THE MATING SYSTEM AND GENETIC DIVERSITY OF THE AUSTRALIAN ARID ZONE MALLEE, EUCALYPTUS-RAMELIANA

Estimates of parameters of the mixed mating model were made for three populations of the bird-pollinated arid zone eucalypt, Eucalyptus rame liana F. Muell. Levels of outcrossing ((t) over cap) varied significan tly between populations from mixed mating with substantial selfing ((t ) over cap = 0.54) to almost completely outcrossed ((t) over cap = 0.9 5). Comparison of single-locus and multilocus estimates suggested that the drop in outcrossing was due to increased self-pollination. The lo west outcrossing rate was attributed to the reduced ability of a popul ation with low numbers of buds to attract bird pollinators. Outcrossin g rates in E. rameliana are proposed to be a more direct reflection of pollination than estimates made for mass flowering, i.e. small-fruite d eucalypts. The distribution of allozyme diversity in E. rameliana al so appeared to reflect the impact of bird pollinators in promoting gen e flow as well as the species capacity for outcrossing and introgressi on. Levels of diversity were comparable with other eucalypts, but the proportion of diversity between populations (G(ST) = 9.2%) was only ab out half the mean for other eucalypts. Genetic distances between popul ations were low, but there was same significant differentiation of pop ulations which was attributed to non-random bird migrations. The impor tance of bird pollination in the mating system and the distribution of genetic diversity in E. rameliana emphasises that enough habitat to s upport nomadic birds should be preserved in order to conserve this euc alypt species.