In ant–plant defense mutualisms, plants known as myrmecophytes provide food and shelter to ant partners in exchange for defense against herbivores and pathogens. To ensure interaction pay-off, myrmecophytes must regulate their investment in ant-rewards depending on local conditions and herbivore pressure. We investigated how myrmecophyte investment in multiple ant-rewards relates to herbivory, ant defense, and ant occupancy over time. Specifically, we examined the plasticity of ant-rewards produced by swollen-thorn acacias (Vachellia collinsii) under different ant occupancy and herbivory conditions. We compared food rewards (number of extrafloral nectaries and pinnules as a proxy for food bodies) and housing rewards (domatia dimensions) of V. collinsii for three conditions: (1) occupied (defended by the obligate mutualist Pseudomyrmex spinicola) versus unoccupied trees, (2) occupied trees subject to an experimental herbivory manipulation versus control trees, and (3) trees occupied by different ant species varying in their level of defense (P. spinicola, P. simulans, Crematogaster crinosa). We found that food rewards were more likely to vary in time depending on ant occupancy and resident species. Conversely, housing rewards varied with the condition (occupancy or species of partner) and less through time. A one-time herbivory manipulation did not cause any changes to the ant-rewards produced. Our results reveal short-term plasticity in V. collinsii ant-rewards and demonstrate that myrmecophytes with constitutive rewards can adjust their investment in ant-rewards depending on the presence and identity of ant partners.

在蚂蚁 - 植物防御共生中，被称为 myrmecophytes 的植物为蚂蚁伙伴提供食物和住所，以换取对食草动物和病原体的防御。为了确保相互作用的回报，蚁群必须根据当地条件和食草动物的压力来调节它们对蚂蚁奖励的投资。我们调查了 myrmecophyte 对多种蚂蚁奖励的投资如何与食草、蚂蚁防御和蚂蚁占有率随着时间的推移而相关。具体来说，我们研究了在不同蚂蚁占据和食草条件下由肿胀刺金合欢（Vachellia collinsii）产生的蚂蚁奖励的可塑性。我们比较了V. collinsii 的食物奖励（花外蜜腺和小叶的数量作为食物体的代表）和住房奖励（domatia 维度）对于三个条件：（1）被占用（由专性互惠者Pseudomyrmex spinicola 保护）与未被占用的树木，（2）受到实验性食草操纵的占用树木与对照树木，以及（3）被不同蚂蚁物种占用的树木，它们的水平不同防御（P. spinicola，P. simulans，Crematogaster crinosa）。我们发现食物奖励更有可能随时间变化，具体取决于蚂蚁的居住情况和常驻物种。相反，住房奖励因条件（入住率或伴侣种类）而异，而随着时间的推移较少。一次性的食草操作不会对产生的蚂蚁奖励造成任何变化。我们的结果揭示了V. collinsii的短期可塑性 ant-rewards 并证明具有组成性奖励的 myrmecophytes 可以根据蚂蚁伙伴的存在和身份来调整他们对 ant-rewards 的投资。