von Beeren Christoph, Brückner Adrian, Hoenle Philipp O, Ospina-Jara Bryan, Kronauer Daniel J C, Blüthgen Nico
Ecological Networks, Department of Biology, Technical University of Darmstadt, Darmstadt, Germany.
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, USA.
Front Zool. 2021 Sep 19;18(1):46. doi: 10.1186/s12983-021-00427-8.
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.
蚁群受到多种节肢动物访客的困扰，这些访客采用各种策略来避免或抵御宿主的攻击。例如，对宿主识别线索的化学拟态是蚁类访客常见的融入策略。长期以来，人们一直认为蚁类访客的形态轮廓和体型也会影响宿主的敌意，但检验这些预测的定量研究在很大程度上缺失。我们在此评估了三种访客特征作为宿主攻击的触发因素——体型、形态轮廓以及化学拟态的准确性——在一个由六种埃氏行军蚁物种和29种访客物种组成的群落中。我们在行为实验中量化了蚂蚁对314个访客的攻击性，并针对相同个体，测定了它们的体型以及模仿蚂蚁表皮碳氢化合物（CHC）谱的准确性。我们将访客分类为以下形态轮廓：保护性、蚁形、隐翅虫形、蚤蝇形和幼虫形。我们预期：（1）CHC拟态准确性较低的访客更容易受到攻击；（2）体型较大的访客更容易受到攻击；（3）不同形态轮廓的访客受到宿主攻击的程度不同。
行军蚁物种具有独特的CHC谱，访客模仿这些谱的准确性各不相同，许多物种表现出较高的拟态准确性。出乎意料的是，我们没有发现化学宿主相似性与宿主攻击性之间存在明确关系，这表明需要考虑其他共生体特征。我们检测到访客体型与所受到的宿主攻击性之间存在关系，即体型微小的形态很少受到攻击。我们的数据还表明，形态轮廓可能是宿主攻击性的一个有价值的预测指标。虽然大多数蚁类与访客的相遇保持平静，但宿主对访客的行为仍存在差异，因为蚂蚁的攻击主要针对那些具有保护性或隐翅虫形形态轮廓的访客。
我们证明CHC拟态准确性不一定能预测宿主对蚁类共生体的攻击性。利用机制多种多样，我们得出结论，除了化学拟态外，其他因素如访客的形态轮廓，尤其是它们的体型，可能是塑造宿主对社会性昆虫共生体敌意程度的重要但被低估的特征。
