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General Introduction
III GENERAL INTRODUCTION
The term “orientation” refers to an animal’s ability to orient in space and time, to maintain a
specific spatial position, or to create new spatial relationships with its environment (Merkel
1980; Zwahr 1993). Finding the way is a necessity for securing territory, food and
reproduction; orientation thus represents a life characteristic and explains the variety of
orientation organs and systems to be found across the animal kingdom (Merkel 1980). How an
organism perceives its environment and how it orients within it, depends on its sensory
organs, which transduce different cues depending on whether they are optical, mechanical,
electrical, olfactory, or other chemical stimuli (Merkel 1980). Stimulus-evoked information
must be 1) localised in space and 2) identified (Ewert 1973); though orientation is based
mainly on these various information types, imprinting, memory or learning also vitally support
the orientation process (Merkel 1980; Zwahr 2003).
Living above ground provides an animal with diverse cues for spatial orientation, but
the underground picture is less colourful: besides darkness, subterranean rodents face
restriction in useful orientation cues such as odours or sounds (Burda et al. 1990a). Targets
and landmarks are not directly perceptible and, as a consequence, distant orientation is heavily
impeded. Subterranean mammals need to solve several major tasks relevant to spatial
orientation: 1) they have to orient quickly and efficiently in their burrow system, in order to
access nest, food chambers, latrines, and harvesting grounds. 2) They must maintain their
course direction when digging longer foraging and dispersing tunnels. Straight tunnelling
conserves energy because the animals do not search in the same area twice. 3) They need to
restore and interconnect damaged burrows, effectively bypass obstacles, etc. 4) Animals
temporarily leaving their burrows while foraging or searching for mates above ground need to
find their way back home. Subterranean living mammals thus need to make use of efficient
orientation capabilities, which are specialized towards this peculiar habitat.
III.1 Subterranean Fukomys Mole-Rats
Mole-rats of the genus Fukomys, formerly denominated as Cryptomys (Kock et al. 2006), are
strictly subterranean rodents of the family Bathyergidae that occur in Africa south of the
Sahara. To our current knowledge, the bathyergid family comprises six genera: Bathyergus,
Cryptomys, Fukomys, Georychus, Heliophobius, and Heterocephalus (Faulkes et al. 2004; Ingram et al.
2004; Kock et al. 2006; van Daele et al. 2004). While the genus Cryptomys is distributed across
South Africa, its sister genus Fukomys is widely distributed across South-central and West
Africa (Ingram et al. 2004).
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