Exploring the fog vegetation in the marginal Atacama Desert: common evolutionary history of species-rich genera and morphological convergence in Nolana and Heliotropium sect. Cochranea

Abstract

The flora of the Atacama-Peru Desert (7{degrees}-30{degrees}S) is characterized by its remarkable diversity and adaptation in the driest place on Earth. It is composed of endemic and diverse genera, with most species having restricted geographic distributions. To infer its evolutionary history, the structure of a fog-dependent plant community in the Marginal Desert (27{degrees}-30{degrees}S) was characterized, with a special focus on congeners of Nolana and Heliotropium sect. Cochranea. Similarity profile analysis (SIMPROF) identified six plant assemblages differentially distributed along the altitudinal gradient. The congeners showed a pattern of niche segregation, with basal species N. rostrata and H. filifolium occupying the fog-influenced altitudinal range, while recently diverged species occurred outside its direct influence. To corroborate phylogenetic convergence, climatic zones were defined based on the presence of Nolana and Cochranea, and these were used to reconstruct ancestral areas and formulate a biogeographic hypothesis. The history of the Atacama Desert flora is marked by two periods: the formation of the hyperarid core (18{degrees}-27{degrees}S) during the late Miocene led to an initial divergence, leaving species isolated in different climatic zones. Then, beginning around 4 Mya, various wet phases promoted the northward geographic expansion of the flora inhabiting the Marginal Desert, with some genera reaching as far as Peru. Following geographic expansion, dry phases led to landscape-scale heterogeneity in water availability, promoting adaptive radiation. The ecological and phylogenetic affinities of N. rostrata and H. filifolium suggest that terete leaf morphology represents a case of evolutionary convergence associated with fog water capture.