A relic of the past: current genetic patterns of the palaeoendemic tree Nothofagus macrocarpa were shaped by climatic oscillations in central Chile.

BACKGROUND AND AIMS The Mediterranean-type forest of central Chile is considered a "biodiversity hotspot" and a relic of a wider ancient distribution produced by past climatic oscillations. Nothofagus macrocarpa, commonly known as 'roble de Santiago', is a threatened palaeoendemism of this forest, poorly represented in the protected area system. This tree has been repeatedly misidentified as the sister species N. obliqua, which has affected its recognition and protection. Only a few populations of N. macrocarpa remain within a matrix of intensive land use that has been affected by recent forest fires. We tested the hypothesis that current populations of N. macrocarpa are a relic state of a previously widespread range, with the aim of contributing to its identification, biogeographic history, and the design of conservation measures using genetic information. METHODS We analysed remnant N. macrocarpa forests using nuclear (nDNA) and chloroplast (cpDNA) DNA sequences, conducted phylogenetic and phylogeographic analyses to reconstruct its biogeographic history, and assessed microsatellites (SSRs) to determine contemporary patters of diversity within and among all remnant populations. We also examined the degree of past, current, and potential future isolation of N. macrocarpa populations using ecological niche models (ENMs). KEY RESULTS The N. macrocarpa species was confirmed by chromosomal nDNA sequences, as previously suggested. Small isolated populations of N. macrocarpa exhibited moderate to high genetic diversity according to SSRs. cpDNA analysis revealed a marked past latitudinal geographic structure, whereas SSRs analysis did not find such current structure. ENM analyses show local expansion-contraction of the N. macrocarpa range during warmer climates, particularly in the northern and central ranges where basal-most cpDNA haplotypes were detected, and recent expansion to the south of the distribution. CONCLUSIONS Genetic patterns confirm that N. macrocarpa is a distinct species and suggest a marked latitudinal relic structure in at least two evolutionarily significant units (ESUs), despite contemporary gene flow among the population. This information must be considered when choosing individuals (seeds and/or propagules) for restoration purposes, to thus avoid the admixture of divergent genetic stocks.