‘Children are the food sent by God’: culinary imagery and the making of persons in the Cameroon Grassfields

The article explores aspects of personhood as these emerge through rites of passage and culinary imagery in Batié, an eastern Grassfields polity in west Cameroon. Food appears as a gendered medium which, by being exchanged, cooked, and ingested by persons – and by collectives perceived as persons – has the power to transform others (persons and collectives) and make them act. Persons and collectives are revealed, at the different stages of their ceremonial journey, as the outcome of similar processes – exchange, cooking, and ingestion of food – occurring each time on different scales, and thus displaying fractal properties. Introducing a split between agent and (cause of) agency, the article finally suggests that agents’ successive (ritual) transformations are the result of their own actions as well as the actions of (‘individual’ or ‘collective’) others upon them.     

Buckling instability in ordered bacterial colonies

Bacterial colonies often exhibit complex spatio-temporal organization. This collective behavior is affected by a multitude of factors ranging from the properties of individual cells (shape, motility, membrane structure) to chemotaxis and other means of cell-cell communication. One of the important but often overlooked mechanisms of spatio-temporal organization is direct mechanical contact among cells in dense colonies such as biofilms. While in natural habitats all these different mechanisms and factors act in concert, one can use laboratory cell cultures to study certain mechanisms in isolation. Recent work demonstrated that growth and ensuing expansion flow of rod-like bacteria Escherichia coli in confined environments leads to orientation of cells along the flow direction and thus to ordering of cells. However, the cell orientational ordering remained imperfect. In this paper we study one mechanism responsible for the persistence of disorder in growing cell populations. We demonstrate experimentally that a growing colony of nematically ordered cells is prone to the buckling instability. Our theoretical analysis and discrete-element simulations suggest that the nature of this instability is related to the anisotropy of the stress tensor in the ordered cell colony.     

Who's really in charge: Diverse follower cell behaviors in collective cell migration

Collective cell migrations drive morphogenesis, wound healing, and cancer dissemination. Cells located at the front are considered leaders while those behind them are defined topologically as followers. Leader cell behaviors, including chemotaxis and their coupling to followers, have been well-studied and reviewed. However, the contributions of follower cells to collective cell migration represent an emerging area of interest. In this perspective, we highlight recent research into the broadening array of follower cell behaviors found in moving collectives. We describe examples of follower cells that possess cryptic leadership potential and followers that lack that potential but contribute in diverse and sometimes surprising ways to collective movement, even steering from behind. We highlight collectives in which all cells both lead and follow, and a few passive passengers. The molecular mechanisms controlling follower cell function and behavior are just emerging and represent an exciting frontier in collective cell migration research.     

Organization and Evolution of Animal Colonies

Based on the theory of organization and evolution of colonies in an extinct group of hemichordate graptolites (Urbanek, 1960, 1990) the relationship between the events in the late astogeny of bryozoan colonies and their somatic and reproductive cycle is proposed. The bryozoan colonies with simple organization are compared with graptoloid colonies and their structure is interpreted within the framework of the morphogen gradient theory. A morphogen produced by the founder-zooid (oozooid) diffuses along the long axis of the colony and controls the phenotypic expression of the size and structure of zooids. Evolutionary changes in the graptoloid colonies involve introduction of new characters and their spreading is also accompanied by gradient changes of their manifestation. Evolutionary mechanisms in bryozoan colonies are considered in terms of penetrance and expressivity of genes. In contrast to graptolites, many bryozoan colonies display multiple zones of astogenetic changes and repetitions.     

The biological principles of swarm intelligence

The roots of swarm intelligence are deeply embedded in the biological study of self-organized behaviors in social insects. From the routing of traffic in telecommunication networks to the design of control algorithms for groups of autonomous robots, the collective behaviors of these animals have inspired many of the foundational works in this emerging research field. For the first issue of this journal dedicated to swarm intelligence, we review the main biological principles that underlie the organization of insects’ colonies. We begin with some reminders about the decentralized nature of such systems and we describe the underlying mechanisms of complex collective behaviors of social insects, from the concept of stigmergy to the theory of self-organization in biological systems. We emphasize in particular the role of interactions and the importance of bifurcations that appear in the collective output of the colony when some of the system’s parameters change. We then propose to categorize the collective behaviors displayed by insect colonies according to four functions that emerge at the level of the colony and that organize its global behavior. Finally, we address the role of modulations of individual behaviors by disturbances (either environmental or internal to the colony) in the overall flexibility of insect colonies. We conclude that future studies about self-organized biological behaviors should investigate such modulations to better understand how insect colonies adapt to uncertain worlds.     

Colony size affects collective decision-making in the ant Temnothorax albipennis

Social insects are well-known for their ability to achieve robust collective behaviours even when individuals have limited information. It is often assumed that such behaviours rely on very large group sizes, but many insect colonies start out with only a few workers. Here we investigate the influence of colony size on collective decision-making in the house-hunting of the ant Temnothorax albipennis. In experiments where colony size was manipulated by splitting colonies, we show that worker number has an influence on the speed with which colonies discover new nest sites, but not on the time needed to make a decision (achieve a quorum threshold) or total emigration time. This occurred because split colonies adopted a lower quorum threshold, in fact they adopted the same threshold in proportion to their size as full-size colonies. This indicates that ants may be measuring relative quorum, i.e. population in the new nest relative to that of the old nest, rather than the absolute number. Experimentally reduced colonies also seemed to gain more from experience through repeated emigrations, as they could then reduce nest discovery times to those of larger colonies. In colonies of different sizes collected from the field, total emigration time was also not correlated with colony size. However, quorum threshold was not correlated with colony size, meaning that individuals in larger colonies adopted relatively lower quorum thresholds. Since this is a different result to that from size-manipulated colonies, it strongly suggests that the differences between natural small and large colonies were not caused by worker number alone. Individual ants may have adjusted their behaviour to their colony’s size, or other factors may correlate with colony size in the field. Our study thus shows the importance of experimentally manipulating colony size if the effect of worker number on the emergence of collective behaviour is to be studied. Received 13 December 2005; revised 9 May 2006; accepted 15 May 2006.     

Dynamic myosin activation promotes collective morphology and migration by locally balancing oppositional forces from surrounding tissue

Migrating cells need to overcome physical constraints from the local microenvironment to navigate their way through tissues. Cells that move collectively have the additional challenge of negotiating complex environments in vivo while maintaining cohesion of the group as a whole. The mechanisms by which collectives maintain a migratory morphology while resisting physical constraints from the surrounding tissue are poorly understood. Drosophila border cells represent a genetic model of collective migration within a cell-dense tissue. Border cells move as a cohesive group of 6−10 cells, traversing a network of large germ line–derived nurse cells within the ovary. Here we show that the border cell cluster is compact and round throughout their entire migration, a shape that is maintained despite the mechanical pressure imposed by the surrounding nurse cells. Nonmuscle myosin II (Myo-II) activity at the cluster periphery becomes elevated in response to increased constriction by nurse cells. Furthermore, the distinctive border cell collective morphology requires highly dynamic and localized enrichment of Myo-II. Thus, activated Myo-II promotes cortical tension at the outer edge of the migrating border cell cluster to resist compressive forces from nurse cells. We propose that dynamic actomyosin tension at the periphery of collectives facilitates their movement through restrictive tissues.     

Colony size,nestmate density and social history shape behavioural variation in Formica fusca colonies

In ants, individuals live in tightly integrated units (colonies) and work collectively for its success. In such groups, stable intraspecific variation in behaviour within or across contexts (personality) can occur at two levels: individuals and colonies. This paper examines how colony size and nestmate density influence the collective exploratory behaviour of Formica fusca (Hymenoptera: Formicidae), in the laboratory. The housing conditions of the colonies were manipulated to vary the size of colonies and their densities under a fully factorial design. The results demonstrate the presence of colony behavioural repeatability in this species, and contrary to our expectations, colonies were more explorative on average when they were kept at lower nestmate densities. We also found that experimental colonies created from larger source colonies were more explorative, which conveys that a thorough understanding of the contemporary behaviour of a colony may require knowing its social history and how it was formed. Our results also convey that the colony size and nestmate density can have significant effects on the exploratory behaviour of ant colonies.     

Connecting the dots in ethology: applying network theory to understand neural and animal collectives

A major goal shared by neuroscience and collective behavior is to understand how dynamic interactions between individual elements give rise to behaviors in populations of neurons and animals, respectively. This goal has recently become within reach, thanks to techniques providing access to the connectivity and activity of neuronal ensembles as well as to behaviors among animal collectives. The next challenge using these datasets is to unravel network mechanisms generating population behaviors. This is aided by network theory, a field that studies structure–function relationships in interconnected systems. Here we review studies that have taken a network view on modern datasets to provide unique insights into individual and collective animal behaviors. Specifically, we focus on how analyzing signal propagation, controllability, symmetry, and geometry of networks can tame the complexity of collective system dynamics. These studies illustrate the potential of network theory to accelerate our understanding of behavior across ethological scales.     

Personality composition is more important than group size in determining collective foraging behaviour in the wild

Describing the factors that shape collective behaviour is central to our understanding of animal societies. Countless studies have demonstrated an effect of group size in the emergence of collective behaviours, but comparatively few have accounted for the composition/diversity of behavioural phenotypes, which is often conflated with group size. Here, we simultaneously examine the effect of personality composition and group size on nest architecture and collective foraging aggressiveness in the social spider Stegodyphus dumicola. We created colonies of two different sizes (10 or 30 individuals) and four compositions of boldness (all bold, all shy, mixed bold and shy, or average individuals) in the field and then measured their collective behaviour. Larger colonies produced bigger capture webs, while colonies containing a higher proportion of bold individuals responded to and attacked prey more rapidly. The number of attackers during collective foraging was determined jointly by composition and size, although composition had an effect size more than twice that of colony size: our results suggest that colonies of just 10 bold spiders would attack prey with as many attackers as colonies of 110 ‘average’ spiders. Thus, personality composition is a more potent (albeit more cryptic) determinant of collective foraging in these societies.     

不同社会等级雄性根田鼠对自身和同性陌生气味的辨别

采用两两遭遇法确定雄性根田鼠的社会等级,然后以新鲜尿作气味源,在行为选择箱中观察不同社会等级雄性根田鼠对自身气味和非自身气味的行为响应模式,结果表明:种群中从属个体对自身尿液存在明显偏好,其对自身尿液的接近潜伏期显著短于非自身尿液,而访问时间、自我修饰频次都显著高于非自身尿液;种群中优势个体则优先访问非自身尿液,其对非自身尿液的访问时间、嗅舔时间、自我修饰及反标记均显著高于自身尿液;对非自身尿液,不同社会等级雄性个体之间存在明显不同的行为反应模式。这说明,不同社会等级雄性根田鼠具有自我识别的能力且模式不同,同时其对非自身尿气味响应模式的差异也与自身的社会等级有关。     

Collective animal behavior from Bayesian estimation and probability matching

Animals living in groups make movement decisions that depend, among other factors, on social interactions with other group members. Our present understanding of social rules in animal collectives is mainly based on empirical fits to observations, with less emphasis in obtaining first-principles approaches that allow their derivation. Here we show that patterns of collective decisions can be derived from the basic ability of animals to make probabilistic estimations in the presence of uncertainty. We build a decision-making model with two stages: Bayesian estimation and probabilistic matching. In the first stage, each animal makes a Bayesian estimation of which behavior is best to perform taking into account personal information about the environment and social information collected by observing the behaviors of other animals. In the probability matching stage, each animal chooses a behavior with a probability equal to the Bayesian-estimated probability that this behavior is the most appropriate one. This model derives very simple rules of interaction in animal collectives that depend only on two types of reliability parameters, one that each animal assigns to the other animals and another given by the quality of the non-social information. We test our model by obtaining theoretically a rich set of observed collective patterns of decisions in three-spined sticklebacks, Gasterosteus aculeatus, a shoaling fish species. The quantitative link shown between probabilistic estimation and collective rules of behavior allows a better contact with other fields such as foraging, mate selection, neurobiology and psychology, and gives predictions for experiments directly testing the relationship between estimation and collective behavior.     

Some peculiarities in the behavioral reactions of the lophophore and the trophic structuring of the colonies of the post-Paleozoic Stenolaemata (bryozoa)

Some peculiarities in the behavioral reactions of the lophophore, a feeding apparatus of the living marine bryozoans, are discussed. In bryozoans of the class Stenolaemata the position of the lophophore is regulated by the autozooidal peristome. In post-Paleozoic Stenolaemata the individual and collective activities of the lophophores are determined by the peculiarities in the trophic structuring of colonies, which are established based on the individual or group arrangement of autozooidal apertures. Two main types of the trophic structuring are distinguished: individual and group structuring. The adaptive significance of the trophic structuring consists in the effective extracting of food particles from water currents. In combination with the peculiarities of the colonial organization of post-Paleozoic Stenolaemata, the types of trophic structuring of colonies can be used when characterizing taxa of different levels.     

Pollen and seed analogies

Abstract

The dispersal units of plants are seeds but pollen is also dispersed and there are many similarities to be found between these two types of diaspores, especially in their environmental interactions. The economy of natural processes suggests that Nature would not “re-invent the wheel” and indeed there are many similarities, if not identical types of mechanisms, in the metabolic activities of seed and pollen responses to environmental conditions. The main differences regard scale and the responses/mechanisms available to bi-or tri-cellular systems compared to those operating at cytological or organ level. Intriguing parallels are highlighted in this paper without implying homologies.     

Nest architecture shapes the collective behaviour of harvester ants

Structures influence how individuals interact and, therefore, shape the collective behaviours that emerge from these interactions. Here I show that the structure of a nest influences the collective behaviour of harvester ant colonies. Using network analysis, I quantify nest architecture and find that as chamber connectivity and redundancy of connections among chambers increase, so does a colony''s speed of recruitment to food. Interestingly, the volume of the chambers did not influence speed of recruitment, suggesting that the spatial organization of a nest has a greater impact on collective behaviour than the number of workers it can hold. Thus, by changing spatial constraints on social interactions organisms can modify their behaviour and impact their fitness.     

The origin and evolution of social life in the Stenogastrinae (Hymenoptera,Vespidae)

The Stenogastrinae are a subfamily of the Vespidae. The main difference between these and other social wasps (Polistinae and Vespinae) is a jelly-like substance that the Stenogastrinae secrete from the Dufour 's gland and use in many functions of their biology. It is suggested that this substance greatly contributed to the evolution of social life in these wasps by making it possible to nourish the brood with liquid food and store it in the nest, thus favoring also the evolution of the behavioral mechanisms which facilitated interactions between adults. Social organization of the colonies may have been kept at a low level through a basic system of continuous temporary helper replacement, while the evolution of large colonies was restrained, as well as by the poor quality of construction material, low egg-laying capacity and limited production of abdominal substance, imperfect social regulatory mechanisms, and the absence of defensive mechanisms of the colonies against large predators.     

Neuroblast formation and patterning during early brain development in Drosophila

The Drosophila embryo provides a useful model system to study the mechanisms that lead to pattern and cell diversity in the central nervous system (CNS). The Drosophila CNS, which encompasses the brain and the ventral nerve cord, develops from a bilaterally symmetrical neuroectoderm, which gives rise to neural stem cells, called neuroblasts. The structure of the embryonic ventral nerve cord is relatively simple, consisting of a sequence of repeated segmental units (neuromeres), and the mechanisms controlling the formation and specification of the neuroblasts that form these neuromeres are quite well understood. Owing to the much higher complexity and hidden segmental organization of the brain, our understanding of its development is still rudimentary. Recent investigations on the expression and function of proneural genes, segmentation genes, dorsoventral-patterning genes and a number of other genes have provided new insight into the principles of neuroblast formation and patterning during embryonic development of the fly brain. Comparisons with the same processes in the trunk help us to understand what makes the brain different from the ventral nerve cord. Several parallels in early brain patterning between the fly and the vertebrate systems have become evident.     

Trait heritability in major transitions

Background

Increases in biological complexity and the origins of life’s hierarchical organization are described by the “major transitions” framework. A crucial component of this paradigm is that after the transition in complexity or organization, adaptation occurs primarily at the level of the new, higher-level unit. For collective-level adaptations to occur, though, collective-level traits—properties of the group, such as collective size—must be heritable. Since collective-level trait values are functions of lower-level trait values, collective-level heritability is related to particle-level heritability. However, the nature of this relationship has rarely been explored in the context of major transitions.

Results

We examine relationships between particle-level heritability and collective-level heritability for several functions that express collective-level trait values in terms of particle-level trait values. For clonal populations, when a collective-level trait value is a linear function of particle-level trait values and the number of particles per collective is fixed, the heritability of a collective-level trait is never less than that of the corresponding particle-level trait and is higher under most conditions. For more complicated functions, collective-level heritability is higher under most conditions, but can be lower when the environment experienced by collectives is heterogeneous. Within-genotype variation in collective size reduces collective-level heritability, but it can still exceed particle-level heritability when phenotypic variance among particles within collectives is large. These results hold for a diverse sample of biologically relevant traits.

Conclusions

Rather than being an impediment to major transitions, we show that, under a wide range of conditions, the heritability of collective-level traits is actually higher than that of the corresponding particle-level traits. High levels of collective-level trait heritability thus arise “for free,” with important implications not only for major transitions but for multilevel selection in general.

     

Cryptic surface-associated multicellularity emerges through cell adhesion and its regulation

The repeated evolution of multicellularity led to a wide diversity of organisms, many of which are sessile, including land plants, many fungi, and colonial animals. Sessile organisms adhere to a surface for most of their lives, where they grow and compete for space. Despite the prevalence of surface-associated multicellularity, little is known about its evolutionary origin. Here, we introduce a novel theoretical approach, based on spatial lineage tracking of cells, to study this origin. We show that multicellularity can rapidly evolve from two widespread cellular properties: cell adhesion and the regulatory control of adhesion. By evolving adhesion, cells attach to a surface, where they spontaneously give rise to primitive cell collectives that differ in size, life span, and mode of propagation. Selection in favor of large collectives increases the fraction of adhesive cells until a surface becomes fully occupied. Through kin recognition, collectives then evolve a central-peripheral polarity in cell adhesion that supports a division of labor between cells and profoundly impacts growth. Despite this spatial organization, nascent collectives remain cryptic, lack well-defined boundaries, and would require experimental lineage tracking technologies for their identification. Our results suggest that cryptic multicellularity could readily evolve and originate well before multicellular individuals become morphologically evident.

This modelling study reveals that cell adhesion can lead to the cryptic origination of surface-associated multicellularity, where collectives cannot be distinguished by eye but nonetheless express emergent multicellular adaptations.