Danielle Mersch

Tracking Individuals Shows Spatial Fidelity Is a Key Regulator of Ant Social Organization

Its an Ants Life Eusocial insects live in highly organized societies where groups of individuals carry out specific tasks; for example, caring for the eggs, cleaning the nest, or foraging, which might suggest the presence of an advanced form of organization, similar to what might be expected from more cognitively advanced species. Mersch et al. (p. 1090, published online 18 April) tracked individual ant movements and interactions to show that their precise social organization results from temporal changes in the spatial location of workers. As they aged, ants largely progressed from being nurses located near the queen, to nest cleaners who move throughout the colony, and finally to foragers moving in and out at the colony edges. Monitoring of individually tagged worker ants revealed three distinct groups that greatly differ in behavior. Ants live in organized societies with a marked division of labor among workers, but little is known about how this division of labor is generated. We used a tracking system to continuously monitor individually tagged workers in six colonies of the ant Camponotus fellah over 41 days. Network analyses of more than 9 million interactions revealed three distinct groups that differ in behavioral repertoires. Each group represents a functional behavioral unit with workers moving from one group to the next as they age. The rate of interactions was much higher within groups than between groups. The precise information on spatial and temporal distribution of all individuals allowed us to calculate the expected rates of within- and between-group interactions. These values suggest that the network of interaction within colonies is primarily mediated by age-induced changes in the spatial location of workers.

Social isolation causes mortality by disrupting energy homeostasis in ants

Social deprivation can have negative effects on the lives of social animals, including humans, yet little is known about the mechanisms by which social withdrawal affects animal health. Here we show that in the carpenter ant Camponotus fellah, socially isolated workers have a greatly reduced life span relative to ants kept in groups of ten individuals. By using a new tracking system, we found that social isolation resulted in important behavioral changes and greatly increased locomotor activity. The higher activity of single ants and their increased propensity to leave the nest to move along the walls suggested that the increased mortality of isolated ants might stem from an imbalance of energy income and expenditure. This view was supported by the finding that while isolated ants ingested the same amount of food as grouped ants, they retained food in the crop, hence preventing its use as an energy source. Moreover, the difference in life span between single and grouped individuals vanished when ants were not fed. This study thus underlines the role of social interactions as key regulators of energy balance, which ultimately affects aging and health in a highly social organism.

The social mirror for division of labor: what network topology and dynamics can teach us about organization of work in insect societies

Division of labor is an emergent and dynamic process that intimately mingles social dynamics and individual behavior. Individuals engage in work, and social interactions between workers couple an individual’s behavior to that of its nestmates, thereby creating flexible and robust division of labor. Because social networks mirror the dual nature of division of labor by representing the individual in the connected web of the society, they are ideally suited to investigate the mechanistic underpinnings that organize social life and drive division of labor. Network analyses provide a panoply of tools that help shed light on the functional role of network structure, and that, if carefully used and combined with well-designed experiments, can revolutionize our comprehension of the distributed regulation of work in social insects. Here, I summarize the emergent nature of division of labor, lay out caveats of social network analysis and then discuss how a selection of network measures can dissect individual level and colony level connectivity to enhance our understanding of division of labor, and provide a more integrated view of how insect societies function.

Automated computer-based detection of encounter behaviours in groups of honeybees

Honeybees form societies in which thousands of members integrate their behaviours to act as a single functional unit. We have little knowledge on how the collaborative features are regulated by workers’ activities because we lack methods that enable collection of simultaneous and continuous behavioural information for each worker bee. In this study, we introduce the Bee Behavioral Annotation System (BBAS), which enables the automated detection of bees’ behaviours in small observation hives. Continuous information on position and orientation were obtained by marking worker bees with 2D barcodes in a small observation hive. We computed behavioural and social features from the tracking information to train a behaviour classifier for encounter behaviours (interaction of workers via antennation) using a machine learning-based system. The classifier correctly detected 93% of the encounter behaviours in a group of bees, whereas 13% of the falsely classified behaviours were unrelated to encounter behaviours. The possibility of building accurate classifiers for automatically annotating behaviours may allow for the examination of individual behaviours of worker bees in the social environments of small observation hives. We envisage that BBAS will be a powerful tool for detecting the effects of experimental manipulation of social attributes and sub-lethal effects of pesticides on behaviour.

Uncovering Latent Behaviors in Ant Colonies

Many biological systems exhibit collective behaviors that strengthen their adaptability to their environment, compared to more solitary species. Describing these behaviors is challenging yet necessary in order to understand these biological systems. We propose a probabilistic model that enables us to uncover the collective behaviors observed in a colony of ants. This model is based on the assumption that the behavior of an individual ant is a time-dependent mixture of latent behaviors that are specific to the whole colony. We apply this model to a large-scale dataset obtained by observing the mobility of nearly 1000 Camponotus fellah ants from six different colonies. Our results indicate that a colony typically exhibits three classes of behaviors, each characterized by a specific spatial distribution and a level of activity. Moreover, these spatial distributions, which are uncovered automatically by our model, match well with the ground truth as manually annotated by domain experts. We further explore the evolution of the behavior of individual ants and show that it is well captured by a second order Markov chain that encodes the fact that the future behavior of an ant depends not only on its current behavior but also on its preceding one.

Synchronised brood transport by ants occurs without communication

Collective behaviours in societies such as those formed by ants are thought to be the result of distributed mechanisms of information processing and direct decision-making by well-informed individuals, but their relative importance remains unclear. Here we tracked all ants and brood movements to investigate the decision strategy underlying brood transport in nests of the ant Camponotus fellah. Changes in environmental conditions induced workers to quickly transport the brood to a preferred location. Only a minority of the workers, mainly nurses, participated in this task. Using a large number of statistical tests we could further show that these transporters omitted to recruit help, and relied only on private information rather than information obtained from other workers. This reveals that synchronised group behaviour, often suggestive of coordinated actions among workers, can also occur in the complete absence of communication.

Camponotus fellah queens are singly mated

The ant Camponotus fellah has been used in several behavioral and life history studies. An important factor that affects the genetic structure and division of labour within a colony is whether queens are singly or multiply mated. To determine whether queens are singly mated in C. fellah, as is the case in some other Camponotus species, we developed nine polymorphic microsatellite markers and sequenced 16 workers each from 20 colonies at six loci. Data in all colonies were compatible with queen monoandry. All the workers of one of the colonies had identical genotypes suggesting that they were clonally produced or that the queen was inbred. We, therefore, genotyped the mother queen as well as 31 more workers of the same colony at the same six loci plus the three remaining loci. These data revealed that the queen was homozygous at eight of the nine loci and that she mated with a male having a shared allele at all but one of the loci. Thus, the queen was apparently not only inbred but also probably mated with a brother.

No Evidence for Moral Reward and Punishment in an Anonymous Context

Human social interactions are regulated by moral norms that define individual obligations and rights. These norms are enforced by punishment of transgressors and reward of followers. Yet, the generality and strength of this drive to punish or reward is unclear, especially when people are not personally involved in the situation and when the actual impact of their sanction is only indirect, i.e., when it diminishes or promotes the social status of the punished or rewarded individual. In a real-life study, we investigated if people are inclined to anonymously punish or reward a person for her past deeds in a different social context. Participants from three socio-professional categories voted anonymously for early career violinists in an important violin competition. We found that participants did not punish an immoral violin candidate, nor did they reward another hyper-moral candidate. On the contrary, one socio-professional category sanctioned hyper-morality. Hence, salient moral information about past behavior did not elicit punishment or reward in an impersonal situation where the impact of the sanction was indirect. We conclude that contextual features play an important role in human motivation to enforce moral norms.