Data from: Innate turning preference of leaf-cutting ants in the absence of external orientation cues

Many ants use a combination of cues for orientation but how do ants find their way when all external cues are suppressed? Do they walk in a random way or are their movements spatially oriented? Here we show for the first time that leaf-cutting ants (Acromyrmex lundii) have an innate preference of turning counter-clockwise (left) when external cues are precluded. We demonstrated this by allowing individual ants to run freely on the water surface of a newly-developed treadmill. The surface tension supported medium-sized workers but effectively prevented ants from reaching the wall of the vessel, important to avoid wall-following behaviour (thigmotaxis). Most ants ran for minutes on the spot but also slowly turned counter-clockwise in the absence of visual cues. Reconstructing the effectively walked path revealed a looping pattern which could be interpreted as a search strategy. A similar turning bias was shown for groups of ants in a symmetrical Y-maze where twice as many ants chose the left branch in the absence of optical cues. Wall-following behaviour was tested by inserting a coiled tube before the Y-fork. When ants traversed a left-coiled tube, more ants chose the left box and vice versa. Adding visual cues in form of vertical black strips either outside the treadmill or on one branch of the Y-maze led to oriented walks towards the strips. It is suggested that both, the turning bias and the wall-following are employed as search strategies for an unknown environment which can be overridden by visual cues.

诸多蚂蚁会结合多种线索进行定向，但当所有外部线索均被屏蔽时，蚂蚁该如何寻路？它们的行进是随机的，还是具备空间定向性？本研究首次证实，切叶蚁（leaf-cutting ants，Acromyrmex lundii）在无外部线索的情况下，天生具有逆时针（向左）转向的偏好。
我们通过让单只蚂蚁在新研发的水面跑步机的水面上自由跑动，验证了这一结论。该装置的表面张力可支撑中型工蚁活动，同时有效阻止蚂蚁接触容器壁，这一设计可避免趋壁行为（thigmotaxis）的干扰。多数蚂蚁可原地跑动数分钟，且在无视觉线索时会缓慢地逆时针转向。对实际行进路径进行重构后发现，其轨迹呈现环状模式，可被视作一种搜索策略。
在对称Y型迷宫中，群体蚂蚁也表现出类似的转向偏好：在无光学线索的情况下，选择左侧分支的蚂蚁数量是右侧的两倍。我们通过在Y型分叉前置入螺旋管，测试了趋壁行为：当蚂蚁经过左向螺旋管后，更多蚂蚁会选择左侧通道，反之亦然。当在跑步机外侧或Y型迷宫的某一分支添加垂直黑色条带作为视觉线索时，蚂蚁会朝着条带方向定向行进。
本研究表明，转向偏好与趋壁行为均可作为未知环境中的搜索策略，且上述两种策略均可被视觉线索所覆盖。