Ventilation response thresholds do not change with age or self-reinforcement in workers of the bumble bee Bombus impatiens

Abstract

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 selfreinforcement (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 (Weidenmüller, 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.

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

“…Many of these organizational strategies are wellstudied, in part because insect colonies are tractable model systems, since colonies can be kept in the laboratory, individuals can be marked and even automatically tracked on video (Charbonneau and Dornhaus In prep. ;Poff et al 2012;Mersch et al 2013;, and their social and environmental conditions can be manipulated Duong and Dornhaus 2012;Cook and Breed 2013;Jandt and Dornhaus 2014) or compared across different species (Bourke and Franks 1995;Murakami et al 2000;Fjerdingstad and Crozier 2006;Powell and Franks 2006;Wenseleers and Ratnieks 2006).…”

Interindividual variability in social insects – proximate causes and ultimate consequences

“…In thermoregulating Bombus terrestris , repeated performance of the task of fanning leads to a decrease in the corresponding temperature response thresholds (Weidenmüller, ); a ‘reinforcement’ process that seems to be reversible when the task is not performed for a while (Westhus et al , ). Duong & Dornhaus () found no effect of experience on the fanning response thresholds of the closely related bumblebee species Bombus impatiens ; and Camponotus rufipes ants that have gathered experience in evacuating brood from rising temperatures do not respond at lower temperatures with increasing experience (Weidenmüller et al , ).…”

A computational model of task allocation in social insects: ecology and interactions alone can drive specialisation

“…Individual task preferences can be determined by an inherent response trait (Duong and Dornhaus 2012;Jeanson et al 2005;Gordon 2010). The response trait of an individual i is modelled as a continuous value 0 ≤ x i ≤ 1 , which represents the fraction of effort that individual i invests into task T. Conversely, worker i will invest 1 − x i effort into task F. This approach is closely related to the familiar concept of a response probability: under the assumption that there is a response probability p i for worker i to engage with task T when faced with the choice between F and T, the expected amount of effort invested in T is directly proportional to p i (and thus to x i ).…”