Format: ORAL

Tim Bhnert1, Federico Luebert2, Maximilian Weigend1

1 Bonn Institute of Organismic Biology, University of Bonn, Bonn, Germany 2 Departamento de Ciencias Ambientales y Recursos Naturales Renovables and Departamento de Silvicultura y Conservación de la Naturaleza, Universidad de Chile, Santiago, Chile

Post-Miocene climate history, particularly in arid environments, has emerged as a key factor in shaping species dispersal and diversification. The Atacama Desert in northern Chile, one of the driest regions on Earth, stands out for its presumed Oligocene-Miocene age, as well its unexpectedly high biodiversity and elevated number of endemic species thriving under hyperarid conditions. Contrary to expectations, the extreme aridity of the Atacama predates the estimated divergence times of most extant genera. The initial onset of hyperaridity cannot have been the primary driver of diversification in these extant groups. We argue that recent climatic history, marked by intervals of pluvial and arid phases, especially during the Pliocene-Pleistocene transition, played an important role in shaping the current desert flora. Our research uses next-generation sequencing and molecular clock dating to unravel how this complex biogeographic and evolutionary history was influenced by past climate variability and Andean orogeny. Here, we briefly review our findings on the historical biogeography of selected Atacama taxa and discuss their broader implications for the existing body of knowledge on the Atacama Desert flora. A striking example is the genus Cristaria (Malvaceae), an element of the Chilean Mediterranean flora that colonized the Atacama during Pliocene pluvial phases. This led to in-situ diversification likely fueled by repeated introgressions and the emergence of new species. Conversely, the ca. 15 endemic species of Atriplex (Amaranthaceae) do not originate from local radiation alone: they arose from multiple colonization events (including by long-distance dispersal) followed by local divergence. The paleoendemic lineage Huidobria fruticosa (Loasaceae), on the other hand, appears to have undergone little if any diversification, despite being genetically separated from its closest relatives for about 50 million years. However, our data suggest that its recent population history can be traced to the Pliocene-Early Pleistocene transition.