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Homer, LE 2009, 'Population structure and distance of gene flow in Avicennia marina (Forsk.) Vierh. (Avicenniaceae) on a local/regional scale in the Northern Rivers of New South Wales, Australia', PhD thesis, Southern Cross University, Lismore, NSW.

Copyright LE Homer 2009


The population structure and distance over which gene flow occurs can inform management decisions regarding conservation and reforestation of Avicennia marina. Massive losses of A. marina have occurred worldwide, leading to increased necessity for better management to reinstate terrestrial and aquatic food webs, biodiversity, coastal stability and water quality. Avicennia marina is the most widespread mangrove species, occurring throughout the Indo-West Pacific between the latitudes of 25oN and 38oS and was once assumed to have little genetic structure throughout its range. It is now clear that discrete subpopulations exist on a global scale, however few studies have characterised genetic structure on a regional scale.

This study examined population structure and the distance of A. marina gene flow on a local/regional scale in the Northern Rivers of New South Wales, Australia. Potential gene flow via pollen and propagules was investigated and these findings were augmented with estimates of actual gene flow within and among 220 individuals from 11 sites, using 8 microsatellite markers.

In this study gene flow was found to occur across approximately 200 kilometres. The level of gene flow was high, with overall FST = 0.065 (P<0.001), 94% of genetic diversity found within individuals and estimated number of migrant per generation (Nm) of 3-5. Inbreeding was not detected. There is evidence for panmixia and complete genetic exchange over a distance of approximately 620 metres. The honeybee Apis mellifera with a reported flight range up to 13.7 kilometres is one pollinator of A. marina. Transition away from panmixia was evident from a small (6%) but significant (p<0.001) among site differentiation. The isolation by distance model was found to explain 54% of the among site variation. In the Northern Rivers A. marina propagules remain viable for up to 12 weeks after fruit-fall and the East Australian Current (EAC) assists dispersal.

This distance of gene flow is site specific and indicators for high gene flow are good connectivity to tidal flow, existence of healthy populations of long range pollinators, buoyant propagules, linking ocean currents, appropriate stranding sites and survival conditions. The presence of these in this study indicated that the distance of approximately 200 kilometres is likely to be toward the maximum distance of gene flow in A. marina