科研人员报告了一种寄生蚁物种与其种植真菌的宿主之间的关系的一种令人惊讶的共生特征。寄生蚁Megalomyrmex的新近交配的蚁后悄悄进入种植真菌的宿主蚁Sericomyrmex的真菌园并建立蚁群。这种寄生蚁通过食用宿主的后代从而妨碍宿主蚁群的生长，并且通过钳制宿主未交配的蚁后的翼从而阻止蚁群的繁殖和扩散。Rachelle Adams及其同事报告说，这种寄生客蚁为它们的宿主带来了一种此前没有被认识到的生存优势，因此也就解释了它们在某些宿主种群中的高出现率。利用实验室实验，这组作者发现这种寄生蚁使用强大的生物碱保卫宿主蚁群不受来袭的农业掠食蚁Gnamptogenys hartmani的伤害，后者会强占Sericomyrmex的真菌园和蚁巢。这组作者报告说，这种寄生蚁比宿主能更有效地杀死这些来袭的掠食者，即便是数量不多的寄生蚁也可能保护它们不受掠食蚁的攻击，有效地减少了宿主蚁的死亡率。此外，这组作者证明了这些掠食蚁的侦察蚁倾向于让同巢的蚁前往气味表明不存在那种寄生客蚁的Sericomyrmex蚁群。这组作者说，Megalomyrmex蚁可能充当了保护其宿主的一种功能性兵蚁，这类似于某些中世纪城市持有的昂贵的雇佣兵部队，这样的部队被用于抵御机动部队的入侵。（生物谷 Bioon.com）
生物谷推荐的英文摘要
PNAS doi: 10.1073/pnas.1311654110
Chemically armed mercenary ants protect fungus-farming societies
Rachelle M. M. Adamsa,b,1, Joanito Libertia, Anders A. Illuma, Tappey H. Jonesc, David R. Nasha,1, and Jacobus J. Boomsma
The ants are extraordinary in having evolved many lineages that exploit closely related ant societies as social parasites, but social parasitism by distantly related ants is rare. Here we document the interaction dynamics among a Sericomyrmex fungus-growing ant host, a permanently associated parasitic guest ant of the genus Megalomyrmex, and a raiding agro-predator of the genus Gnamptogenys. We show experimentally that the guest ants protect their host colonies against agro-predator raids using alkaloid venom that is much more potent than the biting defenses of the host ants. Relatively few guest ants are sufficient to kill raiders that invariably exterminate host nests without a cohabiting guest ant colony. We also show that the odor of guest ants discourages raider scouts from recruiting nestmates to host colonies. Our results imply that Sericomyrmex fungus-growers obtain a net benefit from their costly guest ants behaving as a functional soldier caste to meet lethal threats from agro-predator raiders. The fundamentally different life histories of the agro-predators and guest ants appear to facilitate their coexistence in a negative frequency-dependent manner. Because a guest ant colony is committed for life to a single host colony, the guests would harm their own interests by not defending the host that they continue to exploit. This conditional mutualism is analogous to chronic sickle cell anemia enhancing the resistance to malaria and to episodes in human history when mercenary city defenders offered either net benefits or imposed net costs, depending on the level of threat from invading armies.
