In our publication (Ramírez-Barahona & Eguiarte 2015, Botanical Journal of the Linnean Society) we investigated the spatial genetic structure (SGS) in two populations of the cloud forest tree fern Alsophila firma (Cyatheaceae). Contrary to our expectations, we revealed a strong SGS in both populations of this species, despite it having an outcrossing breeding system, wind dispersal of spores and an arborescent habit. We hypothesize that SGS in ferns is probably being affected by the alternation between the two free-living life stages: the gametophyte and the sporophyte. Interestingly, we found that although tree ferns show strong SGS and are spatially clustered, there is no evidence of inbreeding increasing the levels of homozygosity within populations. To us, this suggests that the reproductive biology of ferns might include undocumented mechanisms that have evolved to avoid the negative consequences of increased inbreeding as genetically close individuals tend to aggregate in space.
Spatial genetic structure (SGS) in plants, namely the spatial aggregation of genetically related individuals, has been linked to several biological attributes of species, such as breeding system and life form. However, little is known about SGS in ferns, which together with lycopods are unique among land plants in having two free-living life stages.