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

Abstract

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.

Genetic signatures of Bassian glacial refugia and contemporary connectivity in a marine foundation species

“…Collection, handling and laboratory methods are described in Sinclair et al . (). Nine polymorphic microsatellite loci ( Pa A1, Pa A105 , Pa A120 , Pa B6 Pa B8 , Pa B112 , Pa D12, Pa D113, Pa 118/9) were genotyped using methods described in Sinclair et al .…”

“…5.7.1 in Jordan et al ., ), and islands in the Bass Strait (Jordan et al ., ). Posidonia australis is a large, slow‐growing, perennial seagrass and can be highly clonal (Sinclair et al ., ). Fruit production is often prolific with fruit containing a single seed (also referred to as a ‘seedling’ since it germinates while still held within the fruit and bears a plumule and root radical) are released in summer (November–January, Kuo & McComb, ).…”

Identifying knowledge gaps in seagrass research and management: An Australian perspective

“…There is growing evidence that sexual reproduction may be more important in maintaining meadows than previous appreciated (e.g., Jones et al, 2008;Sinclair et al, 2014b), however, outcrossing rates have only been estimated for one Australian species to date (Sinclair et al, 2014a) so this remains a significant gap. We need to know how flowering and seed production varies across a species range and what environmental factors cause variation in annual reproductive investment.…”

“…What role do pollen, seeds and vegetative fragments play in gene flow and population connectivity? Knowledge of the dispersal potential of pollen, seeds, and clonal (vegetative) propagules remains poor for most species, although there has been significant progress in synthesizing current knowledge of connectivity (e.g., Kendrick et al, 2012;Sinclair et al, 2014b) and in providing the theoretical and conceptual framework for understanding movement ecology of seagrasses (McMahon et al, 2014). There is a requirement for a better understanding of patterns of connectivity and dispersal at local and regional scales for temperate and tropical species to improve marine conservation planning.…”

Unravelling complexity in seagrass systems for management: Australia as a microcosm

“…Understanding the local context for genetic diversity is important as it can be highly variable among different meadows of the same seagrass species, e.g. contrasting low and high genetic diversity for P. australis along the east and west coasts of Australia (Evans et al, 2014;Sinclair et al, 2014). However, the ongoing loss of genetic diversity might suggest a stressor acting on the population resulting in the selection of maladapted genotypes.…”