Body size but not age influences phototaxis in bumble bee ( Bombus terrestris , L.) workers
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Original article
Body size but not age influences phototaxis in bumble bee (Bombus terrestris , L.) workers Michal MERLING1 , Shmuel EISENMANN2 , Guy BLOCH1,3 1
Department of Ecology, Evolution and Behavior, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Givat-Ram, 91904, Jerusalem, Israel 2 Racah Institute of Physics, Hebrew University, 91904, Jerusalem, Israel 3 The Federmann Center for the Study of Rationality, The Hebrew University of Jerusalem, Givat-Ram, 91904, Jerusalem, Israel Received 30 July 2019 – Revised 19 February 2020 – Accepted 22 March 2020
Abstract – We studied phototaxis, the directional movement relative to light, in the bumble bee Bombus terrestris . We first developed and validated a MATLAB-based system enabling reliable high-resolution tracking of a bee and a measurement of her distance relative to a changing LED light source. Using this system, we found in all our experiments that workers show positive phototaxis. The strength of the phototactic response was influenced by body size but not age, and this effect was significant when the light source was weak. In a separate experiment, foragers showed stronger phototactic response compared with nurses only in one of two trials in which they were larger and tested with weak light intensity. The evidence that phototaxis is associated with size-based division of labor in the bumble bee and with age-related division of labor in the honey bee lends credence to response threshold models implicating the response to light in the organization of division of labor in cavity dwelling social insects. locomotor activity / division of labor / body size / phototaxis / age / Bombus
1. INTRODUCTION Phototaxis is a behavior in which an animal moves towards (positive phototaxis) or away (negative phototaxis) from a source of elevated light intensity. The phototactic behavior is thought to be functionally adaptive because it regulates light exposure and facilitates orientation in space. For example, positive phototaxis may facilitate foraging behavior or escape in flying animals (e.g., Minot 1988; Reisenman et al.,1998), and Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13592-020-00759-0) contains supplementary material, which is available to authorized users.
Corresponding author: G. Bloch, [email protected] Manuscript Editor: Mathieu Lihoreau
negative phototaxis may protect animals by guiding them towards places hidden from predators (Hunte and Myers 1984; Minot 1988), or direct them towards burrowed nutrients (Sawin et al. 1994). Phototactic behavior is sensitive to light intensity and is commonly used to assess the animal capacity to discriminate between levels of light intensity. Pioneering studies with fruit flies showed already early in the twentieth century that strong light can inhibit the phototactic response that is induced by weaker light intensities (Carpenter 1905). Concerning the underlying mechanisms, phototaxis is one of the first behaviors for
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