Caste-specific symbiont policing by workers of Acromyrmex fungus-growing ants

TY - JOUR

T1 - Caste-specific symbiont policing by workers of Acromyrmex fungus-growing ants

AU - Ivens, Aniek B.F.

AU - Nash, David R.

AU - Poulsen, Michael

AU - Boomsma, Jacobus J.

N1 - Key words: evolutionary stability, leaf-cutting ants, mutualism, symbiont policing.

PY - 2009

Y1 - 2009

N2 - The interaction between leaf-cutting ants and their fungus garden mutualists is ideal for studying the evolutionary stability of interspecific cooperation. Although the mutualism has a long history of diffuse coevolution, there is ample potential for conflicts between the partners over the mixing and transmission of symbionts. Symbiont transmission is vertical by default, and both the ants and resident fungus actively protect the fungal monoculture growing in their nest against secondary introductions of genetically dissimilar symbionts from other colonies. An earlier study showed that mixtures of major and minor Acromyrmex workers eliminate alien fungus fragments even in subcolonies where their resident symbiont is not present. We hypothesize that the different tasks and behaviors performed by majors and minors are likely to select for differential responses to alien fungi. Major workers forage and cut new leaves and masticate them after delivery in the upper parts of the fungus garden and so are likely to more frequently encounter alien fungus than minor workers maintaining the established fungus garden and caring for the brood. We show that major workers of Acromyrmex echinatior indeed express stronger incompatibility reactions toward alien fungus garden fragments than minor workers. This implies that only the major workers, through recognition and exclusion of foreign fungus clones at their point of entry to the nest, have a realistic possibility to eliminate alien fungal tissue before it gets incorporated in the fungus garden and starts competing with the resident fungal symbiont.

AB - The interaction between leaf-cutting ants and their fungus garden mutualists is ideal for studying the evolutionary stability of interspecific cooperation. Although the mutualism has a long history of diffuse coevolution, there is ample potential for conflicts between the partners over the mixing and transmission of symbionts. Symbiont transmission is vertical by default, and both the ants and resident fungus actively protect the fungal monoculture growing in their nest against secondary introductions of genetically dissimilar symbionts from other colonies. An earlier study showed that mixtures of major and minor Acromyrmex workers eliminate alien fungus fragments even in subcolonies where their resident symbiont is not present. We hypothesize that the different tasks and behaviors performed by majors and minors are likely to select for differential responses to alien fungi. Major workers forage and cut new leaves and masticate them after delivery in the upper parts of the fungus garden and so are likely to more frequently encounter alien fungus than minor workers maintaining the established fungus garden and caring for the brood. We show that major workers of Acromyrmex echinatior indeed express stronger incompatibility reactions toward alien fungus garden fragments than minor workers. This implies that only the major workers, through recognition and exclusion of foreign fungus clones at their point of entry to the nest, have a realistic possibility to eliminate alien fungal tissue before it gets incorporated in the fungus garden and starts competing with the resident fungal symbiont.

U2 - 10.1093/beheco/arn150

DO - 10.1093/beheco/arn150

M3 - Journal article

SN - 1045-2249

VL - 20

SP - 378

EP - 384

JO - Behavioral Ecology

JF - Behavioral Ecology

IS - 2

ER -