Bigger is better for bumblebee eyes
X-ray microtomography at Diamond generates 3D images of bumblebee eyes and explores the effect of size on vision
Bumblebees buzzing around flowers is one of the sounds of summer, and these insects are important pollinators, particularly in northern Europe. Like all bees, they have to visually navigate complex environments in search of nectar, but although extensive research has been done on honeybees, telling us more about how their tiny eyes work and how they process and learn the visual information necessary for this, we know less about bumblebee eyesight. In work recently published in eLife, researchers demonstrated a new X-ray microCT-based method for quantifying and mapping the vision capacity of insect eyes. After creating 3D models of the compound eyes of buff-tailed bumblebees (Bombus terrestris), they were able to project the surface of each eye onto the world and to map the scaling relationships of eye properties and visual capabilities for bumblebees. Their results showed that larger bumblebees with bigger eyes have better vision, with an improved ability to see small objects in front or slightly above them, and their research may have identified general rules for how compound eyes scale with size.
What an animal sees... and why
Bumblebees come in a range of different sizes, with larger bumblebees known to have larger eyes. Bigger eyes are generally thought to be better, but it’s not entirely clear how eye size affects vision. For example, little is known about how optical sensitivity and visual resolution across a bumblebee’s entire visual field are affected by its eye size. Insects are good models for exploring the effects of size on visual systems, as many insect species exhibit size polymorphism, but previous research has been limited by difficulties in determining the 3D structure of eyes.
The high-throughput, high-contrast, high-resolution 3D imaging at I13-2 enabled high-quality data to be generated for a large number of samples in just a few days.
Allometry and the bumblebee
The team were working with a hypothesis that the compound eyes common in insect species were likely to scale non-uniformly, with an increasing proportion of a larger eye given over to improving vision in a small area of the FOV. To test whether specialised visual regions are developed or improved in larger individuals, they needed to link the allometry of eye properties - the growth of different areas at differing rates, leading to a change in proportions - to visual capabilities.
By giving us a deeper understanding of how bumblebees perceive the world, this research can help us to better understand the pollination behaviour of bees in general and may aid in the development of more efficient strategies for conserving threatened species. Beamline I13-2 at Diamond has helped us to develop and refine our methodology and has been fundamental in making this work possible
To find out more about the Diamond-Manchester Imaging branchline (I13-2), or to discuss potential applications, please contact Principal Beamline Scientist Christoph Rau: firstname.lastname@example.org.
Taylor GJ et al. Bumblebee visual allometry results in locally improved resolution and globally improved sensitivity. eLife, 8, e40613 (2019). DOI:10.7554/eLife.40613.