Abstract
Subterranean rodents are able to dig long straight tunnels. Keeping the course of such “runways” is important in the context of optimal foraging strategies and natal or mating dispersal. These tunnels are built in the course of a long time, and in social species, by several animals. Although the ability to keep the course of digging has already been described in the 1950s, its proximate mechanism could still not be satisfactorily explained. Here, we analyzed the directional orientation of 68 burrow systems in five subterranean rodent species (Fukomys anselli, F. mechowii, Heliophobius argenteocinereus, Spalax galili, and Ctenomys talarum) on the base of detailed maps of burrow systems charted within the framework of other studies and provided to us. The directional orientation of the vast majority of all evaluated burrow systems on the individual level (94%) showed a significant deviation from a random distribution. The second order statistics (averaging mean vectors of all the studied burrow systems of a respective species) revealed significant deviations from random distribution with a prevalence of north–south (H. argenteocinereus), NNW–SSE (C. talarum), and NE–SW (Fukomys mole-rats) oriented tunnels. Burrow systems of S. galili were randomly oriented. We suggest that the Earth’s magnetic field acts as a common heading indicator, facilitating to keep the course of digging. This study provides a field test and further evidence for magnetoreception and its biological meaning in subterranean mammals. Furthermore, it lays the foundation for future field experiments.
Highlights
Across the globe, about 250 rodent species, belonging to different unrelated taxa, have convergently adapted to permanent life in self-excavated extensive underground burrow systems
Considering the second order statistics, a significant deviation from random orientation was found for the Fukomys mole-rats, the silvery mole-rat, and the Talas tuco-tuco (Fig. 1)
An axial directional preference for the North–South axis was observed for the silvery mole-rat (Fig. 1A), while it was slightly shifted to NNW/SSE in the Talas tuco-tuco (Fig. 1B)
Summary
About 250 rodent species, belonging to different unrelated taxa (six families, 38 genera), have convergently adapted to permanent life in self-excavated extensive underground burrow systems (for review see Begall, Burda & Schleich, 2007; Lacey, 2000; Nevo, 1999). The African mole-rat’s ability to maintain its course while digging long, straight tunnels (Eloff, 1951) gave rise to speculations on possible orientation cues: air currents (De Graaff, 1972; Eloff, 1958; Poduschka, 1978) and acoustic cues (Eloff, 1951; Müller & Burda, 1989; Rosevear, 1969) have been discussed, as well as internal mechanisms based on kinesthetic and/or vestibular cues (Teroni et al, 1988) None of these mechanisms provide a satisfactory explanation for the highly efficient directional orientation observed in Cryptomys hottentotus (Eloff, 1951)
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