Genetic evidence for glacial refugia of the temperate tree Eucryphia cordifolia (Cunoniaceae) in southern South America.

摘要

Premise of the study: The temperate forests of southern South America were greatly affected by glaciations. Previous studies have indicated that some cold-tolerant tree species were able to survive glacial periods in small, ice-free patches within glaciated areas in the Andes and in southern Patagonia. Here we asked whether populations of the mesothermic species Eucryphia cordifolia also were able to survive glaciations in these areas or only in unglaciated coastal areas. Methods: The chloroplast intergenic spacer trnV-ndhC was sequenced for 150 individuals from 22 locations. Genetic data were analyzed (standard indexes of genetic diversity, a haplotype network, and genetic differentiation) in a geographical context. Key results: Two of the nine haplotypes detected were widespread in high frequency across the entire range of the species. The highest levels of genetic diversity were found around 40 degrees S, decreasing sharply northward and more moderately southward. No differences in genetic diversity were found between Andean and coastal populations. Notably, seven haplotypes were found in a small area of the Coast Range known as the Cordillera Pelada (40 degrees S). The differentiation coefficients G_ST and N_ST revealed that most of the genetic variation detected was due to variation within populations. Conclusions: The low levels of population differentiation and the high genetic diversity found in the Cordillera Pelada suggest that this area was the main refugium for E. cordifolia during glaciations. Nevertheless, given the high levels of genetic diversity found in some Andean populations, we cannot discount that some local populations also survived the glaciation in the Andes.Digital Object Identifier http://dx.doi.org/10.3732/ajb.1100013