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阻断时，蚂蚁该如何寻路？它们是随机行进，还是运动存在空间定向偏好？本研究首次证实，伦氏切叶蚁（Acromyrmex lundii）在无外部线索可用时，天生具有逆时针（向左）转向的偏好。我们通过将单个蚂蚁置于新型水面跑步机（water surface treadmill）表面自由行走开展实验：该装置利用表面张力支撑中型工蚁，同时有效阻止蚂蚁触及容器壁，以此规避趋壁行为（thigmotaxis）。多数蚂蚁可在原地行进数分钟，但在无视觉线索的情况下会缓慢地逆时针转向。对蚂蚁实际行走路径进行重构后发现，其运动呈现环状模式，可被视作一种搜索策略。在对称Y型迷宫（Y-maze）中对蚁群开展的实验也印证了类似的转向偏好：在无视觉线索时，选择左侧分支的蚂蚁数量是右侧的两倍。我们通过在Y型分叉前插入螺旋管，对趋壁行为展开测试：当蚂蚁经过左旋螺旋管后，更多蚂蚁会选择左侧通道，反之亦然。若在跑步机外侧或Y型迷宫的某一分支添加垂直黑色条带作为视觉线索，蚂蚁的行进方向会朝向这些条带，表现出定向行走。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，且该策略可被视觉线索所抵消。