Hair plate mechanoreceptors associated with body segments are not necessary for three-dimensional path integration in desert ants, Cataglyphis fortis

In formicine ants, the hair fields associated with the neck and the petiole (alitrunk-petiole and petiole-gaster joints) have long been established to function in graviception. Here, we examine a possible role of these hair receptors in three-dimensional (3-D) path integration of the (formicine) desert ant, Cataglyphis fortis. Cataglyphis judge the ground distance when travelling over hills, allowing correct homing even in (unpredictably) uneven terrain. We eliminated the function of these hair sensors in graviception either by shaving the hairs or by immobilising the joints monitored by the hair plates. With that major component of their sense of graviception eliminated, one would expect the ants to disregard, or at least misgauge, the ascents and descents performed across hills during outbound journey. The ants should thus consider the (much longer) actual walking trajectory, instead of the base distance, when calculating their homing distance. Surprisingly, neither shaving nor immobilisation of the hair sensillae affected correct path integration, across both uneven terrain (3-D) and level surface. If anything, the ants underestimated homing distance, which may reflect a general, safety-oriented navigation strategy. Animals that had performed the outbound journey with their gaster fixed in a horizontal position underestimated their homing so dramatically that this latter explanation cannot hold.