Macaronesia Acts as a Museum of Genetic Diversity of Relict Ferns: The Case of Diplazium caudatum (Athyriaceae)

Abstract

Macaronesia has been considered a refuge region of the formerly widespread subtropical lauroid flora that lived in Southern Europe during the Tertiary. The study of relict angiosperms has shown that Macaronesian relict taxa preserve genetic variation and revealed general patterns of colonization and dispersal. However, information on the conservation of genetic diversity and range dynamics rapidly diminishes when referring to pteridophytes, despite their dominance of the herbaceous stratum in the European tropical palaeoflora. Here we aim to elucidate the pattern of genetic diversity and phylogeography of Diplazium caudatum, a hypothesized species of the Tertiary Palaeotropical flora and currently with its populations restricted across Macaronesia and disjunctly in the Sierras de Algeciras (Andalusia, southern Iberian Peninsula). We analysed 12 populations across the species range using eight microsatellite loci, sequences of a region of plastid DNA, and carry out species-distribution modelling analyses. Our dating results confirm the Tertiary origin of this species. The Macaronesian archipelagos served as a refuge during at least the Quaternary glacial cycles, where populations of D. caudatum preserved higher levels of genetic variation than mainland populations. Our data suggest the disappearance of the species in the continent and the subsequent recolonization from Macaronesia. The results of the AMOVA analysis and the indices of clonal diversity and linkage disequilibrium suggest that D. caudatum is a species in which inter-gametophytic outcrossing predominates, and that in the Andalusian populations there was a shift in mating system toward increased inbreeding and/or clonality. The model that best explains the genetic diversity distribution pattern observed in Macaronesia is, the initial and recurrent colonization between islands and archipelagos and the relatively recent diversification of restricted area lineages, probably due to the decrease of favorable habitats and competition with lineages previously established. This study extends to ferns the concept of Macaronesia archipelagos as refugia for genetic variation.

Parallel anagenetic patterns in endemic Artemisia species from three Macaronesian archipelagos

“…2021 ). As proposed by Ben-Menni Schuler et al . (2021) , the absence of a gradient of genetic diversity through Macaronesian archipelagos would disprove that colonization had occurred in a slow stepping stone model (from more diverse to less diverse areas).…”

Genetic Diversity and Phylogeography of the Relict Tree Fern Culcita macrocarpa: Influence of Clonality and Breeding System on Genetic Variation

“…Our findings add to the growing body of evidence demonstrating that island populations are not inherently less diverse (reviewed by [ 84 ]), but rather that other factors need to be considered. For instance, as in the case of C. macrocarpa , the role of islands as climatic refugia (where populations persist over long periods) and the ability of some plant species to disperse their propagules over long distances, as expected for spore-producing plants, (facilitating multiple colonization waves and thus secondary contact and hybridization of lineages) favor large, effective population sizes in island populations, which have been shown to be more genetically diverse than their mainland counterparts, and which can function as migratory stepping stones and can even recolonize the mainland (e.g., [ 19 , 85 , 86 ]).…”

“…Similar results were observed in Diplazium caudatum (Cav.) Jermy [ 86 ], where its presence in Andalusia (its only mainland locality) was attributed to recolonization after a long-distance dispersal event from Macaronesia (presumably the Canary Islands) with subsequent establishment by a single spore or few spores through intra-gametophytic selfing and vegetative propagation, followed by local dispersals.…”

Genetic Structure of Native Blue Honeysuckle Populations in the Western and Eastern Eurasian Ranges

“…This point of view is corroborated by our finding from a cpDNA analysis, which showed no phylogeographic structure among the studied populations. No polymorphism was detected in the two cpDNA regions frequently used in barcoding analyses [ 31 , 63 , 64 ]. However, we cannot exclude the occurrence of microevolutionary processes at the species level.…”