Division of Labor and Task Allocation

The response threshold model is a potential mechanism for task allocation in social insects, and it assumes that workers vary in the levels of task stimuli to which they respond. Furthermore, response thresholds of individual workers may change over time through self-reinforcement (experience), such that workers become more sensitive to task stimuli. However, in addition to self-reinforcement, aging is another process that occurs through time. Distinguishing whether response thresholds change within workers due to self-reinforcement or aging may give insight into the flexibility of this task allocation mechanism. Using a ventilation paradigm, we manipulated workers of Bombus impatiens to have either repeated or lack of exposures to increases in nest air temperature, thereby allowing us to manipulate experience and thus self-reinforcement. Nest air temperature was the task stimulus, and ventilation (fanning) was the behavioral response. We found that ventilation response thresholds do not decrease either with age or experience in workers of B. impatiens, contrary to what has been reported for B. terrestris workers (Weidenmuller, 2004). Instead, we found high levels of intra-individual variation in response thresholds. Our results also show that workers with lower average response thresholds respond to heating events with higher probability than those with higher ventilation thresholds. These results provide insight into the role of the response threshold framework for task allocation; we also discuss how response probabilities may play a role in task allocation among workers.

Division of labour is a key aspect of distributed systems, such as swarm robotics or multi-agent systems. Inspired by social insects known for their task allocation capabilities, most of the models rely on two assumptions: 1) each task is associated with a stimulus, and 2) the execution of this task lowers that stimulus. In short, the stimulus is a representation of the amount of work needed on a task. When these assumptions are not true, we need a mechanism to guide the agent in its decision whether to pursue or to interrupt its current task, as there is no diminishing stimulus to rely on. In this article, we propose a model based on the Response Threshold Model and a mechanism based on the agent’s intrinsic motivation and internal states, allowing to take into account tasks dissociated from stimuli. Agents use their intrinsic motivation to emulate the priority of tasks not associated with any stimuli, and to decide whether to interrupt or pursue their current task. This model has been applied to simulate the division of labour within a simplified honey bee colony, associated with the constantly adapting physiology of honey bees. Preliminary results show that the task allocation is effective, robust and in some cases improved by the interruption mechanism.

Among social insects, task allocation within its group members remains as one of the paramount pillars of social functionality. Division of labor in many eusocial insects is maintained by behavioral flexibility that can shift according to the needs of the colony they reside in. Workers typically, over time as they age, shift from intranidal nurses to extranidal foragers. If the needs of the colony change, either from the needs of the adults or the brood therein, workers shift their behavior in order to compensate for the need of a particular task to be done. This shift, either accelerating towards a behavior associated with an older worker, or regressing back into the nest, is not clearly understood in social insects outside of honeybees. In this study, evaluated how brood type affected the red imported fire ant, Solenopsis invicta, worker task reversion and acceleration. Through observation of worker behaviors performed over multiple time-points per day, we discovered that worker task reversion and acceleration does occur within this ant species. Furthermore, the type of brood influenced the rate at which this occurred, with larvae having the strongest effect of all types. Finally, there was a propensity for workers to maintain their new behavior throughout the experiment. This study shows that the needs of brood within a social insect colony can influence the behavior workers perform, reversing the age polyethism that is common among social insect species.

Deborah Gordon (Behav Ecol Sociobiol. doi:10.1007/s00265-015-2045-3, 2016) advocates abandoning the term “division of labor” (DOL) on the grounds that it implies a process by which individual colony members become persistent specialists by virtue of their “essential internal attributes.” She claims that there is little evidence for such links, and that continued use of the term distracts us from focusing on how distributed processing leads to task allocation (TA) in the colony, which she considers to be sufficient explanation of how colonies organize work. I argue instead that the term DOL as understood by most social insect researchers today is descriptive, useful, and carries no such implications of process or links to internal attributes. I suggest that the confusion can be addressed by recognizing the distinction between the ontogenetic causes of DOL, which set individuals’ response thresholds (RT) during their development, and the behavioral and physiological mechanisms that act in the moment to determine TA via distributed processing. I further suggest that the term “specialization” as applied to social insects should be understood to mean simply “to concentrate on,” without requiring that it be accompanied by increased performance efficiency.

One of the main factors behind the amazing ecological success of social insects is their ability to flexibly allocate the colony's workforce to all the different tasks it has to address. Insights into the self-organised task allocation methods used for this have given rise to the design of an important class of bio-inspired algorithms for network control, industrial optimisation, and other applications. The most widely used class of models for self-organised task allocation, which also forms the core of these algorithms, are response threshold models. We revisit response threshold models with new experiments using temperature regulation in bumblebee colonies as the model system. We show that standard response threshold models do not fit our experiments and present an alternative behavioural model. This captures a fine-grained, time resolved picture of task engagement, which enables us to investigate task allocation with a different set of statistical methods. Using these we show that our model fits the experiment well and explains its salient aspects. We compare the effectiveness of our model behaviour with that of response threshold models and demonstrate that it can lead to more efficient task management when demands fluctuate. Our results have the potential to provide a basis for the design of more efficient task allocation algorithms for dynamic environments and to elucidate important biological questions, such as the functional role of inter-individual variation.

Division of labor is central to the organization of insect societies. Within-colony comparisons between subfamilies of workers (patrilines or matrilines) revealed genetic effects on division of labor in many social insect species. Although this has been taken as evidence for additive genetic effects on division of labor, it has never been experimentally tested. To determine the relative roles of additive and nonadditive genetic effects (e.g., genetic compatibility, epistasis, and parent-of-origin imprinting effects) on worker behavior, we performed controlled crosses using the Argentine ant Linepithema humile. Three of the measured behaviors (the efficiency to collect pupae, the foraging propensity, and the distance between non-brood-tenders and brood) were affected by the maternal genetic background and the two others (the efficiency to feed larvae and the distance between brood-tenders and brood) by the paternal genetic background. Moreover, there were significant interactions between the maternal and paternal genetic backgrounds for three of the five behaviors. These results are most consistent with parent-of-origin and genetic compatibility effects on division of labor. The finding of nonadditive genetic effects is in strong contrast with the current view and has important consequences for our understanding of division of labor in insect societies.

Empirical evidence suggests that division of labor in insect societies is positively related to group size both within and across taxa. Response threshold models (RTM) have been commonly used to analyze patterns of division of labor. However, these models have been explored empirically and theoretically for only a limited number of tasks, and few studies have examined predictions of the model as colony size and work availability change. We theoretically examine how group size influences division of labor using a fixed response-threshold model. We simultaneously explore how expected by-products of increased colony size, including demand (total work need relative to total work force available) and task number, affect this relationship. Our results indicate that both low demand and high task number positively influence division of labor. We suggest that these changes parallel what is observed within social groups as their size increases, and that, in part, the commonly observed increased division of labor with increasing group size is emergent.

Task allocation is an essential strategy to achieve effective cooperation for swarm robots. Self-organized task allocation strategy is studied and efficient labor division and regulation is realized through local interactions among individual robots based on response threshold model. Local communication mechanism is proposed for the purpose of sharing local sensation information, and the simulation experiments verify that the efficiency of task allocation is improved significantly.

Task allocation is a characteristic feature of social insects. This phenomenon is self-organized by workers in a colony without central instructions. Workers perform the necessary tasks while communicating and determining their colony’s local situations or outside environments. They can also allocate the workload of the task to finish quickly. To explain the self-organized phenomenon, we develop a theoretical model that includes the local interaction mechanism among the workers. We extend the fixed response threshold model by introducing the interaction network among workers. The new model is called the interaction network response threshold model. This model analyzes the effects of the interaction network structure on the workload allocation mechanism using the Gini coefficient. We find that the network structure affects the information diffusion process, and the network features affect workload allocation. Our results indicate that communication among the workers in a colony is an essential system for workload allocation.

Assumptions about economies of effort in performance of tasks in the same production sequence and assumptions about constraints on women's geographic mobility due to nursing and child care are used to derive hypotheses about the allocation of tasks in the sexual division of labor in preindustrial societies. The hypotheses constitute a locational model of the division of labor by sex that makes predictions in the form of entailments: for one sex, doing task X entails doing task Y. The predictions of the locational model are tested using a new procedure for statistical entailment analysis applied to a body of data on fifty tasks in the 185 societies of the standard cross‐cultural sample. Assumptions about constraints of nursing and the effect of supplementary feeding of infants on women's participation in task activities are also tested and found to be supported from the evidence on this sample.

Social insects are known for reproductive and behavioral division of labor, but little attention has been paid to metabolic forms of division of labor. Metabolic division of labor is the partitioning of complementary metabolic tasks between individuals, and it is widespread in social insects. We define two forms of metabolic division of labor, homosynergetic and heterosynergetic, we pinpoint trophallaxis, trophic eggs, and cannibalism as the primary transfers underlying the homosynergetic form and discuss their evolution. We argue that homosynergetic metabolic division of labor underpins fundamental aspects of colony physiology and may be a necessary feature of superorganismal systems, impacting many life history traits. Investigating metabolic division of labor is necessary to understand major evolutionary transition(s) to superorganismality in social insects.

The diffraction limit of light microscopy poses a problem that is frequently faced in structural analyses of social insect brains. With the introduction of expansion microscopy (ExM), a tool became available to overcome this limitation by isotropic physical expansion of preserved specimens. Our analyses focus on synaptic microcircuits (microglomeruli, MG) in the mushroom body (MB) of social insects, high-order brain centers for sensory integration, learning, and memory. MG undergo significant structural reorganizations with age, sensory experience, and during long-term memory formation. However, the changes in subcellular architecture involved in this plasticity have only partially been accessed yet. Using the western honeybee Apis mellifera as an experimental model, we established ExM for the first time in a social insect species and applied it to investigate plasticity in synaptic microcircuits within MG of the MB calyces. Using combinations of antibody staining and neuronal tracing, we demonstrate that this technique enables quantitative and qualitative analyses of structural neuronal plasticity at high resolution in a social insect brain.

How does climate change affect social insects?

The existence of personalities has been explored in various invertebrates, but a comprehensive investigation of personality differences across individuals in a eusocial insect has not yet been conducted. The study of personality differences across individuals within the same behavioral caste may contribute to an understanding of how social insects divide labor within the nest. Here, we define and investigate three dimensions of personality within the worker caste of a model social insect, the honey bee Apis mellifera, as follows: (1) consistent individual behavioral differences over time, (2) consistent individual behavioral differences across contexts, and (3) the presence of correlated suites of behaviors. To test whether honey bee workers exhibit dimensions 1 and 2, we repeatedly assessed responses of groups of same-age bees in cages to stimuli that are relevant to bee life history. To test for dimension 3, we examined behavior within a colony context by using observation hives to record the behaviors of individual bees across their lifetimes. Our results provide some evidence for all three dimensions of personality in honey bee workers. In particular, our data suggest some individuals may be more likely to be highly interactive with other workers (e.g., engaging in food sharing), while other individuals are consistently less interactive. These findings expand upon and contribute to previous models for the organization of worker division of labor in honey bees, suggesting that consistent behavioral differences (personalities) of workers within a behavioral caste have the potential to contribute to subcaste division of labor. Behavioral ecologists have become increasingly interested in animal personalities, individual behavioral differences that are consistent over time and in different contexts, with recent focus on understanding the occurrence of personalities across taxa and their adaptive value. The existence and function of personality differences among individuals in complex societies, such as eusocial insects, remain understudied. Here, we provide the first comprehensive investigation of whether workers of the highly eusocial honey bee show hallmarks of personality. Although these workers demonstrate well-documented behavioral changes as they age, we uncovered some aspects of their behavior, in particular, their tendency to physically interact with other bees, remain somewhat consistent even as they age and change roles within the colony. We suggest that individual-level personality differences have the potential to contribute to colony division of labor by creating variation in individual tendencies to perform different tasks.

The ability to form cooperative societies may explain why humans and social insects have come to dominate the earth. Here we examine the ecological consequences of cooperation by quantifying the fitness of cooperative (large groups) and non-cooperative (small groups) phenotypes in burying beetles (Nicrophorus nepalensis) along an elevational and temperature gradient. We experimentally created large and small groups along the gradient and manipulated interspecific competition with flies by heating carcasses. We show that cooperative groups performed as thermal generalists with similarly high breeding success at all temperatures and elevations, whereas non-cooperative groups performed as thermal specialists with higher breeding success only at intermediate temperatures and elevations. Studying the ecological consequences of cooperation may not only help us to understand why so many species of social insects have conquered the earth, but also to determine how climate change will affect the success of these and other social species, including our own.DOI: http://dx.doi.org/10.7554/eLife.02440.001.