Seeds in motion: Genetic assignment and hydrodynamic models demonstrate concordant patterns of seagrass dispersal

Abstract

Movement is fundamental to the ecology and evolutionary dynamics within species. Understanding movement through seed dispersal in the marine environment can be difficult due to the high spatial and temporal variability of ocean currents. We employed a mutually enriching approach of population genetic assignment procedures and dispersal predictions from a hydrodynamic model to overcome this difficulty and quantify the movement of dispersing floating fruit of the temperate seagrass Posidonia australis Hook.f. across coastal waters in south‐western Australia. Dispersing fruit cohorts were collected from the water surface over two consecutive years, and seeds were genotyped using microsatellite DNA markers. Likelihood‐based genetic assignment tests were used to infer the meadow of origin for seed cohorts and individuals. A three‐dimensional hydrodynamic model was coupled with a particle transport model to simulate the movement of fruit at the water surface. Floating fruit cohorts were mainly assigned genetically to the nearest meadow, but significant genetic differentiation between cohort and most likely meadow of origin suggested a mixed origin. This was confirmed by genetic assignment of individual seeds from the same cohort to multiple meadows. The hydrodynamic model predicted 60% of fruit dispersed within 20 km, but that fruit was physically capable of dispersing beyond the study region. Concordance between these two independent measures of dispersal provides insight into the role of physical transport for long distance dispersal of fruit and the consequences for spatial genetic structuring of seagrass meadows.

Integrating genetics, biophysical, and demographic insights identifies critical sites for seagrass conservation

“…2). Significant genetic differentiation on similar spatial scales has been found in an Australian seagrass using assignment tests and F ST (Sinclair et al 2018), and in our study may be partly explained by the geography of narrow fjords that limit genetic exchange.…”

“…The good agreement confirms that migration at the spatial scale of dozens of kilometers is indeed governed by oceanographic dispersal probability of rafting flowering shoots over one generation. We are aware of only one other study from Western Australia (Sinclair et al 2018), that could show such detailed validation of genetic and biophysical estimates at the scale of individual meadows, typical and relevant for practical management.…”

“…Assessments of connectivity on relevant spatial scales are an important part of seascape studies, as dispersal is fundamental to ecology and evolutionary dynamics of metapopulations. Understanding dispersal in the marine environment is difficult due to the high spatial and temporal variability of ocean currents (Cowen and Sponaugle 2009), but mutually enriching genetic and biophysical approaches have been used successfully to assess patterns of seagrass dispersal on small (Sinclair et al 2018) and large geographic scales (Hernawan et al 2016, Jahnke et al 2016, 2017, 2018, Triest et al 2018). Landscape/seascape studies become particularly valuable when different approaches to assess connectivity and identify particularly vulnerable sites are combined.…”

Seagrass Restoration Is Possible: Insights and Lessons From Australia and New Zealand

“…Seagrasses have the potential to disperse over long distances via ocean currents during various life-history stages (Kendrick et al, 2012;McMahon et al, 2018). Population genetic studies in combination with hydrodynamic models have increased our understanding of the role/potential of connectivity in natural seagrass meadow recovery (e.g., Sinclair et al, 2016Sinclair et al, , 2018Smith et al, 2018). Although there is a growing understanding of the movement ecology of seagrasses (McMahon et al, 2014;Smith et al, 2018), studies on propagule viability and survival, and establishment success are currently limited (but see Campbell, 2003;Weatherall et al, 2016).…”

Advances in approaches to seagrass restoration in Australia

“…2012, 2017; Sinclair et al . 2014, 2016, 2018), physiological and growth requirements (Statton et al . 2013; Statton et al .…”