How boat noise affects an ecologically crucial behaviour: the case of territoriality in <Emphasis Type="Italic">Gobius cruentatus</Emphasis> (Gobiidae)

Gobius cruentatus emit sounds during agonistic interactions. In order to evaluate the effect of boat noise exposure on G. cruentatus territorial behaviour, we played a field-recorded diesel engine boat noise during aggressive encounters between an intruder and a resident fish in a laboratory-controlled tank. We tested two factors: role (resident vs. intruder) and condition (noisy vs. silent); the test animals underwent all the treatments in a round-robin design. Agonistic behavior of the residents was modified by boat noise: during the playback residents were more submissive and won less encounters than in the control (silent) condition. We suggest that sound production is an effective tool for territorial defense, since the impairment of acoustic communication due to the recreational boat noise diminished the ability of the resident to maintain its territory.     

The hormonal response of female European Stonechats to a territorial intrusion: the role of the male partner

In many bird species, the female participates in defending a pair's breeding territory, however, the endocrine control mechanism of female aggressive behavior is largely unknown. The general statement that androgens are involved in the regulation of aggressive behavior is based on studies conducted only in males. Here, we tested whether paired female stonechats show a hormonal response to a simulated male territorial intruder. Since in males of territorial bird species androgen levels usually increase following a male-male encounter, we measured androgen-levels before and after a simulated male intrusion. In addition, we measured estradiol, the main gonadal hormone in females, and corticosterone, a stress hormone. The results show that a male intruder does not affect any of the measured hormones in females. In a second experiment, we also tested whether the endocrine state of the male partner affects the hormonal response of females to a male intruder by comparing the hormonal response of females paired with pharmacologically castrated males and females paired with control males. Females paired with pharmacologically castrated males had lower corticosterone levels both before and after the intrusion than females paired with control males. Additionally, in both groups, female corticosterone levels were increased following a male intrusion. We suggest that the differences found between females paired with pharmacologically castrated males and females paired with control males are due to differences in intra-pair interactions.     

Effects of castration and home cage residency on aggressive behavior in rats

The effects of castration of both resident and intruder rats on territorial aggressive behavior were studied. The results suggest that residence in a home cage is more important than gonadal status in determining the outcome of an aggressive encounter. Resident rats were more likely to be dominant especially if they were intact. Intact residents directed less aggressive behavior toward castrated intruders than toward intact intruders. Intruder rats generally showed low levels of aggressive behavior and were only dominant when the resident had been castrated. Thus, the aggressive behavior of a male rat depends upon both his gonadal status and that of his opponent.     

Everybody Needs Good Neighbours: Coalition Formation Influences Floater Fight Choice

In territorial species, it is sometimes less costly to help a neighbour fight off an intruder than to re‐establish territory boundaries with a new, potentially stronger neighbour. In fiddler crabs, a male resident will only help his neighbour if he is larger than the intruder who, in turn, is larger than the challenged neighbour. Does this influence with whom a territory‐seeking male decides to fight? I show that territory‐seeking males appear to choose opponents based partly on the size of the resident’s nearest neighbour. By avoiding challenging resident males with larger neighbours, territory‐seeking males can reduce the likelihood of initiating a fight with a resident who might gain help from his neighbour that decreases the likelihood that the intruder will win the fight.     

Previous agonistic experience determines both foraging behavior and territoriality in the limpet Lottia gigantea (Sowerby)

Lottia gigantea, the owl limpet, is an algal gardener. Territorial individuals actively defend gardens, which consist of clearedareas in the intertidal zone upon which a thick algal filmdevelops and upon which the territory holder feeds. Smaller,nonterritory holders raid these gardens and graze the algalfilm. Territorial individuals must obtain an adequate ration without compromising the productivity of the garden. In contrast,a nonterritory holder grazing on another limpet's territorymust obtain an adequate ration before it contacts the territoryholder and is driven off. In the laboratory, replicate setsof 10 limpets were trained to behave territorially and nonterritorially.Training mimicked natural encounters between territorial andnonterritorial L. gigantea. Limpets given territorial trainingleft significantly (t = -4.92, df = 9, p =.00041) more algalcover behind when grazing (on average 71%) than did limpetstrained to be nonterritorial (on average 50%). Territorial limpets seldom grazed over the same area more than once (4% of the grazedarea). In contrast, nonterritorial limpets frequently foragedover an area more than once; of the area grazed, 20% had beenvisited more than once. Previous agonistic experience determinesboth territorial behavior and foraging strategies, two of thecritical behaviors necessary for successful gardening behavior.Nonterritorial limpets maximize consumption per unit area, whereas territorial limpets appear to forage prudently, leaving a significantly greater proportion of the plant biomass behind.     

Differential effects of moving versus stationary territorial intruders on territory defence in a songbird

1.  In territorial contests, not only acoustic or other signals, but also the movements of a territorial intruder are likely to influence the response of a resident.
2.  We tested this movement hypothesis by simulating moving vs. stationary intruders into the territories of winter wrens Troglodytes troglodytes , using the same non-interactive song playbacks in both treatments.
3.  Male winter wrens showed a different long-term singing reaction in response to a moving than to a stationary intruder.
4.  One day after experiencing an intruder that was switching between three locations, residents started to sing earlier before sunrise, and they sang more and longer songs at dawn than before the intrusion.
5.  Residents receiving the same playback from one location only reacted by starting to sing later relative to sunrise, and by singing fewer and shorter songs than before the intrusion.
6.  We could not discriminate between the treatments when examining the short-term singing reactions during and immediately after the playbacks. However, our results clearly demonstrate an effect of the spatial behaviour of territorial intruders on the long-term territory defence of residents at dawn, about 24 h after an intrusion.
7.  We argue that spatial behaviour of territorial intruders should be an integral part of the study of animal territory defence behaviour. Investigating long-term changes in territory defence at dawn is a sensitive tool for discriminating between different types of intruders.     

Neuromolecular correlates of cooperation and conflict during territory defense in a cichlid fish

Cooperative behavior is widespread among animals, yet the neural mechanisms have not been studied in detail. We examined cooperative territory defense behavior and associated neural activity in candidate forebrain regions in the cichlid fish, Astatotilapia burtoni. We find that a territorial male neighbor will engage in territory defense dependent on the perceived threat of the intruder. The resident male, on the other hand, engages in defense based on the size and behavior of his partner, the neighbor. In the neighbor, we find that an index of engagement correlates with neural activity in the putative homolog of the mammalian basolateral amygdala and in the preoptic area, as well as in preoptic dopaminergic neurons. In the resident, neighbor behavior is correlated with neural activity in the homolog of the mammalian hippocampus. Overall, we find distinct neural activity patterns between the neighbor and the resident, suggesting that an individual perceives and processes an intruder challenge differently during cooperative territory defense depending on its own behavioral role.     

Sex Differences in Territorial Behavior Exhibited by the Spotted Hyena (Hyaenidae, Crocuta crocuta)

Spotted hyenas ( Crocuta crocuta ) are gregarious carnivores that defend group territories against encroachment by neighboring conspecifics. Here we monitored the behavior of members of one clan of free-ranging spotted hyenas during border patrols, 'wars' with neighboring clans, and other interactions with alien intruders, to document differences between the sexes in territorial behavior in this species. We also examined the possibility that the probability or rate of attack on alien hyenas encountered within the clan's territory would vary with the sex of the intruders. Initiation and leadership of most cooperative territorial behaviors were by adult female clan members, although border patrols were occasionally conducted by groups composed exclusively of resident males. The vast majority of alien intruders into the territory of the study clan were males. Resident females were more likely to attack intruding females than intruding males, but hourly rates of aggression directed by females towards aliens did not vary with intruder sex. Resident males were more likely than resident females to attack alien males, and resident males directed significantly higher hourly rates of aggression towards intruding males than females. Although female leadership in most cooperative territorial behaviors distinguishes spotted hyenas from many mammalian carnivores, other sex differences in the territorial behavior of spotted hyenas resemble those documented in other gregarious predators. Sex differences observed in hyena territoriality are consistent with the hypothesis that male and female clan members derive different selective benefits from advertisement and defense of group territories.     

Defensive responses to predatory seastars by two specialist limpets, Notoacmea insessa (Hinds) and Collisella instabilis (Gould), associated with marine algae

The limpets Notoacmea insessa (Hinds) and Collisella instabilis (Gould), which are associated specifically with certain algae, were tested for defensive responses to seastars. Contact with predatory seastars elicited responses by both species of limpets, in contrast to previous work reporting a lack of defensive responses by specialist limpets associated with plants. Non-predatory seastars normally did not elicit defensive responses. The form of the response by Notoacmea insessa differed, depending on whether the limpet was on or off its grazing scar. When the limpet was off its grazing scar, the most common response was movement away from the point of contact. When on the scar, the limpet usually elevated its shell and rocked from side-to-side, but rarely moved from the scar. The responses of Collisella instabilis almost always involved rapid movement away from the point of contact and tended to be more vigorous than those of Notoacmea insessa.     

Female Intrasexual Territoriality and its Potential Adaptive Significance: The Pampean Grassland Mouse as an Ecological Model Species

Territorial behaviour in female small mammals has been proposed as a mechanism to defend limited ecological resources or their pups against conspecific infanticidal or predators. Female territorial behaviour very often is associated with reproductive activity due to the fact that frequency and intensity of aggression are exhibited mainly when females are pregnant or lactating. In vole and mice species, female territoriality would be a counterstrategy to prevent the killing of their pups by conspecific breeding females. To study whether female territoriality is a strategy for pups or nest defence against infanticidal breeding females, and whether time invested in nursing young affects aggressive response of mothers, we used the Pampean grassland mouse (Akodon azarae) as an ecological model species. We conducted resident–intruder tests between lactating females. Differences in residency time (48 vs. 72 h) of focal females in their home territory were also included in the analysis. In all cases, the pups of both resident and intruder mothers were placed with the nesting material from their reproductive cages. Resident mothers were always more aggressive than intruders and they were even more aggressive when they spent more time nursing their pups. Contrarily, intruder females exhibited the greatest values of submissive behaviours. Our results show that female territoriality of A. azarae would represent a strategy to protect pups from potentially infanticidal females. We discuss the extent of female intrasexual territoriality and its potential adaptive significance in relation to strategies which lead to increase their reproductive success.     

Anti-predator behaviour changes following an aggressive encounter in the lizard Tropidurus hispidus

Avoiding predators may conflict with territorial defence because a hiding territorial resident is unable to monitor its territory or defend it from conspecific intrusions. With persistent intruders, the presence of an intruder in the near past can indicate an increased probability of future intrusions. Therefore, following a conspecific-intrusion, territorial residents should minimize costs from future intrusions at the cost of higher predation risks. I conducted experiments with males of the territorial lizard Tropidurus hispidus recording approach distance (distance between predator and prey when the prey escapes) and time to re-emergence from a refuge after hiding. Past aggressive interactions affected anti-predator behaviour: lizards re-emerged sooner (compared to a control) when the predator attacked 5 min after an aggressive encounter. If the predator attacked while an aggressive encounter was ongoing, there was also a reduction in approach distance. The results are consistent with an economic hypothesis which predicts that T. hispidus incur greater predation risks to minimize future territorial intrusion; additionally they show that the effects of past and ongoing aggressive interactions are different, consistent with the minimization of present intrusion costs. These results are relevant for studies of the changes in aggressive behaviour due to changes in the social environment and for studies of the costs and (co) evolution of aggressive and anti-predator strategies.     

Aggression among sea urchins on Caribbean coral reefs

The existence and nature of intra- and interspecific aggression were examined for five species of sea urchins inhabiting Caribbean coral reefs. The studies took place in the San Blas Islands of Panama and involved the following species: Echinometra lucunter (Linnaeus), E. viridis Agassiz, Diadema antillarum Phillipi, Lytechinus williamsi Chesher, and Eucidaris tribuloides (Lamarck). An intruder was placed next to an undisturbed resident and the behaviors and responses of both individuals were followed. All pairwise combinations of resident species and intruder species were tested except for combinations involving D. antillarum as intruder.

For E. viridis and E. lucunter, agonistic interactions occurred commonly (46–79% of trials) between conspecifics and congeners. Almost all of the agonistic encounters involved pushing. Additionally, biting occurred in 8–25 % of the trials. Residents were most often the aggressors and usually succeeded in retaining their location. Intruders only succeeded in forcing residents out of their positions if the intruder was equal to or larger in size than the resident. Surveys of an undisturbed population of E. viridis during the daytime indicated that 16% of the individuals were engaged in intraspecific agonistic interactions at any one time.

D. antillarum exhibited biting behavior against both species of Echinometra in 23–24% of the trials. Biting attacks against L. williamsi and E. tribuloides occurred rarely. L. williamsi only once demonstrated pushing behavior and never was observed biting another sea urchin. E. tribuloides occasionally exhibited pushing and biting behaviors, both as residents and as intruders, and was twice observed biting Echinometra.

These studies suggest that two kinds of agonistic interactions may commonly occur among Caribbean reef-dwelling sea urchins: (1) intraspecific and interspecific aggression among Echinometra, and (2) predatory/aggressive attacks against Echinometra by D. antillarum. The former may result in greater dispersion of Echinometra relative to food and shelter resources and control the spatial distribution and concentration of Echinometra grazing pressure within an area. The attacks by D. antillarum may result in the restriction to, or higher densities of, Echinometra in crevices and rugose microhabitats that provide shelter from the larger-bodied D. antillarum.     

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.     

Circulating steroid hormones during rapid aggressive responses of territorial male mountain spiny lizards, Sceloporus jarrovi

Levels of aggression and circulating steroid hormones were monitored simultaneously in free-living male lizards following a staged territorial aggressive encounter with another male. In the first 15 min following the aggressive encounter, the frequency of territorial patroling and the frequency of agonistic and advertisement displays increased four- to fivefold in resident males. In most cases these increases persisted for at least 90 min after withdrawal of the intruder male and probably persisted for the entire day of the encounter. Blood samples collected at 15-min intervals revealed no changes in circulating levels of testosterone or corticosterone while this behavioral change was occurring. Thus, the increase in aggressive behavior that follows a male-male territorial encounter in this species does not appear to be mediated by simultaneous changes in circulating levels of these hormones. Interspecific comparisons suggest that interspecific variation in steroid hormone involvement in rapid aggressive responses may depend on the mating system and the extent of male parental care.     

Song rate as a signal of male aggressiveness during territorial contests in the wood warbler

Aggressive signaling is an important component in animal communication, as it provides an efficient mechanism for settling conflicts over resources between competitors. In songbirds, a number of singing behaviors have been proposed to be aggressive signals used in territory defense, including song rate. Although aggressive signaling in songbirds has received considerable research attention, adequate evidence for most putative aggressive signals is not available. In this study, we experimentally investigated whether the song rate of male wood warblers Phylloscopus sibilatrix is a signal of their aggressive intent in male–male interactions. We found that males responded differentially to simulated territorial intrusions depending on the song rate of an intruder. Moreover, males that continued to sing during territorial contests increased their song rates, and this behavior predicted the strength of aggressive escalation by the signaler. These results suggest that song rate is an aggressive signal during male–male interactions in the wood warbler. We also found high intra‐individual repeatability in the strength of aggressive response to simulated intrusions, likely reflecting differences in personality (aggressiveness) or quality of male wood warblers. We conclude that changes in singing rate may be an efficient mechanism of signaling immediate shifts in motivation of signalers during territorial contests, especially in species that lack large repertoires or have simple songs.     

Effects of resource distribution on activity and territory defence in house mice, Mus domesticus

How much an animal invests in defending a territory depends, in part, on the quality, quantity and distribution of resources, but do animals target their investment in defence within the territory according to the location of different resources? We examined whether wild-caught male and female house mice increased aggression towards intruders of the same or opposite sex when in areas containing their food/water or nest site. Pairs of resident mice were established in enclosures consisting of two areas. In split enclosures, food and water were in one area and a nest site in the other, while in clumped enclosures all resources were in one area with no resources in the other. Residents of both sexes were quicker to attack intruders, and were more aggressive, in areas containing resources than in an area containing no resources. There was no difference in aggression between areas containing food/water, a nest site or both. The effect of resources on territorial defence was due largely to changes in aggression against intruders of the opposite sex. Residents, especially males, attacked intruders of their own sex more than those of the opposite sex. This bias was much stronger when no resources were present, owing to low aggression against opposite-sex intruders in the absence of resources. There were no differences in intruder aggression, and the relative size of the intruder (heavier or lighter than the resident) had no effect on resident aggression. Residents also spent less time out of their nest in clumped enclosures owing to low activity in the nonresource area.     

Non-migratory stonechats show seasonal changes in the hormonal regulation of non-seasonal territorial aggression

In many birds and mammals, male territorial aggression is modulated by elevated circulating concentrations of the steroid hormone testosterone (T) during the breeding season. However, many species are territorial also during the non-breeding season, when plasma T levels are basal. The endocrine control of non-breeding territorial aggression differs considerably between species, and previous studies on wintering birds suggest differences between migratory and resident species. We investigated the endocrine modulation of territorial aggression during the breeding and non-breeding season in a resident population of European stonechats (Saxicola torquata rubicola). We recorded the aggressive response to a simulated territorial intrusion in spring and winter. Then, we compared the territorial aggression between seasons and in an experiment in which we blocked the androgenic and estrogenic action of T. We found no difference in the aggressive response between the breeding and the non-breeding season. However, similarly to what is found in migratory stonechats, the hormonal treatment decreased aggressive behaviors in resident males in the breeding season, whereas no effects were recorded in the non-breeding season. When we compared the aggressive responses of untreated birds with those obtained from migratory populations in a previous study, we found that territorial aggression of resident males was lower than that of migratory males during the breeding season. Our results show that in a resident population of stonechats T and/or its metabolites control territorial aggression in the breeding but not in the non-breeding season. In addition, our study supports the hypothesis that migratory status does modulate the intensity of aggressive behavior.     

Experimental manipulation of shell color and morphology of the limpets Lottia asmi (Middendorff) and Lottia digitalis (Rathke) (Mollusca: Patellogastropoda)

We experimentally show that substratum can determine an individual patellogastropod's color and morphology. Lottia asmi (Middendorff), previously considered a high-domed, black stenotopic species on trochid gastropods, is similar to other northeastern Pacific limpet species with low profile and tessellated color patterns, when it is translocated to rock substrata. Lottia digitalis (Rathke), a highly variable species with at least two ecological variants that have been considered to be genetically determined, changes between these two forms when translocated from stalked barnacles to rocks. Color changes because the ingested pigments (algal, periostracal, etc.) and other materials (e.g., calcium carbonate) vary between substrata; morphological changes occur as responses to the topographical complexity and constraints of substrata. The geographical distribution of ecological variants of polytypic limpet species, and the ability to achieve cryptic coloration, may be determined by the geographic distributions of algae on which the limpets feed rather than by intrinsic characteristics of the limpets.     

Autumnal territorial aggression is independent of plasma testosterone in mockingbirds

Mockingbirds (Mimus polyglottos) show intense territorial activity in the autumn as newcomers attempt to establish space within resident populations. Examination of autumnal territorial behavior showed that unmated males sing more and engage in more territorial fights than mated males. Newcomers that have just acquired space also sing more and show more territorial fights than birds resident to the population for at least one prior season. Among established residents, the average number of territorial fights was greater in birds that shared more territory boundaries with new residents. Radioimmunoassay of plasma samples taken from males during the molt and following the onset of territorial defense showed that during both periods plasma concentrations of testosterone (T), dihydrotestosterone (DHT), and estradiol were basal or below the sensitivity of the assay system. Moreover, groups of males that differed in song and territorial aggression did not differ in plasma concentrations of T, DHT, or luteinizing hormone (LH). Hormone analyses confirm measurements on several other avian species suggesting that sex steroid concentrations are low in the fall and winter and that variations in aggressive behavior at this time of year may be unrelated to LH and androgen levels. Our observations contribute to a growing body of work in temperate passerines indicating that the role of androgens in mediating aggressive challenge may be restricted to the breeding season. The possible hormonal basis (if any) of song and territorial aggression in mockingbirds outside the breeding season remains obscure.     

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.