Claire Detrain

Information processing in social insects.

The book provides a first comprehensive overview of both experimental and theoretical research on information processing in insect societies. Its purpose is to make the reader familiar with the methodology and ways of thinking followed by scientists at the leading edge of the field. The book is aimed at postgraduate students and researchers working on social insects and insects that live in groups as well as any reader interested in behavioural ecology, communication and social organization.

Social Integration of Robots into Groups of Cockroaches to Control Self-Organized Choices

Collective behavior based on self-organization has been shown in group-living animals from insects to vertebrates. These findings have stimulated engineers to investigate approaches for the coordination of autonomous multirobot systems based on self-organization. In this experimental study, we show collective decision-making by mixed groups of cockroaches and socially integrated autonomous robots, leading to shared shelter selection. Individuals, natural or artificial, are perceived as equivalent, and the collective decision emerges from nonlinear feedbacks based on local interactions. Even when in the minority, robots can modulate the collective decision-making process and produce a global pattern not observed in their absence. These results demonstrate the possibility of using intelligent autonomous devices to study and control self-organized behavioral patterns in group-living animals.

How do ants assess food volume

By comparing the behaviour of Lasius niger scouts at sucrose droplets of different volumes, we empirically identified the criterion used by each scout to assess the amount of food available as well as the rules governing its decision to lay a recruitment trail. When scouts discovered food volumes exceeding the capacity of their crop (3 or 6 µl), 90% immediately returned to the nest laying a recruitment trail. In contrast, when smaller food droplets (0.3, 0.7 or 1 µl) were offered, several scouts stayed on the foraging area, presumably exploring it for additional food. If unsuccessful, they returned to the nest without laying a trail. The droplet volume determined the percentage of trail-laying ants but had no influence on the intensity of marking when this was initiated. The key criterion that regulated the recruiting behaviour of scouts was their ability to ingest their own desired volume. This volume acted as a threshold triggering the trail-laying response of foragers. Collective regulation of foraging according to food size resulted from the interplay between the distribution of these desired volume thresholds among colony members and the food volume available. We relate some aspects of the foraging ecology of aphid-tending ants to this decision-making process. Copyright 2000 The Association for the Study of Animal Behaviour.

Dynamics of Aggregation and Emergence of Cooperation

Aggregation is one of the most basic social phenomena, and many activities of social insects are linked to it. For instance, the selection of a valuable site and the spatial organization of the population are very often by-products of amplifications based on the local density of nestmates. The patterns of aggregation are very diverse, ranging from the gathering of all animals in a unique site to their splitting between several ones. One might question how these multiple patterns emerge. Do ants actively initiate the formation of such patterns by modulating the emission of an attracting signal such as the trail pheromone? Alternatively, do patterns result from quantitative changes in the duration of interaction between animals once they have reached the gathering site, without any active modulation of the communications? To discuss these questions, we present two empirical studies: the gregarious behavior of cockroaches (Blatella) and self-assembly in the weaver ant (Oecophylla). Through experimental and theoretical studies, we show how a single behavior—the resting time—leads to a collective choice in both species. This behavior is a response to the density of conspecifics and can also be modulated by heterogeneities in the environment. In weaver ants, it allows the colony to focus the formation of chains in a given area among several potential sites. In cockroaches, it allows the gathering of individuals in particular shelters, depending on the proximity between strains. These results are discussed with emphasis on the role of aggregation processes in the emergence of cooperativity and task allocation.

Collective Decision-Making and Foraging Patterns in Ants and Honeybees

Publisher Summary This chapter compares collective decisions in hives and in ant nests by relating the properties of recruiting signals to the foraging strategies displayed by these two insect societies. It describes the main positive and negative feedbacks that help foragers self-regulate their activities according to environmental constraints and opportunities. Even though honeybees and ants share a similar recruitment scenario, the nature of their recruiting signals, as well as the ways information about food patches is conveyed to nestmates, differ greatly. In honeybees, tactile signals rule many aspects of recruitment, whereas chemical communication is the backbone of collective foraging in ants. The chapter emphasizes the intimate link that relates the mode of locomotion of one species to the media chosen to communicate information about food resources. In particular, it demonstrates that the distinct properties of chemical and tactile signals match the environmental constraints faced either by ant individuals on the ground or by honeybees in the air. By referring to other group-living arthropods, the chapter addresses generic issues about information processing, its dissemination among conspecifics and the emergence of cooperative behavior.

Caste polyethism and collective defense in the ant, Pbeidole pallidula: the outcome of quantitative differences in recruitment

SummaryDuring agonistic encounters, both minors and majors of the European ant P. pallidula actively cooperate in defense. Minors seize the legs of the intruder and in some cases induce the recruitment of nestmates whereas majors kill the spreadeagled alien ant. The defensive strategy of P. pallidula is very flexible and adapted to both the number of alient ants and to the intruders superiority in fighting. On the one hand, only a massive invasion of alien minors results in a slow mobilization of resident ants to the combat area, elicited by recruiters performing weak tactile invitations and trail-laying behavior. On the other hand, the presence of 10 majors induces a fast and massive recruitment achieved by intense trail-laying and tactile invitations from the recruiters. Because of their high response threshold to invitations, resident majors are mobilized only during these intense recruitments, their exit being additionally enhanced by their preferential stimulation. The adaptiveness of this defensive strategy is discussed. It is also suggested that simple decision-making rules of recruitment and caste differences in behavioral thresholds could account for the complexity of P. pallidula defensive strategies.

Decision-making in foraging by social insects

How are foraging decisions determined in social insects? Investigations implemented within the framework of the optimal foraging theory bring evolutionary and functional answers. In this respect, decisions of solitary foragers like bumblebees seem to be ruled by an optimization of the energy (and time) invested among different feeding sites. Similarly, in insects which can forage collectively, like ants or honeybees, decisions have been interpreted in terms of energetic reward assigned to single workers without any reference to recruitment. Evidence, however, supports the idea that (time and energy) investments in recruitment of nestmates can also alter foraging decisions of the individual. Additional questions arise as to how an insect processes information about food resources and environmental constraints and decides whether or not to recruit nestmates. In ants, adaptive collective decisions emerge from numerous interactions among individuals which use local information and follow simple decisional algorithms to modulate their recruiting behavior. The environment itself contributes to the emergence of foraging decisions by altering the dynamics of recruitment and trail reinforcement. Several experimental and theoretical findings will lead us to re-consider the level of complexity of information processing and coding needed for the emergence of adaptive foraging patterns.

Scavenging by Pheidole pallidula: a key for understanding decision-making systems in ants

The usual evolutionary and ecological approaches to foraging in social insects often lack an investigation at the level of both individual behavioural complexity and social mechanisms ruling the emergence of adaptive collective strategies. The prey scavenging behaviour of the dimorphic ant Pheidole pallidula was used in this study to investigate (1) how individuals estimate the size of prey, (2) how they modulate their behaviour and communication and (3) how these modulations generate the diversity of collective foraging patterns. For a pile of small prey (fruit flies), the recruitment of foragers was slow because of the weak intensity of individual trail-laying behaviour and the long time spent by ants wandering around the food. In contrast, for a large prey item (a cockroach), strong recruitment was induced by ants that dashed back to the nest laying a more continuous chemical trail. Experiments with small immovable prey showed that the tractive resistance of prey was the key parameter the foragers used to estimate prey size and that it ruled their trail-laying intensity. These data allow us to generate a model about decision making in scavenging. The rules leading to collective choice in a foraging or an agonistic context are discussed. On the basis of these findings, some theoretical stances in sociobiology and some shortcomings in current approaches to cooperation in social insects are considered. ? 1997 The Association for the Study of Animal Behaviour

Hydrocarbons in the ant Lasius niger: from the cuticle to the nest and home range marking.

The cuticular hydrocarbons (CHCs) of the ant Lasius niger are described. We observe a high local colony specificity of the body cuticular profile as predicted for a monogynous and multicolonial species. The CHCs show a low geographical variation among different locations in France. The CHCs on the legs also are colony specific, but their relative quantities are slightly different from those on the main body. For the first time, we demonstrate that the inner walls of the ant nest are coated with the same hydrocarbons as those found on the cuticle but in different proportions. The high amount of inner-nest marking and its lack of colony-specificity may explain why alien ants are not rejected once they succeed in entering the nest. The cuticular hydrocarbons also are deposited in front of the nest entrance and on the foraging arena, with a progressive increase in n-alkanes relative amounts. Chemical marks laid over the substrate are colony specific only when we consider methyl-branched alkanes. Our data confirm that these “footprint hydrocarbons” are probably deposited passively by the contact of ant tarsae with the substrate. These results suggest that the CHCs chemical profiles used by ants in colony recognition are much more complex than a single template: ants have to learn and memorize odors that vary depending on their context of perception.

Regulation of ants' foraging to resource productivity

We investigate the behavioural rule used by ant societies to adjust their foraging response to the honeydew productivity of aphids. When a scout finds a single food source, the decision to lay a recruitment trail is an all–or–none response based on the opportunity for this scout to ingest a desired volume acting as a threshold. Here, we demonstrate, through experimental and theoretical approaches, the generic value of this recruitment rule that remains valid when ants have to forage on multiple small sugar feeders to reach their desired volume. Moreover, our experiments show that when ants decide to recruit nest–mates they lay trail marks of equal intensity, whatever the number of food sources visited. A model based on the ‘desired volume’ rule of recruitment as well as on experimentally validated parameter values was built to investigate how ant societies adjust their foraging response to the honeydew productivity profile of aphids. Simulations predict that, with such recruiting rules, the percentage of recruiting ants is directly related to the total production of honeydew. Moreover, an optimal number of foragers exists that maximizes the strength of recruitment, this number being linearly related to the total production of honeydew by the aphid colony. The ‘desired volume’ recruitment rule that should be generic for all ant species is enough to explain how ants optimize trail recruitment and select aphid colonies or other liquid food resources according to their productivity profile.