Ephemeral windows of opportunity for horizontal transmission of fungal symbionts in leaf-cutting ants

Research output: Contribution to journalJournal articleResearchpeer-review

Michael Poulsen, Hermógenes Fernández-Marín, Cameron R. Currie, Jacobus J. Boomsma

Evolutionary theory predicts that hosts are selected to prevent mixing of genetically different symbionts when competition among lineages reduces the productivity of a mutualism. The symbionts themselves may also defend their interests: recent studies of Acromyrmex leaf-cutting ants showed that somatic incompatibility enforces single-clone gardens within mature colonies, thereby constraining horizontal transmission of fungal symbionts. However, phylogenetic analyses indicate that symbiont switches occur frequently enough to remove most signs of host-symbiont cocladogenesis. Here we resolve this paradox by showing that transmission among newly founded Acromyrmex colonies is not constrained. All tested queens of sympatric A. octospinosus and A. echinatior offered a novel fragment of fungus garden accepted the new symbiont. The outcome was unaffected by genetic distance between the novel and the original symbiont, and by the ant species the novel symbiont came from. The colony founding stage may thus provide an efficient but transient window for horizontal transmission, in which the fungus is unable to actively defend its partnership position before the host feeds on it, so that host fecal droplets remain compatible with alternative strains during the early stage of colony founding. We discuss how brief stages of low commitment between partners may increase the evolutionary stability of ancient coevolved mutualisms.
Original languageEnglish
JournalEvolution
Volume63
Issue number9
Pages (from-to)2235-2247
Number of pages13
ISSN0014-3820
DOIs
Publication statusPublished - 2009

Bibliographical note

Keywords: Animals; Ants; Basidiomycota; Behavior, Animal; Evolution; Gene Transfer, Horizontal; Molecular Sequence Data; Phylogeny; Symbiosis

    Research areas

  • Acromyrmex, basidiomycota, fungus-growing ants, host-symbiont specificity, incompatibility, symbiont transmission

ID: 18584618