Brain composition and scaling in social bee species differing in body size
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Original article
Brain composition and scaling in social bee species differing in body size Vishwas GOWDA1,2 , Wulfila GRONENBERG1 1 Department of Neuroscience, The University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721, USA Graduate Interdisciplinary Program Entomology and Insect Science, The University of Arizona, Tucson, AZ 85721, USA
2
Received 22 August 2018 – Revised 16 July 2019 – Accepted 1 September 2019
Abstract – We compare four honeybee and one bumblebee species with similar behaviors and ecological requirements but large differences in body size. The bees show allometric brain-body size relationships and scaling exponents similar to those found in vertebrates. Compared with three Asian honeybee species, the European honeybee Apis mellifera feature larger brains than expected for their body mass. Overall, the brains show moderate regional variation across species with two pronounced differences: A. dorsata have an enlarged visual lamina, possibly an adaptation for crepuscular vision. Second, the mushroom bodies are larger and comprise more intrinsic neurons in bumblebees than in honeybees. While these findings might suggest more advanced sensory associations in bumblebees, it is currently not possible to test this notion in the absence of quantitative and comprehensive behavioral comparisons across bee species. allometric scaling / morphometry / mushroom body / honeybees / bumblebees
Abbreviations MB Mushroom body
1. INTRODUCTION In vertebrates, an allometric relationship exists between the brain and body mass (Jerison, 1973; Striedter, 2005). The allometric exponent of this logarithmic relationship varies across vertebrate taxa, and exact values are a matter of debate (Martin 1981). Likewise, absolute brain size increases in insects, while relative brain size decreases with increasing body size (Neder 1959; Wehner et al. 2007). Larger brains or brain Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13592-019-00685-w) contains supplementary material, which is available to authorized users.
Corresponding author: V. Gowda, [email protected] Manuscript editor : Bernd Grünewald
components generally comprise more and/or larger neurons (Herculano-Houzel et al. 2014), and some studies suggest that they may provide animals with enhanced cognitive ability and enlarged behavioral repertoires (Lefebvre et al. 2004). However, behavioral repertoires and complexity are notoriously difficult to quantify, and the presence of a larger brain may not necessarily translate into greater cognitive abilities. Environmental factors, diet, or social and other behaviors all can have independent implications on the brain and brain component size (Dunbar and Shultz 2007; Byrne and Bates 2007; Healy and Rowe 2007). It would therefore be advantageous to address the question of body size-related brain modifications within animals that differ little in traits other than body size. Here, we ask the question if brain-body scaling relationships established in vertebrates
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