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Eucalyptus tetrapleura

Population genomics and hybridization in Eucalyptus tetrapleura.

Eucalyptus tetrapleura is a rare species of ironbark that is restricted to a 100 km x 40 km area in the Grafton region on the North Coast of New South Wales (600 km north of Sydney). This species is commonly known as the ‘square-fruited ironbark’ because it has four distinctive ribs on the sides of its buds and fruits. Eucalyptus tetrapleura is listed in New South Wales as a threatened species (Vulnerable ROTAP: 2VCa).

The major threats to E. tetrapleura are loss of habitat through land clearing for agriculture, timber harvesting, road construction and maintenance, grazing of seedlings, excessively frequent fires and genetic swamping from more common and widespread related eucalypts. In the last few years, much of the central part of its distribution was reduced to facilitate the upgrade of the Pacific Highway. We aim to provide information about the population genetic structure and hybridization in E. tetrapleura to aid in conservation and revegetation plans for the species.

Therefore, we are investigating the population genomics of E. tetrapleura and closely related and co-occurring ironbarks. This includes the common and widespread species, E. fibrosa and E. siderophloia, as well as the less widespread species, E. fusiformis. Although there are reported sightings of hybrids and intergrades between E. tetrapleura and other related species of eucalypts, there has not been a detailed population genetic analysis of this species. In this study, we collected 2-16 samples for DNA analysis from 18 populations of E. tetrapleura, covering the full range of the species.  

Current research

We are using Diversity Arrays Technology (DArTseq) and population genetic analyses (including Splitstree, LEA, adegenet, GenAlEx) to better understand genetic differentiation within E. tetrapleura and between E. tetrapleura and other co-occurring and closely related ironbark species. In particular, we are using analyses such as NewHybrids and TreeMix, to detect hybrids and patterns of gene flow across lineages in E. tetrapleura and other ironbarks.

Some of our relevant publications:

  1. Rutherford S, van der Merwe M, Wilson PG, Kooyman R, Rossetto M (in prep.) Population genetic structure and hybridization in Eucalyptus tetrapleura (Myrtaceae): conservation of a rare ironbark.

Field sites for Eucalyptus tetrapleura

Castlereagh Nature Reserve

Newfoundland State Forest

Tindal Road