Genetic decline and inbreeding depression in an extremely rare tree

Many endangered species have small population sizes, with less than 10 remaining individuals in some extreme situations. Although the consequences of a small population size have received considerable research attention, few studies have examined the fate of extremely rare plants. Ostrya rehderiana is one such species, with only 5 naturally-regenerated surviving individuals and less than 150 artificially-regenerated progeny. Using amplified fragment length polymorphisms (AFLPs), we found that there was a low percentage of polymorphic loci but moderate heterozygosity in the 5 wild individuals. A severe decline in genetic diversity was observed in the progeny, with a decrease of 36.7% in heterozygosity and of 12% in the number of markers that were amplified per individual compared with the parental generation, a result which was caused by genetic drift and inbreeding. The effective population size was estimated to be 1. A significant positive relationship between parental genetic dissimilarity and the number of surviving offspring was observed, which indicated that inbreeding depression might have purged more inbred offspring. Implications for protection and recovery of the genetic variation of extremely rare plants, such as O. rehderiana, are proposed.