Genetic divergence and the mating system in the endangered and geographically restricted species, Lambertia orbifolia Gardner (Proteaceae)

Abstract

Population genetic structure and the mating system were investigated in the endangered plant Lambertia orbifolia. This species is geographically restricted with two disjunct groups of populations. Twelve out of 19 allozyme loci were polymorphic and four were suitable for mating system studies. Levels of genetic variation within populations were comparable to other long-lived woody shrub endemics. Genetic divergence between population groups was very high (D = 0.252) and the F(ST) over all populations was 0.441. Gene flow estimates within population groups were low even though the maximum geographical distance between any pair of populations is 15 km and could be attributed to the localized movement of bird pollinators. Mating system studies on four populations showed consistently low levels of outcrossing, compared with other Proteaceae. Correlations of outcrossed paternity were moderately high and all were significantly greater than zero. Values ranged from r(p) = 0.33, in the two largest and very dense populations, to the highest value of r(p) = 0.54 in a smaller low-density population. The current population genetic structure in L. orbifolia is probably the result of local extinction of intervening populations because of Pleistocene climatic change and increased aridity, and extended isolation of the two remnants. It is proposed that the phylogenetically distinct Narrikup population group be recognized as a separate conservation unit and be given high priority for conservation action.