Abstract:
Individuals in many types of animal groups show both reproductive and task-related division of labour. In some social insect species, such division of labour may be related to the spatial organization of workers inside the nest. We examined colonies of bumblebees and found that (1) 11-13% of workers maintained small spatial fidelity zones inside the nest, and all workers tended to remain at a specific distance from the colony centre independent of their age; (2) smaller individuals maintained smaller spatial zones and tended to be closer to the centre; and (3) individuals that were more likely to perform the in-nest task of larval feeding tended to remain in the centre of the nest, whereas foragers were more often found on the periphery of the nest when not foraging. Individuals that performed other tasks did not maintain a predictable distance to the centre, and there was no evidence that spatial preferences changed over time. Instead, spatial patterns may result from inherent differences between individuals in terms of activity level, and may be a self-organized sorting mechanism that influences division of labour among workers.
Abstract:
Social insect foragers often transmit information about food sources to nest mates. In bumble bees (Bombus terrestris), for example, successful foragers use excited motor displays and a pheromone as communication signals. In addition, bees could make use of an indirect pathway of information flow, via the honey stores. We show here that, indeed, bees in the nest continuously monitor honeypots and sample their contents, thus obtaining information on supply and demand of nectar. When there is an influx of nectar into the nest, the colony deploys more workers for foraging. The number of new foragers depends on sugar concentration. Foragers returning with high-quality sugar solution display more "excited runs" on the nest structure. The recruits' response, however, does not depend on modulated behavior by foragers: more workers start to forage with high quality of incoming nectar, even when this nectar is brought by a pipette. Moreover, we show that the readiness of bees to respond to recruitment signals or incoming nectar also depends on colony demand. When colony nectar stores are full, the response of bees to equal amounts of nectar influx is smaller than when stores are empty. When colony nectar stores are depleted, foragers spend more time running excitedly and less time probing pots in the nest and run with higher average speed, possibly to disperse the alerting pheromone more efficiently. However, more bees respond to nectar influx to empty stores, whether or not this is accompanied by forager signals. Thus, honeypots serve to store information as well as food. © The Author 2005. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.
Abstract:
In the absence of predators, pollinators can often maximize their foraging success by visiting the most rewarding flowers. However, if predators use those highly rewarding flowers to locate their prey, pollinators may benefit from changing their foraging preferences to accept less rewarding flowers. Previous studies have shown that some predators, such as crab spiders, indeed hunt preferentially on the most pollinator-attractive flowers. In order to determine whether predation risk can alter pollinator preferences, we conducted laboratory experiments on the foraging behavior of bumble bees (Bombus impatiens) when predation risk was associated with a particular reward level (measured here as sugar concentration). Bees foraged in arenas containing a choice of a high-reward and a low-reward artificial flower. On a bee's first foraging trip, it was either lightly squeezed with forceps, to simulate a crab spider attack, or was allowed to forage safely. The foragers' subsequent visits were recorded for between 1 and 4 h without any further simulated attacks. Compared to bees that foraged safely, bees that experienced a simulated attack on a low-reward artificial flower had reduced foraging activity. However, bees attacked on a high-reward artificial flower were more likely to visit low-reward artificial flowers on subsequent foraging trips. Forager body size, which is thought to affect vulnerability to capture by predators, did not have an effect on response to an attack. Predation risk can thus alter pollinator foraging behavior in ways that influence the number and reward level of flowers that are visited. © 2011 Springer-Verlag.
PMID: 19018663;Abstract:
The ecological success of social insects is often attributed to an increase in efficiency achieved through division of labor between workers in a colony. Much research has therefore focused on the mechanism by which a division of labor is implemented, i.e., on how tasks are allocated to workers. However, the important assumption that specialists are indeed more efficient at their work than generalist individuals - the "Jack-of-all-trades is master of none" hypothesis - has rarely been tested. Here, I quantify worker efficiency, measured as work completed per time, in four different tasks in the ant Temnothorax albipennis: honey and protein foraging, collection of nest-building material, and brood transports in a colony emigration. I show that individual efficiency is not predicted by how specialized workers were on the respective task. Worker efficiency is also not consistently predicted by that worker's overall activity or delay to begin the task. Even when only the worker's rank relative to nestmates in the same colony was used, specialization did not predict efficiency in three out of the four tasks, and more specialized workers actually performed worse than others in the fourth task (collection of sand grains). I also show that the above relationships, as well as median individual efficiency, do not change with colony size. My results demonstrate that in an ant species without morphologically differentiated worker castes, workers may nevertheless differ in their ability to perform different tasks. Surprisingly, this variation is not utilized by the colony - worker allocation to tasks is unrelated to their ability to perform them. What, then, are the adaptive benefits of behavioral specialization, and why do workers choose tasks without regard for whether they can perform them well? We are still far from an understanding of the adaptive benefits of division of labor in social insects. © 2008 Anna Dornhaus.
