A micro-CT-based standard brain atlas of the bumblebee

Richard J Gill,Dylan B Smith,Basil El Jundi,Nadine Kraft,Keram Pfeiffer,Lisa Rother

doi:10.1007/s00441-021-03482-z

Richard J Gill, Dylan B Smith + Show 4 more

Open Access

https://doi.org/10.1007/s00441-021-03482-z

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Abstract

In recent years, bumblebees have become a prominent insect model organism for a variety of biological disciplines, particularly to investigate learning behaviors as well as visual performance. Understanding these behaviors and their underlying neurobiological principles requires a clear understanding of brain anatomy. Furthermore, to be able to compare neuronal branching patterns across individuals, a common framework is required, which has led to the development of 3D standard brain atlases in most of the neurobiological insect model species. Yet, no bumblebee 3D standard brain atlas has been generated. Here we present a brain atlas for the buff-tailed bumblebee Bombus terrestris using micro-computed tomography (micro-CT) scans as a source for the raw data sets, rather than traditional confocal microscopy, to produce the first ever micro-CT-based insect brain atlas. We illustrate the advantages of the micro-CT technique, namely, identical native resolution in the three cardinal planes and 3D structure being better preserved. Our Bombus terrestris brain atlas consists of 30 neuropils reconstructed from ten individual worker bees, with micro-CT allowing us to segment neuropils completely intact, including the lamina, which is a tissue structure often damaged when dissecting for immunolabeling. Our brain atlas can serve as a platform to facilitate future neuroscience studies in bumblebees and illustrates the advantages of micro-CT for specific applications in insect neuroanatomy.

Highlights

Standard brain atlases have become an important tool in insect neuroanatomy, serving as an important reference for neurobiological studies
Worker bumblebees sampled for micro-CT imaging of the brain were from Biobest colonies delivered to Silwood Park, Imperial College London (UK) which were kept in a controlled environment room at 23 °C and 60% relative humidity under continual red light and provisioned ad-libitum food
Workers sampled for the anti-synapsin staining and confocal microscopy of the brain were from Koppert colonies delivered to the University of Würzburg (Germany) and kept in large climate chambers at 25 °C and 55% relative humidity (rH) under white light (12:12 LD) and provisioned ad-libitum food

Summary

Introduction

Standard brain atlases have become an important tool in insect neuroanatomy, serving as an important reference for neurobiological studies. The generation of standard brain atlases is important to allow comparative anatomical studies, with standard brain atlases currently available for a variety of model insect species: flies (Drosophila melanogaster: Rein et al 2002; Peng et al 2011; Ostrovsky and Jefferis 2014; Arganda-Carreras et al 2018; Bogovic et al 2020), beetles (Tribolium castaneum: Dreyer et al 2010), locusts (Schistocerca gregaria: Kurylas et al 2008), wasps (Nasonia vitripennis: Groothuis et al 2019), and lepidopteran species (Manduca sexta: el Jundi et al 2009; Heliothis virescens: Kvello et al 2009; Agrotis infusa: Adden et al 2020). An ecologically as well as economically important insect pollinator group, only the honeybee Apis mellifera has a standard brain atlas (Brandt et al 2005). Creating a standard atlas for other bee groups, such as the bumblebees which are being increasingly considered as a model organism in insect neurobiology research (e.g., Paulk and Gronenberg 2008; Paulk et al 2008; Pfeiffer and Kinoshita 2012; Stone et al 2017), can facilitate bee and hymenoptera comparative neurobiology

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