Establishment Of Dominance Hierarchies Research Articles

Improving the acceptability of social robots: Make them look different from humans.

The social robots market will grow considerably in the coming years. What the arrival of these new kind of social agents means for society, however, is largely unknown. Existing cases of robot abuse point to risks of introducing such artificial social agents (ASAs) without considerations about consequences (risks for the robots and the human witnesses to the abuse). We believe that humans react aggressively towards ASAs when they are enticed into establishing dominance hierarchies. This happens when there is a basis for skill comparison. We therefore presented pairs of robots on which we varied similarity and the degree of stimulatability of their mechanisms/functions with the human body (walking, jumping = simulatable; rolling, floating = non-simulatable). We asked which robot (i) resembled more a human, (ii) possessed more "essentialized human qualities" (e.g. creativity). To estimate social acceptability, participants had also (iii) to predict the outcome of a situation where a robot approached a group of humans. For robots with simulatable functions, rating of essentialized human qualities decreased as human resemblance decreased (jumper < walker). For robots with non-simulable functions, the reversed relation was seen: robots that least resembled humans (floater) scored highest in qualities. Critically, robot's acceptability followed ratings of essentialized human qualities. Humans respond socially to certain morphological (physical aspects) and behavioral cues. Therefore, unless ASAs perfectly mimic humans, it is safer to provide them with mechanisms/functions that cannot be simulated with the human body.

Ca2+ imaging of self and other in medial prefrontal cortex during social dominance interactions in a tube test

The study of social dominance interactions between animals offers a window onto the decision-making involved in establishing dominance hierarchies and an opportunity to examine changes in social behavior observed in certain neurogenetic disorders. Competitive social interactions, such as in the widely used tube test, reflect this decision-making. Previous studies have focused on the different patterns of behavior seen in the dominant and submissive animal, neural correlates of effortful behavior believed to mediate the outcome of such encounters, and interbrain correlations of neural activity. Using a rigorous mutual information criterion, we now report that neural responses recorded with endoscopic calcium imaging in the prelimbic zone of the medial prefrontal cortex show unique correlations to specific dominance-related behaviors. Interanimal analyses revealed cell/behavior correlations that are primarily with an animal's own behavior or with the other animal's behavior, or the coincident behavior of both animals (such as pushing by one and resisting by the other). The comparison of unique and coincident cells helps to disentangle cell firing that reflects an animal's own or the other's specific behavior from situations reflecting conjoint action. These correlates point to a more cognitive rather than a solely behavioral dimension of social interactions that needs to be considered in the design of neurobiological studies of social behavior. These could prove useful in studies of disorders affecting social recognition and social engagement, and the treatment of disorders of social interaction.

Short- and Long-Term Social Recognition Memory Are Differentially Modulated by Neuronal Histamine.

The ability of recognizing familiar conspecifics is essential for many forms of social interaction including reproduction, establishment of dominance hierarchies, and pair bond formation in monogamous species. Many hormones and neurotransmitters have been suggested to play key roles in social discrimination. Here we demonstrate that disruption or potentiation of histaminergic neurotransmission differentially affects short (STM) and long-term (LTM) social recognition memory. Impairments of LTM, but not STM, were observed in histamine-deprived animals, either chronically (Hdc−/− mice lacking the histamine-synthesizing enzyme histidine decarboxylase) or acutely (mice treated with the HDC irreversible inhibitor α-fluoromethylhistidine). On the contrary, restriction of histamine release induced by stimulation of the H3R agonist (VUF16839) impaired both STM and LTM. H3R agonism-induced amnesic effect was prevented by pre-treatment with donepezil, an acetylcholinesterase inhibitor. The blockade of the H3R with ciproxifan, which in turn augmented histamine release, resulted in a procognitive effect. In keeping with this hypothesis, the procognitive effect of ciproxifan was absent in both Hdc−/− and αFMH-treated mice. Our results suggest that brain histamine is essential for the consolidation of LTM but not STM in the social recognition test. STM impairments observed after H3R stimulation are probably related to their function as heteroreceptors on cholinergic neurons.

Trade-offs between fighting and breeding: a social network analysis of bison male interactions.

In most polygynous species, males compete for access to females using agonistic interactions to establish dominance hierarchies. Typically, larger and stronger males become more dominant and thus gain higher mating and reproductive success over subordinate males. However, there is an inherent trade-off between time and energy invested in dominance interactions versus courtship and mating activities. Individuals may overcome this trade-off by selectively engaging in more effective mating tactics. North American bison (Bison bison) are a species of conservation concern that exhibit female-defense polygyny with two predominant mating tactics: (1) tending individual females; or (2) challenging tending males as a satellite and then mating opportunistically. Here, we use social network analysis to examine the relationship between position in the agonistic interaction network of bison males and their mating, reproductive success, and reproductive tactics and effort. To assess the potential for social network analysis to generate new insights, we compare male (node) centrality in the interaction network with traditional David’s score and Elo-rating dominance rankings. Local and global node centrality and dominance rankings were positively associated with prime-aged, heavy males with the most mating success and offspring sired. These males invested more effort in the “tending” tactic versus the “satellite” tactic, and they tended more females for longer periods during peak rut, when most females were receptive. By engaging in the most effective mating tactic, dominant males may mitigate the trade-off between allocating time and energy to agonistic interactions that establish dominance, versus courtship and mating. While less dominant males participated more in the alternative mating tactic, network analysis demonstrated that they were still important to the interaction network on both a local and global scale.

Juvenile hormone interacts with multiple factors to modulate aggression and dominance in groups of orphan bumble bee (Bombus terrestris) workers

Juvenile hormone (JH) is a key regulator of insect development and reproduction. Given that JH commonly affects adult insect fertility, it has been hypothesized to also regulate behaviors such as dominance and aggression that are associated with reproduction. We tested this hypothesis in the bumble bee Bombus terrestris for which JH has been shown to be the major gonadotropin. We used the allatoxin Precocene-I (P-I) to reduce hemolymph JH titers and replacement therapy with the natural JH to revert this effect. In small orphan groups of workers with similar body size but mixed treatment, P-I treated bees showed lower aggressiveness, oogenesis, and dominance rank compared with control and replacement therapy treated bees. In similar groups in which all bees were treated similarly, there was a clear dominance hierarchy, even in P-I and replacement therapy treatment groups in which the bees showed similar levels of ovarian activation. In a similar experiment in which bees differed in body size, larger bees were more likely to be dominant despite their similar JH treatment and ovarian state. In the last experiment, we show that JH manipulation does not affect dominance rank in groups that had already established a stable dominance hierarchy. These findings solve previous ambiguities concerning whether or not JH affects dominance in bumble bees. JH positively affects dominance, but bees with similar levels of JH can nevertheless establish dominance hierarchies. Thus, multiple factors including JH, body size, and previous experience affect dominance and aggression in social bumble bees.

Photoperiod-dependent release of suppression pheromone in the male lobster cockroach Nauphoeta cinerea.

The complex agonistic repertoire between male lobster cockroaches (Nauphoeta cinerea) makes this species an excellent model for aggression studies. During the establishment of dominance hierarchies, 3-hydroxy-2-butanone (3H-2B) functions as a suppression pheromone, keeping the rivals in a submissive state. In the present study, we evaluated the release of 3H-2B by dominant individuals across four different time phases within the 24-h photoperiod, i.e., early scotophase (ES), late scotophase (LS), early photophase (EP), and late photophase (LP). For each time phase, we collected volatile pheromones during a 60-min first-encounter fight to measure the level of released 3H-2B. Subsequently, the amount of 3H-2B remaining in the sternal glands of dominant and subordinate individuals was measured and compared to socially naïve male controls. Release of 3H-2B was relatively high during ES or LP first-encounter fights, compared to LS or EP encounters. The attack duration and aggressive posture intensity in dominant males were positively correlated with the amount of 3H-2B release in all four phases. A similar statistical distribution was found between the amount of 3H-2B released by dominant males and the amount of 3H-2B in the sternal glands of naïve male sternal during LS, EP, and LP. However, during ES, the statistical distribution of 3H-2B released by the dominant was significantly greater than the distribution of 3H-2B content in socially naïve male sternal glands. The observed phase-dependence of 3H-2B release might be due to variations in 3H-2B biosynthesis or the scotophase-specific behavior of naïve males, wherein an aggressive posture is spontaneously adopted with concomitant 3H-2B release.

Partial cage division significantly reduces aggressive behavior in male laboratory mice.

Aggression in mice often results in injury leading to unplanned euthanasia or the initiation of protocols to isolate animals, thereby increasing research costs and straining resources. Here, we tested if adding a partial cage divider into existing mouse cages affected aggressive-like behavior in group-housed male mice (18 mice; 3 per cage). Mice were randomly assigned to one of two groups upon arrival to the vivarium: (1) standard cage; (2) cage with a partial cage divider. Behavioral observation over 12 hours were conducted at day one, two, and seven after receipt at the facility in order to assess aggression during the course of establishing dominance hierarchies. Observers blinded to study design and hypothesis scored each video for the number and type of aggressive behaviors, which were summed for each hour and analyzed. Results indicated a statistically significant decrease in aggressive behaviors of mice in cages with dividers compared to mice in standard cages. We conclude that cage dividers, which resemble burrows and provide access to common food/water, may promote rigorous research by reducing the number of animals used in a study and refining housing, thus, improving animal welfare.

Are pumas subordinate carnivores, and does it matter?

BackgroundInterspecific competition affects species fitness, community assemblages and structure, and the geographic distributions of species. Established dominance hierarchies among species mitigate the need for fighting and contribute to the realized niche for subordinate species. This is especially important for apex predators, many of which simultaneous contend with the costs of competition with more dominant species and the costs associated with human hunting and lethal management.MethodsPumas are a widespread solitary felid heavily regulated through hunting to reduce conflicts with livestock and people. Across their range, pumas overlap with six apex predators (gray wolf, grizzly bear, American black bear, jaguar, coyote, maned wolf), two of which (gray wolf, grizzly bear) are currently expanding in North America following recovery efforts. We conducted a literature search to assess whether pumas were subordinate or dominant with sympatric apex predators, as well as with three felid mesocarnivores with similar ecology (ocelot, bobcat, Canada lynx). We also conducted an analysis of the spatial distributions of pumas and their dominant sympatric competitors to estimate in what part of their range, pumas are dominant versus subordinate.ResultsWe used 64 sources to assess dominance among pumas and other apex predators, and 13 sources to assess their relationships with felid mesocarnivores. Evidence suggested that wolves, grizzly bears, black bears, and jaguars are dominant over pumas, but that pumas are dominant over coyotes and maned wolves. Evidence suggested that pumas are also dominant over all three felid mesocarnivores with which they share range. More broadly, pumas are subordinate to at least one other apex carnivore in 10,799,252 (47.5%) of their 22,735,268 km2 range across North and South America.DiscussionSubordinate pumas change their habitat use, suffer displacement at food sources, likely experience increased energetic demands from harassment, exhibit increased starvation, and are sometimes directly killed in competitive interactions with dominant competitors. Nevertheless, we lack research clearly linking the costs of competition to puma fitness. Further, we lack research that assesses the influence of human effects simultaneous with the negative effects of competition with other sympatric carnivores. Until the time that we understand whether competitive effects are additive with human management, or even potentially synergistic, we encourage caution among managers responsible for determining harvest limits for pumas and other subordinate, apex carnivores in areas where they are sympatric with dominant species. This may be especially important information for managers working in regions where wolves and brown bears are recolonizing and recovering, and historic competition scenarios among multiple apex predators are being realized.

Body measurements and testosteron level of male Timor deer (Rusa timorensis) at various hierarchies

The aim of this research was to observe body (neck, chest and scrotum) circumferences and testosterone level of α-male, β-male and subordinate male Timor deer reared under captivity after establisment of the dominance hierarchy. Twelve males (51 ± 6 months old; 68.29 ± 8.41 kg body weight and in same antler stages) were used in this research. The bucks was grouped into three stall each containing four bucks. ELISA kit and tape measurements were used for plasma Testosterone assay and body measurement, respectively. Data was collected before and 43 days after establishment of the dominance hierarchy. Wilcoxon signed ranks test and Kruskal-Wallis H test of non-parametric analysis was used. Significant difference was tested with Mann-Whitney U test. The results showed no significantly different for body circumferences (neck, chest, scrotum) and testosterone level of male Timor deer before establishment of dominance hierarchy. Chest and scrotum circumferences of male Timor deer after establihment of dominance hierarchy showed no significantly different. Significantly difference shown on parameter neck circumference (P&lt;0.05; χ2 = 8.74) and testosteron level (P&lt;0.05; χ2 = 7.87) after establishment of dominance hierarchy. In conclusion, dominance hierarchy affected the testosterone level and body measurement.

Ethology may be related to the genetic structure of a population: Chaetodipus siccus as a study case

Philopatry is a biological trait present in a wide variety of zoological taxa. Such conduct is considered as the basis of social behavior among rodents as well as a promoter of spatial distribution of individuals. Females are typically philopatric, thereby they have access to resources to breed offspring. This philopatric tendency is partly responsible of the genetic structuring in the natural populations of mammals. Heteromyid rodents conform complex communities and the agonistic interactions among them are common. Aggressiveness is the way to establish dominance hierarchies. By means of setting a hierarchy, dominant individuals have priority access to critical resources. Chaetodipus siccus is an endemic heteromyid of the Baja California peninsula, distributed on an area of ~270 km 2 , in which a particular pattern of high variation of matrilineal lineages has been observed. That is why it is hypothesized the presence of multiple spatially segregated matrilineal lineages, which are promoted by the aggressive nature of the species, which leads to limited panmixia in the range of C. siccus . To test these hypotheses, it has been conducted a statistically parsimonious haplotype network study using matrilineal markers and behavioral experiments of intra and interspecific dominance. Thirty-four localities were surveyed through C. siccus distribution to capture specimens ( n = 143) for the statistically parsimonious network. Muscle tissue was employed to DNA extraction and fragments of Cytb and COI genes were sequenced. To study intraspecific and interspecific dominance, ethological experiments under different conditions were conducted between females. For this purpose, 52 adult females of C. siccus and five adult females of C. arenarius , C. ammophilus , C. spinatus and C. rudinoris were captured alive and maintained in captivity. Encounters took place inside neutral arenas every other night. Individuals were housed individually inside social cages. Fifty-three haplotypes of Cytb and 15 of COI were identified from 143 individuals of C. siccus . A high variety of private haplotypes were observed (31 for Cytb and 5 for COI). The presence of a dominant individual over another was observed in all conditions of experiments of intraspecific and interspecific dominance. Dominant females were statistically more aggressive than subordinated females ( P < 0.001) even C. siccus dominated the other species. A marked genetic structure is observed, with considerable presence of private haplotypes. It is considered that genetic structure occurs when subpopulations are at least partially isolated from each other. There are no appreciable physical barriers within the range of the species. This is why it is considered that ethological interactions more than geographical features may limit gene flow within the population of C. siccus . Structures with an unusual number of haplotypes in small geographical areas, such as C. siccus , have been previously recognized for other mammal species. It is argued that this pattern is the result of a philopatric character of females; such conduct restricts gene flow between areas. The existence of several matrilineal lineages geographically restricted proposes that females do not disperse, but remain within a very small geographic area. This points directly to the presence of philopatry in females. Agonistic behaviors are the means by which an individual maintains its hierarchy over others, defining its preferential access to resources. For females of C. siccus , its extremely aggressive nature and a territorial behavior have resulted in segregation of matrilineal lineages.

Subsocial Cockroaches Nauphoeta cinerea Mate Indiscriminately with Kin Despite High Costs of Inbreeding.

Many animals have evolved strategies to reduce risks of inbreeding and its deleterious effects on the progeny. In social arthropods, such as the eusocial ants and bees, inbreeding avoidance is typically achieved by the dispersal of breeders from their native colony. However studies in presocial insects suggest that kin discrimination during mate choice may be a more common mechanism in socially simpler species with no reproductive division of labour. Here we examined this possibility in the subsocial cockroach Nauphoeta cinerea, a model species for research in sexual selection, where males establish dominance hierarchies to access females and control breeding territories. When given a binary choice between a sibling male and a non-sibling male that had the opportunity to establish a hierarchy prior to the tests, females mated preferentially with the dominant male, irrespective of kinship or body size. Despite the lack of kin discrimination during mate choice, inbred-mated females incurred significant fitness costs, producing 20% less offspring than outbred-mated females. We discuss how the social mating system of this territorial cockroach may naturally limit the probability of siblings to encounter and reproduce, without the need for evolving active inbreeding avoidance mechanisms, such as kin recognition.

Body mass and immune function, but not bill coloration, predict dominance in female mallards

Competition over indivisible resources is common and often costly. Therefore, selection should favor strategies, including efficient communication, that minimize unnecessary costs associated with such competition. For example, signaling enables competitors to avoid engaging in costly asymmetrical contests. Recently, bill coloration has been identified as an information-rich signal used by some birds to mediate aggressive interactions and we evaluated this possibility in female mallards Anas platyrhynchos. Specifically, we conducted two rounds of competitive interactions among groups of unfamiliar adult female ducks. By recording all aggressive behaviors exhibited by each individual, as well as the identity of attack recipients, we were able to assign dominance scores and evaluate links between numerous physiological, morphological, and experimental variables that we predicted would influence contest outcome and dominance. Contrary to our predictions, dominance was not linked to any aspect of bill coloration, access to dietary carotenoids during development, two of three measures of immune function, or ovarian follicle maturation. Instead, heavier birds were more dominant, as were those with reduced immune system responses to an experimentally administered external immunostimulant, phytohemagglutinin. These results suggest that visual signals are less useful during the establishment of dominance hierarchies within multi-individual scramble competitions, and that immune function is correlated with contest strategies in competitions for access to limited resources.

A sublethal imidacloprid concentration alters foraging and competition behaviour of ants.

Neonicotinoid pesticides, such as the widely used compound imidacloprid, are suspected to impair cognitive capacity, behaviour, and fitness of a number of non-target species. We tested whether sublethal imidacloprid concentrations alter the foraging and aggression behaviour of two European ant species. Even though the nestmate-recruitment of Lasius niger was not affected by pesticide exposure, these ants required more time to become active and the number of foraging workers was lower than in sub-colonies not exposed to imidacloprid. In interspecific confrontations, imidacloprid increased the aggressiveness of a usually subordinate species (Lasius flavus) enormously (3.7-fold increase in average number of aggressive encounters), whereas they did not affect a subdominant species (L. niger) that severely (1.2-fold increase in average number of aggressive encounters). The high frequency of aggressive encounters of L. flavus vs. non-exposed L. niger workers, reduced their survival probability significantly down to 60%. The observed behavioural alterations of the two ant species have the potential to impair their viability and co-occurrence with behaviourally dominate species due to a decreased exploitative competition and a reduced chance to locate and use resources before competitors. As competition is considered key in structuring ant communities, changes in aggressiveness are likely to alter established dominance hierarchies and thereby the dynamic and structure of ant communities.

Fighting for independence.

Male crickets (Gryllus bimaculatus) establish dominance hierarchies within a population by fighting with one another. Larger males win fights more frequently than their smaller counterparts, and a previous study found that males recognise one another primarily through sensory input from the antennae. This study therefore investigated whether the success of larger crickets is influenced by sensory input from the antennae, in part by assessing the number of fights that large ‘antennectomized’ crickets won against small crickets, compared with the number that large, intact crickets won. The success rate was significantly lower in antennectomized males, though they still won the majority of fights (73/100 versus 58/100, Fisher’s exact test P < 0.05); the authors thus conclude that sensory input from the antennae affects the fighting success of large males, but that other size-related factors also play a part.

Quantifying Aggressive Behavior in Zebrafish.

Aggression is a complex behavior that influences social relationships and can be seen as adaptive or maladaptive depending on the context and intensity of expression. A model organism suitable for genetic dissection of the underlying neural mechanisms of aggressive behavior is still needed. Zebrafish has already proven to be a powerful vertebrate model organism for the study of normal and pathological brain function. Despite the fact that zebrafish is a gregarious species that forms shoals, when allowed to interact in pairs, both males and females express aggressive behavior and establish dominance hierarchies. Here, we describe two protocols that can be used to quantify aggressive behavior in zebrafish, using two different paradigms: (1) staged fights between real opponents and (2) mirror-elicited fights. We also discuss the methodology for the behavior analysis, the expected results for both paradigms, and the advantages and disadvantages of each paradigm in face of the specific goals of the study.

Ergonomic skew and reproductive queuing based on social and seasonal variation in foraging activity of eastern carpenter bees (Xylocopa virginica)

Reproductive division of labour in social carpenter bees differs from that in classically eusocial insects because reproductive output and ergonomic inputs are positively correlated—dominant females monopolize both foraging and reproduction. We quantified ergonomic skew in the facultatively social bee Xylocopa virginica (L., 1771) (eastern carpenter bee) based on detailed observations of foraging activity by individually marked females in 2009. Unusually for a univoltine bee, this species exhibits a spring foraging phase during which females feed pollen to other adults, probably as part of behavioural interactions to establish dominance hierarchies. During brood-provisioning, foraging in social nests was dominated by one female at a time, with replacement by a succession of foragers as dominants disappeared and were succeeded by a subordinate. The principal foragers (individuals that did the largest share of foraging in each colony) did 85%–100% of all pollen trips, so contributions to pollen-provisioning by female nest mates were highly uneven. Individual foraging rate was unaffected by group size and total colony foraging effort was a function of the number of foragers per group. Transient females that moved to new nests were as successful in achieving dominant forager status as females resident in their natal nests. This evidence indicates that colony social organisation is based on reproductive queues, whereby the first-ranked bee is the dominant forager and subordinates queue for opportunities to replace her.

Dominance hierarchies and associated signalling in a cooperative passerine

In animal societies, individuals face the dilemma of whether to cooperate or to compete over a shared resource. Two intertwined mechanisms may help to resolve this enduring evolutionary dilemma by preventing conflicts and thereby mediating the costs of living in groups: the establishment of dominance hierarchies and the use of ‘badge-of-status’ for signalling dominance. We investigated these two mechanisms in the sociable weaver (Philetairus socius), a colonial and social passerine which cooperates over multiple tasks. We examined the sociable weavers’ dominance structure in 2 years by recording 2563 agonistic interactions between 152 individuals observed at a feeder at eight colonies. We tested which individual traits, including sex, age, relatedness and two melanin-based plumage traits, predicted variation in social status. First, using social network analysis, we found that colonies were structured by strongly ordered hierarchies which were stable between years. Second, medium-ranked birds engaged more in aggressive interactions than highly ranking individuals, suggesting that competition over food is most pronounced among birds of intermediate social status. Third, we found that colony size and kinship influenced agonistic interactions, so aggression was less pronounced in smaller colonies and among relatives. Finally, within- and between-individual variation in social status and the presence of an individual at the feeder were associated with variation in bib size, as predicted by the badge-of-status hypothesis. These results suggest that dominance hierarchies and bib size mediate conflicts in sociable weaver societies.

Transitive inference in two lemur species (Eulemur macaco and Eulemur fulvus).

When confronted with tasks involving reasoning instead of simple learning through trial and error, lemurs appeared to be less competent than simians. Our study aims to investigate lemurs' capability for transitive inference, a form of deductive reasoning in which the subject deduces logical conclusions from preliminary information. Transitive inference may have an adaptative function, especially in species living in large, complex social groups and is proposed to play a major role in rank estimation and establishment of dominance hierarchies. We proposed to test the capacities of reasoning using transitive inference in two species of lemurs, the brown lemur (Eulemur fulvus) and the black lemur (Eulemur macaco), both living in multimale-multifemale societies. For that purpose, we designed an original setup providing, for the first time in this kind of cognitive task, pictures of conspecifics' faces as stimuli. Subjects were trained to differentiate six photographs of unknown conspecifics named randomly from A to F to establish the order A > B > C > D > E > F and select consistently the highest-ranking photograph in five adjacent pairs AB, BC, CD, DE, and EF. Then lemurs were presented with the same adjacent pairs and three new and non-adjacent pairs BD, BE, CE. The results showed that all subjects correctly selected the highest-ranking photograph in every non-adjacent pair, reflecting lemurs' capacity for transitive inference. Our results are discussed in the context of the still debated current theories about the mechanisms underlying this specific capacity.

Tilapia male urinary pheromone stimulates female reproductive axis

Mozambique tilapia males congregate in leks where they establish dominance hierarchies and attract females to spawn in sandy pits. Dominant males store more urine than subordinates and the pattern of urination and the high sensitivity of females to male urine suggest chemical signalling via the urine. Here we show that pre-ovulated and post-spawn females when exposed to dominant male urine increased significantly, in less than 1h, the release rate of the maturation-inducing steroid 17,20β-dihydroxypregn-4-en-3-one which is maintained elevated for at least 6h. This indicates a pheromonal role for male urine in the synchronisation of spawning. Furthermore, we show that the lack of affinity of 17,20βP to sex steroid binding globulin explains, at least partly, its rapid release and lack of detection in the blood. Thus tilapia urine involvement in several communication processes confirms that cichlids have evolved a sophisticated chemical signalling system together with their complex visual, acoustic and behavioural displays.

The acoustic signature of the male northern elephant seal: Individual variation supports recognition during competitive interactions

Northern elephant seals (Mirounga angustirostris) have a polygynous breeding system in which adult males establish dominance hierarchies that determine access to females. Acoustic signaling plays an important role in settling fights between males, as stereotyped displays elicit appropriate behavioral responses from individuals without contact during an energetically demanding breeding season. To determine whether reliable differences exist in the acoustic displays of individuals and whether these differences function to convey identity, we behaviorally and acoustically sampled male seals during the breeding season. Vocalizations were recorded during competitive interactions and analyzed for spectral, temporal, and amplitude characteristics. A cross-validated discriminant function analysis revealed small differences within—and significant differences between—the calls produced by 17 adult males of known dominance status. To determine whether acoustic displays serve as individual signatures that males learn to recognize during the breeding season, we conducted playback experiments to test if having prior experience with a particular caller would influence the approach or avoidance response of the listener. Our findings reveal that these unique acoustic signals serve as individual vocal signatures, and males likely remember the identity of their rivals based on call features that have been associated with the outcome of previous competitive interactions.