Multi-modal imaging and analytical approaches to the study of magnetoreception in the honey bee Apis mellifera

[Truncated] Despite a wealth of behavioural studies demonstrating that many animals are able to sense and respond to the Earth’s geomagnetic field, comparatively few have attempted to locate and characterise the mechanistic basis of magnetoreception. The magnetite hypothesis states that nanoparticles of magnetite (Fe3O4) are responsible for mediating the sense. This model is supported by numerous behavioural and electrophysiological studies. However, attempts to locate the magnetoreceptor cells in tissue have been marred with misidentified biological iron and magnetic contaminants.

Two main factors have impeded the discovery of a magnetite particle based magnetoreceptor system. The first relates to the potential rarity of these magnetoreceptor cells, often referred to as the “needle-in-a-haystack” problem. The second is the ubiquitous nature of iron in biological systems and the environment, which has led to a number of false positives when attempting to identify the cells in tissue.

In light of these two fundamental issues, it was the aim of this study to investigate a combination of novel and revisited analytical techniques to ascertain their utility for magnetoreception research. To trial these approaches, the worker caste of the honey bee Apis mellifera was chosen as a model system. Honey bees are known to be magnetoreceptive, and possess many other characteristics that make them ideal for studying magnetoreception. The viability and sensitivity of techniques was also assessed using biogenic magnetic particles derived from magnetotactic bacteria (MTB).

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to quantitatively assess iron levels in honey bee body parts over their lifespan. This showed that the thorax and abdomen possess sufficient iron to form the large magnetoreception system theorised for a map-based magnetic field detection sense, while the antennae and head do not. All body parts contain adequate iron to form the theorised compass sense.