The Social Insect Lab

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Uni of AZ

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Current research in the Social Insect Lab

Research in our lab focuses on three main areas, all using social insects as model systems. First, the emergence of complexity and increased efficiency through collective behavior; second, effects of scaling in complex systems; and third, the role of learning and individual variability for collective success. We use a combination of empirical lab studies and theoretical approaches, such as individual-based simulations, supplemented by some fieldwork where necessary. Our main model systems are the bumble bee Bombus impatiens and various species of ants, recently primarily the ‘rock ants’ Temnothorax rugatulus/albipennis and Camponotus festinatus.

Spatial Distribution of Bumble Bees (Bombus impatiens) Inside the Nest: Evidence for Spatial Fidelity Zones among Workers   Jenny Jandt, Anna Dornhaus	Through self-organization, social insects achieve robust and flexible division of labor between workers. This may be correlated with individual spatial fidelity zones, meaning that individuals distribute themselves inside the nest non-randomly. However, there is little empirical data on the spatial distribution of social insect workers inside the nest. Spatial fidelity zones may determine which task a worker performs, and thus influence the division of labor within the colony. For example, individuals located near the center of the nest may be more likely to take care of brood, whereas individuals on the edge of the nest may be more likely to engage in foraging behavior. Alternatively, spatial fidelity zones may be a consequence, rather than a cause, of division of labor, whereby an individual that participates in a task tends to remain in particular areas of the nest as a result. In this study, we looked at the spatial distribution of individual bumble bee workers (Bombus impatiens) inside the nest over the course of the colony cycle. We compared distributions of workers to those of the queen and other nest characteristics. We show that some bumble bee workers maintain positions close to the center of the nest and the queen, and others remain at the fringes of the nest. Furthermore, we found that these characteristics of workers predicted worker behavior in other ways. We also investigate the relationship of spatial fidelity zones to task allocation, dominance hierarchy, and age. This is the first empirical study to investigate whether social bees maintain spatial fidelity zones. We are also looking at the influence of dominance by looking at worker reproduction.
Individual search... rules!   Amelie Schmolke, Anna Dornhaus	While recruitment to known food sources by ants has been studied extensively, it is not as clear how individuals discover new food sources. Moreover, the search strategies used by ants lacking mass recruitment are not well known. We approach these questions by characterizing the foraging behavior of Temnothorax rugatulus ants. Their small colony size allows the observation of the foraging activity of the entire colony as well as each individual. In this study, T. rugatulus colonies were attached to uniform foraging arenas that did not provide any food sources. We compared the search areas between foragers of the same colony and within individuals on different days. We found that the search path of T. rugatulus foragers can be described as a random walk, i.e. the ants show no significant bias in direction choice at any point of their (unsuccessful) search. This is also reflected in the area the foragers cover during their search: foragers visit wide areas, and their space use is not influenced by the areas visited by their nest mates. Hence, T. rugatulus foragers act independently on their food search and do not divide up the nest surroundings into individual search areas. While foragers act individually outside the nest, the nutritional status of the colony determines the number of ants leaving the nest to forage. The longer time a colony remains without food intake, the more individuals will go out to search for food. Is this strategy of food search optimal for small colonies? And does it depend on the distribution of food sources the ants tend to exploit? We introduce an individual-based model of ant foraging that allows the comparison of different strategies with respect to colony-level foraging success.
Task allocation in the ant Temnothorax albipennis: specialists or elites?   Anna Dornhaus, Jo-Anne Holley, Nigel Franks	Social insects are highly successful ecologically, and the classic explanation is that by dividing labor among specialists, colonies achieve high collective efficiency. However, empirical data on the degree to which different species exhibit division of labor and specialization is lacking. In a large study, involving individually marking more than 1200 ants of the species Temnothorax albipennis, we quantify the degree to which workers are specialized on different tasks. We show that there is only very weak, but nevertheless statistically significant, specialization. We did not find any effects of colony size, that is small and large colonies exhibited the same degree of division of labor. We are planning to extend this analysis to other species. Furthermore, the fundamental assumption here, that specialization enables individuals to become more efficient, remains largely untested. Preliminary results for this ant show that individual efficiency is not necessarily correlated with how much a worker engages in a task. We are now studying how efficiency and specialization are related for multiple tasks, including foraging, nest emigrations, nest building, and nest cleaning (removing dead workers) in ants. Testing multiple tasks on the same individuals is crucial to differentiate between true specialists and ‘elites’ who work above average at all tasks.
Task allocation mechanisms and colony-level performance   Anna Dornhaus, Franziska Kluegl	In spite of much research on potential mechanisms for allocating tasks to workers, very little is known on how different such mechanisms impact colony-level efficiency. We are using a computational model to predict which mechanisms, and what degree of specialization, would optimize colony function under different conditions. This model will generate predictions as to which species should be expected to display a high degree of individual specialization, and also whether colony size or environmental variability is more likely to influence this. Results from this project will also be useful for engineers, for choosing the appropriate task allocation mechanism in artificial complex systems, such as distributed computing networks.
Communication, learning, and polydomy in weaver ants, Oecophylla smaragdina   Tuan Cao, Anna Dornhaus
Task allocation and sensory thresholds in bumble bees   Margaret Couvillon, Anna Dornhaus, Wulfila Gronenberg	Bumble bee (Bombus spp.) workers exhibit size polymorphism, and their division of labor appears to be based not on age but on body size (Goulson et al., 2002). However, like the honey bee’s temporal polyethism, the morphological differences do not account for all of the variability in task allocation. Mostly, it is assumed that the larger bumble bees are better suited for foraging because they can fly faster, carry more weight (Goulson et al., 2002), learn quicker and remember longer (Worden et al., 2005). The latter is probably based on their larger brain size (Mares et al., 2005) that might improve their foraging ability. However, sensory thresholds have never been tested in bumble bees; it is unknown if these bees differ in such thresholds (e.g. for sugar) and if these correlate with body size or if task allocation is instead independent of sensory thresholds. Such information would help us understand what evolutionary constraints are behind division of labor and whether the sensory threshold hypothesis only applies to honey bees or may provide a possible mechanism for division of labor in social insects in general. Here I propose to test behaviorally and physiologically the sensory thresholds of bumble bees and honey bees in order to understand the universal mechanisms for division of labor.
Ant cognition: variance between individuals and colonies in learning performance   Anna Dornhaus