Global Biogeography And Evolutionary Drivers Of Ferns With Chlorophyllous Spores

About 14% of all fern species have chlorophyllous spores. Unlike their counterparts, chlorophyllous spores lack dormancy and have a shorter viability (i.e. only a few days in some species). Such spores should limit long-distance dispersal and be more susceptible to harsher climatic conditions raising questions about the evolutionary and ecological advantages of this trait. This study aims to assess the global biogeography of chlorophyllous-spored ferns evaluating their underlying environmental and evolutionary drivers. We studied the global distribution of 10,995 fern taxa across 556 geographical regions, and assessed the association of the proportional representation of 1387 chlorophyllous-spored species (CSS) with environmental variables using generalized linear mixed models. To assess the influence of phylogenetic relationships on the distribution of this trait across the phylogeny and across geographic regions, we calculated the phylogenetic signal and phylogenetic distances among species in different assemblages. Species richness of chlorophyllous-spored ferns peaked in the tropics while their proportional representation was highest in temperate and island floras. The proportion of CSS was positively influenced by water availability, but negatively by variables associated with temperature. Spore type was strongly conserved phylogenetically, and CSS assemblages were phylogenetically clustered towards higher latitudes. Our study provides strong evidence that chlorophyllous spores do not limit the geographical distribution of fern species. Their latitudinal distribution patterns can be explain both for environmental and phylogenetic drives.