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.     

Vaginal scent marking: effects on ultrasonic calling and attraction of male golden hamsters

Male hamsters were tested for their responses to areas that had been scent marked by intact or vaginectomized females to determine the effects of naturally deposited vaginal secretions on male behavior. In the first experiment males produced more ultrasonic courtship calls when investigating areas marked by intact females than areas scented by vaginectomized females, demonstrating that vaginal marks facilitate such calling. In a wind-tunnel preference test situation in which scent-marked alleys and clean alleys served as sources of odor, males approached the scented alley first if it had been freshly marked by intact females but not if it had been scented by vaginectomized females or other males. Thus, the odors of vaginal marks are sufficient to attract males over short distances. After males entered these alleys they showed a preference for odors of both intact and vaginectomized females over no odors, but still spent significantly more time investigating the odors of intact females than those of vaginectomized females. These experiments indicate that vaginal secretions are one of the primary cues that elicit male courtship calling, and the small quantities of vaginal secretions deposited by females in vaginal marks are sufficient to elicit ultrasonic calling and attract males over short distances. Thus it is likely that vaginal scent marking and ultrasonic calling by females interact to facilitate attraction and location of mates during courtship.     

Social dominance and individual aggressiveness

Male rats exhibiting high, moderate, or low levels of offensive aggressive behavior in interactions with intruders in their home cage were grouped in mixed-sex colonies with 1 male of each aggression-level group in each colony. Agonistic interactions measured 1, 2, 3, 7, 14, 21, and 22 days after colony formation indicated that highly aggressive males on pretests continued to be more aggressive, becoming the dominant colony male in five of seven colonies and attacking intruders more often than less aggressive males. In the two remaining colonies the moderately aggressive male became dominant. This relationship, which was consistent over a number of indices, including offensive and defensive behaviors, and wound counts and wound sites, was seen even when a substantial weight differential favored the less aggressive animal. Dominance relationships were rapidly established and within-group fighting declined significantly over the 21-day test period. Pretest offensive levels also influenced the behavior of subordinates, with high or moderately aggressive subordinates showing more defense in interactions with dominants and receiving more wounds than did low-aggression subordinates. Dominant males also showed more defense in interacting with those subordinates which had been more aggressive during pretests. This pattern of results suggests that aggression level of the subordinate as well as the dominant may be an important factor determining the intensity of agonistic interactions in male rats.     

The effects of urine on aggressive responses by male golden hamsters

Twenty adult male golden hamsters were isolated into individual cages for a period of six weeks, at the end of which time they had introduced into their home cages, on three occasions, a castrated male intruder. On each occasion the castrated intruder was daubed on the anogenital region with urine from one of three sources: (1) intact females, (2) other castrated males, and (3) intact males. Urine from a different source was applied to the castrated intruder on each of the three tests. Resident males consistently showed more aggression, sniffing, and following and less defensive behavior than the intruders. However, aggression by the resident males showed a significant variance over the three urine treatments given to the intruder. It is concluded that like male mouse urine, male hamster urine contains attack-provoking cues, but that unlike that of the mouse, female urine does not appear to be attack-inhibiting in this species.     

Effects of social isolation in adulthood on odor preferences and urine-marking in male rats

Male rats isolated for 60 days in adulthood spent less time investigating odors of females and urine-marked less over these odors than did males kept in groups of three. Isolated males did not differ from grouped males in their responses to odors of unfamiliar males or their own odors. After social experience the isolated males showed an increase in urine-marking but no change in odor preferences. Individual housing therefore appears to alter olfactory communication in the same way that it does other social behaviors and these changes may be mediated by the same mechanisms.     

Effects of novel odors on intermale attack behavior in mice

Offensive, defensive, and nonagonistic social behaviors of resident male mice toward unfamiliar intruders were examined during exposure to the novel odors of chocolate or sheep's wool. Both novel odors reduced lateral attacks and boxing when compared to familiar sawdust odor. Chocolate, but not sheep's wool, also reliably increased flight behavior by residents. Neither social behaviors nor self-grooming were affected by these odors. The novel odors had no effect upon, or actually decreased, the defensive responses of intruders towards residents. The equivalent effectiveness of both predator and nonpredator odors in elevating risk assessment and suppressing attack during firsttime exposure, and the decreased potency of cat odors following repeated exposure, suggests that novelty contributes to the enhanced defensiveness seen among subjects during initial exposure to predator odors. © 1995 Wiley-Liss, Inc.     

Similarity in the qualities of individual odors among kin and species in Turkish (Mesocricetus brandti) and golden (Mesocricetus auratus) hamsters.

In this investigation, the authors used habituation techniques to explore similarities and differences in the qualities of individual odors from hamsters. In Experiment 1, male Turkish hamsters (Mesocricetus brandti) treated flank-gland odors of 2 males from 1 litter as similar compared with the odor of a male from another litter, whether the odor donors were familiar or unfamiliar. At the same time, the Turkish hamsters discriminated between the subtle differences in the individual odors of their familiar brothers. In Experiment 2, male Turkish and golden hamsters (Mesocricetus auratus) treated the flank-gland odors of 2 unfamiliar, unrelated conspecifics as similar compared with the flank odor of a heterospecific individual. The results suggest that similarities in individual odors are related to genetic similarity of the odor donors. These similarities could provide a basis for different types of social recognition, including kin and species recognition.     

Odor cue determinants of urine marking in male rats (Rattus norvegicus)

This study examined the spatial distribution of urine marking by sexually inexperienced male rats under six odor conditions: minimum odor (baseline), conspecific male urine, conspecific female urine, an animal's own urine, male gerbil urine, and amyl acetate. The gerbil urine and amyl acetate conditions were included to test the theory that marking, rather than being elicited by and directed as a display to appropriate conspecifics, occurred to the introduction of any novel or disruptive odor. The subject's own urine was used to test the theory that the animal marked to maintain an optimum level of its own odor in the environment. The results showed that marking was directed predominantly at objects in the environment over which the animal could readily pass. All odor conditions except "own odor" sharply increased marking over baseline levels. Marking decreased with repeated exposure to particular stimuli. The results strongly supported the theory that urine marking, at least in sexually inexperienced male rats, is produced by novel odor stimuli introduced into a familiar environment.     

Scent marking by male dwarf hamsters (Phodopus sungorus campbelli) in response to conspecific odors

Male hamsters (Phodopus sungorus campbelli) scent marked at greater frequencies in the presence of conspecific odor, either male or female, than in clean areas. Marking rates were not different between male and female odor conditions. In contrast, the pattern of investigation in response to conspecific odor did differ between the male and the female odor conditions. When male odors were used as stimuli, investigative sniffing increased at the scent marking sites but when female odors were used as stimuli investigative sniffing increased throughout the arena. Thus, male dwarf hamsters direct their scent marks at both male and female conspecifics, discriminate between male and female odor, and investigate in a different manner areas scent marked by males and females.     

The introduction of a group of alien mice (Mus musculus L.) into hierarchically organized groups of five male mice

Groups of 3 male or female Mus musculus were introduced into hierarchically organized colonies of 5 male mice for a period of 8 days. The colonies were of 2 kinds; high-level aggressive (HLA), which had been set up 3 days prior to the introduction of the aliens, and low-level aggressive (LLA), which had been established for 21 days before strangers were introduced. Both males and anestrous females were attacked, but males were attacked 5 times more frequently than females. In HLA colonies most of the attacks on the aliens were by the dominant; in LLA colonies there was no difference in the behavior of dominant and subordinate mice toward strangers. Both aggression toward aliens and intracolony aggression declined over the 8 day experimental period. In HLA colonies the dominant mouse mounted females 5 times more frequently than did either his subordinates or male mice in the LLA colonies. In HLA colonies aliens huddled with subordinates to form a single colony with 1 dominant and 7 subordinates. In LLA colonies alien males remained as a discrete group spatially separated in the cage. Female aliens were incorporated into the main colony. In all cases dominant male mice made more attacks on aliens as compared with familiar mice.     

Mouse aggression and the intruder-familiarity effect: evidence for multiple-factor determination c57bl

Male house mice attack their familiar cagemates less than novel intruders-an effect often attributed to habituation of aggression toward odors emanating from the cagemate. This interpretation is overly simplistic in that the effects of familiarizing preexposure depend additionally upon two factors. One factor is the aggression-inhibiting odors emanating from the test male that are deposited onto the cagemate by cohabitation. Supporting evidence is that attack inhibition to the cagemate failed to generalize to noncohabiting same-strain intruders and that eliminating physical contact between subject and cagemate during preexposure prevented the usual postexposure decline in aggression. The second factor is nonolfactory social stimuli emanating from the cagemate during aggressive encounters. The same intruder odors that elicited aggression when placed on a socially active mouse elicited only investigation when placed on models. When subjects were preexposed to an intruder's odor while prevented from socially interacting with the intruder, this investigation subsequently declined while aggression paradoxically increased.     

Pregrouping aggression and defense scores influences alcohol consumption for dominant and subordinate rats in visible burrow systems

Five male/two female rat colonies were established in visible burrow systems, with males selected for pregrouping attack scores and also evaluated in open field and cat odor tests. Dominant-subordinate pregrouping attack differences suggested that the males becoming dominant are those showing more persistent and higher level attack. For six colonies showing dominant-subordinate behavioral differences, pregrouping defense tests failed to predict subordinate status. However, pregrouping defense scores were reliably correlated with subordinate pre-postgrouping change scores for voluntary ethanol consumption. Subordinates showed higher ranked ethanol consumption than dominants, but these groups were not different on pregrouping ethanol consumption. Subordinate postgrouping ethanol consumption was positively correlated with pregrouping attack toward an adult intruder, consonant with previous findings that highly aggressive subordinates are the targets of more intense attack by dominants. These results provide further support for a view that subordination stress increases voluntary ethanol consumption in male rats and suggest some additional individual differences factors that may be involved in increased ethanol consumption for male subordinates. © 1992 Wiley-Liss, Inc.     

Male–male combats in a polymorphic lizard: residency and size,but not color,affect fighting rules and contest outcome

Theoretical models predict that the outcome of dyadic agonistic encounters between males is influenced by resource‐holding potential, resource value, and intrinsic aggressiveness of contestants. Moreover, in territorial disputes residents enjoy a further obvious competitive advantage from the residency itself, owing to the intimate familiarity with their territory. Costs of physical combats are, however, dramatically high in many instances. Thus, signals reliably reflecting fighting ability of the opponents could easily evolve in order to reduce these costs. For example, variation in color morph in polymorphic species has been associated with dominance in several case studies. In this study, we staged asymmetric resident‐intruder encounters in males of the common wall lizard Podarcis muralis, a species showing three discrete morphs (white, yellow, and red) to investigate the effects of asymmetries in color morph, residency, and size between contestants on the outcome of territorial contests. We collected aggression data by presenting each resident male with three intruders of different color morph, in three consecutive tests conducted in different days, and videotaping their interactions. The results showed that simple rules such as residency and body size differences could determine the outcome of agonistic interactions: residents were more aggressive than intruders, and larger males were competitively superior to smaller males. However, we did not find any effect of color on male aggression or fighting success, suggesting that color polymorphism in this species is not a signal of status or fighting ability in intermale conflicts. Aggr. Behav. 35:274–283, 2009. © 2009 Wiley‐Liss, Inc.     

Sex differences in aggressive behaviour in various strains of mice

Two nonalbino inbred (C57 BL/6 and C3H/He) and one albino strain (Swiss) of mice were compared for female aggression toward intruders: 1 in period of lactation, 2 in nonlactating state and (3) in nonlactating state but previously rubbed with urine of lactating females; and for male aggression toward familiar or unfamiliar opponents. The results showed that resident females of the C57 and Swiss strain vigorously attack lactating intruders introduced into their cages. This effect was mediated by urinary cues emitted by the latter mice. It was also shown that Swiss residents displayed aggression towards nonlactating females, irrespective of their strain. Groups of C57 residents reacted most aggressively towards Swiss females, less aggressively towards C3H intruders, but did not show any aggression towards their own nonlactating conspecifics. In contrast, none of the C3H resident female groups displayed aggression towards intruding females of any category or strain. The results also showed that the males of the three strains displayed little (Swiss and C3H) or no aggression (C57) towards familiar opponents, whereas they directed increased aggressive responses towards unfamiliar ones. Comparisons among the three strains of mice revealed that Swiss males were the most aggressive in either situation. On the other hand, the finding that C3H males showed aggressive responses suggested that male and female aggression are, in this strain, under separate genetic or hormonal control.     

Mate recognition by urine odors in the Mongolian gerbil (Meriones unguiculatus)

We examined the responses of male and female gerbils housed in opposite- or same-sex pairs to the urine odors from their cage-mate and those of an unfamiliar gerbil of the same sex. Gerbils housed in mated pairs spent more time investigating the odor of their partner. They also emitted more modulated ultrasonic vocalizations in the presence of their partner's odor than in the presence of the unfamiliar odor. Gerbils housed in same-sex pairs did not respond differentially to the odor of their cage-mate. There were sex differences in the frequency of ventral scent-marking and modulated vocalizations, with males showing more of these behaviors than females. The urine odor of the gerbil's mate can thus be discriminated from those of other gerbils. Recognition of individual odors may promote affiliative behavior and reduce aggression, thus playing an important role in pair maintenance in gerbils.     

Effects of prior agonistic experience on risk assessment and approach behavior evoked by familiar or unfamiliar conspecific odors

Risk assessment and appetitive behaviors in response to familiar and unfamiliar conspecific odors were measured in mice rendered dominant or subordinate by a series of resident-intruder encounters. Subordinate mice showed elevated levels of risk assessment in response to the odors of both familiar dominant and unfamiliar males. These behaviors were almost totally absent among dominant males exposed to familiar subordinate or unfamiliar male odors. Subordinate mice showed a marginally significant elevation in latencies to approach familiar, but not unfamiliar, dominant odors. Dominant and subordinate mice spent comparable amounts of time in the cage area containing familiar antagonist odors, however, and the durations of subordinates were mildly elevated, rather than decreased, when unfamiliar conspecific odors were present. There were no group differences in any of the appetitive behaviors. These findings suggest that apparent preferences for conspecific odors may arise from quantitatively and/or qualitatively differing emotional states. The inclusion of risk assessment measures is suggested to be a useful adjunct for studies of olfactory preference/rejection. © 1994 Wiley-Liss, Inc.     

Differences between two strains of mice,selectively bred for high and low aggressiveness,in the capacity of male odors to affect aggressive behavior

The connection between a genetic disposition for aggressive behavior and the odor signal system in male mice was studied. The males belonged to two strains of mice which have been developed by selective breeding for high- (TA) and low aggressiveness (TNA). Urine from the high aggressive strain (TA), when applied to castrates, stimulated the aggressiveness of NMRI males while TA-soiled bedding suppressed their aggressiveness. In response to male odors from the low aggressive strain (TNA), the NMRI males showed quite contrasting reactions. The results provide evidences of a correlation between the hereditarily determined disposition for aggressive behavior and the odor signal system in TA- and TNA males.     

Analysis of ultrasonic vocalizations emitted by residents during aggressive encounters among rats (Rattus norvegicus)

This investigation was concerned with the extent to which aggressive resident rats emit 40-70-kHz vocalizations and the effect of these signals on intruders. In Experiment 1, deafened and intact intruder males were given two encounters with resident animals. Deafened intruders engaged in a higher duration of immobile or freezing postures than intact animals. Experiment 2 indicated that the augmentation of freezing found among deafened intruders was not due to an inability to detect ultrasounds made by residents since intruders encountering devocalized resident males showed no reliable differences in specific motor patterns from intruders paired with intact residents. The results further demonstrated that 40-70-kHz vocalizations are produced almost entirely by intruding animals since there were no significant changes in occurrence of these calls when resident males were devocalized. Under the constraints of the testing procedures employed, the role of ultrasonic communication during the initial formation of agonistic relations could not be determined experimentally.     

Evidence that rats discriminate between familiar and unfamiliar putative urinary odorants of adult male conspecifics

Adam [1976; Lehman and Adams, 1977] suggested that a resident rat makes an olfactory comparison of cage odor and other rat odor prior to attacking an unfamiliar conspecific intruder. The findings of the present study are consistent with the notion that rats discriminate between familiar and unfamiliar putative urinary odorants Adult male albino rats were tested for preferences between areas treated with familiar urine (11 hours pretest exposure), unfamiliar urine (no pretest exposure), and untreated areas. Subjects (N = 12) preferred areas treated with familiar urine over ones treated with unfamiliar urine (p < 0.05). Also, they (N = 12 per preference-test group) preferred areas treated with either urine over untreated ones (familiar versus clean, p < 0.01; unfamiliar versus clean, p < 0.05).     

Maternal aggression in mice and rats towards male and female conspecifics

Although postpartum aggression is primarily studied in laboratory mice and rats, it is unclear how the two species compare in terms of the factors associated with peak levels of aggressive behavior. Using the same experimental protocol, we assessed the relative effect of intruder sex and time since parturition on the frequency of maternal aggression in Long-Evans rats and CFW mice. Females were studied for 2 consecutive cycles of pregnancy and lactation. During the first lactation, aggression was tested 2 times per week for 3 weeks in order to select animals that attacked at least once. During the second lactation, both pup care and aggressive behavior were assessed in detail. Testing occurred twice in each lactation week, with postpartum days 1–7, 8–14, and 15–21 considered weeks 1, 2, and 3, respectively. Maternal behavior towards 3 pups was observed for 5 minutes, followed by a confrontation with an intruder. Lactating females encountered female intruders once per week, and male intruders in the alternate weekly test. The same behaviors were measured in the 2 species, except for the tail rattle exhibited by mice and the aggressive posture shown by rats. Lactating rats and mice show similar decreases in pup care behavior as lactation progresses in time; yet the factors associated with peak levels of aggression differ between species. In Long-Evans rats, female intruders receive more attacks, threats, and aggressive postures than males. Frequency of attack bite and sideways threat declines in each passing week of lactation. Lactating mice are more aggressive toward male intruders throughout the lactation period. Mice still attack and threaten during the third week of lactation, but less often in comparison to the first week. Therefore, peak levels of aggression vary in mice and rats both as a function of intruder sex and lactation week.