Neutral and adaptive genetic structure of the South American species of Nothofagus subgenus Lophozonia. Natural history, conservation, and tree improvement implications

The combined analysis of neutral and adaptive genetic variability is important to evaluate the genetic structure of forest trees and to help developing strategies of conservation and tree genetic improvement. I investigate the genetic diversity of the South American species of Nothofagus subgenus Lophosonia--N. obliqua, N. alpina, and N. glauca--emphasizing their intra- and interpopulational variability. I analyzed their genetic diversity by 1) measuring neutral variability at nuclear microsatellite DNA loci, and 2) measuring morphological traits on progeny-provenance trials (i.e. common gardens). For neutral markers I found relatively high genetic diversity levels (HE=0.50, 0.62, and 0.66 for N. glauca, N. alpina, and N. obliqua , respectively) and low but significant genetic structure ( RST=9, 11, and 15% for N. glauca, N. obliqua, and N. alpina, respectively). In N. obliqua , this limited structure was spatially organized in three latitudinal groups. I also detected what appears to be introgression of N. alpina genes into N. obliqua in the northern populations. For growth traits (morphological) I found higher genetic structure ( =0.57-0.89) than for neutral markers, and in N. obliqua these estimates were substantially higher ( =0.85-0.89) than in N. alpina ( =0.57-0.63).;Heritabilities in growth traits were higher for N. obliqua (h2=0.14-0.30) than for N. alpina ( h2=0.06-0.14). There was a trend of faster growth in N. obliqua populations adapted to warmer and rainier environments and a tendency of presenting less dense stomata in populations adapted to colder environments. My neutral nuclear marker results support the multiple refugia hypothesis, suggesting several centers of genetic diversity. Moreover, these results indicate that N. obliqua and N. alpina are more genetically similar to each other than to N. glauca , and N. obliqua does not have sufficiently differentiated subgroups that could represent new taxa. The morphological traits demonstrate that natural selection plays an important role in generating adaptive variation in N. obliqua, indicating that this species may have a better chance to adapt to future climatic changes and should respond better to artificial selection than N. alpina. Finally, combining both data types, I propose conservation priorities among and within species, and breeding zones within species for tree improvement strategies. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html).