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

Abstract

Premise: Antheridiogen systems are a set of pheromonal mechanisms that control sex expression in fern gametophytes. However, antheridiogen has rarely been studied outside of the laboratory, and little is known about its function in natural settings. Combining predictions based on field and laboratory study, we tested whether the sexual structure of gametophytic colonies of a tree fern were attributable to antheridiogen. Methods: Gametophytic colonies of the antheridiogen-producing tree fern Cyathea multiflora were collected at La Selva Biological Station in Costa Rica in January 2019. The sex of each gametophyte was determined, mapped, and spatial statistic approaches were used to examine the distribution of sex in each colony.Results: In all gametophytic colonies, males were most common, representing 62-68% of individuals. No hermaphroditic gametophytes were identified in any colony. A quadrat-based method showed female gametophytes were not clustered in each colony, while male gametophytes were clustered. In two of the colonies, the K(r) test statistic for males was greater than expected compared to random simulations of sex expression, indicating male sex expression was spatially associated with females. Conclusions: This study provides the first documentation of spatial sex expression in natural settings of gametophytes of an antheridiogen-producing tree fern species. The profound impact of antheridiogen on gametophytic sex expression in field settings suggests this system is intimately tied to mating system, fitness, and genetic diversity in Cyathea multiflora.

In Situ Observations of the Gametophytes of Six Fern Species of Costa Rica

“…However, field and lab work focusing on the ecology of fern gametophytes have clearly demonstrated the feasibility of working with this stage and has generated novel insights into fern biology. This phase of the life cycle is highly variable (reviewed by Farrar et al 2008), with gametophytes occupying a range of growth forms and habits (e.g., subterranean vs. terrestrial, short vs. longlived) at times beyond the range of their associated sporophytes (Nitta et al, 2021), exhibiting physiological niche space larger than the sporophyte (Nitta et al, 2021;Watkins et al, 2007;Watkins, Mack, and Mulkey, 2007), and playing important roles in mico-scale community ecology (Harrington et al 2022).…”

“…Such work has been welcomed as gametophytes have historically received less attention compared to the sporophyte, partly owing to their small size, ephemeral nature in temperate climates, locations where much of pteridology has been focused ( e.g., Pelosi and Sessa, 2021), and the general difficulty of identifying field collected material. Recent work has clearly demonstrated the importance of gametophyte field identification in understanding both the ecology ( e.g., de Groot et al, 2011; Harrington, Blake-Mahmud, and, Watkins, 2022) and evolution of ferns ( e.g., and Moran 2019; Nitta et al, 2021).…”