Origin and biogeography of subgenus Podocarpus

PAULA QUIROGA; PAULA MATHIASEN; ANDREA PREMOLI; ARI IGLESIAS

Mendoza

Congreso; 4th International Paleontological Congress,; 2014

IANIGLA CCT CONICET Mendoza

The genus Podocarpus widely distributed in the Southern Hemisphere provides a great opportunity to contrast biogeographical hypotheses. Given that Podocarpus reaches tropical latitudes, it offers the chance to analyze divergence between disjunct forests within South America and even more among continents. The genus Podocarpus consists of two subgenera, Foliolatus found in Asia and Oceania, and Podocarpus (Eupodocarpus) present in Australia, Africa, New Zealand, New Caledonia, Madagascar, and tropical and temperate South America, with 50 species approximately each one. We present the phylogenetic relationships specially among South American Podocarpus species using nuclear and chloroplast DNA regions, estimate the divergence time of clades within Eupodocarpus subgenus, and finally propose reviewing the subgeneric classification. The phylogeny includes new sequences of species from South America not included in previous studies; the first record of macrofossil of Podocarpus from Patagonia with age constrained fossil data, which comes from precise isotope geochronology or can be well correlated to a specific geological frame. The phylogenetic hypotheses suggest a strong geographical association within Eupodocarpus clades. The Austral subclade includes species from southern landmasses. The other clade is composed by two subclades, including species of tropical and subtropical distribution in the Americas and Africa. The African species are sister to subtropical South American species, and the tropical species from America are included in an independent subclade. The molecular dating suggests a minimal age of 87 (63.35 - 117.84) My for the minimum age of the genus Podocarpus. Our results suggest that disjunctions among clades in southern continents are the product of vicariance events due to continental drifting. In addition, disjunctions within South America are associated to vicariance after specifical geographic and climatic episodes occurred during the Paleogene and Neogene times. The differentiation between tropical-subtropical and southern South American species is probably associated with an ancient presence of an extended and persistent arid barrier that impeded the migration between both areas. Finally, as a strong evidence of molecular and morfological monophyly of each subgenera, we propose revisiting the subgeneric classification and rise the subgenera Podocarpus and Foliolatus to the genus level.