Species expansions into new habitats are often associated with physiological adaptations, for instance when rain forest lineages colonize dry habitats. Although such shifts have been documented for the Brazilian savanna (Cerrado), little is known about the biogeographic origin of species occupying an extreme South American habitat type, the coastal dunes (Restinga). We examined the formation of this poorly known, endangered habitat by reconstructing the evolutionary history of two endemic species. Due to the proposed recency and uniqueness of this habitat, we hypothesized that Restinga species of the palm genus Allagoptera to be recently evolved and to present derived morphological characters. To detect habit shifts in absolute time, we used one plastid and nine nuclear genes to reconstruct the phylogenetic and biogeographic history of Allagoptera. We used light microscopy and stable isotope analysis to explore whether morphological adaptations occurred concomitantly with habitat shifts. Phylogenetic relationships were well supported and we found ancestral lineages of Allagoptera to be widely distributed throughout habitats that are currently occupied by extant species. Over the last ca. 7 Ma Allagoptera has shifted its preference to increasingly dry habitats. Coincident with the colonization of the Cerrado and Restinga, morphological adaptations also evolved, including subterranean stems that are fire-resistant and long underground stem and root systems that facilitate water access. We did not find differences in metabolic pathway or modifications to pollen morphology when compared to other palm lineages. Assuming that the evolutionary history of Allagoptera is indicative of the habitat in which it occurs, our results infer a recent origin for Cerrado species. Although little is known about the formation of the Restinga habitat, our results also suggest a longer history than currently proposed; with an origin of Restinga habitats dating back to the Late Pliocene.
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