Data from: I smell where you walked: how chemical cues influence movement decisions in ants

Interactions between animals are not restricted to direct encounters. Frequently, individuals detect the proximity of others through cues unintentionally left by others, such as prey species assessing predation risk based on indirect predator cues. However, while the importance of indirect cues in predator-prey interactions has been intensely studied, their role in interactions among competitors, and their consequences for community structure, are little known to date. Ant communities are usually structured by aggressive interactions between competing species. Responding to cues of others should be useful to avoid competitors or discover food sources. In ants and other insects, such cues include chemical footprints, which they leave while walking.

Here, we investigated how different ant species respond to footprints of others. Ant colonies were confronted with footprints of other colonies or species, and the workers chose between cue-bearing and cue-free areas. Moreover, we determined the chemical composition of footprints, and compared the absolute quantities of footprint and cuticular hydrocarbons.

Ants of the species Lasius niger avoided footprints of non-nestmate conspecifics, and tended to avoid footprints of two other species. We suggest that they avoided encounters with competitors to reduce costly fights. In contrast, three other ant species approached allospecific footprints, which may represent eavesdropping to find resources discovered by others. Three of the four ant species responded differently to nestmates and non-nestmate footprints either through footprint-following or antennation behavior. The chemical composition of footprints was species-specific and largely congruent to cuticular hydrocarbons. Footprint quantities left by single workers represented 1/170 to 1/64 of the quantity of their cuticular hydrocarbons.

We showed that chemical footprints represent an important cue for behavioral decisions in ants. The ability to identify and respond to chemical footprints may represent an important strategy for insects to cope with competing species or colonies in their habitat.

动物间的互动并非局限于直接接触。个体往往可通过其他个体无意遗留的信号感知同类的存在，例如猎物种群可借助间接捕食者信号评估自身被捕食风险。尽管学界已对捕食者-猎物互动中间接信号的重要性开展了大量研究，但截至目前，人们对这类信号在竞争者间互动中的作用，及其对群落结构的影响仍知之甚少。蚁群的群落结构通常由竞争物种间的攻击性互动所塑造。对同类信号作出响应，可帮助蚂蚁规避竞争者或发现食物源。在蚂蚁及其他昆虫中，这类信号包括其行走时遗留的化学足迹（chemical footprints）。

本研究探究了不同蚂蚁物种对其他个体遗留足迹的响应模式。实验中将蚁群暴露于其他蚁群或其他物种的足迹中，供工蚁在带有信号的区域与无信号区域间做出选择。此外，我们还测定了足迹的化学成分，并对比了足迹与表皮碳氢化合物（cuticular hydrocarbons）的绝对含量。

黑毛蚁（Lasius niger）会规避非巢群同物种个体的足迹，且倾向于规避另外两个物种的足迹。我们推测，这类规避行为旨在减少代价高昂的打斗。与之相反，另外三种蚂蚁则会趋近异种个体的足迹，这可能代表了一种窃听策略，以获取其他个体发现的资源信息。四种蚂蚁中有三种，会通过追踪足迹或触角拍打行为，对巢群同伴与非巢群同伴的足迹产生差异化响应。足迹的化学成分具有物种特异性，且与表皮碳氢化合物大体一致。单只工蚁遗留的足迹量，相当于其表皮碳氢化合物含量的1/170至1/64。

本研究证实，化学足迹是蚂蚁做出行为决策的重要信号。识别并响应化学足迹的能力，可能是昆虫在栖息地中应对竞争物种或竞争蚁群的重要策略。