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Intraspecific social dominance hierarchies should be influenced by environmental variation; however, in colour polymorphic species, dominance hierarchies are often assumed fixed, and thus insensitive to environmental variability. We ran a series of experiments using the colour polymorphic long-tailed brush lizard (Urosaurus graciosus) to challenge this assumption. We staged contests between orange and yellow morph males over a single heated perch, two perches at the same temperature, or two perches differing in temperature. Our first experiment revealed that orange-throated males are socially dominant. However, this hierarchy collapsed in our other experiments as yellow males became more aggressive. Interestingly, both males only ever secured their own perch where the perches differed in temperature. These findings mirror observations of morph behavioural flexibility in nature and studies of behaviour-environment interactions in non-polymorphic taxa. We conclude that colour morphs may have an underappreciated ability to assess resource-level changes and respond with concomitant flexibility in behaviour. [ABSTRACT FROM AUTHOR]

The teleost fish nonapeptides, arginine vasotocin (AVT) and isotocin (IT), have been implicated in the regulation of social behavior. These peptides are expected to be involved in acute and transient changes in social context, in order to be efficient in modulating the expression of social behavior according to changes in the social environment. Here we tested the hypothesis that short-term social interactions are related to changes in the level of both nonapeptides across different brain regions. For this purpose we exposed male zebrafish to two types of social interactions: (1) real opponent interactions, from which a Winner and a Loser emerged; and (2) mirror-elicited interactions, that produced individuals that did not experience a change in social status despite expressing similar levels of aggressive behavior to those of participants in real-opponent fights. Non-interacting individuals were used as a reference group. Each social phenotype (i.e. Winners, Losers, Mirror-fighters) presented a specific brain profile of nonapeptides when compared to the reference group. Moreover, the comparison between the different social phenotypes allowed to address the specific aspects of the interaction (e.g. assessment of opponent aggressive behavior vs. self-assessment of expressed aggressive behavior) that are linked with neuropeptide responses. Overall, agonistic interactions seem to be more associated with the changes in brain AVT than IT, which highlights the preferential role of AVT in the regulation of aggressive behavior already described for other species. [ABSTRACT FROM AUTHOR]

The nature of individual social interactions can have a profound influence on group structure and function. Here, we use social network analysis to examine patterns of dominance interactions and spatial associations in 14 captive social groups of the cooperatively breeding cichlid, Neolamprologus pulcher. In this cichlid, social groups are composed of a dominant breeding pair and 1–20 nonbreeding subordinate helpers that form size-based queues for breeding positions. In the current study, we performed the first quantitative analysis of N. pulcher dominance hierarchies. We found that dominance hierarchies of N. pulcher were highly linear and that interactions within dyads were directionally consistent. We also found that dominance interactions were not equally distributed across the network, but instead occurred most frequently at the top of the social hierarchy. Contrary to our predictions, neither body size asymmetry nor sex predicted the observed dominance interactions and patterns of associations. However, breeders were more connected than helpers within the networks, perhaps due to their policing role. This study is one of a small handful to conduct network analysis on replicate social groups, and thus is one of few studies able to make general conclusions on the social structure of its focal species. The patterns uncovered suggest that conflict over breeding position inheritance has a strong impact on relationships among group members in N. pulcher. [Copyright &y& Elsevier]

The hierarchical organization of dominance relations among animals has wide-ranging implications in social evolution. The structure of dominance relations has often been measured using indices of linearity (e.g. Landau’s h, Kendall’s K): the degree to which dominance relations adhere to a linear hierarchy. An alternative measure is the transitivity of dominance relations among sets of three players that all interact with each other, a measure we call triangle transitivity (t tri). Triangle transitivity and linearity are essentially equivalent when dominance relations of all dyads are known, but such complete observations are rare in empirical studies. Triangle transitivity has two major advantages: it does not require ‘filling in’ of unobserved relations, and its expected value is constant across group sizes. We use a social network perspective to demonstrate a property of transitivity in random directed networks (on average, three-fourths of complete triads are transitive) and show that empirical dominance networks are often significantly more transitive than random networks. Using 101 published dominance matrices we show that published algorithms for assessing linearity underestimate the level of social orderliness, particularly in larger groups, which tend to have more null dyads. Thus, previous puzzlement over the decrease in estimated linearity in larger groups could be due largely to the bias introduced by random filling of null dyads. We argue that triangle transitivity will allow researchers to focus on important processes underlying the dynamics of dominance, such as spatial segregation, avoidance of interactions by certain individuals and detailed temporal patterns in the ontogeny of hierarchy formation. [Copyright &y& Elsevier]

Abstract: We have previously reported that mice with a targeted disruption of their vasopressin 1b receptor gene, Avpr1b, have mild impairments in social recognition and reduced aggression. The reductions in aggression are limited to social forms of aggression, i.e., maternal and inter-male aggression, while predatory aggression remains unaffected. To further clarify the role of the Avpr1b in the regulation of social behavior we first examined anxiety-like and depression-like behaviors in Avpr1b knockout (Avpr1b −/−) mice. We then went on to test the ability of Avpr1b −/− mice to form dominance hierarchies. No major differences were found between Avpr1b −/− and wildtype mice in anxiety-like behaviors, as measured using an elevated plus maze and an open field test, or depression-like behaviors, as measured using a forced swim test. In the social dominance study we found that Avpr1b −/− mice are able to form dominance hierarchies, though in early hierarchy formation dominant Avpr1b −/− mice display significantly more mounting behavior on Day 1 of testing compared to wildtype controls. Further, non-socially dominant Avpr1b −/− mice spend less time engaged in attack behavior than wildtype controls. These findings suggest that while Avpr1b −/− mice may be able to form dominance hierarchies they appear to employ alternate strategies. [Copyright &y& Elsevier]

Captive studies can make a unique contribution to primate socioecology by documenting species-typical social dispositions under controlled conditions. Recent theories seek to connect the dominance relationships, group cohesiveness, and feeding ecology of primates. The present study explores the first to aspects by comparing the social organization of rhesus (Macaca mulatta) and stumptail monkeys (M. arctoides). Data were collected over a period of eight years, with five different methods, on three well-established captive groups in identical environments. The groups were found to share one characteristic: a clear-cut, linear formal dominance hierarchy as expressed in teeth-bearing displays. The two main study groups (one of each species) differed significantly, however, with respect to nine of eleven behavioral measures. In addition to a previously reported higher frequency of reconciliation in the stumptail group, this group showed 1) more frequent but less severe aggressive behavior, 2) greater symmetry of contests, 3) greater social tolerance, 4) more nonagonistic approaches, and 5) more allogrooming. The differences can be summarized as a contrast in dominance "style," with the stumptails having a more relaxed style and placing greater emphasis on social cohesion than the rhesus monkeys. An egalitarian attitude was also reflected in approach behavior: contacts in the rhesus group were initiated dominants, whereas contacts in the stumptail group were initiated independent of rank. Comparisons with a second rhesus group, and with published reports, suggest that while some of the observed differences are probably representative of the two species, considerably intraspecific variation does exist, and a more comprehensive program of comparative studies is needed. [ABSTRACT FROM AUTHOR]

Social dominance rank in red grouse has a large inherited component. The relative contributions of mothers and fathers to the dominance ranks of their sons and daughters were studied by breeding a dominant and a subordinate strain and crossing them. Both parents contributed equally to the dominance ranks of both sons and daughters. Cocks from the dominant strain were more aggressive and had bigger combs than cocks from the subordinate strain. Dominant cocks and hens, however, did not weigh more than subordinates. [ABSTRACT FROM AUTHOR]

The social relations of three adult males in a captive chimpanzee group were evaluated for 12 months. The observations encompassed a period of transition in the dominance hierarchy providing an opportunity to assess behavioral patterns involved in the initiation of status changes. This study shows that dominance in the chimpanzee is expressed primarily through ritualized and non-contact behavior rather than by overt aggression. In particular, display behavior is important for indicating dominance rank, in communicating aggressive intent, and as a prelude to status struggles. The functional relationships between status, displays and other socio-sexual behavior patterns are presented. [ABSTRACT FROM AUTHOR]