Effects of fighting decisions on formation and structure of dominance hierarchies

The characteristics of complex social systems often cannot be predicted from exploring individual agonistic interactions in isolation. In a series of models, this study linked the decision-making processes that govern dyadic interactions with the emergent properties of hierarchical structures in social groups. Contrary to the intuitive expectation that resolution of ambiguities in fighting between closely matched opponents effectively promotes the formation of a social hierarchy, engagement in contests with opponents of dissimilar status lead to a faster emergence of hierarchical structures. The increased certainty of outcome in such asymmetric contests both reinforced the previously established dominance, and allowed for an indirect resolution of existing ambiguous relationships. High-return fights also resulted in a more rapid hierarchy formation, while escalating in fights decreased the costs of maintaining hierarchical relationships and increased their stability.     

Social dominance does not increase oxidative stress in a female dominance hierarchy of an African cichlid fish

In many group living animal species, individuals use aggression to gain and maintain social dominance to secure access to ecological resources and potential mates. While social dominance has many fitness benefits, there are also potential costs associated with frequent agonistic interactions and status display. One potential cost of social dominance is oxidative stress, the imbalance of reactive oxygen species and antioxidant capacity. In the cichlid species Astatotilapia burtoni, dominant males are aggressive, hold a breeding territory, and have an activated reproductive system resulting in larger gonads. Subordinate males are submissive, school with females, and are nonreproductive. Females are submissive under natural conditions, but in a female-only group, a dominance hierarchy will form with dominant females taking on male-typical behaviours including aggression, territory defence, and increased androgen levels. However, in contrast to males, social dominance is not linked to increased activation of the reproductive system in females, allowing us to test whether social dominance alone exposes individuals to increased oxidative stress. We compared dominant and subordinate females in female-only groups in five markers of oxidative stress. Dominant females did not have higher levels of oxidative damage compared to same-sex subordinates. This result contrasted to the trend in males in which dominant males had higher oxidative damage than their subordinate counterparts. Our findings suggest that the oxidative cost of social dominance is limited and support the notion that previously reported associations between high rank and increased oxidative stress is most likely driven by increased investment in reproduction.     

不同地位克氏原螯虾对社会环境改变的行为反应

为探究不同社会地位的亚成体克氏原螯虾(Procambarus clarkii)对利益的分配,以及对社会环境改变(体型较大的入侵同类)各自做出的行为反应,本文统计已确立等级序列的成对同性别螯虾对隐蔽所的占有情况,并视频拍摄同性别螯虾入侵时,入侵者及不同地位的原居者的格斗行为,分析格斗次数、格斗时间、首次攻击及被首次攻击对象多个参数。在隐蔽所占有实验中,71%为优势者占有隐蔽所,7%为从属者占有,共同占有或没有占有的各11%。在入侵-反入侵实验中,雄性入侵者对2只原居虾之间的攻击选择无显著差异,雌性入侵者首次攻击显著选择与原优势者格斗;雄性原居者中优势者对入侵者和原从属者的攻击无显著差异,雌性优势者则显著选择与入侵者格斗;雄性原居者中从属者显著选择与入侵者格斗,雌性从属者对入侵者和原优势者的攻击无显著差异。上述结果表明,优势者优先占有资源;雌雄螯虾在入侵和面临入侵时有各自不同的策略;不同地位的螯虾在反入侵时行为反应也各有不同。     

Cross- and auto-correlation in early vision

Neurons that respond selectively to the orientation of visual stimuli were discovered in V1 more than 50 years ago, but it is still not fully understood how or why this is brought about. We report experiments planned to show whether human observers use cross-correlation or auto-correlation to detect oriented streaks in arrays of randomly positioned dots, expecting that this would help us to understand what David Marr called the 'computational goal' of V1. The streaks were generated by two different methods: either by sinusoidal spatial modulation of the local mean dot density, or by introducing coherent pairs of dots to create moiré patterns, as Leon Glass did. A wide range of dot numbers was used in the randomly positioned arrays, because dot density affects cross- and auto-correlation differently, enabling us to infer which method was used. This difference stems from the fact that the cross-correlation task is limited by random fluctuations in the local mean density of individual dots in the noisy array, whereas the auto-correlation task is limited by fluctuations in the numbers of randomly occurring spurious pairs having the same separation and orientation as the deliberately introduced coherent pairs. After developing a new method using graded dot luminances, we were able to extend the range of dot densities that could be used by a large factor, and convincing results were obtained indicating that the streaks generated by amplitude modulation were discriminated by cross-correlation, while those generated as moiré patterns were discriminated by auto-correlation. Though our current results only apply to orientation selectivity, it is important to know that early vision can do more than simple filtering, for evaluating auto-correlations opens the way to more interesting possibilities, such as the detection of symmetries and suspicious coincidences.     

Fight for your breeding right: hierarchy re-establishment predicts aggression in a social queue

Social aggression is one of the most conspicuous features of animal societies, yet little is known about the causes of individual variation in aggression within social hierarchies. Recent theory suggests that when individuals form queues for breeding, variation in social aggression by non-breeding group members is related to their probability of inheriting breeding status. However, levels of aggression could also vary as a temporary response to changes in the hierarchy, with individuals becoming more aggressive as they ascend in rank, in order to re-establish dominance relationships. Using the group-living fish, Neolamprologus pulcher, we show that subordinates became more aggressive after they ascended in rank. Female ascenders exhibited more rapid increases in aggression than males, and the increased aggression was primarily directed towards group members of adjacent rather than non-adjacent rank, suggesting that social aggression was related to conflict over rank. Elevated aggression by ascenders was not sustained over time, there was no relationship between rank and aggression in stable groups, and aggression given by ascenders was not sex-biased. Together, these results suggest that the need to re-establish dominance relationships following rank ascension is an important determinant of variation in aggression in animal societies.     

Beyond the Food Web Connections to a Deeper Industrial Ecology

Industrial ecology is a school of thought based, in part, upon a simple analogy between industrial systems and ecological systems in terms of their material and energy flows. This article argues for a more sophisticated connection between these diverse systems based on the fact that they are all complex self-organizing systems, operating far from thermodynamic equilibrium. As such, industrial and ecological systems have in common certain constraints and dynamic properties that move beyond the central metaphor of industrial ecology and could align these systems under a more comprehensive analytical framework. If incorporated at a fundamental level, the complex systems framework could add depth and sophistication to the field of industrial ecology.     

Partner notification methods for African American men being treated for trichomoniasis: a consideration of main men, Second Hitters, and Third Players

This pilot study sought information on African American men's preferences for partner notification methods for a common sexually transmitted infection called trichomoniasis. Two focus groups of African American men were convened at a public STI clinic where they were being treated for trichomoniasis. The groups identified a sexual hierarchy in men's preferences for methods of partner notification. The hierarchy consisted of main men (Cake Daddies), second men (Second Hitters), and third or fourth men (Third Players), with placement depending on age, income, and social status. Health department employees affirmed the existence of a sexual hierarchy in a separate focus group. Sexual and economic bartering formed the basis of the hierarchy, and the secrecy involved in such arrangements presented a considerable challenge for STI control. Disease intervention specialists who were responsible for contact tracing spoke of cat-and-mouse methods in contacting the men without understanding fully exactly how the hierarchy influenced men's responses to partner notification. The findings suggest that STI control efforts must take the sexual hierarchy and its privacy implications into account if partner notification methods are to be acceptable to African American men.     

Assessment of dominance hierarchy through urine scent marking and its chemical constituents in male blackbuck Antelope cervicapra, a critically endangered species

In ungulates the process of chemical communication by urinary scent marking has been directly related to reproductive dominance, territorial defense and proximity to resources. The differences in the frequency of urine marking and chemical composition of urine of males Antelope cervicapra before, during and after the dominance hierarchy period were assessed. The variations in the urine marking and its chemical profiles of dominant males (n = 9), bachelors (n = 5) and sub-adult males (n = 5) were compared to find out how the dominance hierarchy influences the confined blackbuck herd under semi-natural captive conditions. The frequency of urine marking is significantly higher (p < 0.001) in dominant males. Twenty-eight major constituents were identified in the urine of dominant males (before, during and after the dominance hierarchy period), bachelor and sub-adult males. Among these, three specific compounds namely, 3-hexanone (I), 6-methyl-5-hepten-2-one (II) and 4-methyl-3-heptanone (III) were seen only in dominant males urine during the dominance hierarchy period. Based on the behavioural observation and the unique chemical constituents in the urine, it is concluded that the dominant male scent odor suppresses aggression, scent marking, scent production and territorial patrolling activities of subordinate males, through which the dominant male establish their hierarchy and attains success in reproduction.     

Risk Assessment of Transgenic Virus-resistant White Clover: Non-target Plant Community Characterisation and Implications for Field Trial Design

One of the most difficult elements of the ecological risk assessment of transgenic plants is investigation of their potential impact on biodiversity in complex non-target communities. This problem is particularly acute for pasture plants, since many have a track record of invasiveness. In this paper we develop an understanding of some aspects of the ecology of Trifolium repens L. (white clover) in montane vegetation communities in southeastern Australia as part of a larger project investigating potential ecological risks associated with commercial release of newly-developed transgenic virus-resistant T. repens cultivars. We use a combination of floristic surveys and biomass sampling to determine the habitat affinity of T. repens, the structure and composition of associated communities, and the scale at which different abiotic and biotic factors correlate with T. repens abundance. We also compare the abundance of native and exotic species within specific morpho-functional groups and use this to determine the relative significance of T. repens as a community constituent, and to identify native species that would be most at risk by expanding populations of T. repens. We found that T. repens comprises a relatively small component of the total community cover and biomass, but is one of the most abundant herbaceous species in mesic Poa – dominated grasslands and Poa-Eucalyptus woodlands in the study area, and that T. repens abundance is correlated at the within-community scale primarily with soil moisture and fertility. At smaller scales T. repens is limited by the hierarchical dominance of native graminoids and we conclude that competition for inter-tussock space in mesic communities is the most likely mechanism by which expanding populations of T. repens would influence populations of associated native species. These results have significant implications for the manner in which future analysis and risk quantification stages of the risk assessment of virus-resistant T.␣repens and other transgenic pasture plants in complex plant communities are performed.