Evolution in the high-altitude Páramo ecosystem

Abstract

The Páramo ecosystem is the most diverse high-altitude ecosystem on Earth with more than 4000 species of vascular plants. A naturally fragmented ecosystem, it also houses one of the youngest and fastest evolving biota. In this thesis, molecular data from the South American species of Oreobolus (Cyperaceae) and Páramo representatives within the Melastomeae tribe (Melastomataceae) were used to investigate the impact of Andean orogeny and recent climatic fluctuations on diversification processes. Chapter Two highlights the role of Andean uplift in the diversification of Páramo species of Oreobolus as shown by their faster diversification rates compared to other southern hemisphere species. It is suggested that Oreobolus may have reached South America from Australia during the Pliocene through two independent long-distance dispersal events to the northern and southern Andes. This strong north-south geographic structure is evident in the species phylogeny. Chapter Three is a phylogeographic study of the South American species of Oreobolus that reveals complex relationships between and within species. Levels of haplotype sharing, measures of genetic distinctiveness and recent divergence times point to incomplete lineage sorting confounding species boundaries. Additionally, the role in species diversification of the contraction and expansion of Páramo islands during the climatic fluctuations of the Quaternary is supported by genetic data. Chapter Four showed that colonisation of Páramo within the largely Neotropical Melastomeae tribe occurred repeatedly during the Pliocene. Species-poor Páramo lineages such as Castratella may highlight a possible role for extinction in some taxa. In Chapter Four I also suggested that frost adapted temperate lineages may have had an adaptative advantage that may have contributed towards a greater number of species at higher elevations.