Plant evolution and diversity at the dry limit

Abstract

With 750 to 1000 plant species the Atacama Desert has a rich flora that evolved to its extreme and harsh arid environmental conditions. We focused on a variety of plant groups with different life history traits from the families Asteraceae, Bromeliaceae, Cactaceae, Loasaceae, Malvaceae and Zygophyllaceae to decipher their evolutionary history in the Atacama Desert and trace down colonization patterns in the past and the future, as well as the genetic basis of their adaptation to this (hyper-)arid desert. In an interdisciplinary setting we place our population genetic and genomic/transcriptomic analyses in the context of geological, geomorphological and climatic data. Our results point to an evolutionary young flora that originated mainly during the Paleogene and Neogene with accelerated diversification radiations taking place since the last 5-6 million years. The onset of hyper‐aridity during the late Miocene as well the Quaternary climate oscillation have played a major role in the diversification of various plant groups. Population genetic analyses indicate that the dry core of the northern part of the Atacama acts as powerful barrier for floristic exchange and gene flow (e.g., Ophryosporus (Asteraceae), Huidobria, (Loasaceae)) which does not hold true for the southern part of the Atacama that is characterized by ravines and valleys connecting the coast to the Andean foothills. Observed genetic clusters are linked to ravines linking the coast with the Andes and are mirrored in gene expression patterns thus offering valuable insights into the genetic adaptation of desert plants (e.g., Huidobria chilensis). In addition, genetic isolation of coastal taxa is indicated due to recent climatic variability (e.g., Cristaria (Malvaceae)). Our results stemming from the Atacama flora is tested in the corresponding desert system of the Namib (e.g., Kissenia (Loasaceae), Zygophyllum (Zygophyllaceae)). in southern Africa and will enable us to find general patterns of plant evolution in arid environments.