Antheridiogen controls spatial dynamics of sex‐expression in naturally occurring gametophytes of the tree fern Cyathea multiflora

<p>Background and aims: Antheridiogen systems are an important and widespread mechanism by which sex expression is controlled and genetic diversity maintained in fern gametophyte populations. However, antheridiogens have rarely been studied outside of the laboratory and little is known about their function in natural populations. Combining predictions based on field and laboratory study, we document the sexual structure of tree fern gametophyte populations and test the effects of antheridiogen <em>in situ</em>. </p> <p>Key results: In all populations, sex ratios indirectly indicate antheridiogen activity. No hermaphroditic gametophytes were identified in any population. Female gametophytes are randomly distributed in each population while male gametophytes tend to cluster. In two of the populations, male sex expression is spatially dependent on females, providing direct evidence of antheridiogen function <em>in situ</em>.</p> <p>Conclusions: This study provides the first documentation of spatial sex expression in natural gametophyte populations of an antheridiogen-producing tree fern species. The profound impact of antheridiogen on gametophyte sex expression in field settings suggests this system is intimately tied to mating systems, fitness, and genetic diversity in <em>Cyathea multiflora</em>.</p>