Genetic variation in a geographically restricted and two widespread species of South American Nothofagus

Abstract

The amount and distribution of genetic variation is compared using starch get electrophoresis among populations of the three evergreen species of South American Nothofagus: the geographically restricted Nothofagus nitida (Phil.) Krasser and the widespread Nothofagus betuloides (Mirb.) Oerst. and Nothofagus dombeyi (Mirb.) Oerst. Ten enzyme systems were resolved coding for fifteen putative genetic loci. N. betuloides and N. dombeyi were more genetically variable than N. nitida; they had higher total number of alleles, mean number of alleles per locus, percent of polymorphic loci, mean expected heterozygosity, and mean total genetic diversity. These results are in agreement with the hypothesis that widespread species are often associated with historically large and more continuously distributed populations which in turn can maintain higher levels of genetic variation. Conversely, the genetic structure of N. nitida including its low genetic identity with the other two species and the presence of four unique alleles support the hypothesis that N. nitida has been isolated from the other two species for a considerable period of time. Genetic data in concert with the fossil record indicate that these taxa may be members of a pre-Pleistocene flora and consequently their genetic structures reflect a more ancient evolutionary history than previously hypothesized.