex bias, but courtship rates were significantly lower in male-biased treatments. We further propose that this response, whereby males constrain courtship in the presence of potential rivals, may be adaptive in the context of sperm competition avoidance. [Copyright &y& Elsevier]

Males with elaborate secondary sexual traits can enhance their mating success both by choosing to display at a site that increases the efficacy of their signal and by displaying at a site where the population is structured to provide inclusive fitness benefits via kin selection. Theoretical models and field studies reveal that, across a range of species and especially those with nonresource-based mating systems, males do display with kin. Bowerbirds use a nonresource-based mating system where males show spatial site fidelity and females visit the sites for the purpose of mate choice. However, neighbours can interfere with bower display by marauding (destroying and decoration stealing). Models suggest that local nonaggression pacts provide the best conditional strategy for males, a situation that may be facilitated by kin-mediated inclusive fitness benefits if males displayed together. We used a novel method of calculating relatedness, based on amplified fragment length polymorphism (AFLP), in a population of spotted bowerbirds, Chlamydera maculata, and found no evidence of fine-scale genetic structuring of display sites. Furthermore, males did not display next to kin, but instead an owner''s neighbours were those most likely to maraud his bower. Marauders did not discriminate between kin and nonkin as their victims. Such theft and destruction may affect the mating success of the targeted bower owner. [Copyright &y& Elsevier]

Scent marking is common among male and female rodents and might be used in male-male competition and as a mechanism for mate attraction. I tested the hypotheses that females would choose males based on their frequency and placement of scent marks, and that a female would advertise interest in a particular male by placing her scent marks on or near those of a preferred mating partner. In a series of experiments conducted with prairie voles, Microtus ochrogaster, females did not choose mates based on the frequency or placement of scent marks by males nor did they advertise their interest in a particular male through the frequency or placement of scent marks. The number of males chosen that scent-marked more than their opponents did not differ significantly between females exposed (11 of 15) and not exposed (10 of 15) to scents of males. Females exposed and not exposed to scents of males preferred seven of the same males that had scent-marked more than their opponents. When a third group of females was exposed to four times more scent of the less preferred than preferred males, they still chose the preferred males. Thus, the frequency and placement of scent marks by males were not used to assess males for mate choice nor did female prairie voles use scent to advertise their preference for a mating partner. In that scent marking is common in male and female mammals, scent quality might be more important than quantity in male-male competition and mate attraction. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that Eurasian beavers, Castor fiber, display the dear enemy phenomenon; that is, they respond less aggressively to intrusions by their territorial neighbours than to intrusions by nonterritorial floaters (strangers). This ability could be advantageous in facilitating differential treatment of wandering strangers versus established neighbours. Territorial beavers were presented with scent from neighbouring and stranger adult males. Thirty-nine different active beaver families, 18 in 1998 and 21 in 1999, were presented with a two-way choice between two pairs of experimental scent mounds; mounds with castoreum from a neighbour and a stranger, and mounds with anal gland secretion from a neighbour and a stranger. Direct observations of the families during evenings showed that: (1) beavers sniffed both castoreum and anal gland secretion from a stranger significantly longer than from a neighbour, and (2) beavers responded aggressively (stood on the mound on their hind feet, pawing and/or overmarking) significantly longer to castoreum, but not to anal gland secretion, from a stranger than from a neighbour. When experimental scent mounds were allowed to remain overnight and the beavers' responses were measured the following morning, the beavers' responses were significantly stronger to both castoreum and anal gland secretion from a stranger than from a neighbour. These findings indicate that Eurasian beavers can use scent to discriminate between neighbours and strangers, thereby supporting existence of the dear enemy phenomenon in this species. [ABSTRACT FROM AUTHOR]