Plain solutions for plane environments?
In conclusion, the abilities of desert ants to navigate within a three-dimensional environment appear to somewhat lag behind their impressive feats in two dimensions. Our findings suggest that Cataglyphis fortis memorizes the features of a 3-D run to a feeder only in a rather general, cursory manner. The occurrence of a sloped part of its itinerary is reflected in a general acceptance of slopes in subsequent runs. But this is neither associated with a specific point on the way between nest and food source, nor does it have to occur in the same sequence as experienced during earlier trips to the feeder.
The choices that ants made in Homebound and Outbound tests revealed that ascents and descents are neither stored with their distances from nest and feeder, nor with their correct sequence. Still, the occurrence of sloped path sections in preceding foraging trips results in more frequent and longer descents and ascents in subsequent choice experiments.
The general acceptance of slopes, given that they were encountered on earlier trips to a feeder, is reminiscent of the way how local landmarks trigger learnt changes in direction, irrespective of its congruency with the state of the path integrator [30], or the skylight compass [21].
Accepting ascents or descents on a foraging trip if they were encountered before, and rejecting them if they are new, could be a simple safety mechanism that ensures that ants do not accidentally take a "wrong turn". But such a generalized safety rule does not imply that the ants' neural representation of their environment truly possesses a property of the vertical dimension. The correction of slope distances to ground distances, coupled with the general rule not to use novel ascents and descents along a known route, may well be fully sufficient to ensure an accurate and safe orientation.
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