Biotic Interactions between the Gametophytes of Wall Rue (Asplenium ruta-muraria) and Other Fern Species

Abstract

Premise of research. The gametophytes of ferns are nutritionally independent of the sporophytes and are potentially hermaphroditic. The sexual expression of fern gametophytes is based on environmental cues. To prevent excessive self-fertilization, fern gametophytes employ strategies to increase mating between gametophytes. One of these strategies relies on antheridiogens, pheromones released by older gametophytes and absorbed by younger gametophytes. There are multiple distinct antheridiogen types, some of which are poorly understood and in need of further examination. A still-unresolved antheridiogen type was described in Asplenium ruta-muraria.Methodology. We employed cultivation experiments using spores of 12 fern species to assess the extent and uniqueness of the antheridiogen released by A. ruta-muraria. We tested antheridiogen interactions between representatives of three well-established antheridiogen types and A. ruta-muraria to assess their uniqueness. Furthermore, the effect of potentially antheridiogen-releasing gametophytes of A. ruta-muraria on multiple Asplenium species was examined. Germination in darkness in response to antheridiogens was also tested.Pivotal results. The younger gametophytes of A. ruta-muraria did not respond to the presence of older conspecific gametophytes in a way that could be attributed to antheridiogens. No antheridiogen interactions between A. ruta-muraria and any other species were observed. Nevertheless, the exudates of older A. ruta-muraria gametophytes may affect the development of younger conspecific and interspecific gametophytes.Conclusions. On the basis of its interaction with representatives of known antheridiogen types and the lack of germination in darkness, we conclude that our sample of A. ruta-muraria does not use antheridiogens. This discrepancy between our experiment and the initial publication describing antheridiogens in A. ruta-muraria may have been caused by intraspecific genetic variability within the species. The studied individual of A. ruta-muraria may be able to affect the growth of other gametophytes by other means, possibly via allelopathy, although this aspect of gametophyte interaction is poorly understood.