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Summary
I SUMMARY
Subterranean living animals must handle orientation in their habitat with limited cues, among
which is light scarcity. Zambian mole-rats belong to the rodent genus Fukomys and spend the
majority of their lifetime underground in extensive burrow systems. These mole-rats have
generally been considered as functionally blind, but recent morphological findings have
suggested that their visual capabilities must have been underestimated. The odds of cue
scarcity underground have also apparently led to the use of a sensory system for orientation
quite uncommon in mammals: magnetoreception.
This thesis deals with new findings on both the visual and the magnetic sense in small
Zambian mole-rat species of the Genus Fukomys – two senses coupled to the minuscule,
inconspicuous eye. While the retina provides the basis for light perception, the cornea is
probably the site where magnetic perception takes place.
Firstly, I show in part A that the formerly thought ‘blind’ Fukomys mole-rats can
distinguish between light and dark even until at least a light intensity of 0.6 µmol
photons
−2 −1
⋅ m ⋅ s (approximately 33 lux). This thesis has also undergone the first approach
to measure wavelength propagation in a tunnel, showing that long wavelengths (600-700 nm)
travel, as expected, furthest in a horizontal tunnel, and that photons in this spectral range can
still be detected, though at a very low (scotopic) level, at 70 cm apart from a tunnel opening
illuminated with a light intensity resembling that on a clear day.
Secondly, in part B, I also show that the hitherto poorly understood transduction
mechanism of the magnetic sense in mole-rats is based on magnetite rather than on
biochemical processes. The site of the respective magnetite-harbouring receptors can be
confined to the ocular region, more specifically the cornea, where ferrous inclusions with
magnetic properties might be coupled with the receptors for mediating magnetic information.
The magnetic sense is not lateralised. This thesis also contributes to a further understanding of
the neuronal processing of magnetic information in mammals, finding that hippocampal
structures, e.g. structures coordinating spatial memories, are also involved in magnetic
orientation. Magnetic cues might supply the animal with both directional compass and map
information.
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