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Regalado, Ledis; Loriga, Josmaily; Bechteler, Julia; Beck, Andreas; Schneider, Harald; Heinrichs, Jochen (2018): Phylogenetic biogeography reveals the timing and source areas of the Adiantum species (Pteridaceae) in the West Indies, with a special focus on Cuba. In: Journal of Biogeography, Vol. 45, No. 3: pp. 541-551
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Abstract

Aim: The processes that shaped the West Indian fern flora remain poorly understood. We attempt to investigate earlier biogeographical patterns described for the region using the genus Adiantum as model. These patterns propose that the West Indian fern flora has (1) an essentially continental rather than insular character, having a rich representation of species occurring in tropical America;(2) the Greater Antilles have a higher fern diversity and higher endemism than the Lesser Antilles, and (3) adaptive speciation has been an important process in shaping the fern diversity of the Greater Antilles. Location: West Indies. Methods: Adiantum is a subcosmopolitan genus that comprises 200-225 species of which 33 occur in the West Indies. We compiled the most comprehensive molecular dataset of Adiantum available to date, including the chloroplast markers rbcL, atpA, atpB and trnL-F of 407 accessions belonging to 101 species, 24 of which occur in the West Indies. Maximum likelihood and Bayesian inference approaches were applied to generate phylogenetic hypotheses. Divergence times were estimated using published substitution rates. Ancestral areas were estimated using BioGeoBEARS. Results: The extant West Indian Adiantum species originate from at least 17 predominantly Miocene immigration events, 11 from South America and six from Central America, in combination with two cladogenetic events. The Cuban endemics Adiantum alomae and A. sericeum, as well as the Greater Antillean A. deltoideum, A. cristatum and A. pyramidale first appeared during the Pleistocene. The emergence of A. alomae and A. deltoideum coincides with the formation of the karstic relief of the Cuban coasts. Main conclusions: Immigration, rather than cladogenesis, governed the evolution of the West Indian Adiantum species. Our results concur with theoretical models proposed for island communities, suggesting that geologically younger and smaller island assemblages mainly derive from immigration, whereas cladogenesis plays an important role in older and larger islands.