Origin and biogeography of subgenus Podocarpus

QUIROGA, M.P., P. MATHIASEN, A.C. PREMOLI & A. IGLESIAS

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

The genus Podocarpus has a widespread distribution and provides the opportunity to contrast hypotheses of long-distance dispersal and vicariance in the Southern Hemisphere. These have been traditionally tested among different land masses using, for example, genera of austral origin as Nothofagus. Given that Podocarpus reaches tropical latitudes, it offers the chance to analyze divergence between disjunct forests within all South America and even more, within continents. The genus Podocarpus consists of two subgenera, Foliolatus found in Asia and Oceania, and Podocarpus present in Australia, Africa, New Zealand, New Caledonia, Madagascar, and tropical and temperate South America. We hereby calibrated the phylogeny of genus Podocarpus, using Bayesian analysis, including novel DNA sequences and fossil records to unravel the biogeographical history within subgenus Podocarpus. Sequences of the chloroplast (rbcL and matK) and two regions of the nuclear (ITS 1 and 2) were obtained by standard sequencing methods. The outgroup consisted of one species of Araucaria and also one species for each genus of the Podocarpaceae family. Our results suggest that subgenus Podocarpus is organized into two well supported and geographically differentiated clades. One includes Austral species, including those from southern South America, Australia, New Zealand, and New Caledonia. A second clade is composed of two subclades, including species of tropical and subtropical distribution in the Americas and Africa. Surprisingly, our data strongly suggest that those species distributed in subtropical South America are closed affiliated to African species, remaining far differentiated from other monophyletic tropical clade integrated by northern South America and the Caribbean. The molecular dating suggests a minimal age of 87 My for the origin of the genus Podocarpus, 30 My older than previously estimated minimal origin. The analysis suggesting disjunctions among southern continent clades are the result of vicariance events due to continental drifting. Disjunctions within South America are associated with vicariance after specifically geographic and climatic episodes happened in Paleogene and Neogene times. The differentiation between tropical-subtropical and southern South American species is probably associated with the presence of an extended and persistent arid barrier that impeded the migration between areas since the Paleogene. [Contribution to BID PICT2010 Nº430].