Department of Entomology, University of Arizona, Tucson, AZ, USA.
J Insect Sci. 2010;10:1. doi: 10.1673/031.010.0101.
Army ants are well known for their destructive raids of other ant colonies. Some known defensive strategies include nest evacuation, modification of nest architecture, blockade of nest entrances using rocks or debris, and direct combat outside the nest. Since army ants highly prefer Pheidole ants as prey in desert habitats, there may be strong selective pressure on Pheidole to evolve defensive strategies to better survive raids. In the case of P. obtusospinosa Pergande (Hymenoptera: Formicidae), the worker caste system includes super majors in addition to smaller majors and minor workers. Interestingly, P. obtusospinosa and the six other New World Pheidole species described to have polymorphic major workers are all found in the desert southwest and adjacent regions of Mexico, all co-occurring with various species of Neivamyrmex army ants. Pheidole obtusospinosa used a multi-phase defensive strategy against army ant raids that involved their largest major workers. During army ant attacks, these super majors were involved in blocking the nest entrance with their enlarged heads. This is the first description of defensive head-blocking by an ant species that lacks highly modified head morphology, such as a truncated or disc-shaped head. P. obtusospinosa super majors switched effectively between passive headblocking at the nest entrance and aggressive combat outside the nest. If this multi-phase strategy is found to be used by other Pheidole species with polymorphic majors in future studies, it is possible that selective pressure by army ant raids may have been partially responsible for the convergent evolution of this extra worker caste.
军蚁以其对其他蚁群的破坏性袭击而闻名。一些已知的防御策略包括巢撤离、巢结构的修改、用岩石或碎片堵塞巢入口，以及在巢外进行直接战斗。由于军蚁在沙漠栖息地中非常喜欢捕食 Pheidole 蚂蚁，因此 Pheidole 可能面临强烈的选择性压力，需要进化出防御策略以更好地抵御袭击。在 P. obtusospinosa Pergande（膜翅目：蚁科）的情况下，工蚁等级系统除了较小的大工蚁和小工蚁之外还包括超级大工蚁。有趣的是，P. obtusospinosa 和其他六种被描述为具有多态性大工蚁的新世界 Pheidole 物种都在墨西哥西南部和相邻地区的沙漠中发现，都与各种 Neivamyrmex 军蚁共同存在。Pheidole obtusospinosa 对军蚁袭击使用了一种多阶段的防御策略，涉及到其最大的大工蚁。在军蚁攻击期间，这些超级大工蚁参与用它们扩大的头部堵塞巢口。这是第一种描述缺乏高度特化头部形态（如截断或盘状头部）的蚂蚁物种进行防御性头部堵塞的描述。P. obtusospinosa 超级大工蚁有效地在巢口进行被动头部堵塞和在巢外进行积极战斗之间切换。如果在未来的研究中发现其他具有多态性大工蚁的 Pheidole 物种也使用这种多阶段策略，那么军蚁袭击的选择性压力可能部分导致了这种额外工蚁等级的趋同进化。
