Johnson Christine A, Herbers Joan M
Department of Evolution, Ecology and Organismal Biology, The Ohio State University, Aronoff Laboratory, Columbus 43210, USA.
Ecology. 2006 Feb;87(2):382-94. doi: 10.1890/05-1093.
Slave-making ants are specialized social parasites that steal the young from colonies of their host species to augment their slave supply. The degree of parasite-host specialization has been shown to shape the trajectory along which parasites and hosts coevolve and is a prime contributor to the geographic mosaic of coevolution. However, virtually nothing is known about extrinsic influences on parasite-host dynamics, although the simple addition of a competing slave-maker may significantly alter selection pressures. Here we report the effect of two sympatric slave-makers on a single host. We measured temporal and spatial changes in colonies of the primary host Temnothorax curvispinosus that had been placed in field enclosures along with a single colony of either one or both species of the North American slave-making ants Protomognathus americanus and Temnothorax duloticus. Each slave-maker species alone had a negative impact on its hosts, although one slave-maker species more frequently decimated its host assemblage and then went extinct. Nevertheless, the combined effect in mixed-parasite enclosures was, surprisingly, greatly attenuated. Virulent slave-maker growth and prudent slave-maker decay in these shared enclosures, together with field data showing an inverse proportional relationship between the two slave-makers in natural populations, suggest that their checkered distribution is a consequence of direct asymmetrical antagonism between parasites. Thus, our results imply a tripartite coevolutionary arms race, whereby intraguild interactions among social parasites strongly affect the realized selection pressures on hosts and contribute to the geographic mosaic of coevolution.
蓄奴蚁是一类特殊的社会性寄生虫，它们从宿主物种的蚁群中窃取幼蚁以增加其奴隶数量。寄生虫 - 宿主的特化程度已被证明塑造了寄生虫和宿主共同进化的轨迹，并且是协同进化地理镶嵌体的主要促成因素。然而，尽管简单地引入一个竞争蓄奴蚁可能会显著改变选择压力，但实际上对于寄生虫 - 宿主动态的外在影响却知之甚少。在此，我们报告了两种同域蓄奴蚁对单一宿主的影响。我们测量了主要宿主弯刺胸切叶蚁（Temnothorax curvispinosus）蚁群的时间和空间变化，这些蚁群被放置在野外围栏中，同时还放入了北美蓄奴蚁美洲原颚切叶蚁（Protomognathus americanus）和劫掠胸切叶蚁（Temnothorax duloticus）这两个物种中任一种或两种的单个蚁群。单独的每种蓄奴蚁对其宿主都有负面影响，尽管其中一种蓄奴蚁更频繁地使宿主群体数量大幅减少然后灭绝。然而，令人惊讶的是，在混合寄生虫围栏中的综合影响大大减弱。在这些共享围栏中，毒性强的蓄奴蚁生长以及审慎的蓄奴蚁衰退，再加上野外数据表明在自然种群中这两种蓄奴蚁之间存在反比关系，这表明它们棋盘式的分布是寄生虫之间直接不对称拮抗作用的结果。因此，我们的结果意味着存在三方协同进化的军备竞赛，社会性寄生虫之间的公会内相互作用强烈影响宿主所面临的实际选择压力，并促成了协同进化的地理镶嵌体。
