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We develop an abstract model to explore specialization and generalization in task performance by individuals within biological populations. Individuals follow simple rules of increasing and decreasing task propensities that could, for... more
We develop an abstract model to explore specialization and generalization in task performance by individuals within biological populations. Individuals follow simple rules of increasing and decreasing task propensities that could, for example, be based on learning and forgetting. The model does not explore efficiency per se, but makes the prediction that where behavioural specialization occurs in nature, organisms, are likely to be reaping sufficient benefits from improved handling efficiency to offset the costs of increased search time. A second prediction is that among specialists, there will be a trade-off between stability and responsiveness. The model reveals potential similarities between a wide range of complex biological systems.
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Preliminary optimization models for social insects suggested that efficiency should be promoted by having one specialist worker caste per essential task. However, such extreme specialization would greatly limit the ability of colonies to... more
Preliminary optimization models for social insects suggested that efficiency should be promoted by having one specialist worker caste per essential task. However, such extreme specialization would greatly limit the ability of colonies to respond to changing situations and could lead to long periods of recession in a colony's economy. Recent studies show that by using simple behavioural rules social insects can reallocate tasks and form cooperative groups and even assembly lines that have far greater flexibility than would be the case with extremely specialized physical castes.
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We show that ants can reconnoitre their surroundings and in effect plan for the future. Temnothorax albipennis colonies use a sophisticated strategy to select a new nest when the need arises. Initially, we presented colonies with a new... more
We show that ants can reconnoitre their surroundings and in effect plan for the future. Temnothorax albipennis colonies use a sophisticated strategy to select a new nest when the need arises. Initially, we presented colonies with a new nest of lower quality than their current one that they could explore for one week without a need to emigrate. We then introduced a second identical low quality new nest and destroyed their old nest so that they had to emigrate. Colonies showed a highly significant preference for the (low quality) novel new nest over the identical but familiar one. In otherwise identical experiments, colonies showed no such discrimination when the choice was between a familiar and an unfamiliar high-quality nest. When, however, either all possible pheromone marks were removed, or landmarks were re-orientated, just before the emigration, the ants chose between identical low-quality new nests at random. These results demonstrate for the first time that ants are capable o...
Research Interests: Computer Science, Pheromones, Ecology, Medicine, Learning, and 15 moreMemory, Biological Sciences, Ants, Cues, Orientation, Animals, Research article, Spatial Behavior, Nesting Behavior, Exploratory Behavior, Preference, Private Information, Choice Behavior, Collective Decision Making, and Medical and Health Sciences
The sharing and collective processing of information by certain insect societies is one of the reasons that they warrant the superlative epithet 'super–organisms‘ (Franks 1989,Am. Sci.77 , 138–145). We describe a detailed experimental... more
The sharing and collective processing of information by certain insect societies is one of the reasons that they warrant the superlative epithet 'super–organisms‘ (Franks 1989,Am. Sci.77 , 138–145). We describe a detailed experimental and mathematical analysis of information exchange and decision–making in, arguably, the most difficult collective choices that social insects face: namely, house hunting by complete societies. The key issue is how can a complete colony select the single best nest–site among several alternatives? Individual scouts respond to the diverse information they have personally obtained about the quality of a potential nest–site by producing a recruitment signal. The colony then deliberates over (i.e. integrates) different incoming recruitment signals associated with different potential nest–sites to achieve a well–informed collective decision. We compare this process in honeybees and in the antLeptothorax albipennis. Notwithstanding many differences – for e...
Research Interests: Sociology, Decision Making, Collective Intelligence, Medicine, Animal communication, and 13 moreKnowledge, Biological Sciences, Information Flow, Social behavior, Ants, Bees, Animals, Social Insect, Nesting Behavior, Social Behavior, Species Specificity, Uncategorized, and Medical and Health Sciences
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There are claims in the literature that certain insects can count. We question the generality of these claims and suggest that summation rather than counting ( sensu stricto ) is a more likely explanation. We show that Temnothorax... more
There are claims in the literature that certain insects can count. We question the generality of these claims and suggest that summation rather than counting ( sensu stricto ) is a more likely explanation. We show that Temnothorax albipennis ant colonies can discriminate between potential nest sites with different numbers of entrances. However, our experiments suggest that the ants use ambient light levels within the nest cavity to assess the abundance of nest entrances rather than counting per se . Intriguingly, Weber's Law cannot explain the ants' inaccuracy. The ants also use a second metric, independent of light, to assess and discriminate against wide entrances. Thus, these ants use at least two metrics to evaluate one nest trait: the configuration of the portals to their potential homes.
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A simple model of the emergence of pillars in termite nests by Deneubourg is modified to include several additional features that break the homogeneity of the original model: (i) a convection air stream that drives molecules of pheromone... more
A simple model of the emergence of pillars in termite nests by Deneubourg is modified to include several additional features that break the homogeneity of the original model: (i) a convection air stream that drives molecules of pheromone along a given direction; (ii) a net flux of individuals in a specific direction; (iii) a well–defined self–maintained pheromone trail; and (iv) a pheromonal template representing the effect of the presence of a queen that continuously emits pheromone. It is shown that, under certain conditions, pillars are transformed into walls or galleries or chambers, and that this transformation may not be driven by any change in the termites' behaviour. Because the same type of response at the individual level can generate different patterns under different conditions, and because previous construction modifies current building conditions, we hypothesize that nest complexity can result from the unfolding of a morphogenetic process that progressively generat...
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. Colonies ofthis species have up to 200 000 foragers and transport more than 3000 prey items per hour over raidingcolumns that exceed 100 m. It is an ideal species in which to test the predictions of our model becauseit forms pheromone... more
. Colonies ofthis species have up to 200 000 foragers and transport more than 3000 prey items per hour over raidingcolumns that exceed 100 m. It is an ideal species in which to test the predictions of our model becauseit forms pheromone trails that are densely populated with very swift ants. The model explores the influ-ences of turning rates and local perception on traffic flow. The behaviour of real army ants is such thatthey occupy the specific region of parameter space in which lanes form and traffic flow is maximized.
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Collective decisions in animal groups emerge from the actions of individuals who are unlikely to have global information. Comparative assessment of options can be valuable in decision-making. Ant colonies are excellent collective... more
Collective decisions in animal groups emerge from the actions of individuals who are unlikely to have global information. Comparative assessment of options can be valuable in decision-making. Ant colonies are excellent collective decision-makers, for example when selecting a new nest-site. Here, we test the dependency of this cooperative process on comparisons conducted by individual ants. We presented ant colonies with a choice between new nests: one good and one poor. Using individually radio-tagged ants and an automated system of doors, we manipulated individual-level access to information: ants visiting the good nest were barred from visiting the poor one and vice versa. Thus, no ant could individually compare the available options. Despite this, colonies still emigrated quickly and accurately when comparisons were prevented. Individual-level rules facilitated this behavioural robustness: ants allowed to experience only the poor nest subsequently searched more. Intriguingly, som...
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Many individual decisions are informed by direct comparison of the alternatives. In collective decisions, however, only certain group members may have the opportunity to compare options. Emigrating ant colonies ( Temnothorax albipennis )... more
Many individual decisions are informed by direct comparison of the alternatives. In collective decisions, however, only certain group members may have the opportunity to compare options. Emigrating ant colonies ( Temnothorax albipennis ) show sophisticated nest-site choice, selecting superior sites even when they are nine times further away than the alternative. How do they do this? We used radio-frequency identification-tagged ants to monitor individual behaviour. Here we show for the first time that switching between nests during the decision process can influence nest choice without requiring direct comparison of nests. Ants finding the poor nest were likely to switch and find the good nest, whereas ants finding the good nest were more likely to stay committed to that nest. When ants switched quickly between the two nests, colonies chose the good nest. Switching by ants that had the opportunity to compare nests had little effect on nest choice. We suggest a new mechanism of colle...
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A simple model of the emergence of pillars in termite nests by Deneubourg is modified to include several additional features that break the homogeneity of the original model: (i) a convection air stream that drives molecules of pheromone... more
A simple model of the emergence of pillars in termite nests by Deneubourg is modified to include several additional features that break the homogeneity of the original model: (i) a convection air stream that drives molecules of pheromone along a given direction; (ii) a net flux of individuals in a specific direction; (iii) a well–defined self–maintained pheromone trail; and (iv) a pheromonal template representing the effect of the presence of a queen that continuously emits pheromone. It is shown that, under certain conditions, pillars are transformed into walls or galleries or chambers, and that this transformation may not be driven by any change in the termites' behaviour. Because the same type of response at the individual level can generate different patterns under different conditions, and because previous construction modifies current building conditions, we hypothesize that nest complexity can result from the unfolding of a morphogenetic process that progressively generates a diversity of history–dependent structures.
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Colonies of the ant Leptothorax albipennis naturally inhabit flat rock crevices. Scouts can determine, before initiating an emi-gration, if a nest has sufficient area to house their colony. They do so with a rule of thumb: the Buffon’s... more
Colonies of the ant Leptothorax albipennis naturally inhabit flat rock crevices. Scouts can determine, before initiating an emi-gration, if a nest has sufficient area to house their colony. They do so with a rule of thumb: the Buffon’s needle algorithm. Based on a derivation from the classical statistical geometry of Comte George de Buffon in the 18th century, it can be shown that it is possible to estimate the area of a plane from the frequency of intersections between two sets of randomly scattered lines of known lengths. Our earlier work has shown that individual ants use this Buffon’s needle algorithm by laying individual-specific trail pheromones on a first visit to a potential nest site and by assessing the frequency at which they intersect that path on a second visit. Nest area would be inversely proportional to the intersection frequency. The simplest procedure would be for individual ants to keep their first-visit path-length constant regardless of the size of the nest they...
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A high-quality home can be a major factor determining fitness. However, when house hunting becomes necessary, animals might often face a speed-versus-accuracy trade-off and therefore be unable to survey their environment extensively for... more
A high-quality home can be a major factor determining fitness. However, when house hunting becomes necessary, animals might often face a speed-versus-accuracy trade-off and therefore be unable to survey their environment extensively for the optimum site. We found that the ant Leptothorax albipennis was able to correct errors made in such a hurried decision by continuing to survey even after a colony had settled in a nest site. Colonies moved from intact undisturbed nests to another nest site whenever the new nest site ...
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Theory suggests that evolutionary branching via disruptive selection may be a relatively common and powerful force driving phenotypic divergence. Here, we extend this theory to social insects, which have novel social axes of phenotypic... more
Theory suggests that evolutionary branching via disruptive selection may be a relatively common and powerful force driving phenotypic divergence. Here, we extend this theory to social insects, which have novel social axes of phenotypic diversification. Our model, built around turtle ant (Cephalotes) biology, is used to explore whether disruptive selection can drive the evolutionary branching of divergent colony phenotypes that include a novel soldier caste. Soldier evolution is a recurrent theme in social insect diversification that is exemplified in the turtle ants. We show that phenotypic mutants can gain competitive advantages that induce disruptive selection and subsequent branching. A soldier caste does not generally appear before branching, but can evolve from subsequent competition. The soldier caste then evolves in association with specialized resource preferences that maximize defensive performance. Overall, our model indicates that resource specialization may occur in the ...
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Prediction for social systems is a major challenge. Universality at the social level has inspired a unified theory for urban living but individual variation makes predicting relationships within societies difficult. Here, we show that in... more
Prediction for social systems is a major challenge. Universality at the social level has inspired a unified theory for urban living but individual variation makes predicting relationships within societies difficult. Here, we show that in ant societies individual average speed is higher when event duration is longer. Expressed as a single scaling function, this relationship is universal because for any event duration an ant, on average, moves at the corresponding average speed except for a short acceleration and deceleration at the beginning and end. This establishes cause and effect within a social system and may inform engineering and control of artificial ones.
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Research Interests: Conservation, Gene Flow, Biology, Medicine, Panama, and 15 moreMolecular Ecology, Biological Sciences, Ants, Mitochondrial DNA, Microsatellites, Female, Animals, Male, Deforestation, Habitat fragmentation, Dispersal, Ecosystem, Linkage Disequilibrium, Geographic Information Systems, and Molecular Sequence Data
Behavioural lateralization in invertebrates is an important field of study because it may provide insights into the early origins of lateralization seen in a diversity of organisms. Here, we present evidence for a leftward turning bias in... more
Behavioural lateralization in invertebrates is an important field of study because it may provide insights into the early origins of lateralization seen in a diversity of organisms. Here, we present evidence for a leftward turning bias in Temnothorax albipennis ants exploring nest cavities and in branching mazes, where the bias is initially obscured by thigmotaxis (wall-following) behaviour. Forward travel with a consistent turning bias in either direction is an effective nest exploration method, and a simple decision-making heuristic to employ when faced with multiple directional choices. Replication of the same bias at the colony level would also reduce individual predation risk through aggregation effects, and may lead to a faster attainment of a quorum threshold for nest migration. We suggest the turning bias may be the result of an evolutionary interplay between vision, exploration and migration factors, promoted by the ants' eusociality.
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SUMMARY Tandem runs are a form of recruitment in ants. During a tandem run, a single leader teaches one follower the route to important resources such as sources of food or better nest sites. In the present study, we investigate what... more
SUMMARY Tandem runs are a form of recruitment in ants. During a tandem run, a single leader teaches one follower the route to important resources such as sources of food or better nest sites. In the present study, we investigate what tandem leaders and followers do, in the context of nest emigration, if their partner goes missing. Our experiments involved removing either leaders or followers at set points during tandem runs. Former leaders first stand still and wait for their missing follower but then most often proceed alone to the new nest site. By contrast, former followers often first engage in a Brownian search, for almost exactly the time that their former leader should have waited for them, and then former followers switch to a superdiffusive search. In this way, former followers first search their immediate neighbourhood for their lost leader before becoming ever more wide ranging so that in the absence of their former leader they can often find the new nest, re-encounter th...
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SUMMARY Self-organisation underlies many collective processes in large animal groups, where coordinated patterns and activities emerge at the group level from local interactions among its members. Although the importance of key... more
SUMMARY Self-organisation underlies many collective processes in large animal groups, where coordinated patterns and activities emerge at the group level from local interactions among its members. Although the importance of key individuals acting as effective leaders has recently been recognised in certain collective processes, it is widely believed that self-organised decisions are evenly shared among all or a subset of individuals acting as decision-makers, unless there are significant conflicts of interests among group members. Here, we show that certain individuals are disproportionately influential in self-organised decisions in a system where all individuals share the same interests: nest site selection by the ant Temnothorax albipennis. Workers that visited a good available nest site prior to emigration (the familiar nest) memorised its location, and later used this memory to navigate efficiently and find that nest faster than through random exploration. Additionally, these w...
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Research Interests: Animal Behavior, Pheromones, Biological Sciences, Social behavior, Ants, and 12 moreComputer Simulation, Animals, Traffic Flow, Mathematical Model, Self Organization, Social Insect, Collective Choice, Social Behavior, Individual Based Model, Generic model, parameter space, and Medical and Health Sciences
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Individual specialization underpins the division of labour within ant societies, but only in a small minority do morphological specialists, or physical castes, exist in the workforce. The genetic conditions that allow such castes to... more
Individual specialization underpins the division of labour within ant societies, but only in a small minority do morphological specialists, or physical castes, exist in the workforce. The genetic conditions that allow such castes to evolve are well understood, but the ecological pressures that select for them are not. We provide compelling evidence that the task of transporting novel prey selected for an exaggerated transport caste, or ‘submajor’, in the army ant Eciton burchellii . This species is the only Eciton that preys upon large arthropods as well as ants, the ancestral prey type, and by comparing load-transport among Eciton species and within E. burchellii , we show that this mixed diet significantly constrains transport efficiency. Crucially, however, we also show that E. burchellii submajors are highly specialized on transporting non-ant prey, and we demonstrate experientially that it is specifically this prey type that constrains prey-transport efficiency. Our study also ...
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... LUCAS W. PARTRIDGE1*, NICK F. BRITTON2 AND NIGEL R. FRANKS3 ... Colonies are monogynous (singly queened) and re-produce by fission to form two daughter colonies: one is inherited by a new daughter queen and the other is retained by... more
... LUCAS W. PARTRIDGE1*, NICK F. BRITTON2 AND NIGEL R. FRANKS3 ... Colonies are monogynous (singly queened) and re-produce by fission to form two daughter colonies: one is inherited by a new daughter queen and the other is retained by the old queen or inherited by ...
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Many animals nest or roost colonially. At the start of a potential foraging period, they may set out independently or await information from returning foragers. When should such individuals act independently and when should they wait for... more
Many animals nest or roost colonially. At the start of a potential foraging period, they may set out independently or await information from returning foragers. When should such individuals act independently and when should they wait for information? In a social insect colony, for example, information transfer may greatly increase a recruit's probability of finding food, and it is commonly assumed that this will always increase the colony's net energy gain. We test this assumption with a mathematical model. Energy gain by a colony is a function both of the probability of finding food sources and of the duration of their availability. A key factor is the ratio of pro-active foragers to re-active foragers. When leaving the nest, pro-active foragers search for food independently, whereas re-active foragers rely on information from successful foragers to find food. Under certain conditions, the optimum strategy is totally independent (pro-active) foraging because potentially val...
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Self-organization can account for certain patterns of behaviour in social insects, and simple rules of interaction between individuals can lead to emergent patterns in the colony. We demonstrate algorithms that enable an ant colony to... more
Self-organization can account for certain patterns of behaviour in social insects, and simple rules of interaction between individuals can lead to emergent patterns in the colony. We demonstrate algorithms that enable an ant colony to solve complex path choice problems. It is possible for the colony to select one foraging site out of many without any global knowledge or comparative judgements by individual ants. We show how this can lead to a greatly enhanced probability of each forage returning to the nest with food.
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The prospect of generic principles of biological organization being uncovered through the increasingly broad use of the concepts of ‘self–assembly’ and ‘self–organization’ in biology will only be fulfilled if students of different levels... more
The prospect of generic principles of biological organization being uncovered through the increasingly broad use of the concepts of ‘self–assembly’ and ‘self–organization’ in biology will only be fulfilled if students of different levels of biological organization use the same terms with the same meanings. We consider the different ways the terms ‘self–assembly’ and ‘self–organization’ have been used, from studies of molecules to studies of animal societies. By linking ‘self–assembly’ and ‘self–organization’ with division of labour, we not only put forward a distinction between the underlying concepts but we are also able to relate them to the question: Why has a certain structure been favoured by natural selection? Using the particularly instructive case of social resilience in ant colonies, we demonstrate that the principle of self–organizing self–assembly may apply to higher levels of biological organization than previously considered. We predict that at the level of interactions...