No evidence for social immunity in co-founding queen associations

Ant queens often associate to found new colonies, yet the benefits of this behaviour remain unclear. A major hypothesis is that queens founding in groups are protected by social immunity and can better resist disease than solitary queens, due to mutual grooming, sharing of antimicrobials, or higher genetic diversity among their workers. We tested this hypothesis by manipulating the number of queens in incipient colonies of Lasius niger and measuring their resistance to the fungal entomopathogen Metarhizium brunneum. We found no evidence for social immunity in associations of founding queens. First, co-founding queens engaged in self-grooming, but performed very little allo-grooming or trophallaxis. Second, co-founding queens did not exhibit higher pathogen resistance than solitary queens, and their respective workers did not differ in disease resistance. Finally, queens founding in groups increased their investment in a component of individual immunity, as expected if they do not benefit from social immunity but respond to a higher risk of disease. Overall, our results provide no evidence that joint colony founding by L. niger queens increases their ability to resist fungal pathogens.

蚁后通常会结伴建立新蚁群，但该行为的演化收益仍未明确。主流假说认为，集群建群的蚁后可通过社会免疫（social immunity）获得保护，相较单只蚁后能更好地抵御病害，其优势来源包括同伴间的相互理毛、抗菌物质共享，或是工蚁群体更高的遗传多样性。我们通过调控黑毛蚁（Lasius niger）初期蚁群中的蚁后数量，检验了上述假说，并测定了蚁群对昆虫病原真菌（fungal entomopathogen）布鲁姆氏绿僵菌（Metarhizium brunneum）的抗性。我们未发现结伴建群的蚁后存在社会免疫相关的证据。首先，结伴蚁后仅会进行自我理毛，几乎未发生异亲理毛（allo-grooming）或交哺行为（trophallaxis）；其次，结伴蚁后的病原菌抗性并未高于单只蚁后，其各自繁育的工蚁的病害抗性也无显著差异；最后，集群建群的蚁后会提升个体免疫相关的投入——这一结果与“它们未从社会免疫中获益，而是对更高的病害风险做出响应”的预期相符。总体而言，我们的研究结果并未证明黑毛蚁蚁后结伴建群能够提升其抵御真菌性病原体的能力。