Genetic Diversity and Population Structure of Olearia flocktoniae Maiden & Betche (Asteraceae) - A Comparison of Aboveground and Seed Bank Populations

Abstract

<i>Olearia flocktoniae</i> Maiden & Betche (Asteraceae) is an endangered shrub found within a 45 x 45 km area in the Dorrigo District of northern NSW, Australia. A genetic diversity study using allozyme loci was conducted comparing 14 aboveground and 6 seed bank (2 extinct and 4 extant) populations. The degree of polymorphism (P) and allelic frequencies (A) for aboveground populations (0.32 and 1.32, respectively) was comparable to that found for endemic species; expected heterozygosity (H_e) (0.15) was closer to values expected for widespread species. The fixation index (F_ST) (0.15) indicated moderately substructured populations while observed heterozygosity to expected heterozygosity H_o/H_e (1.35) and the inbreeding coefficient (F_IT) (-0.13), suggested an excess of heterozygotes. The age of aboveground populations was significantly related to the number of effective alleles (A_e) and H_e. No significant differences between extant and extinct populations were found in terms of P, A and A_e. Significant differences were found between seed bank populations and their respective aboveground populations in three out of four allozyme loci. Seed bank populations were more homozygous (F_IT = -0.09) than aboveground ones (F_IT = -0.59) indicating selection against homozygote individuals from surviving to the next life stages. Both aboveground and seed bank populations were marked with high genetic identities (0.9677 and 0.9596, respectively). Allelic richness (A_e) in populations was significantly related to population age. Though there was a general clustering of the populations' genetic distances in relation to geographical distance, some populations from the opposite sides of the metapopulation had high identities whereas some neighbouring populations had low identities. This supports previous suggestions that seed are moved by vehicles associated with logging activities. The rapid decline of <i>Olearia flocktoniae</i> populations in the last five years as reported in annual field surveys may be a natural pattern for this rare species. However, maintaining populations for extended periods (5 years+) through active management is likely to increase the number of effective alleles. Routine genetic assays (c. every 5 years) of the populations should be a part of its management plan.