Sexual dimorphism in the olfactory system of a solitary and a eusocial bee species

Authors

  • Martin Streinzer,

    1. Department of Evolutionary Biology, Faculty of Life Sciences, University of Vienna, A-1090 Vienna, Austria
    2. Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Würzburg, D-97074 Würzburg, Germany
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  • Christina Kelber,

    1. Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Würzburg, D-97074 Würzburg, Germany
    2. Department of Biology, Technical University of Darmstadt, D-64287 Darmstadt, Germany
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  • Sarah Pfabigan,

    1. Department of Evolutionary Biology, Faculty of Life Sciences, University of Vienna, A-1090 Vienna, Austria
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  • Christoph J. Kleineidam,

    1. Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Würzburg, D-97074 Würzburg, Germany
    2. Department of Biology, University of Konstanz, D-78457 Konstanz, Germany
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  • Johannes Spaethe

    Corresponding author
    1. Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Würzburg, D-97074 Würzburg, Germany
    • Department of Evolutionary Biology, Faculty of Life Sciences, University of Vienna, A-1090 Vienna, Austria
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CORRESPONDENCE TO: Johannes Spaethe, Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany. E-mail: johannes.spaethe@uni-wuerzburg.de

Abstract

Sexually dimorphic sensory systems are common in Hymenoptera and are considered to result from sex-specific selection pressures. An extreme example of sensory dimorphism is found in the solitary bee tribe Eucerini. Males of long-horned bees bear antennae that exceed body length. This study investigated the pronounced sexual dimorphism of the peripheral olfactory system and its representation in higher brain centers of the species Eucera berlandi. Eucera males have elongated antennae, with 10 times more pore plates and three times more olfactory receptor neurons than females. The male antennal lobe (AL) comprises fewer glomeruli than the female AL (∼100 vs. ∼130), of which four are male-specific macroglomeruli. No sex differences were found in the relative volume of the mushroom bodies, a higher order neuropil essential for learning and memory in Hymenoptera. Compared with the Western honeybee, the degree of sexual dimorphism in Eucera is more pronounced at the periphery. In contrast, sex differences in glomerular numbers are higher in the eusocial honeybee and a sexual dimorphism of the relative investment in mushroom body tissue is observed only in Apis. The observed differences between the eusocial and the solitary bee species may reflect differences in male-specific behavioral traits and associated selection pressures, which are discussed in brief. J. Comp. Neurol. 521:2742–2755, 2013. © 2013 Wiley Periodicals, Inc.

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