Spatial phylogenetics of the grasses in the Southern Cone provides insights into ecology and evolution of the family in South America

Abstract

In this study we explored the distributions of grass genera in the Southern Cone of South America, applying several phylogenetic diversity metrics and randomization tests. Grasses appear to have been present in South America since its early evolution as tropical understory species more than 60 My years ago. During the course of evolution, grasses have adapted to all terrestrial biomes and become one of the most successful plant families on earth. At present, the Southern Cone contains nearly all terrestrial biomes and a wide range of humid to arid ecoregions. Analyzing 126.514 point occurrences and four plastid markers for 148 genera (91% of the native grass genera), we found that tropical humid regions hold the highest phylogenetic diversity with no observed bias in branch lengths. These results indicate that niche conservatism dominates the diversity pattern of grasses in the Southern Cone. We found significantly low phylogenetic diversity in the Arid Chaco and in the Patagonian Steppe, which suggest ecological filtering in both warm and cold arid regions. The Patagonian Steppe also holds significantly longer branches than expected by chance, as the native grass flora is mainly composed of distantly related Pooideae genera with a northern hemisphere origin. Short branches are found in the Uruguayan Savanna suggesting that these grasslands could be a cradle for grass diversity within the Southern Cone. The dated phylogeny supported the current view of a relatively recent evolution of the family within the Southern Cone with most diversification taking place from the middle Miocene and onwards.