Elsevier

Animal Behaviour

Volume 74, Issue 3, September 2007, Pages 559-566
Animal Behaviour

Individual choice of building material for nest construction by worker ants and the collective outcome for their colony

https://doi.org/10.1016/j.anbehav.2006.12.019Get rights and content

Animal groups can gather disproportionately more information and often outperform solitary individuals in ecologically important activities. Collective decisions, however, may involve costly mechanisms for reaching a consensus. Nest building is a prime example. In a previous study on foraging for building materials by the ant Temnothorax albipennis, we showed that colonies prefer larger building blocks (bigger sand grains) at all distances but always collect some smaller building blocks too. Walls made of mixtures of big and small grains are stronger and more compact. Here we study colonies with marked individuals to look at the foraging decisions of individuals that underlie the collective outcome for the colony. We found that at short distances some foragers preferred big grains and others small grains. However, at longer distances the proportion of foragers preferring big grains increased, whereas no foragers preferred small grains at the greatest distance. We found no evidence of an effect of individual morphology or foraging experience on preference. At all three distances foragers assessed grains before making a choice and were more likely to choose a big grain as a consequence. This likelihood increased with increasing distance. However, even at the greatest distance ants included small grains in the final wall after their initial preference for big grains. Therefore, we conclude that individual decisions to retrieve small grains are not simply errors. Instead, the construction itself may provide cues for the organization of the foraging activity of individuals into the collective building of an approximately optimal mixed wall by the colony.

Section snippets

Methods

The experiments involved 29 T. albipennis colonies. In five of them, workers were individually marked. These were the treatment colonies. The remaining 24 colonies served as controls. The control and treatment colonies were collected from Dorset, England in June and October 2005, respectively, and each had a single queen.

We marked the workers from the treatment colonies with individual paint marks as described in Sendova-Franks & Franks (1993). The median number of workers was 130 with a

Results

In accordance with earlier colony-level analysis (Aleksiev et al. 2007), the average number of grains collected by all individual foragers from each colony during the observation period changed with increasing distance of the grain pile from the nest (two-way ANOVA: distance: F2,8 = 32.84, P < 0.0001). On average, individuals collected significantly more grains at 3 cm compared with either 40 or 80 cm (Tukey test: mean difference between 40 and 3 cm: T = −6.402, P = 0.0005; mean difference between 80 and 3

Discussion

Colonies showed partial preferences for large and small sand grains at all three foraging distances, but with an increasing bias towards big grains at larger foraging distances (Fig. 4). This is consistent with our findings in an earlier study (Aleksiev et al. 2007). This pattern is also clear in the data from individual foragers (Figure 2, Figure 3). Both figures represent all the data from individually marked foragers that were directly observed to retrieve at least 20 grains. For this

Acknowledgments

We gratefully acknowledge an Overseas (Postgraduate) Research Studentship for ASA at the University of Bristol.

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    A. B. Sendova-Franks is at the School of Mathematical Sciences, CEMS, University of the West of England, Bristol, Frenchay Campus, Coldharbour Lane, Bristol BS16 1QY, U.K.

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