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Naturwissenschaften

, Volume 94, Issue 9, pp 733–739 | Cite as

Size determines antennal sensitivity and behavioral threshold to odors in bumblebee workers

  • Johannes Spaethe
  • Axel Brockmann
  • Christine Halbig
  • Jürgen Tautz
Original Paper

Abstract

The eusocial bumblebees exhibit pronounced size variation among workers of the same colony. Differently sized workers engage in different tasks (alloethism); large individuals are found to have a higher probability to leave the colony and search for food, whereas small workers tend to stay inside the nest and attend to nest duties. We investigated the effect of size variation on morphology and physiology of the peripheral olfactory system and the behavioral response thresholds to odors in workers of Bombus terrestris. Number and density of olfactory sensilla on the antennae correlate significantly with worker size. Consistent with these morphological changes, we found that antennal sensitivity to odors increases with body size. Antennae of large individuals show higher electroantennogram responses to a given odor concentration than those of smaller nestmates. This finding indicates that large antennae exhibit an increased capability to catch odor molecules and thus are more sensitive to odors than small antennae. We confirmed this prediction in a dual choice behavioral experiment showing that large workers indeed are able to respond correctly to much lower odor concentrations than small workers. Learning performance in these experiments did not differ between small and large bumblebees. Our results clearly show that, in the social bumblebees, variation in olfactory sensilla number due to size differences among workers strongly affects individual odor sensitivity. We speculate that superior odor sensitivity of large workers has favored size-related division of labor in bumblebee colonies.

Keywords

Bumblebees Division of labor EAG Foraging Olfactory threshold Perception Scaling 

Notes

Acknowledgment

We thank R. F. Chapman, J. G. Hildebrand, and J. Schachtner for their valuable comments on an earlier version of the manuscript and C. Lutz and S. Beshers for comments on the present version. J.S. and A.B. were supported by the German Research Foundation DFG (SFB554 and Graduiertenkolleg 200). The experiments in this study comply with the current laws of Germany.

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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Johannes Spaethe
    • 1
    • 2
  • Axel Brockmann
    • 1
    • 3
  • Christine Halbig
    • 1
  • Jürgen Tautz
    • 1
  1. 1.BEEgroup, Zoologie II, BiozentrumUniversity of WürzburgWürzburgGermany
  2. 2.Department of Evolutionary BiologyUniversity of ViennaViennaAustria
  3. 3.Department of EntomologyUniversity of Illinois at Urbana-ChampaignUrbanaUSA

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