Intra- and Inter-seasonal Variation in the Socio-Spatial Behavior of Adult Male Collared Lizards, Crotaphytus collaris (Reptilia, Crotaphytidae)

When individuals maintain strong inter‐seasonal philopatry to the same territories, males may be able to re‐establish territory occupancy without intense intra‐sexual aggression, and instead spend more time courting females early in the reproductive season. Furthermore, when some males have prior experience defending the same territories, it may be necessary for young males to exhibit higher levels of aggression because they are establishing a territory for the first time. We tested these hypotheses by examining within‐season (1992 and 1997) temporal variation in the social behavior of adult male collared lizards of known age and prior territorial experience in a population where inter‐season philopatry to territories is high. Contrary to expectations, the frequency of aggression exhibited by males with and without prior territorial experience did not differ. The frequency of intra‐sexual aggression was higher in 1992 than in 1997, perhaps because male competitors were more abundant in 1992. Although there was an interactive effect of year, male display and patrol were low at the beginning of the reproductive season in Apr. and May, reached peaks during midseason in June, and then decreased as reproduction ended in July. The size of territories showed a similar pattern, with males defending larger areas in June. Our data support the philopatry hypothesis in that the establishment of territories occurred without high levels of aggression early in the season, perhaps because territory boundaries have been well defined by high rates of patrol and advertisement during the middle of the previous season. Inter‐sexual interactions were most frequent in June rather than at the beginning of the reproductive season. Adult females are producing their second clutches and yearling females are producing their first clutches in June. The high rate of inter‐sexual encounters in June supports the hypothesis that males allocate more time to courtship when females are receptive because there are more reproductively active females at this time. The temporal pattern of activities in adult Crotaphytus collaris appears to function as a compromise between competing intra‐ and inter‐sexual social demands on males, allowing males to maximize mating opportunities as well as maintain future access to productive territories.     

Adaptive significance of permanent female mimicry in a bird of prey

Permanent female mimicry, in which adult males express a female phenotype, is known only from two bird species. A likely benefit of female mimicry is reduced intrasexual competition, allowing female-like males to access breeding resources while avoiding costly fights with typical territorial males. We tested this hypothesis in a population of marsh harriers Circus aeruginosus in which approximately 40 per cent of sexually mature males exhibit a permanent, i.e. lifelong, female plumage phenotype. Using simulated territorial intrusions, we measured aggressive responses of breeding males towards conspecific decoys of females, female-like males and typical males. We show that aggressive responses varied with both the type of decoys and the type of defending male. Typical males were aggressive towards typical male decoys more than they were towards female-like male decoys; female-like male decoys were attacked at a rate similar to that of female decoys. By contrast, female-like males tolerated male decoys (both typical and female-like) and directed their aggression towards female decoys. Thus, agonistic responses were intrasexual in typical males but intersexual in female-like males, indicating that the latter not only look like females but also behave like them when defending breeding resources. When intrasexual aggression is high, permanent female mimicry is arguably adaptive and could be seen as a permanent 'non-aggression pact' with other males.     

Dominance and aggression in social groups of male and female rats

Two experiments were performed to examine aggression and dominance in domestic male and female $\text{Rattus norvegicus}$ living in small mixed-sex (3 males and 3 females) groups. Experiment 1 examined the development of aggression in females. A single female (alpha) within each of the six colonies tested showed the preponderance of attacks on male intruders placed into the home-cage when male colony residents were absent. Over 12 weeks of intruder-aggression training female alphas showed only a mild nonsignificant elevation of aggressive behavior. A comparison of aggression of male and female colony alphas tested with opponents of each sex revealed that aggression was mainly directed at like-sex opponents, and that female attack was more defensive in character than male attack regardless of opponent sex. The highest intensity of aggression occurred when male alphas confronted male intruders. Although intruders never showed offense toward male residents, 61% of intruding males showed offense in response to attack by females.Experiment 2 investigated the relationship between aggressive dominance and competitive measures of dominance within each of 10 mixed-sex colonies. Alpha stat s of male and female colony residents did not reliably predict priority of access to food or water in tests of direct resource competition with like-sex colony members. When colony males were simultaneously tested for copulation, the copulatory behavior of alpha males was significantly greater than that of other colony males. Results are discussed in relation to the role of aggression in the reproductive strategy of male and female $\text{Rattus norvegicus}$.     

Intergroup Relationships in Western Black-and-White Colobus, <Emphasis Type="Italic">Colobus polykomos polykomos</Emphasis>

We investigated patterns of intergroup relationships in western black-and-white colobus, Colobus polykomos, in Taï National Park, Côte d'Ivoire, between 1993 and 1999. They live in one-male multifemale units, and demonstrate male dispersal and occasional dispersal by females. Solitary males and all-male bands are absent or very rare. Our aim was to investigate the function of female and male aggression during intergroup interactions. The species is particularly interesting because, in contrast to predictions from socioecological models, female aggression occurs during intergroup interactions in combination with female dispersal. Home ranges of neighboring groups overlapped considerably and groups lacked an area of exclusive access. Intergroup interactions occurred once every 6.6 observation days. Encounters were either peaceful (12%), or involved displays and threats (25%) or chases and fights (63%). Females interacted in 74% and males in 98% of aggressive intergroup encounters. We found little to no indication that male and female aggression correlated with the presence of food, importance of a location, or presence of infants or receptive females. However, females were more often aggressive during the months when the group depended strongly on seeds from Pentaclethra macrophylla. We also observed forays by males to other groups. Forays occurred on average once every 20 observation days. In 75% of the forays, the intruding male chased members of the target group. In 25% of the forays 1–3 females joined their male but females never attacked the target group. Our main study group was the target of such forays significantly more often when young infants were present in the group than when not. We conclude that female aggression between groups was related to food procurement and that male forays might be related to infanticide.     

Sociality in Callithrix penicillata: II. Individual Strategies During Intergroup Encounters

In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil. Agonistic interactions occurred at low frequencies during intergroup encounters. The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.     

Determinants of Pair‐Living in Red‐Tailed Sportive Lemurs (Lepilemur ruficaudatus)

Pair‐living and a monogamous mating strategy are rare and theoretically unexpected among mammals. Nevertheless, about 10% of primate species exhibit such a social system, which is difficult to explain in the absence of paternal care. In this study, we investigated the two major hypotheses proposed to explain the evolution of monogamy in mammals, the female defence hypothesis (FDH) and the resource defence hypothesis (RDH), in red‐tailed sportive lemurs (Lepilemur ruficaudatus), a nocturnal primate from Madagascar. We analysed behavioural data from eight male–female pairs collected during a 24‐mo field study to illuminate the determinants of pair‐living in this species. Male and female L. ruficaudatus were found to live in dispersed pairs, which are characterised by low cohesion and low encounter rates within a common home range. Social interactions between pair partners were mainly agonistic and characterised by a complete absence of affiliative interactions – body contact was only observed during mating. During the short annual mating season, males exhibited elevated levels of aggression towards mates, as well as extensive mate guarding and increased locomotor activity. In addition, males were exclusively responsible for the maintenance of proximity between pair partners during this period, and they defended their territories against neighbouring males but not against females. Together, these results point towards the importance of female defence in explaining pair‐living in L. ruficaudatus. We discuss the spatial and temporal distribution of receptive females in relation to the female defence strategies of males and suggest possible costs that prevent male red‐tailed sportive lemurs from defending more than one female.     

Reproductive Consequences of Aggression in a Territorial Songbird

Territorial aggression can influence males’ ability to obtain high‐quality resources and access to mates; however, in many species, the reproductive consequences of variation in aggression are unknown. In this study, we investigated how individual variation in aggressive behavior relates to reproductive success in socially monogamous, genetically polygynous song sparrows (Melospiza melodia). Prior research in this species shows that male song sparrows differ in their willingness to engage in agonistic interactions with territorial intruders and that individual variation in aggression appears to have functional significance. Aggressive males have been shown to obtain territories where females produce larger clutch sizes, suggesting that individuals who display high levels of territorial aggression are defending high‐quality territories or females. Further, aggressive males are considered a greater threat to territory‐holding males than less aggressive males. In this study, we ask whether individual differences in aggression are linked to differences in extra‐pair reproductive success, annual reproductive success, and offspring quality. We did not uncover a relationship between aggression and annual reproductive success or patterns of extra‐pair paternity. However, we found that the nestlings of aggressive males grew at a faster rate than the nestlings of less aggressive males. Future studies should attempt to identify mechanisms to explain the relationship between offspring growth rate and male aggression and investigate whether faster offspring growth rates translate to greater survival and recruitment of offspring.     

The Payoff of Fighting in House Crickets: Motivational Asymmetry Increases Male Aggression and Mating Success

Motivational asymmetry caused by differences in subjective resource value is a key component of strategic models of aggression. We study the role of motivational asymmetry in determining differential aggression and mating success of male house crickets, Acheta domesticus. We also assess the extent to which mating differences associated with motivational asymmetry are due to direct male–male fighting vs. male–female interactions. We manipulated male motivation to compete for a mating opportunity by providing males with either no access or nightly access to females for 4 d prior to the experiment. As predicted, when males from each treatment had to compete for the female, those with lower prior access were more aggressive and mated more often. In contrast, when males from each treatment were paired individually with females, there was no significant difference in the frequencies with which they pursued, courted or mated with females. We also found no evidence for female choice based on motivational asymmetry; the rate of successful courtship did not differ between treatments. We conclude that prior mate encounter rate can generate motivational asymmetry, leading to differential mating success mediated by direct male–male aggression.     

Male dominance status,female choice and mating success in the brown lemming, Lemmus trimucronatus

The objective of this study was to determine whether female brown lemmings would selectively mate with dominant conspecific males. In dyadic encounters, oestrous females paired with dominant males engaged in more frequent lordosis and contact social behaviours than those paired with subordinate males. However, the mount and thrust scores of dominant and subordinate males did not differ significantly. When females had simultaneous access to tethered dominant and subordinate males, they spent more time in close proximity to dominant males and avoided contact with subordinate males. Copulation scores were higher with dominant males. In triadic encounters with free-moving dominant and subordinate males, oestrous females spent more time near, and engaged in more sexual behaviour with, dominant males. Intermale agonistic interactions resulted in ‘privileged access’ to females by dominant males. Sexual behaviour scores were lower and there was a 10-fold increase in intermale aggression in triadic encounters between females and unfamiliar dominant and subordinate males. Both intermale agonistic interactions and female ‘choice’ behaviour accounted for the differential copulatory success of dominant males.     

Social interactions among female rhesus macaques (Macaca mulatta) during the nonbreeding season: Responses to the introduction of males

When rhesus monkeys are observed in social groups during the breeding season, increases in interfemale aggression coincide with midcycle increases in sexual activity between males and females. However, some investigators have suggested that both aggressive and affiliative interactions between females are influenced by the presence or absence of males, irrespective of menstrual cycle stage. In the present study, social interactions among members of a captive group of rhesus females were measured during the non-breeding season in response to the introduction of rhesus males. Ovariectomized rhesus females (estrogen-treated or untreated) served as stimulus controls. Tests with males were characterized by significantly decreased interfemale proximity and grooming and significantly increased aggression from that seen in tests with stimulus females or in the absence of stimulus animals. Only interfemale proximity declined significantly during stimulus female tests, but results suggest that this may merely reflect a decline in this behavior that occurs across the course of the day. Estrogen treatment did not alter either the aggressive or affiliative behavior of stimulus females or group female response to stimulus females. The possibility is discussed that changes in interfemale interactions during tests with males reflect female interest in interacting with the male, particularly under social conditions that may limit such interactions.     

Weaponry,size, and sex ratio affect spatial distribution within small and large groups of the maritime earwig (Anisolabis maritima)

Dispersion patterns within a group can reveal important aspects about social interactions and sexual selection within a species. We examined the distribution patterns of the maritime earwig (Anisolabis maritima), an insect well suited for studies of aggression, sociality, and sexual selection since both sexes live in close proximity and possess weaponry in the form of sexually dimorphic pincers. To examine intra‐ and intersexual interactions within small groups, we conducted trials with three earwigs with limited access to shelters. In single‐sex trios, we found that both males and females exhibited strong size‐based intrasexual aggression, as larger individuals were less likely to be excluded from shelters; however, males were more likely to cohabitate than females. In mixed‐sex trios, we found that both males and females preferred smaller opposite‐sex partners, and cohabitation patterns indicate that both sex‐ and size‐based differences in aggression can influence overall spatial distribution. We also examined larger single‐sex and mixed‐sex groups of 18 earwigs to determine whether they had random, uniform, or clumped distributions. Similar to previous field observations, males tended to form aggregations, whereas females were distributed uniformly, a pattern indicative of territoriality. Mixed‐sex groups, on the other hand, were uniform during nocturnal periods of high activity but then become clumped after settling into more stable daytime positions. Overall, our results suggest that females have high levels of aggression regardless of the social context, whereas males alter their aggressive behavior in the presence of females.     

Fighting and Mating Between Groups in a Cooperatively Breeding Mammal, the Banded Mongoose

Many cooperatively breeding animals actively defend a territory containing resources such as food and shelter, which are essential for reproduction. Some observations, however, indicate that conflicts between groups are often triggered by the attempts of males or females, or both, to gain extra‐group copulations. We studied interactions between 12 groups of banded mongooses (Mungos mungo) in Uganda to test whether the frequency of inter‐group encounters was linked to the reproductive status of females, and conducted an experiment to examine the responses of individuals to mongooses from other groups. The rate at which focal groups fought with other groups was higher when its females were in estrous, suggesting that many fights take place over access to mates. Both males and estrous females were instrumental in instigating encounters with rival groups, and extra‐group copulation in the midst of a fight was observed on three occasions. We experimentally simulated encounters with foreign individuals by presenting each of six groups with cages containing a male and a female from a rival group. Subordinate males were the first to investigate these ‘intruders’, spent more time around the intruders' cages, and were more aggressive to the intruders than either dominant males or females. Subordinate males directed more attention and aggression towards the male intruder than the female intruder. We suggest that male banded mongooses actively seek extra‐group copulations in pursuit of paternity, while females may actively seek extra‐group copulations as a way of reducing inbreeding depression.     

Sex differences in the social behavior of wild spider monkeys (Ateles geoffroyi yucatanensis)

Competition for resources and the need for cooperation are reported to affect patterns of social interactions and thus the quality of social relationships in primates. Relationships may be described as high quality when both individuals behave in a way that benefits their partner. We investigated the distribution of a wide range of social behaviors across sex partner combinations of adult spider monkeys with specific reference to contested resources. Data were collected from two communities of wild spider monkeys (Ateles geoffroyi yucatanensis) in the Otoch Ma'ax Yetel Kooh reserve in Yucatan, Mexico. Affiliative behavior was exchanged most frequently between males, and as male-male aggression was rare, male-male social relationships were characterized as high quality. Female-female social relationships were best described as low quality as females showed no preference to be in proximity with other females and female-female affiliative behavior was rare. Relationships between the sexes generally were characterized by high rates of female-directed male aggression, although additional investigation into the effects of kinship and female reproductive state on male-female relationships is required before further conclusions can be drawn. Dyadic and coalitionary female-female aggression was significantly higher than expected in a feeding context, confirming that female spider monkeys primarily compete for access to food. Male-male aggression did not increase significantly when in the presence of females, but males embraced at higher rates when in mixed-sex subgroups. As embraces serve to reduce the likelihood of aggression during tense situations, high rates of male-male embraces in mixed-sex subgroups may mitigate male conflicts over access to females.     

Welcome Back: Responses of Female Bonobos (Pan paniscus) to Fusions

In species with a high degree of fission-fusion social dynamics, fusions may trigger social conflict and thus provide an opportunity to identify sources of social tension and mechanisms related to its alleviation. We characterized behavioral and endocrine responses of captive female bonobos (Pan paniscus) to fusions within a zoo facility designed to simulate naturalistic fission-fusion social dynamics. We compared urinary cortisol levels and frequencies of aggression, grooming and socio-sexual interactions between female bonobos while in stable sub-groups and when one “joiner” was reunited with the “residents” of another sub-group. We hypothesized that fusions would trigger increases in aggression and cortisol levels among reunited joiners and resident females. We further predicted that females who face more uncertainty in their social interactions following fusions may use grooming and/or socio-sexual behavior to reduce social tension and aggression. The only aggression on reunion days occurred between reunited females, but frequencies of aggression remained low across non-reunion and reunion days, and there was no effect of fusions on cortisol levels. Fusions did not influence patterns of grooming, but there were increases in socio-sexual solicitations and socio-sexual interactions between joiners and resident females. Joiners who had been separated from residents for longer received the most solicitations, but were also more selective in their acceptance of solicitations and preferred to have socio-sexual interactions with higher-ranking residents. Our results suggest that socio-sexual interactions play a role in reintegrating female bonobos into social groups following fusions. In addition, females who receive a high number of solicitations are able to gain more control over their socio-sexual interactions and may use socio-sexual interactions for other purposes, such as to enhance their social standing.     

Factors influencing aggressive behavior and risk of trauma in the pigtail macaque (Macaca nemestrina).

Several experiments and surveys were conducted in a large colony of pigtail macaques (Macaca nemestrina) to determine some of the influences of spatial and social factors on aggressive behavior and risk of trauma. Female subjects exhibited more aggression when they had access to two-room suites than when they had access to single rooms. The frequency of aggressive interactions among females was positively related to the number of females per group. The presence of one or more males in groups inhibited aggressive interaction among females. Less aggression occurred among females in groups containing infants than in groups containing no infants. Provision of cover by introduction of concrete cylinders into rooms reduced aggression among members of stable groups. Subjects in newly-formed groups composed of unfamiliar animals sustained fewer injuries than did those in groups formed by merger of groups or subgroups of familiar animals.     

Female dominance and feeding priority in a prosimian primate: experimental manipulation of feeding competition

Female dominance and feeding priority are considered unique behavioral strategies in many Malagasy lemuriformes, particularly Lemur catta. Two hypotheses have been introduced to explain these behavior patterns: 1) females are agonistically dominant over males to mitigate female-male food competition so that females can compensate for high energy demands and inefficient reproductive physiology, and 2) males defer to females when feeding as a reproductive strategy. We tested these hypotheses by conducting controlled feeding experiments on free-ranging ring-tailed lemurs (Lemur catta) on St. Catherine's Island, GA. Food was dispersed in three ways to simulate varying patch sizes. All feeding and agonistic interactions were recorded during each trial (n = 24). The degree of relatedness between individuals was determined using DNA fingerprinting. There was a clear relationship between food dispersion and both expression of female dominance and feeding priority. Elements of both hypotheses were supported because male and female L. catta used different strategies depending on rank and the dispersion of food. Interpretation of the impact of male rank was complicated because the younger, low-ranking males had female relatives in the group. Females fed more than males, and rates of aggression decreased as food dispersion increased. High-ranking, older unrelated males deferred to females and received little aggression. The top-ranking male deferred the most and sired most if not all of the offspring. Low-ranking, younger related males fought with females for access to food sources, received more aggression, and did not sire offspring.     

Intraspecific competition and the maintenance of monogamy in tree swallows

Intraspecific competition for access to breeding resources maylimit male mating success typically monogamous birds. We examinedthe potential for intraspecific competition to limit polygynyin tree swallows at Beaverhill Lake, Alberta, Canada. In thispopulation, polygynous males raisedmore fledglings than monogamousmales, and there was little or no cost to females from nestingpolygynously. Under these conditions one might expect polygynyto be more common than that observed(8% of males). We foundthat females were most aggressive toward conspecific intrudersearly in the breeding season. This aggression was associatedwith (1) females settling farther apart than expected underrandom settlement, (2) later settlement by secondary than bymonogamous females, and (3) no relationship between female settlementdate and male territory size instead of the negative correlationexpected if females settled randomly without competition. Earlyin the season, males also settled farther apart than expectedif they had settled randomly, and among males with two or morenest boxes on their territory, males with widely separated nestboxes were more likely to be polygynous. Monogamy is probablythe most common pairing association in this population becauseintraspecific competition for nest sites prevents most malesfrom gaining a territory with nest sites far enough apart topermit two females to breed without one female excluding theother. Females appeared to be defending an area surroundingtheir nest box to limit nest usurpation or intraspecific broodparasitism, rather than to limit any loss of male parental carefrom polygyny.     

Patterns of female dominance in Propithecus diadema edwardsi of Ranomafana National Park, Madagascar

Many lemur species are characterized by some form of female dominance, ranging from female feeding priority to complete female dominance, although this is a rare trait in primates and other mammals. The status of the Milne-Edwards' sifaka (Propithecus diadema edwardsi), a diurnal lemur, is ambiguous. Some short-term studies have found little or no aggression. The aim of the current, long-term study was to quantify the intersexual-dominance patterns of this sifaka. The distribution, outcome, and context of aggressive interactions were studied in four groups of wild sifakas. The majority of intersexual aggressive interactions were decided, with the loser expressing submissive behavior. Intersexual aggressive interactions occurred in all social contexts, and within all social contexts the females won the vast majority (92.7-96.0%) of aggressive interactions. While aggression rates were low (0.22/hr), this evidence suggests female dominance. We propose that female dominance exists because it provides a fitness advantage to both males and females.     

Post-conflict Social Events in Wild Mountain Gorillas. II. Redirection,Side Direction,and Consolation

Inevitably, members of primate groups sometimes have aggressive contests with each other. Targets of aggression can engage in several types of interaction with third parties to ameliorate its adverse effects. They can redirect aggression, which may reduce the risk of further aggression from the initial opponents and reduce tension, or they can initiate affinitive interactions with third parties, in order to seek protection or reassurance. They can also receive reassuring acts from them (‘consolation’). Researchers have documented high levels of redirection in many primate species, but consolation is thus far known only in chimpanzees. Data on post-conflict social interactions between targets of aggression and third parties in two groups of wild mountain gorillas (Gorilla gorilla beringei) show that immatures and subordinate males, but not females, redirect aggression at high rates. Furthermore, immatures seek affinitive interactions with their mothers, and adult females seek them with adult males, at elevated rates. Affinitive interactions between females and males seem mainly to have a protective function and are associated with decreased risks of further aggression between female opponents. Redirection by females after female-female conflicts may be uncommon because targets commonly retaliate against aggressors. Males may offer females protection and consolation as services, and the results support the argument that such services are important when dominance relationships between females are often undecided and retaliation between opponents is common.     

Distinguishing behavioral interactions from visual cues as causes of adult sex change in a coral reef fish

Two experiments tested the hypothesis that adult female-to-male sex reversal in protogynous fish is induced by the loss of close-contact behavioral interactions between males and females, and not by the loss of simple visual cues from the male. Twenty-six laboratory groups of Anthias squamipinnis were manipulated so that females within each group (1) retained chemical and acoustic access to a male, (2) were denied behavioral access to a male, and (3) were either allowed or denied visual access to a male alone or to a male interacting with another female. At least one female subsequently changed sex in each of 22 groups. While acoustic and chemical cues were not completely eliminated as possible causes, sex change is apparently induced by loss of male-female behavioral interaction in combination with continued interaction between females.