Multiple Pleistocene refugia in the widespread Patagonian tree Embothrium coccineum (Proteaceae)

Abstract

Embothrium coccineum J.R.Forst. & G.Forst is an endemic tree of the Patagonian temperate forest. The objective of this study is to evaluate the impact of last glaciation events on the genetic structure of this widespread and ecologically tolerant species, to postulate possible refugial areas. Phylogeographic analyses were performed using chloroplast DNA sequences (trnL-trnF spacer and ndhC-trnV spacer) from individuals collected in 34 populations along the total range of the species, and these results were compared with a similar study in Nothofagus. A total of 22 haplotypes were found, three of which were widely distributed while 13 were found at only one location. Historical demography suggests a long period of stable effective population size, decreasing gradually towards the Last Glacial Maximum (LGM), followed by an increase in population size that stabilised 2500 years ago. The phylogeographic analyses reflect recent events of colonisation after the LGM from multiple refugia. In the northern area of its distribution probably the species survived in several pockets within the Andes mountain range and in Cordillera de la Costa in Chile. In the south, it is suggested that Embothrium survived the glacial period at the edge of the glaciers. These findings are in agreement with the fossil pollen record that shows 10 000-year-old grains in the south, suggesting colonisation from nearby areas when ice retreated. Embothrium is a coloniser that naturally occurs as scattered individuals within mixed forests. Hence, the shallow phylogeographic structure reported here reflects a Pleistocene signature highly impacted by drift resulting in the randomly fixation of new variants reducing the cpDNA structure.