Genetic variation in an endangered cedar (Widdringtonia cedarbergensis) versus two congeneric species

Widdringtonia cedarbergensis is a southern African conifer species under threat of extinction. This study explored the genetic status of the species to assess whether loss of genetic variation may be contributing to population declines. Widdringtonia nodiflora and W. schwarzii were used as benchmarks against which to compare genetic diversity in W. cedarbergensis. Isozyme electrophoresis was used to resolve seventeen isozyme loci in seedlings of the three species. Genetic diversity was greatest in W. nodiflora, followed by W. cedarbergensis and W. schwarzii. There is no evidence that W. cedarbergensis has undergone a genetic bottleneck relative to its sister species. Patterns of genetic variation varied between species with most of the variation occurring within populations of W. cedarbergensis, between populations of W. schwarzii, and within population ‘neighbourhoods’ of the more widespread W. nodiflora. The isozyme data indicate inbreeding,probably due to self-pollination, in W. cedarbergensis and W. nodiflora. Populations of W. schwarzii were outbreeding. Selfing in W. cedarbergensis may be caused by a change in population density from dense to sparse stands with potentially deleterious genetic consequences