Ant colonies are plagued by a diversity of arthropod guests, which adopt various strategies to avoid or to withstand host attacks. Chemical mimicry of host recognition cues is, for example, a common integration strategy of ant guests. The morphological gestalt and body size of ant guests have long been argued to also affect host hostility, but quantitative studies testing these predictions are largely missing. We here evaluated three guest traits as triggers of host aggression—body size, morphological gestalt, and accuracy in chemical mimicry—in a community of six Eciton army ant species and 29 guest species. We quantified ant aggression towards 314 guests in behavioral assays and, for the same individuals, determined their body size and their accuracy in mimicking ant cuticular hydrocarbon (CHC) profiles. We classified guests into the following gestalts: protective, myrmecoid, staphylinid-like, phorid-like, and larval-shaped. We expected that (1) guests with lower CHC mimicry accuracy are more frequently attacked; (2) larger guests are more frequently attacked; (3) guests of different morphological gestalt receive differing host aggression levels. Army ant species had distinct CHC profiles and accuracy of mimicking these profiles was variable among guests, with many species showing high mimicry accuracy. Unexpectedly, we did not find a clear relationship between chemical host similarity and host aggression, suggesting that other symbiont traits need to be considered. We detected a relationship between the guests’ body size and the received host aggression, in that diminutive forms were rarely attacked. Our data also indicated that morphological gestalt might be a valuable predictor of host aggression. While most ant-guest encounters remained peaceful, host behavior still differed towards guests in that ant aggression was primarily directed towards those guests possessing a protective or a staphylinid-like gestalt. We demonstrate that CHC mimicry accuracy does not necessarily predict host aggression towards ant symbionts. Exploitation mechanisms are diverse, and we conclude that, besides chemical mimicry, other factors such as the guests’ morphological gestalt and especially their body size might be important, yet underrated traits shaping the level of host hostility against social insect symbionts.

中文翻译：

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多种表型特征作为宿主攻击蚂蚁共生体的触发因素：体型、形态格式塔和化学模拟准确性

蚁群受到各种节肢动物客人的困扰，它们采取各种策略来避免或抵御宿主的攻击。例如，宿主识别线索的化学模拟是蚂蚁客人的常见整合策略。长期以来，蚂蚁客人的形态格式塔和体型一直被认为也会影响敌意，但测试这些预测的定量研究在很大程度上缺失。我们在这里评估了三个客体特征作为宿主攻击的触发因素——体型、形态格式塔和化学模拟的准确性——在一个由六种 Eciton 军蚁和 29 种客体物种组成的群落中。我们在行为分析中量化了蚂蚁对 314 位客人的攻击行为，并且对于同一个人，确定了他们的体型和模仿蚂蚁表皮碳氢化合物 (CHC) 特征的准确性。我们将客人分为以下格式塔：保护性、myrmecoid、staphylin-like、phorid-like 和 larval-shaped。我们预计 (1) CHC 模仿准确度较低的客人会更频繁地受到攻击；（2）较大的客人更频繁地受到攻击；(3)不同形态格式塔的客人受到不同的宿主攻击程度。陆军蚂蚁物种具有不同的 CHC 特征，模仿这些特征的准确性因客人而异，许多物种表现出很高的模仿准确性。出乎意料的是，我们没有发现化学宿主相似性和宿主攻击性之间的明确关系，这表明需要考虑其他共生体特征。我们检测到客人的体型与受到的主人攻击之间存在关系，因为小型形式很少受到攻击。我们的数据还表明，形态格式塔可能是宿主攻击的一个有价值的预测因子。虽然大多数蚂蚁与客人的相遇仍然是和平的，但宿主对客人的行为仍然不同，因为蚂蚁的攻击主要针对那些拥有保护性或类似葡萄胺的格式塔的客人。我们证明 CHC 模仿准确性不一定能预测宿主对蚂蚁共生体的攻击性。开发机制是多种多样的，我们得出结论，除了化学模仿之外，其他因素，如客人的形态格式塔，尤其是他们的体型可能很重要，但被低估的特征塑造了宿主对社会昆虫共生体的敌意程度。主人对客人的行为仍然不同，因为蚂蚁的攻击主要针对那些拥有保护性或类似葡萄胺的格式塔的客人。我们证明 CHC 模仿准确性不一定能预测宿主对蚂蚁共生体的攻击性。开发机制是多种多样的，我们得出结论，除了化学模仿之外，其他因素，如客人的形态格式塔，尤其是他们的体型可能很重要，但被低估的特征塑造了宿主对社会昆虫共生体的敌意程度。主人对客人的行为仍然不同，因为蚂蚁的攻击主要针对那些拥有保护性或类似葡萄胺的格式塔的客人。我们证明 CHC 模仿准确性不一定能预测宿主对蚂蚁共生体的攻击性。开发机制是多种多样的，我们得出结论，除了化学模仿之外，其他因素，如客人的形态格式塔，尤其是他们的体型可能很重要，但被低估的特征塑造了宿主对社会昆虫共生体的敌意程度。