Directed network Laplacians and random graph models

We consider spectral methods that uncover hidden structures in directed networks. We establish and exploit connections between node reordering via (a) minimizing an objective function and (b) maximizing the likelihood of a random graph model. We focus on two existing spectral approaches that build and analyse Laplacian-style matrices via the minimization of frustration and trophic incoherence. These algorithms aim to reveal directed periodic and linear hierarchies, respectively. We show that reordering nodes using the two algorithms, or mapping them onto a specified lattice, is associated with new classes of directed random graph models. Using this random graph setting, we are able to compare the two algorithms on a given network and quantify which structure is more likely to be present. We illustrate the approach on synthetic and real networks, and discuss practical implementation issues.

Social hierarchy position in female mice is associated with plasma corticosterone levels and hypothalamic gene expression

Social hierarchies emerge when animals compete for access to resources such as food, mates or physical space. Wild and laboratory male mice have been shown to develop linear hierarchies, however, less is known regarding whether female mice have sufficient intrasexual competition to establish significant social dominance relationships. In this study, we examined whether groups of outbred CD-1 virgin female mice housed in a large vivaria formed social hierarchies. We show that females use fighting, chasing and mounting behaviors to rapidly establish highly directionally consistent social relationships. Notably, these female hierarchies are less linear, steep and despotic compared to male hierarchies. Female estrus state was not found to have a significant effect on aggressive behavior, though dominant females had elongated estrus cycles (due to increased time in estrus) compared to subordinate females. Plasma estradiol levels were equivalent between dominant and subordinate females. Subordinate females had significantly lower levels of basal corticosterone compared to dominant females. Analyses of gene expression in the ventromedial hypothalamus indicated that subordinate females have elevated ERα, ERβ and OTR mRNA compared to dominant females. This study provides a methodological framework for the study of the neuroendocrine basis of female social aggression and dominance in laboratory mice.

Dominance relationships in a family pack of captive arctic wolves (Canis lupus arctos): the influence of competition for food, age and sex

BackgroundDominance is one of the most pervasive concepts in the study of wolf social behaviour but recently its validity has been questioned. For some authors, the bonds between members of wolf families are better described as parent-offspring relationships and the concept of dominance should be used just to evaluate the social dynamics of non-familial captive pack members (e.g., Mech & Cluff, 2010). However, there is a dearth of studies investigating dominance relationships and its correlates in wolf family packs.MethodsHere, we applied a combination of the most commonly used quantitative methods to evaluate the dominance relationships in a captive family pack of 19 Arctic wolves.ResultsWe found a significant linear and completely transitive hierarchy based on the direction of submissive behaviours and found that dominance relationships were not influenced by the competitive contexts (feeding vs. non-feeding context). A significant linear hierarchy also emerges amongst siblings once the breeding pair (the two top-ranking individuals) is removed from analyses. Furthermore, results suggest that wolves may use greeting behaviour as a formal signal of subordination. Whereas older wolves were mostly dominant over younger ones, no clear effect of sex was found. However, frequency of agonistic (submissive, dominant and aggressive) behaviours was higher between female–female and male–male dyads than female–male dyads and sex-separated linear hierarchies showed a stronger linearity than the mixed one. Furthermore, dominance status was conveyed through different behavioural categories during intra-sexual and inter-sexual interactions.DiscussionCurrent results highlight the importance of applying a systematic methodology considering the individuals’ age and sex when evaluating the hierarchical structure of a social group. Moreover, they confirm the validity of the concept of dominance relationships in describing the social bonds within a family pack of captive wolves.

Indigenous African Leadership: Key differences from Anglo-centric thinking and writings

This article draws on historical explorers’ accounts, ethnography and organisational approaches to examine practices, discourses and perceptions of leadership in 12 prototypical indigenous communities in West and Central Africa. By so doing, it highlights how leadership meanings from this context differ from Anglo-centric thinking and writings. Key to this contribution is an unravelling of ways in which historical cultural hegemonies impose particular discursive formations, constructed practices and mind-programming in a non-Anglo-Saxon socio-cultural context. Dramaturgical power arrangement, lucid role substitution and the notion of leadership as non-human emerge as dominant themes in the analysis. Also, featuring significantly are representations of leadership in symbols, mythology and as transcendental and metaphysical. These conceptualisations are different from predominant Anglo-Saxon writings that frequently present leadership as linear hierarchies, dyadic (leader-follower) relationship, acts and behaviours of heroic figures and as an essentially human action. An Afro-centric indigenous concept of leadership reflecting the context is proposed which challenges heroism, linearity, individualism and objectivism.

Introduction to double issue 41.1–2 on Features

<p>This special double issue (41.1 and 41.2) contains 11 articles on the formal properties of linguistic feature systems, all of which were presented at a conference in Tromsø in the fall of 2013.</p><p>The issue was jointly edited by Martin Krämer, Sandra Ronai, and Peter Svenonius.</p><p>A version of the original call for papers posted in 2013 follows.</p><p>All formal models of linguistics assume sets of features in terms of which generalizations can be stated. But the nature of the features themselves is often not explicitly addressed. In this special double issue of <em>Nordlyd</em> we focus on the nature of features across phonology and syntax and related domains of linguistics. </p><p>One group of questions concerns the ‘grounding’ of features in substance or content. For example, phonological features may be grounded in phonetics, and syntactic features may be grounded in semantics. Innatist traditions have sometimes posited innate universal inventories of grounded features. The ‘substance-free’ movement in phonology argues instead that the formal properties of features can and should be radically dissociated from their grounding in content. Sign language phonology would seem to support this position, as the featural system of sign language phonology operates with a completely different set of articulators from those used in spoken languages. Minimalist syntax also frequently promotes the dissociation of formal properties of features from their content (as in the proposal that tense is simply one of a variety of ways in which Infl may be ‘grounded,’ favored in Indo-European languages but with various other languages opting for other content for Infl). Such proposals raise many questions concerning how feature systems are constrained to be uniform across languages and to what extent they are free to vary. The radically opposing view in phonology denies the existence of categorical features altogether and attempts to model phonological patterns as statistical computation of phonetic data.</p><p>The formal structure of features raises another set of questions. Complex patterns of feature locality gave rise to feature geometries in phonology, and these have been developed further to account for dependencies among features, not only in phonology but also in syntax. Cartographic work typically assumes linear hierarchies. To what extent are the various geometries and hierarchies motivated, and how might they be grounded in a broader explanatory theory?</p><p>Interacting with these questions about the “geometric” relations among features is the algebraic structure of the features. For example, it is often assumed that privativity, in which opposition is marked by presence versus absence, is conceptually simplest and therefore the zero hypothesis. While in phonology the pendulum currently swings towards privativity, recently arguments have come from morphosyntax that features have binary values. While apparent ternary patterns in phonology have been taken as arguments in favor of binarity, such patterns have more recently been accounted for by reference to class nodes. Theories such as HPSG or Government Phonology assume much more complex relations among features (with HPSG even allowing feature-value matrices in which the values are feature-value matrices, extending to a kind of feature recursion, and GP positing government and licensing relations between features and positions).</p><p>In this volume, a selection of researchers address these and other questions about the nature of features in linguistic theory.</p>

Introduction to double issue 41.1–2 on Features

<p>This special double issue (41.1 and 41.2) contains 11 articles on the formal properties of linguistic feature systems, all of which were presented at a conference in Tromsø in the fall of 2013.</p><p>The issue was jointly edited by Martin Krämer, Sandra Ronai, and Peter Svenonius.</p><p>A version of the original call for papers posted in 2013 follows.</p><p>All formal models of linguistics assume sets of features in terms of which generalizations can be stated. But the nature of the features themselves is often not explicitly addressed. In this special double issue of <em>Nordlyd</em> we focus on the nature of features across phonology and syntax and related domains of linguistics. </p><p>One group of questions concerns the ‘grounding’ of features in substance or content. For example, phonological features may be grounded in phonetics, and syntactic features may be grounded in semantics. Innatist traditions have sometimes posited innate universal inventories of grounded features. The ‘substance-free’ movement in phonology argues instead that the formal properties of features can and should be radically dissociated from their grounding in content. Sign language phonology would seem to support this position, as the featural system of sign language phonology operates with a completely different set of articulators from those used in spoken languages. Minimalist syntax also frequently promotes the dissociation of formal properties of features from their content (as in the proposal that tense is simply one of a variety of ways in which Infl may be ‘grounded,’ favored in Indo-European languages but with various other languages opting for other content for Infl). Such proposals raise many questions concerning how feature systems are constrained to be uniform across languages and to what extent they are free to vary. The radically opposing view in phonology denies the existence of categorical features altogether and attempts to model phonological patterns as statistical computation of phonetic data.</p><p>The formal structure of features raises another set of questions. Complex patterns of feature locality gave rise to feature geometries in phonology, and these have been developed further to account for dependencies among features, not only in phonology but also in syntax. Cartographic work typically assumes linear hierarchies. To what extent are the various geometries and hierarchies motivated, and how might they be grounded in a broader explanatory theory?</p><p>Interacting with these questions about the “geometric” relations among features is the algebraic structure of the features. For example, it is often assumed that privativity, in which opposition is marked by presence versus absence, is conceptually simplest and therefore the zero hypothesis. While in phonology the pendulum currently swings towards privativity, recently arguments have come from morphosyntax that features have binary values. While apparent ternary patterns in phonology have been taken as arguments in favor of binarity, such patterns have more recently been accounted for by reference to class nodes. Theories such as HPSG or Government Phonology assume much more complex relations among features (with HPSG even allowing feature-value matrices in which the values are feature-value matrices, extending to a kind of feature recursion, and GP positing government and licensing relations between features and positions).</p><p>In this volume, a selection of researchers address these and other questions about the nature of features in linguistic theory.</p>

Female, but not male, agonistic behaviour is associated with male reproductive success in stable bluebanded goby (Lythrypnus dalli) hierarchies

In many social species, there are important connections between social behaviour and reproduction that provide critical insights into the evolution of sociality. In this study, we describe associations between agonistic behaviour and male reproductive success in stable social groups of bluebanded gobies (Lythrypnus dalli). This highly social, sex-changing species forms linear hierarchies of a dominant male and multiple subordinate females. Males reproduce with each female in the harem and care for the eggs. Since aggression tends to be associated with reduced reproduction in social hierarchies, we hypothesized that males in groups with high rates of aggression would fertilise fewer eggs. We also hypothesized that a male’s agonistic behaviour would be associated with his reproductive success. Dominants often exert substantial control over their harem, including control over subordinate reproduction. To address these hypotheses, we quantified egg laying/fertilisation over 13 days and observed agonistic behaviour. We show that there was a significant, negative association between male reproductive success and the total rate agonistic interactions by a group. While no male behaviours were associated with the quantity of eggs fertilised, female agonistic behaviour may be central to male reproductive success. We identified a set of models approximating male reproductive success that included three female behaviours: aggression by the highest-ranking female and approaches by the lowest-ranking female were negatively associated with the quantity of eggs fertilised by males in their groups, but the efficiency with which the middle-ranking female displaced others was positively associated with this measure. These data provide a first step in elucidating the behavioural mechanisms that are associated with L. dalli reproductive success.