Historical Biogeography and Macroevolution of the Atacama Desert Flora

Abstract

Located in northern Chile, the Atacama Desert is not only one of the oldest deserts but also one of the driest places on earth with hyperarid conditions prevailing since the Miocene or earlier. Despite the extreme conditions documented for the desert, its flora is surprisingly rich in terms of species diversity and degree of endemism. Objective of this thesis is to better understand the floristic composition of the coastal and Andean vegetation of the desert and to explore whether the origin of plant lineages coincides with climatic and geological factors responsible for the hyperaridity in the Atacama Desert during the middle and late Miocene. Further, to find out if the diversification of speciose plant lineages in the Atacama Desert correlates with increasing aridity during the Miocene and Pliocene as well as with the Quaternary climate oscillation. The floristic composition of the Andean foothills was studied based on plot-based vegetation assessments along four altitudinal transects. A nomenclatural correction of the genus <i>Atriplex</i> L. (Amaranthaceae) is presented applying the priority rule of the botanical code of nomenclature for plants. In order to understand the colonization history for the genera <i>Atriplex</i> and <i>Cristaria</i> Cav. (Malvaceae) as well as the five representatives of Zygophyllaceae in the Atacama Desert, phylogenic studies have been conducted using plastid sequencing information. These datasets were analyzed using Maximum Likelihood and Bayesian molecular clock dating and an ancestral area reconstruction approach under the Dispersal Extinction Cladogenesis. Two chapters are devoted to the results of a modified restriction site associated DNA sequencing approach, termed genotyping-by-sequencing (GBS). The vegetation of the Andean foothills is highly dissimilar to the vegetation at coastal range of the Atacama Desert and the floras of the Peruvian and Chilean coast are equally dissimilar, while a floristic connection along the Andes between those two countries does exist. This floristic connection is underpinned by genetic connection shown for <i>Atriplex</i> and <i>Cristaria</i>. Furthermore, for both genera relatively young crown node ages have been estimated. In fact, member of the genus <i>Atriplex</i> has colonized the Atacama Desert at least three times in the late Pliocene and Pleistocene, while the genus <i>Cristaria</i> evolved through a vicariant separation from its sister genus due to Andean uplift during early and mid-Miocene. Ancestral area reconstruction suggests a possible origin in what is called today Mediterranean Chile, with a colonization of the Atacama Desert during the Pliocene and Pleistocene, similar to what was estimated for the genus <i>Atriplex</i> and other speciose genera in the Atacama Desert. In fact, most of the diversification processes seem to be the result of recent climatic history during the Quaternary. The onset and persistence of hyperaridity in the Atacama Desert had little effect on the present flora and its spatiotemporal development, compared to the major impact of the Quaternary climate oscillation.