Minding the gap: Learning and visual scanning behaviour in nocturnal bull ants

Insects possess small brains but exhibit sophisticated behaviour, specifically their ability to learn to navigate within complex environments. To understand how they learn to navigate in a cluttered environment, we focused on learning and visual scanning behaviour in the Australian nocturnal bull ant, Myrmecia midas, which are exceptional visual navigators. We tested how individual ants learn to detour via a gap and how they cope with substantial spatial changes over trips. Homing M. midas ants encountered a barrier on their foraging route and had to find a 50-cm gap between symmetrical large black screens, at 1m distance towards the nest direction from the centre of the releasing platform in both familiar (on-route) and semi-familiar (off-route) environments. Foragers were tested for up to 3 learning trips with the changed conditions in both environments. Results showed that on the familiar route, individual foragers learned the gap quickly compared to when they were tested in the semi-familiar environment. When the route was less familiar, and the panorama was changed, foragers were less successful at finding the gap and performed more scans on their way home. Scene familiarity thus played a significant role in visual scanning behaviour. In both on-route and off-route environments, panoramic changes significantly affected learning, initial orientation and scanning behaviour. Nevertheless, over a few trips, success at gap finding increased, visual scans were reduced, the paths became straighter, and individuals took less time to reach the goal.昆虫虽拥有小巧的脑容量，却展现出复杂精妙的行为模式，其中尤为突出的是它们在复杂环境中学习导航的能力。为阐明昆虫如何在杂乱环境中学习导航，本研究以澳洲夜行公牛蚁（Australian nocturnal bull ant, Myrmecia midas）——一种卓越的视觉导航者——为对象，重点考察其学习行为与视觉扫描行为（visual scanning behaviour）。我们通过实验探究了单个蚂蚁如何学会通过间隙绕行，以及它们在多次往返过程中如何应对显著的空间变化。归巢的澳洲夜行公牛蚁在觅食路线上会遭遇障碍物，需在对称的大型黑色屏障之间找到一处50厘米宽的间隙；该间隙位于释放平台中心朝向巢穴方向1米处，实验设置了熟悉路线（on-route）与半熟悉路线（off-route）两种环境。在两种环境中，我们均对觅食蚁开展了最多3次带有环境变化的学习往返实验。实验结果显示，相较于半熟悉环境中的测试结果，熟悉路线上的单个觅食蚁能更快学会定位该间隙。当路线熟悉度较低且视觉全景（panorama）发生变化时，觅食蚁找到间隙的成功率更低，归巢过程中也会进行更多次视觉扫描。由此可见，场景熟悉度对视觉扫描行为具有显著影响。无论是熟悉路线还是半熟悉路线环境，视觉全景的变化均会显著影响蚂蚁的学习、初始定向以及扫描行为。尽管如此，经过数次往返实验后，觅食蚁找到间隙的成功率有所提升，视觉扫描次数减少，行进路径愈发笔直，抵达目标的耗时也更短。