The interaction of environment and genetic diversity within meadows of the seagrass Posidonia australis (Posidoniaceae)

Understanding the extent and impact of factors influencing the levels and structuring of genetic diversity within natural populations is a key objective of ecological genetics. For marine angiosperms, variation in abiotic environmental factors at the local scale can have a major influence on levels of clonality and spatial genetic structure, and thus influence mating systems, sexual reproduction, and recruitment. Identifying the key drivers of genetic structuring is critical for genetic management of ecological restoration success, especially in systems where the nature and extent of clonality is highly variable. Here, we quantify clonality and patterns of genetic structure in the temperate Australian seagrass Posidonia australis. We examine the location of meadows in relation to water movement and prevailing winds to assess their relative influence on local spatial genetic structuring. Measures of genetic diversity, assessed with 7 polymorphic microsatellite loci, were highly variable across 13 meadows sampled within and around a natural embayment on the west coast of Australia. The overall structure of P. australis meadows across this region is best explained as one of 'chaotic' genetic patchiness, with significant differentiation among most meadows (pairwise F-ST values), high levels of genetic diversity in meadows that are in more open waters, and lower genetic diversity at inshore sites facing strong prevailing winds at the time of seed dispersal or that have little water movement. A strong isolation by distance relationship within the embayment is consistent with prevailing winds (which create surface currents) at the time of peak pollen and seed release, strongly influencing dispersal direction.