Genetic diversity and differentiation in south-western Australian bloodwoods (Corymbia section Calophyllae, Myrtaceae) with different ranges and abundance.

An understanding of how variation is shared within and among closely related species is important for understanding evolutionary processes and managing biological diversity. We studied genetic structure in the three species occurring in south-western Australia that form the small and distinct monophyletic section Calophyllae of the genus Corymbia. We compared diversity in nuclear microsatellites and chloroplast DNA sequences in two species with patchy distributions, namely, Corymbia haematoxylon (Maiden) K.D. Hill & L.A.S. Johnson and Corymbia ficifolia (F. Muell.) K.D. Hill & L.A.S. Johnson, with that in the widespread congener, C. calophylla (Lindl.) K.D. Hill & L.A.S. Johnson. Consistent with predictions for the influence of range and abundance on genetic structure in the Australian flora, population differentiation was higher in the two restricted patchy species than in the widespread, semicontinuous C. calophylla. Genetic diversity in C. haematoxylon was similar to that in C. calophylla , but diversity was lower in the highly localised C. ficifolia , likely owing to genetic bottlenecks. All three species were distinguished by nuclear SSR variation, but C. haematoxylon and C. ficifolia each shared chloroplast haplotypes with C. calophylla from incomplete lineage sorting of ancestral variation and introgression. Limited evidence of recent hybridisation in two populations of C. haematoxylon was also present. Understanding how genetic variation is shared between species is important for managing biological diversity. There are only three bloodwood tree species in south-western Australia and the species are closely related through shared ancestry. Genetic differentiation was higher among species with patchy distributions, whereas diversity was lower only in the species with a highly localised range, and probably indicates the impact of severe reductions in population size in species with very restricted distributions. [ABSTRACT FROM AUTHOR]