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First published online August 22, 2008
Journal of Experimental Biology 211, 2817-2826 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.019927
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Exploration and navigation in the blind mole rat (Spalax ehrenbergi): global calibration as a primer of spatial representation

Reut Avni, Yael Tzvaigrach and David Eilam*

Department of Zoology, Tel-Aviv University, Ramat-Aviv 69978, Israel


Figure 1
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  		Fig. 1. (A) Distribution of time (s) spent in the 36 arena zones. For each mole rat, the time spent in each zone was measured and ranked from high to low. Each rank was then averaged for the 12 mole rats and values are given ±s.e.m. As shown, there was one zone in which the mole rats spent significantly greater time compared with the next rank. To quantify the change across ranks, the difference between each two successive ranks was calculated (i.e. the difference between ranks 1 and 2, between ranks 2 and 3, 3 and 4, and so on). A one-way repeated measures ANOVA was then carried out on the differences between ranks, revealing a significant difference between differences of consecutive ranks (F34, 374=13.7; P<0.00001). Tukey HSD post-hoc test revealed that the difference between the first two ranks was different from all other differences (*P<0.0001). Inset: number in each corner indicates the number of mole rats that spent the highest amount of time in that corner. Arrow represents the start corner, where the mole rats were introduced into the arena. As shown, eight mole rats favoured the top right corner, and only one favoured the start (bottom right) corner. (B) Distribution of visits in the arena zones. For each mole rat, the number of visits (entries) into each of the 36 arena zones was counted and ranked from high to low. Each rank was then averaged for the 12 mole rats and values are given ±s.e.m. As shown, there was no one zone to which the mole rats paid significantly more visits, as opposed to the distribution of time spent in zone (A).

 

Figure 2
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  		Fig. 2. The gradual build-up of the first lap of one representative mole rat. The lap is shown in cumulative path segments, with the duration of each depicted below as seconds ('') or minutes (') from start of the trial. As shown, by 1' the mole rat had extended the path from the start corner (where it was introduced into the arena) to the next corner. By 3' it had reached the furthest corner, and for the next 3 min it retraced the previous path, until 7', when it progressed to the fourth corner and then completed the perimeter path (8').

 

Figure 3
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  		Fig. 3. (A) Travelling speed in the first four laps (cm s–1). Results are shown for males (open circles) and females (filled squares). There was a significant increase in travelling speed between laps (two-way repeated measures ANOVA, F3, 30=5.5; P<0.004), with a Tukey HSD post-hoc test revealing that the first lap differed from all other laps (P<0.05). No significant difference between males and females was found (F1, 10=0.16; P=0.69). Lap x gender interaction was not significantly different (F3, 30=2.03; P=0.13). (B) Travelled distance in the first four laps (m). Results are shown for males (open circles) and females (filled squares). There was a considerable decrease in travelled distance between lap, however, this difference was not significant (two-way repeated measures ANOVA, F3, 30=1.94; P=0.14). There was a significant difference between males and females (F1, 10=37.8; P<0.0002), indicating that in each lap females travelled greater distance than males. Lap x gender interaction was not significantly different (F3, 30=0.49; P=0.69).

 

Figure 4
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  		Fig. 4. (A) Exemplary travel paths of three representative mole rats. The first four laps for each mole rat are depicted from left to right. The right column shows the cumulative path for the entire test. In the first lap, the mole rats travelled along the perimeter while retracing travelled segments, with very short detachments from the arena wall. In the following laps, few retracing are seen and the mole rats start to perform corner shortcuts and crosscuts through the centre. As shown in the cumulative path of the entire test, crosscuts did not converge to a specific location. (B) Representative paths of home base behaviour of three other rodent species: a jird (Meriones tristrami), a vole (Microtus socialis) and a laboratory Long-Evans hooded rat, tested in a 1.8 mx1.8 m (jird), or 2 mx2m (vole and rat) illuminated arena similar to that used in the present study. Paths were taken after the period of home base establishment. As illustrated in these exemplary paths, crosscuts through the centre converge to the home base (the bottom left corner in each rodent path schema), in contrast to the crosscuts of the mole rats (Fig. 3A), which did not regularly converge to a specific sector of the arena. [Image of travel path of a jird was modified from Zadicario et al. (Zadicario et al., 2005Go).]

 

Figure 5
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  		Fig. 5. (A) Shortcuts taken at a corner. In the first visit to the corner (left), the mole rat travelled into the corner. In the second visit (right) it did not reach the corner, but rather travelled in an arc to form a shortcut. Arrows indicate the direction of travel. (B) Number (average ± s.e.m.) of corner shortcuts (filled diamonds) and crosscuts through the centre (open squares) throughout the duration of the test, shown for 5 min intervals. Definition of corner shortcuts and crosscuts are depicted at the top part of the figure. In the first 5 min interval the number of corner shortcuts and crosscuts was very low, but in subsequent 5 min intervals they increased and stabilized. A paired t-test comparing the first (0–5 min) and second (5–10 min) interval revealed significant differences in both the number of corner shortcuts (t11=–2.75, P<0.019) and the number of crosscuts (t11=–2.5, P<0.029).

 

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© The Company of Biologists Ltd 2008