Phylogeography of Eucalyptus deglupta

A collaborative project undertaken by Royal Botanic Gardens Melbourne, The University of Melbourne, and Bogor Botanic Garden, Indonesia, and supervised by Frank Udovicic (Royal Botanic Gardens Melbourne)

Eucalyptus deglupta is one of the four species of Eucalyptus that are not endemic to Australia.  Eucalyptus deglupta has a distribution that extends from Papua New Guinea, through the islands of Indonesia, to the southern Philippines.   One of its common names is ‘Rainbow Gum’, due to the beautiful colours of young bark on the trunk.  It is a variable fast growing species that is widely used in forestry for pulp, paper and timber, especially in tropical regions.   Different provenances of E. deglupta vary in morphology, growth and pest resistance, but there has been no systematic study of those differences and there is no molecular data available at the population level. A comprehensive collection of specimens from across the range is crucial for answering questions on the phylogeography of E. deglupta.


The position of E. deglupta in the eucalypt phylogeny is also uncertain, with it being placed by eucalypt authority, Ian Brooker, in subgenus Minutifructus with 3 Australian species, E. brachyandra, E. raveretiana and E. howittiana; however, molecular studies suggest these species may lie within the large subgenus Symphyomyrtus.  Molecular phylogenetic markers from our population samples will be used to address this knowledge gap.


Eucalyptus deglupta is endangered in parts of its natural range due to loss of habitat and logging for timber and firewood.   A better understanding of its population structure will help in managing its conservation, provide a basis for future research into inter-provenance variation, and may lead to improved understanding of the species for commercial applications.


Over the two years of the project, Indonesia-based members of our team undertook fieldwork in Seram and Sulawesi to collect samples for voucher specimens and DNA analysis, and we also received specimens from the Philippines and New Britain. Fieldwork in Papua New Guinea was also conducted but native specimens were not located.


Previous work by our group has indicated that, in some Eucalyptus species, chloroplast markers may be variable enough to use for population studies; therefore initial work was carried out using the JLA+, rpl32-trnL and trnQ-rps16 regions on the available Seram, Sulawesi and Philippine samples. However, in this case, these markers did not exhibit enough polymorphisms for a population study. We then tested ten nuclear chloroplast markers, of which nine amplified reliably and one was variable, and ten nuclear microsatellites, which did not amplify reliably. Taken together, this work indicated that the Seram samples were distinct from the Sulawesi and Philippine samples.


On receipt of the New Britain specimens in September 2011, we began sequencing the JLA+, rpl32-trnL and trnQ-rps16 regions, and also reassessed the nine chloroplast microsatellite loci, with 3 loci now exhibiting variation between the different populations. We have completed data generation for these markers for a total of 75 specimens from across the range. The New Britain samples are quite distinct from the Seram, Sulawesi and Philippine samples and we tentatively conclude that the E. deglupta from Seram, Sulawesi and the Philippines will form one major clade, and the New Britain samples will form a separate major clade. We are currently assembling alignments for the sequence markers, and incorporating the microsatellite data. The phylogenetic trees generated can be interpreted in the context of terrane movements and changes in sea levels to test hypotheses about how E. deglupta dispersed among the islands of eastern Malesia.


In addition, we have successfully generated ITS and ETS sequences from the same 75 specimens for phylogenetic analysis to clarify the position of E. deglupta within the genus Eucalyptus.  There is variation within E. deglupta and also between E. deglutpa and other Symphyomyrtus/Minutifructus species. Currently, we are preparing alignments with other members of the Symphyomyrtus clade from GenBank for phylogenetic analysis.


We expect that this work will be published in early 2012.

Figure Legends

Figure 1. Colourful trunk of Eucalyptus deglupta (Rainbow Gum), Mual River, Seram Island, Maluku, Indonesia

Figure 2. Buds and fruits of Eucalyptus deglupta, Isal River, Manusela National Park, Seram Island, Maluku, Indonesia

Figure 3. Gillian Dean (second from left) and Sita Ariati (third from left) with field assistants processing samples of Eucalyptus deglupta Isal River, Manusela National Park, Seram Island, Maluku, Indonesia

Figure 4. Habitat of Eucalyptus deglupta, Isal River, Manusela National Park, Seram Island, Maluku, Indonesia

Figure 5. Field assistant climbing neighbouring rough-barked tree to sample from canopy of smooth-barked Eucalyptus deglupta Enrekang, South Sulawesi, Indonesia

 

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