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.
Highlights
A growing amount of evidence, mainly from population genetics and phylogeographic studies of endemic angiosperms, supports the Macaronesian archipelagos acted as efficient refugia for genetic diversity of relict taxa [5,6,7,8,9,10]
Samples of D. caudatum were obtained from 12 populations in four geographical regions across its distribution range: Andalusia, Azores, Canary Islands and Madeira
100% of the MLGs of D. caudatum are resolved as shown in the genotypic accumulation curve (Figure S1)
Summary
Macaronesia, which comprises the mid-Atlantic oceanic archipelagos of the Azores, Canaries, Cape Verde, Madeira and Selvagems, is considered an exceptional biogeographical and evolutionary model system [1]. [2] proposed the relictualism hypothesis for the Macaronesian flora, since the Macaronesian endemic element was a relict of the formerly widespread subtropical lauroid flora that lived in Southern Europe during the Tertiary, especially during the Palaeogene Period (66–23.03 Ma; [3,4]). A growing amount of evidence, mainly from population genetics and phylogeographic studies of endemic angiosperms, supports the Macaronesian archipelagos acted as efficient refugia for genetic diversity of relict taxa [5,6,7,8,9,10]. Has been revealed general patterns of colonization and dispersal, including single colonization of a common ancestor followed by rapid radiation, multiple independent colonizations, back-colonization to the continent from
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