Territorial defence of space and feeding sites by a plethodontid salamander

Two series of experiments were conducted, one in field enclosures and another in the laboratory, to test the hypothesis that the salamander Desmognathus monticola (family Plethodontidae) defends its refuges and feeding sites against conspecific intruders. When two identical cover sites were provided as refuges in the laboratory, residents and intruders occupied separate cover sites significantly more often than the same sites. Residents did not, however, show strong preference for the same site, nor did they consistently defend a specific site. When food supplements were provided consistently at the same cover sites in field enclosures, resident D. monticola occupied and defended the feeding sites significantly more frequently against intruders than the non-feeding cover sites. Individuals not receiving food supplements also excluded intruders from the occupied cover sites but did not defend a specific cover site. Residents in enclosures where no food supplements were provided were significantly more active at night, outside cover sites, than residents receiving food supplements. Individual D. monticola exhibit territoriality by excluding intruders from the refuges they occupy. Providing food supplements increases the site specificity of individuals and decreases the amount of time spent in nocturnal activity.     

Aggressive behaviour of female prairie deer mice in laboratory populations

Prairie deer mice (Peromyscus maniculatus bairdii), living in asymptotic laboratory populations established two years earlier, were observed for agonistic responses to conspecific intruders. In the first experiment, intruders of six age-sex classes were placed into 10 of the populations for 10 min. The sex of the intruder did not influence the behaviour of the residents, but juveniles elicited more aggression than did adults. A second experiment revealed that female residents were responsible for almost all of the attacks upon juveniles. Experiment 3, in which the responses of pairs of deer mice to juvenile intruders were recorded, demonstrated that the aggressiveness of a female was enhanced by the presence of a male. In the final experiment, females were observed to be highly aggressive during the first few days after giving birth. The aggressive behaviour of the female deer mouse may have greater significance for population dynamics than that of the male.     

Territorial behaviour reflects sexual status in groups of false clown anemonefish (Amphiprion ocellaris) under laboratory conditions

Anemonefishes (genus Amphiprion) are well known as protandrous sex-changing fish. They live symbiotically with sea anemones and form a social unit that consists of a breeding pair and several sexually immature individuals with ambisexual gonads. In general, the hierarchy of the social rank is strictly maintained in a group, and this hierarchy is considered to be one of the critical factors that induce sex change or sex differentiation in anemonefishes. Field observations have shown that behavioural characteristics of anemonefishes vary depending on the environment. In this study we examined the differences in territorial aggression directed at conspecific intruders according to sexual status in the false clown anemonefish, Amphiprion ocellaris, under laboratory conditions. Resident–intruder tests were conducted on groups consisting of three anemonefish: a dominant female, a second-ranked male and a subordinate ambisexual individual. Females and males showed more aggressive behaviour than did ambisexual individuals, and behaviours were specifically directed at intruders of the same sexual status, not at those of the opposite sex. Notably, the female residents displayed fierce aggressive behaviours particularly toward female intruders, whereas male residents engaged more often in side-by-side swimming with male intruders than with female or ambisexual intruders. Ambisexual intruders were threatened by all residents, rarely attacked. We observed only few aggressive acts towards tank mates. These results suggest that sexually mature resident anemonefish in a confined space, such as under laboratory conditions, perceive intruders of the same sexual status as competitors for reproductive status and thus, dominant social rank.     

Territorial behaviour of the red-backed salamander: Expulsion of intruders

Red-backed salamanders, Plethodon cinereus, were paired in laboratory chambers where they defended areas against each other by threat display and biting. Difference in sizes of paired individuals was not correlated with which one would enter the other's area or be more aggressive after an intrusion. We also found no sexual differences in agonistic behaviour. Both defenders and intruders assumed a threat posture for about 50% of the invasion periods, but defenders exhibited a higher rate of biting. Defenders expelled intruders in 74% of all encounters, while intruders expelled defenders in 18%, with 8% of the encounters a draw. Intruders frequently left the contested area even in the absence of biting or threat display by the defender, apparently in response to the defender's pheromones or to the high potential cost of an escalated aggressive contest (damage to the chemosensory structures). These data provide behavioural evidence that a salamander can evict intruders from a defended area and thus support the hypothesis of territoriality among terrestrial salamanders.     

Territorial behavior of the Korean wood-feeding cockroach, <Emphasis Type="Italic">Cryptocercus kyebangensis</Emphasis>

We investigated the territorial behavior of Cryptocercus kyebangensis from the viewpoint of offspring protection. Aggressive behavior against adult intruders occurred more frequently in resident adults with their young than those without their young. Resident adults without offspring more frequently attacked intruders of the same sex than those of the opposite sex, whereas those with offspring attacked regardless of the sex of adult intruders. In paired residents, cooperative territorial behavior occurred in a higher proportion in pairs with offspring than those without offspring. Responses of residents to nymphal intruders depended on the head capsule size of the intruders. Resident adults rarely attacked intruders smaller than their own offspring but frequently attacked larger intruders. Resident nymphs frequently attacked intruders smaller than themselves, whereas they escaped or showed jerking behavior when they encountered larger intruders. Electronic Publication     

Sexual dimorphism in responses to unfamiliar intruders in the tamarin, Saguinus oedipus

Aspects of social structure in group-living species can be inferred by observing the responses of individuals to unfamiliar animals. This study examined the responses of mated pairs of cotton-top tamarins (Saguinus oedipus oedipus) to presentation of either unfamiliar conspecifics or members of a related tamarin species, the saddle-back tamarin (Saguinus fuscicollis fuscicollis). Male and female responses to intruders differed: resident males threatened, displayed piloerection, approached, and attacked intruders, especially males, while resident females showed increases in suprapubic scentmarking in the presence of intruders. Both males and females discriminated between the species of intruders, exhibiting more threats, scent-marking, piloerection, and approaches in the presence of conspecific intruders. There are pronounced sex differences in the signals and behaviour patterns that are elicited in an aggressive or territorial encounter with unfamiliar conspecifics in this monogamous primate.     

Intruders in Nests of the Spotless Starling: Prospecting for Public Information or for Immediate Nesting Resources?

The prospective behaviour for nests by conspecific intruders may be a strategy to gather public information for future reproduction or to secure resources for immediate reproduction. Although the relationship between the sex, age and breeding experience of intruders and the sex and age of residents may be crucial for understanding the significance of nest‐prospecting behaviour, a precise determination of these traits has rarely been addressed in field studies. In a free‐ranging population of spotless starlings ( Sturnus unicolor), inexperienced birds were the predominant intruders. The ratio of male‐to‐female intruders was higher among birds without previous breeding experience, although our results did not allow us to determine whether more inexperienced males or females intruded nests. The average annual rate of intrusion of either sex was strongly correlated with the number of fledglings produced in the study colony the previous year, which seems to indicate that the inexperienced intruders were, in general, yearlings. The proportion of the sexes among the intruders in each study year was correlated with the average age of male owners but not with the age of female owners. This result suggests that the presence of intruding males in the nests was affected by an increased opportunity to find vacancies in nesting territories as resident males became older. This finding supports the hypothesis that, in most cases, birds visited nests to obtain personal information about nesting resources. However, the intrusion rates were higher when there were nestlings than during the incubation period, which suggests that collecting public information was also involved in the intruding behaviour. Both sexes regularly attacked intruders, which implies that the intruders inflicted some kind of cost on the owners. Female floaters were more frequently chased, probably because they regularly lay parasitically in conspecific nests.     

Behavioral interactions between salamanders and centipedes: competition in divergent taxa

Red-backed salamanders, Plethodon cinereus, use territorialadvertisement in the form of agonistic displays and pheromonalscent marking as a mechanism for intraspecific interferencecompetition. Although ecological and behavioral interactionsamong species of salamanders have been well studied, littleis known about the interactions between territorial P. cinereusand other ecologically similar species, such as large predatoryinvertebrates. Our field data indicate that P. cinereus anda large syntopic centipede, Scolopocryptops sexspinosus, exhibitnegative spatial associations in natural habitats, possiblyindicating interspecific territoriality. Only seven instancesof salamander/centipede co-occurrence were recorded from a fieldsample of 247 occupied cover objects. Cover object size waspositively correlated with salamander SVL (tip of the snoutto the anterior end of the cloaca), but there was no correlationof cover object size to centipede length. Data on the abilityof P. cinereus to differentiate among chemicals on the substratesuggest that visual cues are not necessary to elicit a territorialresponse from intruding salamanders. Although in laboratorytrials salamanders behaved similarly toward intruders of bothspecies, biting was directed only toward centipedes. Salamandersspent significantly more time approaching centipedes than theydid approaching other salamanders. Approach behavior was oftenassociated with nose tapping and may be an investigative, ratherthan aggressive, behavior. We suggest that territorial P. cinereusrespond similarly to intruding salamanders and centipedes, butthat they escalate more readily to biting centipedes becauseS. sexspinosus is sightless and thus unable to respond to visualsignals.     

Habitat selection by two streamside plethodontid salamanders

Summary A series of experiments was conducted to test the hypothesis that habitat selection by the salamanders Desmognathus monticola and Desmognathus quadramaculatus is influenced differently by interspecific interference than by intraspecific interference. Individuals of neither species were influenced differently by the presence of heterospecifics than by the presence of conspecifics in their activity away from cover sites, in selection of different substrate moisture levels, in selection of different substrate textures, nor in selection of microhabitats relative to the streambed. Both species generally selected substrates with the highest moisture and the coarsest texture. Selection of different cover sizes by D. monticola depended on microhabitat, with larger rocks being selected most frequently when salamanders were farther from the streambed. D. quadramaculatus was seldom found away from the streambed and did not discriminate among the cover sizes available. The strong affinity of D. quadramaculatus for streambed microhabitat, compared with the much more variable microhabitat selection of D. monticola, resulted in spatial separation of individuals of the two species most of the time. Results of this study do not support the hypothesis that interspecific inference is more important than intraspecific interference in the microhabitat distributions of D. monticola and D. quadramaculatus.     

The Good,the Bad,and the Ugly: Agonistic Behaviour in Juvenile Crocodilians

We examined agonistic behaviour in seven species of hatchling and juvenile crocodilians held in small groups (N = 4) under similar laboratory conditions. Agonistic interactions occurred in all seven species, typically involved two individuals, were short in duration (5–15 seconds), and occurred between 1600–2200 h in open water. The nature and extent of agonistic interactions, the behaviours displayed, and the level of conspecific tolerance varied among species. Discrete postures, non-contact and contact movements are described. Three of these were species-specific: push downs by C. johnstoni; inflated tail sweeping by C. novaeguineae; and, side head striking combined with tail wagging by C. porosus. The two long-snouted species (C. johnstoni and G. gangeticus) avoided contact involving the head and often raised the head up out of the way during agonistic interactions. Several behaviours not associated with aggression are also described, including snout rubbing, raising the head up high while at rest, and the use of vocalizations. The two most aggressive species (C. porosus, C. novaeguineae) appeared to form dominance hierarchies, whereas the less aggressive species did not. Interspecific differences in agonistic behaviour may reflect evolutionary divergence associated with morphology, ecology, general life history and responses to interspecific conflict in areas where multiple species have co-existed. Understanding species-specific traits in agonistic behaviour and social tolerance has implications for the controlled raising of different species of hatchlings for conservation, management or production purposes.     

Nest and Egg Recognition by Salamanders in the Genus Desmognathus: A Comprehensive Re‐Examination

We conducted a comparative investigation of nest relocation and egg recognition by four species of streamside salamanders indigenous to eastern North America: Seepage Salamander (Desmognathus aeneus), Santeetlah Salamander (Desmognathus santeetlah), Ocoee Salamander (Desmognathus ocoee), and Northern Dusky Salamander (Desmognathus fuscus). Females of all four species were able to relocate their nest sites following displacement of 1 m. Upon return to a nest site following natural displacement, females must be able to recognize their eggs and, in some instances, choose between their own clutch and the unattended clutch of a conspecific. In two‐choice behavioral tests, female salamanders of all four species moved randomly within the test chamber in the absence of eggs, but preferred their own eggs to a filter paper blank. One species, D. fuscus, exhibited a similar attraction to conspecific eggs suggesting that the presence of eggs, regardless of their origin, may stimulate maternal care in physiologically primed females. We found that egg discrimination is not as infallible as previously reported. All four species spent more time with their own eggs than they did with the eggs of a conspecific female; however, this trend was significant for D. ocoee only. Interspecific variation in egg discrimination is attributed to differential selection associated with the life history of individual species.     

Communication in coral reef fish: the role of ultraviolet colour patterns in damselfish territorial behaviour

Many coral reef fish possess ultraviolet (UV) colour patterns. The behavioural significance of these patterns is poorly understood and experiments on this issue have not been reported for free-living reef fish in their natural environment. The damselfish Pomacentrus amboinensis has UV facial patterns, and spectroradiometric ocular media measurements show that it has the potential for UV vision. To test the potential behavioural significance of the UV patterns, I studied the response of males, in natural territories on the reef and in aquaria, to two conspecific intruders, one presented in a UV-transmitting (UV+) container and the other in a UV-absorbing (UV−) one. Territory owners attacked intruders viewed through UV+ filters significantly more often and for longer than intruders viewed through the UV− filter. In general, the results of the field experiment confirmed those of the laboratory experiment. The results support the hypothesis that P. amboinensis males are sensitive to UV light and that reflectance patterns, which appear in high contrast only in UV, modulate the level of aggressive behaviour. A recent survey showed that many predatory fish may not have UV vision and the use of UV colours in select species of reef fish may therefore serve as a ‘private communication channel’.     

Sexual differentiation and seasonal variation in response to conspecific and heterospecific acoustic signals

Interspecific territoriality is frequently reported between closely related species; however, few studies have demonstrated interspecific territoriality between distantly related species living in sympatry. We conducted playback experiments to investigate territorial behaviour in male and female White‐bellied Wrens (Uropsila leucogastra) in response to simulated conspecific and heterospecific intruders during the breeding and non‐breeding seasons. We explored whether heterospecific songs of the Happy Wren (Pheugopedius felix), a distantly related species and ecological competitor, elicited antagonistic responses from focal White‐bellied Wrens, and whether such responses differed between the sexes. We also examined whether male and female responses to conspecific and heterospecific rivals varied with season. We found that male White‐bellied Wrens always responded to conspecific song, and responded significantly more to heterospecific song compared to a control stimulus (Tropical Parula, Setophaga pitiayumi). In contrast, although female White‐bellied Wrens responded strongly to conspecific song, their response to heterospecific song did not differ significantly from the control stimulus. The proportion of males that responded to heterospecific songs and the proportion of females that responded to conspecific songs varied seasonally, showing significantly lower responses during the breeding season. The intense responses of male White‐bellied Wrens to playback of heterospecific songs suggest that they recognise ecological competitors based on their vocal signals. Furthermore, the decrease in agonistic interactions during the breeding season is in line with the hypothesis that aggressive behaviour may be detrimental to reproductive and parental activity, and the hypothesis that heterospecific animals pose less of a threat during the breeding season.     

Colony fusion in a termite: What makes the society "open"?

Summary. Sociobiological theories assume that insect societies are closed, i.e., members always act aggressively toward alien conspecific individuals. However, introduction of non-nestmate workers into a host colony of a lower termite, Reticulitermes speratus revealed various levels of agonism: from genocide to colony fusion. Members of the host colony attacked and killed the intruders having a higher nymph ratio (the number of nymphs/the number of workers) than the host colony had. In contrast, the intruders were accepted if they had a lower nymph ratio than the host colony. Acceptance of a lower-nymph-ratio colony could be beneficial for the host colony because it would gain additional labor force to feed its own nymphs. However, acceptance of a higher-nymph-ratio colony might be disadvantageous because the workers must rear non-relative nymphs additionally. Here we show that termites facultatively change their agonistic response toward non-nestmates according to the cost and benefit of colony fusion. Contrary to the existent concept, we report for the first time that colony fusion is an adaptive tactic in social insects.     

Lack of Evidence for the Prior Residence Effect in the Allegheny Mountain Dusky Salamander (Desmognathus ochrophaeus)

Territorial disputes are frequently settled by an advantage afforded to one of the contestants by asymmetries such as size difference, strength and motivation. Allegheny Mountain Dusky Salamanders (Desmognathus ochrophaeus) are reported to defend cover objects, a form of territorial behaviour. We conducted an experiment to determine whether or not adult salamanders of this species exhibit prior residence effect during staged encounters involving size‐matched, same sex conspecifics (i.e. does familiarity with a territory predict successful defence?). We tested 154 adult salamanders (72 female, 82 male) in reciprocal trials in which each animal acted as a resident and as an intruder. We recorded multiple agonistic behaviours including: front‐trunk raised, all‐trunk raised, nudge, bite, bite‐and‐hold and jaw‐lock. We assigned these behaviours scaled point values and calculated an index of aggression for each animal as a resident and as an intruder. We found that in same sex trials, males were significantly more aggressive than females. Although D. ochrophaeus exhibited stereotypical, agonistic behaviours similar to those reported for Plethodon, unlike Plethodon the outcomes of symmetrical social encounters were not influenced by residential status. Prior residence is documented to be a major determinant of territorial disputes among diverse animal taxa, including salamanders. However, our research suggests that the phenomenon is not universal and may depend on qualities of the microhabitat in which a species has evolved.     

Maternal aggression as a deterrent to infanticide in Peromyscus leucopus and P. maniculatus

Adult male and female white-footed mice (Peromyscus leucopus) and deermice (P. maniculatus) from sympatric populations commit infanticide on neonates of either species. A laboratory experiment was conducted to determine whether aggression in maternal females could effectively deter infanticidal intruders. Females of both species exhibited post-partum aggression and dominated intruders of either sex or species in 83 of 88 trials. In the absence of the mother, neonates were attacked by intruders in 82 out of 84 trials. Maternal females were considerably more aggressive than anoestrous females. The implications for female territorially as a mechanism to prevent infanticide are discussed.     

Inter-male aggression with regard to polygynous mating system in Pampean grassland mouse, Akodon azarae (Cricetidae: Sigmodontinae)

Based on the hypothesis that, in Akodon azarae, polygyny operates through female defence, we studied inter-male aggression in order to test the following predictions: during the breeding period (1) resident males are more aggressive than intruder males in the presence of females (FP), and (2) aggressive behaviour is independent of male condition (resident or intruder) in the absence of females (FA). To test our predictions, we used the resident male behavioural response towards an intruder male in relation to FP or FA. We conducted 30 encounters in FP and 27 in FA in 0.79-m² round enclosures placed in the Espinal Reservation. Our results support the prediction that, in FP, the intensity of aggressive behaviour exhibited by males varied in relation to resident or intruder condition. Resident males showed high levels of aggression towards intruders, and intruders exhibited the greatest values of submissive behaviours with residents. In FA, the intensity of aggressive behaviour did not vary in relation to resident or intruder condition. Both resident and intruder males exhibited low aggressive behaviour and inter-male encounters resulted mainly in non interactive behaviours. Our results support the hypothesis that, in A. azarae, the polygynous mating system operates through female defence.     

Multiple Plumage Ornaments as Signals of Intrasexual Communication in Golden‐Winged Warblers

Avian plumage represents some of the greatest diversity in integument coloration of all animals. Plumage signals are diverse in function, including those that allow for assessing potential mates or the mitigation of agonistic interactions between rivals. Many bird species possess multiple ornamental traits that have the potential to serve as multiple or redundant signals. For example, male golden‐winged warblers (Vermivora chrysoptera) have brilliant carotenoid‐based yellow crowns, melanin‐based black throats, and structurally based white patches on their outer tail feathers. Using a correlative approach, we investigated whether plumage ornaments have the potential to reliably signal ability to acquire higher quality territory, aggressive response to simulated territorial intrusions, and reproductive success. We found that both crown chroma and tail brightness were significantly related to habitat quality and aggression; more ornamented birds held territories with higher quality habitat and were less aggressive toward simulated conspecific stimuli. Older birds sang less threatening songs than younger birds and were more likely to sing their mate attraction song type (type 1) rather than songs typically reserved for agonistic interactions (type 2). Finally, despite our previous research demonstrating that habitat strongly predicts reproductive success in this warbler population, we found no evidence of a direct link between ornamentation and reproductive success. Overall, these data suggest that younger males, and those with lower quality ornaments, compensate with more aggressive behaviors. Additional research is needed to investigate the dynamics between behavioral traits and ornaments to better understand complex signaling and how golden wing signals function in conspecific interactions (male–male interactions and mate‐choice).     

The Role of Wing Coloration in Sex Recognition and Competitor Recognition in Rubyspot Damselflies (Hetaerina spp.)

The decision rules that animals use for distinguishing between conspecifics of different age and sex classes are relevant for understanding how closely related species interact in sympatry. In rubyspot damselflies (Hetaerina spp.), the red wing coloration of mature males is hypothesized to be a key trait for sex recognition and competitor recognition within species and the proximate trigger for interspecific male–male aggression. We tested this hypothesis by manipulating the wing coloration of tethered conspecific intruders and measuring the responses of territory holders of three species in the field. As predicted, covering the red spots of mature males with black ink nearly eliminated territorial responses, and in some cases, territorial holders clasped the blackened males as if they were females. Adding red spots to female wings triggered territorial responses and nearly eliminated sexual responses. Immature males with artificial red spots were attacked at the same rate as mature male intruders, and much more frequently than were immature male controls. The results varied somewhat by species. In H. titia, the only species of Hetaerina with substantial black wing pigmentation, the effects of blackening the red spots of intruders varied both geographically and seasonally. But even when blackening the red spots of male intruders did not reduce the aggressive response of H. titia territory holders, adding artificial red spots to female wings elicited aggressive responses and nearly eliminated sexual responses. The results of this study further strengthen the evidence that interspecific aggression in Hetaerina results from overlap in territorial signals and that the derived black wing pigmentation of H. titia reduces interspecific aggression.     

Territorial aggression can be sensitive to the status of heterospecific intruders

Territorial animals are known to be able to differentiate between intruding individuals posing a low or high threat and adjust their aggressive response accordingly. However, plastic territorial aggression based on recognising individuals with different attributes is typically assumed to be relevant only in the context of conspecific interactions. In this study, we investigated territorial aggression of neotropical cichlid fish in their natural habitat to assess whether responses to different types of individuals of another species can also be plastic. We show that arrow cichlids (Amphilophus zaliosus) adjusted their territorial aggression regarding the status of heterospecific intruders: breeding individuals of Amphilophus astorquii received a lower level of aggression than non-breeders. The same pattern was also found for the two different types of A. astorquii individuals intruding into conspecific territories. These results suggest that heterospecific individuals should not be ignored when considering selection pressures shaping plasticity of aggressive behaviour in territorial animals.