Biogeography of succulent spurges from Brazilian Seasonally Dry Tropical Forest (SDTF)

Seasonally Dry Tropical Forests (SDTFs) are found scattered throughout the Neotropics, from northwestern Mexico to northern Argentina, and southwestern and eastern Brazil, with eastern Brazil having the largest and most isolated fragment of SDTF, known as Caatinga. Growing knowledge from dated phylogenies and ancestral reconstruction studies suggests that SDTF lineages are nested in geographically structured phylogenies with clades highly restricted to each disjunct patch. To address these hypotheses, we investigated the biogeographic history of Euphorbia sect. Brasilienses, a group of succulent spurges from eastern Brazil's SDTF. To this aim, we assembled a concatenated matrix from 126 accessions with four markers (302 sequences from previous studies and 19 newly generated): one nuclear (ITS1) and three plastid (matK, ndhF, trnL-trnF) loci. Our results showed that clade Brasilienses and its sister group Stachydium diverged from a common ancestor during the Miocene around 16.5 Ma. Clade Stachydium was recovered with a mean crown age of 7.7 Ma, while clade Brasilienses was recovered as a relatively young group that started diversifying about 3.1 Ma. Biogeographic results showed that the ancestral range of the clade Stachydium + Brasilienses comprised the Andes and eastern Brazil's SDTF, therefore suggesting past connections between western and eastern South America. The ancestral range of clade Brasilienses was restricted to eastern Brazil SDTF, which contrasts with clade Stachydium, which was recovered with a broader ancestral range around Late Miocene. Our results suggest limited dispersal abilities, niche conservatisms and an origin for E. sect. Brasilienses pre-dating the Pleistocene. By contributing to the understanding of the origin and diversification of this group of endemic spurges, our study provides insights into the history of this SDTF in eastern South America.

Automated summary

This study found that the succulent spurge group Euphorbia sect. Brasilienses in eastern Brazil's SDTF originated in the Miocene, with its sister group Stachydium diverging around 7.7 million years ago and Brasilienses beginning to diversify around 3.1 million years ago. The ancestral range of the clade Stachydium + Brasilienses included the Andes and eastern Brazil's SDTF, indicating connections between western and eastern South America. The ancestral range of clade Brasilienses was limited to eastern Brazil's SDTF, showing limited dispersal abilities and niche conservatisms.