High genetic identities between three oil mallee taxa, Eucalyptus kochii ssp. kochii, ssp. plenissima and E. horistes, based on nuclear RFLP analysis

Population genetic analysis and phylogeny reconstruction in Eucalyptus (Myrtaceae) using high-throughput, genome-wide genotyping

A set of over 8000 Diversity Arrays Technology (DArT) markers was tested for its utility in high-resolution population and phylogenetic studies across a range of Eucalyptus taxa. Small-scale population studies of Eucalyptus camaldulensis, Eucalyptus cladocalyx, Eucalyptus globulus, Eucalyptus grandis, Eucalyptus nitens, Eucalyptus pilularis and Eucalyptus urophylla demonstrated the potential of genome-wide genotyping with DArT markers to differentiate species, to identify interspecific hybrids and to resolve biogeographic disjunctions within species. The population genetic studies resolved geographically partitioned clusters in E. camaldulensis, E. cladocalyx, E. globulus and E. urophylla that were congruent with previous molecular studies. A phylogenetic study of 94 eucalypt species provided results that were largely congruent with traditional taxonomy and ITS-based phylogenies, but provided more resolution within major clades than had been obtained previously. Ascertainment bias (the bias introduced in a phylogeny from using markers developed in a small sample of the taxa that are being studied) was not detected. DArT offers an unprecedented level of resolution for population genetic, phylogenetic and evolutionary studies across the full range of Eucalyptus species.

Extensive pollen dispersal in a bird-pollinated shrub,Calothamnus quadrifidus, in a fragmented landscape

Pollen dispersal was investigated in six populations of Calothamnus quadrifidus, a bird-pollinated shrub in the fragmented agricultural region of southern Western Australia. Paternity analysis using six microsatellite loci identified a pollen source within populations for 67% of seedlings, and the remainder were assumed to have arisen from pollen sources outside the populations. Outcrossing was variable, ranging from 5% to 82%, and long-distance pollen dispersal was observed in all populations with up to 43% of pollen sourced from outside the populations over distances of up to 5 km. This extensive pollen immigration was positively associated with population size but not isolation. Comparison of two populations of similar size but different density showed greater internal pollination and less selfing in the denser population, suggesting an influence of density on pollinator behaviour. The study revealed extensive long-distance pollen dispersal for C. quadrifidus within this fragmented agricultural landscape and highlighted the interaction between reserve populations and isolated road verge remnants in maintaining genetic connectivity at the landscape scale.

Salinity mitigation versus weed risks — can conflicts of interest in introducing new plants be resolved?

Southern Australia’s annual-based agricultural system has come at a large cost to the landscape. Dryland salinity is a rapidly expanding environmental problem that is reducing the amount of land available for agriculture, and causing a significant ecological cost to remnant and riparian vegetation. There is an urgent need to increase the area of the landscape that is sown to deep-rooted herbaceous perennials to reduce the increase in dryland salinity, and for their successful adoption by landowners it is recognised that these perennials must be economically viable. Australian perennials are unlikely to provide such options in the short term and therefore there is a need to search for species overseas. Many agricultural weeds have arisen as a direct result of deliberately introduced species escaping cultivation and naturalising in the Australian environment. They cause a huge cost to agriculture in terms of both lost production and control. There is also a cost to natural ecosystems as a result of lost biodiversity and weed management. A conflict of interest thus arises. This paper follows on from a workshop held between the CRC for Plant-based Management of Dryland Salinity and the CRC for Australian Weed Management. It discusses 4 key areas where potential conflict exists between the maintenance of biodiversity in natural ecosystems and the development and introduction of new herbaceous perennials. Each of the issues within pre-entry weed risk assessment, post-entry weed risk assessment, weed risk of translocating native species and field assessments of new species is discussed in detail and suggestions are given on the means to resolve the conflicts. Actions to address the recommendations are urgently required if we are going to resolve the current conflicts of interest between the need for managing present and future environmental weeds and for mitigating dryland salinity.

Regional genetic differentiation in Western Australian sandalwood (Santalum spicatum) as revealed by nuclear RFLP analysis

Western Australian sandalwood, Santalum spicatum, is widespread in the semi-arid and arid regions of Western Australia, and there is some morphological variation suggestive of two ecotypes. The level and structuring of genetic diversity within the species was investigated using anonymous nuclear RFLP loci. Santalum spicatum showed moderate levels of genetic diversity compared to other Australian tree species. The northern populations in the arid region showed greater levels of diversity and less population differentiation than the southern populations in the semi-arid region due to differences in the distribution of rare alleles. Equilibrium between drift and gene flow in the northern populations indicated that they have been established for a long period of time with stable conditions conducive to gene flow. In contrast, the southern populations showed a relationship between drift and gene flow indicative of a pattern of fragmentation and isolation where drift has greater effect than gene flow. The different patterns of diversity suggest that the ecotypes in the two regions have been subject to differences in the relative influences of drift and gene flow during their evolutionary history.

Phylogenetics and the conservation of a diverse and ancient flora

Phylogenetics has a valuable role in the conservation of the flora of Western Australia particularly in the south-west where the complex evolutionary history has resulted in a diverse flora with both relictual and recently evolved components. Phylogenetic analysis contributes to conservation of plants through clarification of taxonomic status, identification of unique evolutionary lineages, determination of relictual and recently derived species, determination of phylogenetic value for conservation priority setting, and identifying phylogenetically independent comparisons between rare and widespread species. The contribution of phylogenetic analysis to these aspects of effective conservation management are discussed with examples from various species in Western Australia.

Nuclear RFLP variation in Eucalyptus camaldulensis Dehnh. from northern Australia

Eucalyptus camaldulensis Dehnh. is the most widely planted eucalypt in the tropics. Natural populations are riparian and sampling strategies for breeding programmes have assumed that gene flow among drainage basins is limited. RFLP variation, within and among 31 populations from river systems across northern Australia, was analysed to test this hypothesis. To allow comparisons within and between river systems, trees were sampled from up to three populations per river system. Allele frequencies were correlated with longitude for more than half the 33 RFLP loci surveyed. Genetic identity was greatest between populations in closest geographic proximity, irrespective of river system, suggesting that sampling strategies for breeding programmes should be based on geographic distance rather than river system. The level of genetic variation was similar throughout the geographic range examined (mean H(E) = 0.49). However, there was evidence of a barrier to gene flow between populations in the east and west of the species range. The RFLP data support morphological evidence of hybridisation between E. camaldulensis and E. tereticornis Sm. in several populations in northeast Queensland and the genetic divergence of E. camaldulensis subsp. simulata Brooker and Kleinig.

Genetic differentiation between mallee and tree forms in the Eucalyptus loxophleba complex

The Eucalyptus loxophleba complex comprises two tree taxa (E. loxophleba ssp. loxophleba and ssp. supralaevis), two mallee taxa (E. loxophleba ssp. lissophloia and ssp. gratiae), and three rare mallee species, of which one, E. blaxellii, is included in this study. The genetic diversity and phylogenetic relationships between the taxa, particularly in relation to habit, were assessed using anonymous nuclear RFLP loci. The level of diversity in the taxa was high and similar to that detected in other eucalypt species. The populations showed low differentiation at both the subspecies and the species levels. Phylogenetic relationships showed some genetic separation between the tree and mallee habit but no separation of the two taxa within the tree habit or within the mallee habit. The genetic analysis does not support the recognition of E. gratiae as a separate species. The geographically restricted E. blaxellii showed similar levels of diversity to populations of the other widespread taxa of E. loxophleba.