The mating system and population genetic structure in a bird-pollinated mallee, Eucalyptus rhodantha

Abstract

The mating system and spatial genetic structure of the rare and endangered bird-pollinated mallee Eucalyptus rhodantha were investigated in a remnant stand, using progeny arrays and pollen assayed at four polymorphic allozyme loci. Comparisons of the genetic diversity within and between the pollen pools and maternal parents of two arbitrary subpopulations indicated the presence of spatial genetic heterogeneity which was not broken down by pollen flow. It was suggested that this is the result of a high level if inbreeding and limited pollen dispersal by birds. Estimates of outcrossing rate ranged between t=0·59 and t=0·67 and were at the low end of the range reported for other eucalypts. It was concluded that E. rhodantha has a mixed mating system with a significant proportion of self-pollination. Biparental inbreeding within small neighbourhoods probably also contributed to the high level of inbreeding. The low level of outcrossing observed in E. rhodantha was not consistent with the hypothesis that bird pollination leads to high levels of outcrossing in the Australian flora. However, the level of outcrossing achieved through bird pollination together with high levels of gene flow between populations contribute to the maintenance of the relatively high levels of diversity which characterise the dissected populations of this species.