Anna Dornhaus

University of Arizona, Ecology and Evolutionary Biology, Faculty Member

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Papers by Anna Dornhaus

Costs of task allocation with local feedback: Effects of colony size and extra workers in social insects and other multi-agent systems

PLoS computational biology, Dec 1, 2017

Adaptive collective systems are common in biology and beyond. Typically, such systems require a t... more Adaptive collective systems are common in biology and beyond. Typically, such systems require a task allocation algorithm: a mechanism or rule-set by which individuals select particular roles. Here we study the performance of such task allocation mechanisms measured in terms of the time for individuals to allocate to tasks. We ask: (1) Is task allocation fundamentally difficult, and thus costly? (2) Does the performance of task allocation mechanisms depend on the number of individuals? And (3) what other parameters may affect their efficiency? We use techniques from distributed computing theory to develop a model of a social insect colony, where workers have to be allocated to a set of tasks; however, our model is generalizable to other systems. We show, first, that the ability of workers to quickly assess demand for work in tasks they are not currently engaged in crucially affects whether task allocation is quickly achieved or not. This indicates that in social insect tasks such as...

format_quoteEstimated time for honey bee task reallocation during threats is 5-10 rounds if sensing needs; 700 rounds without direct sensing.format_quote

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Peripheral sensory organs vary among ant workers but variation does not predict division of labor

Behavioural Processes, 2018

A. (2019). Peripheral sensory organs vary among ant workers but variation does not predict divisi... more

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Temnothorax rugatulus ant colonies consistently vary in nest structure across time and context

PLOS ONE, 2017

A host of animals build architectural constructions. Such constructions frequently vary with envi... more A host of animals build architectural constructions. Such constructions frequently vary with environmental and individual/colony conditions, and their architecture directly influences behavior and fitness. The nests of ant colonies drive and enable many of their collective behaviors, and as such are part of their 'extended phenotype'. Since ant colonies have been recently shown to differ in behavior and life history strategy, we ask whether colonies differ in another trait: the architecture of the constructions they create. We allowed Temnothorax rugatulus rock ants, who create nests by building walls within narrow rock gaps, to repeatedly build nest walls in a fixed crevice but under two environmental conditions. We find that colonies consistently differ in their architecture across environments and over nest building events. Colony identity explained 12-40% of the variation in nest architecture, while colony properties and environmental conditions explained 5-20%, as indicated by the condition and marginal R 2 values. When their nest boxes were covered, which produced higher humidity and lower airflow, colonies built thicker, longer, and heavier walls. Colonies also built more robust walls when they had more brood, suggesting a protective function of wall thickness. This is, to our knowledge, the first study to explicitly investigate the repeatability of nestbuilding behavior in a controlled environment. Our results suggest that colonies may face tradeoffs, perhaps between factors such as active vs. passive nest defense, and that selection may act on individual construction rules as a mechanisms to mediate colony-level behavior.

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Who Are the “Lazy” Ants? The Function of Inactivity in Social Insects and a Possible Role of Constraint: Inactive Ants Are Corpulent and May Be Young and/or Selfish

Integrative and Comparative Biology, 2017

Social insect colonies are commonly thought of as highly organized and efficient complex systems,... more Social insect colonies are commonly thought of as highly organized and efficient complex systems, yet high levels of worker inactivity are common. Although consistently inactive workers have been documented across many species, very little is known about the potential function or costs associated with this behavior. Here we ask what distinguishes these "lazy" individuals from their nestmates. We obtained a large set of behavioral and morphological data about individuals, and tested for consistency with the following evolutionary hypotheses: that inactivity results from constraint caused by worker (a) immaturity or (b) senescence; that (c) inactive workers are reproducing; that inactive workers perform a cryptic task such as (d) acting as communication hubs or (e) food stores; and that (f) inactive workers represent the "slow-paced" end of inter-worker variation in "pace-of-life." We show that inactive workers walk more slowly, have small spatial fidelity zones near the nest center, are more corpulent, are isolated in colony interaction networks, have the smallest behavioral repertoires, and are more likely to have oocytes than other workers. These results are consistent with the hypotheses that inactive workers are immature and/or storing food for the colony; they suggest that workers are not inactive as a consequence of senescence, and that they are not acting as communication hubs. The hypotheses listed above are not mutually exclusive, and likely form a "syndrome" of behaviors common to inactive social insect workers. Their simultaneous contribution to inactivity may explain the difficulty in finding a simple answer to this deceptively simple question.

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Sampling and tracking a changing environment: persistence and reward in the foraging decisions of bumblebees

Interface focus, Jan 6, 2017

The question of when to collect new information and how to apply that information is central to m... more The question of when to collect new information and how to apply that information is central to much of behaviour. Theory suggests that the value of collecting information, or sampling, depends on environmental persistence and on the relative costs of making wrong decisions. However, empirical tests of how these variables interact are lacking. We tested whether bumblebee foraging decisions are indeed influenced by these two factors. We gave bees repeated choices between a resource providing a steady, mediocre reward and a resource fluctuating between a low reward and a high reward. In this paradigm, we manipulated environmental persistence by changing how long the quality of a fluctuating resource remained stable at one reward level. We manipulated the costs of decision errors by changing the relative values of the available rewards. Bees sampled the fluctuating resource more frequently when it changed quality more frequently, indicating that they measured environmental persistence ...

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Foraging Bumble Bees Weigh the Reliability of Personal and Social Information

Current Biology, 2016

Highlights d Foraging bumble bees use the reliability of both social and personal information d I... more

format_quoteBee preferences for cues were determined by their relative reliability during training, favoring strong social cues consistently in tests.format_quote

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When doing nothing is something. How task allocation strategies compromise between flexibility, efficiency, and inactive agents

Journal of Bioeconomics, 2015

We expect that human organizations and cooperative animal groups should be optimized for collecti... more We expect that human organizations and cooperative animal groups should be optimized for collective performance. This often involves the allocation of different individuals to different tasks. Social insect colonies are a prime example of cooperative animal groups that display sophisticated mechanisms of task allocation. Here we discuss which task allocation strategies may be adapted to which environmental and social conditions. Effective and robust task allocation is a hard problem, and in many biological and engineered complex systems is solved in a decentralized manner: human organizations may benefit from insights into what makes decentralized strategies of group organization effective. In addition, we often find considerable variation among individuals in how much work they appear to contribute, despite the fact that individual selfishness in social insects is low and optimization occurs largely at the group level. We review possible explanations for uneven workloads among workers, including limitations on individual information collection or constraints of task allocation efficiency, such as when there is a mismatch between the frequency of fluctuations in demand for work and the speed at which workers can be reallocated. These processes are likely to apply to any system in which worker agents are allocated to tasks with fluctuating demand, and should therefore be instructive to understanding optimal task allocation and inactive workers in any distributed system. Some of these processes imply that a certain proportion of inactive workers can be an adaptive strategy for collective organization.

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Crematogaster torosa ants form polydomous nests and outstations independently of food distance

Polydomy, in which one ant colony maintains multiple, spatially segregated nests that routinely e... more Polydomy, in which one ant colony maintains multiple, spatially segregated nests that routinely exchange workers and brood, is a common nest structure. However, ants also build a number of intermediate structures, including outstations that contain workers but no brood. Although little is currently known about the function of outstations, they may increase foraging efficiency of colonies by shortening foraging distances. In this study, we investigated whether Crematogaster torosa colonies created outstations or polydomous nests in response to consistently available food at different distances from the queenright nest. At least some workers moved closer to food in all 21 colonies tested. Fourteen colonies became polydomous by moving both workers and brood, while the remainder moved only workers and formed outstations. The proportion of ants moved decreased significantly with increasing distance to food, but there was no effect of distance on whether colonies formed outstations or pol...

Body size, metabolism, and longevity in worker bumble bees (Bombus impatiens)

Longevity is an important life history trait. Body size and metabolism generally affect longevity... more Longevity is an important life history trait. Body size and metabolism generally affect longevity such that larger organisms have lower mass-specific metabolic rates and live longer. However, results from intraspecific studies that analyze the relationships between body size, metabolism, and longevity are inconsistent. In social insects, defining these relationships can be useful in understanding social organization and the evolution of sociality. Bumble bee workers (Bombus impatiens), which show significant variation in body size, were used in this study which investigated the relationships between body size, metabolic rate, and lifespan. In the first experiment, the relationship between body size (measured as thorax width) and lifespan were analyzed. In the second experiment, respirometry was used to track worker metabolic rate from eclosion to death. We found that 1) larger bees lived longer; 2) workers with lower mass-specific metabolic rates at eclosion had significantly longer...

Quitting time: When do honey bee foragers decide to stop foraging on natural resources?

Frontiers in Ecology and Evolution, 2015

Honey bee foragers may use both personal and social information when making decisions about when ... more Honey bee foragers may use both personal and social information when making decisions about when to visit resources. In particular, foragers may stop foraging at resources when their own experience indicates declining resource quality, or when social information, namely the delay to being able to unload nectar to receiver bees, indicates that the colony has little need for the particular resource being collected. Here we test the relative importance of these two factors in a natural setting, where colonies are using many dynamically changing resources. We recorded detailed foraging histories of individually marked bees, and identified when they appeared to abandon any resources (such as flower patches) that they had previously been collecting from consistently. As in previous studies, we recorded duration of trophallaxis events (unloading nectar to receiver bees) as a proxy for resource quality and the delays before returning foragers started trophallaxis as a proxy for social need for the resource. If these proxy measures accurately reflect changes in resource quality and social need, they should predict whether bees continue foraging or not. However, neither factor predicted when individuals stopped foraging on a particular resource, nor did they explain changes in colony-level foraging activity. This may indicate that other, as yet unstudied processes also affect individual decisions to abandon particular resources.

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The trail less traveled: individual decision-making and its effect on group behavior

PloS one, 2012

Social insect colonies are complex systems in which the interactions of many individuals lead to ... more Social insect colonies are complex systems in which the interactions of many individuals lead to colony-level collective behaviors such as foraging. However, the emergent properties of collective behaviors may not necessarily be adaptive. Here, we examine symmetry breaking, an emergent pattern exhibited by some social insects that can lead colonies to focus their foraging effort on only one of several available food patches. Symmetry breaking has been reported to occur in several ant species. However, it is not clear whether it arises as an unavoidable epiphenomenon of pheromone recruitment, or whether it is an adaptive behavior that can be controlled through modification of the individual behavior of workers. In this paper, we used a simulation model to test how symmetry breaking is affected by the degree of non-linearity of recruitment, the specific mechanism used by individuals to choose between patches, patch size, and forager number. The model shows that foraging intensity on d...

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Task-switching costs promote the evolution of division of labor and shifts in individuality

Proceedings of the National Academy of Sciences, 2012

From microbes to humans, the success of many organisms is achieved by dividing tasks among specia... more From microbes to humans, the success of many organisms is achieved by dividing tasks among specialized group members. The evolution of such division of labor strategies is an important aspect of the major transitions in evolution. As such, identifying specific evolutionary pressures that give rise to group-level division of labor has become a topic of major interest among biologists. To overcome the challenges associated with studying this topic in natural systems, we use actively evolving populations of digital organisms, which provide a unique perspective on the de novo evolution of division of labor in an open-ended system. We provide experimental results that address a fundamental question regarding these selective pressures: Does the ability to improve group efficiency through the reduction of task-switching costs promote the evolution of division of labor? Our results demonstrate that as task-switching costs rise, groups increasingly evolve division of labor strategies. We ana...

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Ecology: A Prerequisite for Malaria Elimination and Eradication

PLoS Medicine, 2010

Existing front-line vector control measures, such as insecticide-treated nets and residual sprays... more Existing front-line vector control measures, such as insecticide-treated nets and residual sprays, cannot break the transmission cycle of Plasmodium falciparum in the most intensely endemic parts of Africa and the Pacific N The goal of malaria eradication will require urgent strategic investment into understanding the ecology and evolution of the mosquito vectors that transmit malaria N Priority areas will include understanding aspects of the mosquito life cycle beyond the blood feeding processes which directly mediate malaria transmission N Global commitment to malaria eradication necessitates a corresponding longterm commitment to vector ecology

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Temporal dynamics and network analysis

Methods in Ecology and Evolution, 2012

1. Network analysis is widely used in diverse fields and can be a powerful framework for studying... more 1. Network analysis is widely used in diverse fields and can be a powerful framework for studying the structure of biological systems. Temporal dynamics are a key issue for many ecological and evolutionary questions. These dynamics include both changes in network topology and flow on the network. Network analyses that ignore or do not adequately account for the temporal dynamics can result in inappropriate inferences. 2. We suggest that existing methods are currently under-utilized in many ecological and evolutionary network analyses and that the broader incorporation of these methods will considerably advance the current field. Our goal is to introduce ecologists and evolutionary biologists interested in studying network dynamics to extant ideas and methodological approaches, at a level appropriate for those new to the field. 3. We present an overview of time-ordered networks, which provide a framework for analysing network dynamics that addresses multiple inferential issues and permits novel types of temporally informed network analyses. We review available methods and software, discuss the utility and considerations of different approaches, provide a worked example analysis and highlight new research opportunities in ecology and evolutionary biology.

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