Abstract

Disjunct clades between the southern and the tropical Andes represent a biogeographical pattern that has not been studied. One of the plant groups showing this disjunction is the clade formed by the genera Archidasyphyllum, Arnaldoa and Fulcaldea (Asteraceae, Barnadesioideae). Archidasyphyllum is distributed in central and southern Chile and adjacent Argentina and is sister to the latter two, which in turn form a clade centered in northern Peru and southern Ecuador, with one species of Fulcaldea in Bahia, Brazil. The western American clades are separated by a distance of ca. 2500 km in direct line and have no representatives through the entire arid and hyperarid regions of the Pacific deserts and the dry Puna. We hypothesized that the Neogene origin of aridity in this intervening area might be responsible for this disjunction. To address this hypothesis, we estimated divergence times and ancestral range and quantified the climatic niches of the respective clades and compared them to each other and with the intervening area. Our results suggest a Miocene split of this clade from an ancestor previously distributed in the Central Andes, where the species of this clade are currently absent. Colonization of NE Brazil by Fulcaldea may have occurred during the Pliocene. The niche analysis rejects climatic niche conservatism and the intervening area is found to be climatically different from the current ranges occupied by either clade. We suggest that the global cooling trend in the Miocene and concomitant hyperaridity in the Pacific deserts and southern Central Andean highlands played a crucial role in the formation of this disjunct pattern and that the climatic niches of each clade have subsequently shifted in different directions.