Pheromone‐mediated intrasexual aggression in male lizards,Podarcis hispanicus

Sex recognition is based on color signals in many species of lizards. However, olfactory stimuli are also clearly involved, and many species might rely primarily on chemoreception. We aimed to examine whether color pattern or odors, or a combination of both factors, induce the aggressive response of males of the lizard P. hispanicus. We experimentally manipulated the coloration and odor of male P. hispanicus, thereby creating groups with all combinations between coloration and odor of males or females. Using data from staged encounters, we compared the responses of resident males to the experimental groups of manipulated males and their response to unmanipulated individuals (males and females). Responding males reacted significantly more aggressively to intruders with male odors independent of their coloration, whereas intruders with female odors did not elicit aggressive responses but were preferentially courted, irrespective of their actual sex and body coloration. In addition, intruders with female odors elicited a higher number of tongue‐flick explorations than male odor ones. Comparisons with unmanipulated male and female intruders agreed with these expectations. Therefore, at least at close range, odoriferous cues seem to be more important than color patterns in sex recognition and intrasexual aggression by male P. hispanicus. We suggest that this might be a pattern commoner than expected in many species of reptiles.Aggr. Behav. 28:154–163, 2002. © 2002 Wiley‐Liss, Inc.     

Effects of female presence on intrasexual aggression in male lizards,Podarcis hispanicus

Resource value and expected gain in reproduction may affect motivation to fight and the likelihood of winning. Previous experiments have showed that males increase their fighting effort when defending a territory that contains females. However, we hypothesized that for an intruding lizard, the value of a new territory may be lower if he already has a female in his own territory, and consequently, aggressivity should be lesser than if he has no access to any female. We staged encounters between males of the lizard Podarcis hispanicus in outdoor terraria to analyze the outcome and detailed behaviors involved in agonistic interactions in the presence or absence of a female in the terraria of resident and intruders. Our results showed that when a female was present, the level of aggressivity of the resident male was higher; the probability of winning the contest also increased, but only if the intruding male had no females in his own terraria. In contrast, when the intruding male was also the owner of another territory containing a female, residents were less aggressive. We suggest that the lack of information on the reproductive state of an unfamiliar female may be enough to decrease fighting motivation of an intruding male, if he has more expectations of success with his own familiar female. We conclude that differences in expected reproductive success with different females may help to decide the outcome of conflicts between males quicker and cheaper. Aggr. Behav. 28:491–498, 2002. © 2002 Wiley‐Liss, Inc.     

Territorial prior residence,size asymmetry,and escalation of aggression in convict cichlids (Cichlasoma nigrofasciatum Günther)

The present study was designed to assess the effects of resident versus intruder size differences upon the territorial prior-residence effect and level of territorial aggression in convict cichlids. Prior to a direct territorial dominance encounter, pairs of fish were randomly composed for one of three experimental treatment conditions: 1) the resident having a body-length 20–30% larger than that of the intruder, 2) the intruder having a body-length 20–30% larger than the resident, or 3) the combatants' body-lengths differing by no more than 5%. After a 3-day territorial acclimation period in their individual territories, the subject designated as the intruder was introduced to the resident's territory. For each encounter the pairmember that attacked first and the one that ultimately established dominance were recorded. Also measured during the encounter were the total number of bites, resident bites, intruder bites, and jaw-locking frequency and duration. The results revealed that there was a significant resident advantage in the resident-larger group. The intruder-larger group resulted in a significant intruder dominance advantage. However, no significant dominance advantage occurred in the same-size group. As predicted by game theory, there was significantly less escalation of aggression in contests in which one combatant held both designated asymmetric cues (prior residence, size) than in contests in which one combatant had prior residence, or when these two asymmetric cues were divided between the pairmembers. The size asymmetry is more important in determining dominance than the prior-residence asymmetry, for the particular size-difference range selected in the present study.     

Intra- and lnterspecific aggression in two species of field crickets,Gryllus integer and G. alogus

Adult, laboratory-reared, and singly caged field crickets, Gryllus integer, of known ages and representing F1 to F4 generations, were exposed to 15–20-minute bouts of social interaction with introduced adult intruder males on alternate days from approximately 1 week after adult molt to time of death. A total of 3,523 paired-male bouts for 116 male G. integer were recorded over a 2.5-year study period. Adult males used as intruders were wild-caught or laboratory reared G. integer, but for nine of the 116 experimental males, wild-caught intruders of a closely related sympathetic species, G. alogus, were used for all or many of the bouts. Bouts between male G. integer and conspecific intruders were characterized by significantly elevated levels of aggression (t=6.04, P<0.001) compared with males exposed to heterospecific G. alogus intruders in interspecific interactions. Significant differences (p<0.005, chi-squared test of independence) existed at four out of five levels in a hierarchy of agonistic behaviors. Most G. integer males exposed to both G. integer and G. alogus intruders showed significantly reduced aggression levels during the interspecific interactions (p<0.001, Mann-Whitney U test). Conspecific G. integer dyads in the intraspecific interactions showed significantly stable dominant-subordinate relationships over time. Confusion surrounding the use of the term aggression is described with reference to Arthropods in general and Orthopteran insects in particular, and some likely proximate and ultimate bases for reduced interspecific aggression in field crickets are discussed.     

Diversity in agonistic behavior of croaking gouramis (Trichopsis vittata,T. schalleri,and T. pumila; Anabantoidei) and the paradise fish (Macropodus opercularis; Anabantoidei)

Agonistic encounters of all three species of the vocalizing genus Trichopsis were observed in order to compare species-specific fighting strategies and the specific investment in acoustics. Additionally, these encounters were compared to agonistic encounters of Macropodus opercularis which was considered to be mute. The aim of this comparison was to investigate if mute fishes stress visual or tactile displays. Within the genus Trichopsis, significant differences among the three species were found in qualitative and quantitative analysis of displays. Frontal display occurred only in Trichopsis vittata, whereas a strong tail-beating while vocalizing was only observed in Trichopsis pumila. Fight duration and the number of sounds and circlings were highest in Trichopsis schalleri. The largest relative distances between circling opponents occurred in T. pumila, the smallest species. Also, the number of attacks was lowest in T. pumila. Fighting assessment seemed to be different in each species. For the first time, sound production has been reported for Macropodus opercularis (infrequently and with extreme low sound pressure levels), but much more investment in visual and tactile displays has been demonstrated. Lowering the branchiostegal membrane and spreading the opercula occurred only in M. opercularis and was never observed in any of the Trichopsis species. The number of attacks was higher in Macropodus than in any Trichopsis species. The relative distance between Macropodus opponents while circling was closest compared to the three Trichopsis species. Visual and contact displays are reduced in extensively vocalizing fish species, like Trichopsis sp., compared to mute or seldom vocalizing species, like Macropodus. © 1996 Wiley-Liss, Inc.     

Aggression in wood ants (Formica polyctena Foerst., Hymenoptera,Formicidae)

The relationship between aggression and predation was surveyed in Red wood ants, in the field as well as under laboratory conditions. Aggression between wood ant nests is highest in early spring, and many wood ant wars break out then. The end of these wars coincides with a strong increase in prey density. Since the casualties are taken as food to the warring nests, a hypothesis is formulated that warfare between wood ant nests only occurs in periods when prey demand exceeds the supply. Protein-rich food in early spring is mainly for the benefit of the queens and the sexual larvae. Although the most obvious function of warfare is the defence of a foraging area, the main function may be the advancement of the mating flight dates of the queens in order to make the chance of propagating their genes greatest.     

Effect of residence and size asymmetries upon the agonistic interactions between juvenile white‐seabream (Diplodus sargus cadenati de la Paz,Bauchot and Daget, 1974)

The behavioural patterns of juvenile white‐seabream suggest that asymmetry in residence is an important factor governing the outcome of contest between individuals of this species. Asymmetries due to resident status had strong effects on agonistic behaviour, with asymmetries in body sizes producing weaker effects. Resident fish won all the combats against intruders of lower or similar length. However, when the intruder was larger than the residents (higher than 5% in length and 20% in weight), the percentage of combats won by the residents decreased to 85.7%. There was a significant correlation between fight intensity and size asymmetry in favour of the resident fish. The resident fish was more aggressive and persistent in attacks, and contests were more intense when the size of the intruder was greater. During agonistic interactions, the frontal attacks and lateral displays were more frequent when the intruders were similar or larger than residents. Attacks to the flanks and chases were more frequent in pairs where the intruders were smaller. Aggr. Behav. 25:297–303, 1999. © 1999 Wiley‐Liss, Inc.     

Effects of neonatal treatment with 1-(2,5-dimethoxy-4-lodophenyl)-2 aminopropane HCI (DOI) and ritanserin on agonistic behavior in adult male and female rats

The role played by the neonatal 5-hydroxytryptamine (5HT) system in the organization and sexual differentiation of adult agonistic behavior was investigated in rats. Focus was on the 5HT2 receptor subtype, which has been demonstrated to be involved in agonism control in the adult. 5HT2 activity was experimentally manipulated by administration of a specific agonist [1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI)] or antagonist (ritanserin) during the second week of life, when serotonin is known to concur to anatomical and behavioral sexual differentiation. Interactions between early 5HT2 activity, genetic sex, and neonatal circulating testosterone (T) were studied by administering the ligands to males, females, and androgenized females. At adulthood, the animals were tested for both aspects of agonism, i. e., aggression and defense, in a 20-min confrontation with an unfamiliar conspecific of the same sex, age, body weight, and social experience. Neonatal administration of the 5HT2 antagonist ritanserin increased aggression independently of sex; it also increased defense, but this effect was confined to males. The agonist DOI had no effect on aggression, but enhanced defense in males and androgenized females, with an effect which depended therefore more on neonatal T than genetic sex. Females appeared in general less sensitive to neonatal 5HT2 manipulation than both androgenized females and males; this suggests that neonatal T is crucial for experimental modifications of neonatal 5HT2 activity to have any consistent effect on adult agonistic behavior. On the other hand, effects observed in males and androgenized females were dependent on the behavior considered and the drug administered. This was especially evident for defense, enhanced by ritanserin in males only, and in both males and androgenized females by DOI. Neonatal 5HT2 activity seems therefore to play a role in the modulation of adult agonistic behaviors, which depends on the behavior considered and is under multiple control of genetic sex and hormonal neonatal substrate. © 1994 Wiley-Liss, Inc.     

Further experiments on the social interactions of domestic “Norway” rats

Domestic rats, Rattus norvegicus, aged nearly one year, were studied in artificial colonies in large cages with attached nest boxes. As in previous experiments on younger domestic rats, but not those on wild rats, the colonies were peaceful. Questions concerning the “aggressive” or “agonistic” behavior of domestic rats are further discussed.     

Aggressive interactions among female,semi-captive pampas deer (Ozotoceros bezoarticus) increase within the hierarchy and after short-term removal of the male

Two trials were carried out to determine: (a) if there is a positive relation between the frequency of aggressive interactions among female pampas deer and their position within the hierarchy (HI), (b) if short-term removal of the male triggers an increase in the frequency of aggression, and (c) if the magnitude of this increase is related to the individual rank position of the female. Each of 19 breeding groups comprised one adult male and from four to six adult females. The HI was determined for each female and all aggressive interactions were recorded. These were recorded while the male was present (i.e., all of Trial 1 and the “with male” period in Trial 2) and after removal of the male (i.e., the “without male” period in Trial 2). The individual percentage change in the frequency of aggressive interactions after male removal was calculated. In Trial 1 the HI, the frequency of different types of aggressive interaction and the total of aggressive interactions were positively related (all: p < .001; General Linear Mixed Model [GLMM]). In Trial 2, the frequency of total aggressive interactions increased after male removal (F(1, 27) = 3.5; p < .001; GLMM). The individual percentage changes in aggressive interaction between periods were positively related to HI (F(6, 24) = 2.56; p = .05; GLMM). For female pampas deer maintained in breeding groups, we conclude that the frequency of aggressive interactions increases within the hierarchy. Aggression also increases after the short-term removal of the male, mainly among females of higher social status.     

Laboratory and field observations of attack by the red wood ant Formica lugubris Zett. On Formica cunicularia Latr. (Hymenoptera: Formicidae)

Attack by red wood ants (Formica lugubris Zett.) on an “alien” species (Formica cunicularia Latr.) was analyzed both in the laboratory and in the field. Elements of such attack were recorded. Attack and conflict were observed in each encounter and follow immediately after the first contact. This overt attack was vigorous and generally led to the death of the alien. Laboratory data were confirmed by field observations, although under these conditions aggressiveness of F lugubris appeared increased possibly because of the animal's familiarity with its surroundings.     

Ontogeny of agonistic behaviour in dispersing blind mole rats (spalax ehrenbergi)

The blind mole rat (Spalax ehrenbergi) is a solitary and aggressive fossorial rodent that inhabits its own individual tunnel system. Mole rats breed mainly in the winter, giving birth to a litter of three to four young on average [Nevo (1961) Mammalia 25:127–143]. Intraspecific interactions between adults occur mostly during the winter, which is the rainy season in Israel; after parturition, interactions occur between the mother and her offspring and between the siblings themselves until dispersal. Until now, the subterranean habitat of mole rats has prevented direct observation in the wild. Thus, there has been no direct evidence for the proximal factors that drive juvenile mole rats out of the maternal tunnel system as they shift from the social life-style of the young to the solitary life-style of the adult. In the present study, female mole rats were caught in the wild with their offspring and brought to the laboratory. The dispersal process of the young from the maternal nest was followed under two housing conditions: (1) restricted housing, simulating the physical conditions under which dispersal is delayed past the usual age, as often occurs during late winter floods in the field in areas of nonporous clay soils, and (2) nonrestricted housing, simulating the physical conditions that allow the young to disperse from their maternal tunnels at any time. In each housing condition, the mothers raised either one or three pups. During pup development, we monitored both maternal and juvenile agonistic variables during intraspecific interactions. Five major behavioural phases were identified during the ontogeny of the mole rat pups. Maternal aggression toward pups increased mainly in the first three phases of pup development, and sibling aggression increased from the third phase until dispersal. Under the restricted housing conditions, there was a delay in both the appearance of aggression in the “family group” as well as in dispersal age compared with the nonrestricted conditions. In the nonrestricted conditions, increased litter size resulted in delay in dispersal age. We suggest that the main proximate factor initiating natal dispersal is increased intolerance and aggression among siblings rather than maternal aggression. Only after the young began dispersing from the maternal tunnels did maternal aggression dramatically increase, thus preventing the offspring from returning. However, following floods, inhibition of aggression may enable the mole rat pups to stay with the family group and to disperse later when the physical conditions permit it. Aggr. Behav. 24:455–470, 1998. © 1998 Wiley-Liss, Inc.     

Rapid spatial learning in a velvet ant (<Emphasis Type="Italic">Dasymutilla coccineohirta</Emphasis>)

Spatial learning has been examined in a variety of animals to determine what cues are used to navigate through a complex environment. A common feature of previously studied vertebrates and invertebrates is their need to return to a previously visited site for mating, nesting, foraging or predator avoidance. Velvet ants (Hymenoptera: Mutillidae) are cursorial parasitoids with flightless females that must walk through complex terrain to find ground dwelling host larvae burrows. Velvet ants are not central-place foragers (they do not return to an established nest site) so much of the previous work on spatial learning does not directly apply in this context. It was assumed that females primarily use chemosensory cues for navigation and burrow location instead of visual learning. This study, however, demonstrates that velvet ant females are able to use visual landmarks to find an inconspicuous exit in an aversion-motivation spatial learning task. A significant number of velvet ants learned to locate the exit after seven training trials and went to the previous location of the exit even after the maze had been rotated, showing that landmarks external to the maze were used to learn the escape location.     

Effect of competitor density on the aggressiveness of juvenile white seabream (Diplodus sargus cadenati de la Paz,Bauchot and Daget, 1974)

The number of aggressive interactions displayed by juveniles of Diplodus sargus cadenati increases progressively in proportion to the number of intruders, with an upper threshold of more than 16 to 18 intruder fish. Beyond this density, resident aggressiveness decreases. The number of aggressive interactions that the resident fish devotes to expelling each intruder shows a clear and significant tendency to decrease as competitor density increases. The resident fish is incapable of rapidly evaluating the outweighing of its capacity for defense. Moreover, the strategy of aggressive defense of the resource against the density of competitors does not seem to be only profitability criteria dependent, but rather there is also a significant influence of the ability to fight shown by the resident. Aggr. Behav. 29:279–284, 2003. © 2003 Wiley‐Liss, Inc.     

Identification of the possible origin of the body target that differentiates play fighting from serious fighting in syrian golden hamsters (Mesocricetus auratus)

Play fighting in the Syrian Golden hamster Mesocricetus auratus can be distinguished from serious fighting by the targets attacked in each case. In play fighting, the animals attack and defend the cheeks and cheek pouches, whereas in serious fighting they attack and defend the rump and lower flanks. Since play typically involves the use of behaviors borrowed from other functional contexts, this paper investigates the origin of the cheek target during play fighting. Comparison of resident-intruder serious fighting with awake and anesthetized intruders does not reveal the cheek to be an inhibited target for serious attack. Similarly, analysis of social investigation and allog-rooming, while revealing the ears to be important targets, do not show the cheeks to be targets in these behaviors. Sniffing, licking, and nibbling of the cheek area appear to occur mainly during sexual encounters by males. This area, seemingly a sexual target, may be the one utilized during play fighting.     

Dominance structure in small groups of juvenile white-seabream (Diplodus sargus cadenati de la paz,Bauchot and Daget 1974)

Experiments were conducted to investigate the intraspecific aggressive interactions between juveniles of white-seabream (Diplodus sargus cadenati de la Paz, Bauchot and Daget 1974) in relation to dominance hierarchy in small groups. The agonistic interactions between juvenile white-seabream in small groups originated a peck-dominance hierarchy. The dominant (α-fish) generally interacted aggressively and most frequently with the subordinate that was next in line (β-fish) within the dominance hierarchy. This β-fish interacted aggressively more frequently with the γ-fish, and so on. Results demonstrated that fish do not attack subordinates at random. The level of subordination in small groups of juvenile white-seabream was related to body size. Generally, the more aggressive fish manifest a higher growth rate. Aggr. Behav. 24: 197–204, 1998. © 1998 Wiley-Liss, Inc.     

In judo,Randori (free fight) and Kata (highly ritualized fight) differentially change plasma cortisol,testosterone, and interleukin levels in male participants

Two forms of competitive encounters namely Randori (free fight) and Kata (highly ritualized fight) were studied in 22 professional male judo fighters. The dyadic, symmetrical (in terms of body weight and fighting ability) encounters were videotaped to assess relationships between agonistic behavior and individual variations in plasma levels of testosterone (T), cortisol (C) and interleukins (IL‐6 and IL‐1β) measured before and after the competition. Unremarkably, winners showed longer attack but devoted less time to defensive behaviors when compared to losers. T increased only during Randori but the individual pre‐ and post‐competition T levels recorded in such fights were strongly correlated with the corresponding measures in the Kata for the same individuals. Interestingly, the pre‐ and post‐Randori competition T levels were higher in losers than in winners and T variations positively correlated with the frequencies of attacks and with the duration of defensive postures. The T response shows individual variation and seems to reflect evaluation of the likelihood of winning or losing. Both Randori and Kata induced a marked C increase, although the pre‐ and post‐Randori hormonal titers were higher than those found for the Kata. IL‐6 significantly increased between the pre‐ and the post‐Randori competition, but no such changes occurred during the Kata. No correlations were found between individual pre‐ and post‐competition C and IL‐6 and IL‐1β levels in either Randori or Kata. This suggests that C and cytokine release are unrelated to emotional or cognitive perception of the possible outcome of fighting but are a consequence of general motor activity. Martial arts appear to provide good human models to understand: (a) the relationships between conflict, hormones and the immune system and (b) the relationships between mood and physiological responses to competitive aggression. Aggr. Behav. 32:1–9, 2006. © 2006 Wiley‐Liss, Inc.     

Genotype and environment in the social interactions of wild and domestic “Norway” rats

Wild rats, Rattus norvegicus, (a) trapped as adults or (b) of the second generation in captivity (lab-wild), and domestic rats of two strains, were studied for 28 days in artificial colonies in large cages with attached nest boxes. Controls were kept in mated pairs in small cages. Each colony consisted of six males and six females. The interactions of the males in six colonies of trapped rats were highly “stressful;” 61% died; and most of the survivors lost weight and had greatly enlarged adrenals. In each colony, however, there was a male (an alpha) that gained in weight and spent much time, during the dark hours, in the open on the floor of the cage; and in three colonies there were also other males (“betas”) that gained in weight. The adrenals of alphas and betas weighed about the same as those of the controls. In one of the 12 colonies of domestic rats one male behaved like a wild male; but in the other colonies the males gained in body weight and their adrenal weights resembled those of the controls. In three colonies of lab-wild rats 22% of the males died, but there was no evidence of males of different status. The findings confirm that the “agonistic” behavior of domestic rats is usually much attenuated in comparison with that of the wild type; a number of methodologic implications are discussed.     

Role of female aggression in prevention of infanticidal behavior in male common voles,Microtus arvalis (Pallas, 1779)

Infanticidal behavior of male common voles (Microtus arvalis) was investigated in relation to the age of unfamiliar pups. Sires from 18 pairs were removed after parturition of their offspring and replaced by unfamiliar males at different ages of the neonates. In group 1, containing six females with their offspring, the new male was introduced into the females' cages on day 1 after the parturition. In group 2 the new male was introduced on day 5 after parturition and in group 3 on day 9 after parturition. The male was removed after 3 days and the neonates recounted. Male common voles killed up to 100% of the neonates in litters containing neonates younger than 9 days by rapid bites to the head of the neonates (groups 1 and 2, mortality rates of 0.86 and 0.38). However, with older pups, a mortality rate of 0.06 was observed while 33% of the intruder males showed signs of injuries (group 3). These findings show that infanticidal behavior of male common voles represents one factor of pup mortality. The results are discussed in relation to changes in the degree of maternal aggression and in the context of the social system of the common vole for solving the conflict between postpartum estrous mating and infanticidal behavior of male common voles. Aggr. Behav. 23:293–298, 1997. © 1997 Wiley-Liss, Inc.     

Effect of anosmia on the behavior of standard non-aggressive male mice opponents during agonistic encounters

This study assessed whether the differences observed in a previous experiment [Martinez M, Salvador A, Simon VM (1994): Aggressive Behavior 20:441–451] in the behavior of isolated male mice over several agonistic encounters in which they confronted either an “anosmic” or an “intact” non-aggressive “standard opponent” were due to the differences in the behavior of the opponents themselves. Ethologically-inspired analysis was used to assess the behavior of the opponents during the first agonistic encounter. Anosmic opponents spent less time in social investigation and defense and more time in immobility than intact ones. These results suggest that the differences in the behavior of the opponents could be one of the causes of the differences observed in the behavior of the aggressive males confronting them. However, more research is needed to study if other variables, such as the production of odors, are also affected by the state (deprived or intact) of the olfactory sense. These findings provide additional support for the view that the type of opponent used in studies on intermale aggression is of paramount importance.Aggr. Behav. 23:179–181, 1997.© 1997 Wiley-Liss, Inc.