Assessment of the genetic relationship between the recently established benthic population and the adjacent floating populations of Sargassum horneri (Phaeophyceae) in Dalian of China by newly developed trinucleotide microsatellite markers

Abstract

Sargassum horneri is a conspicuous canopy-forming brown seaweed growing on solid substrates or floating on sea surface. A recently established benthic population was discovered in a bay in Dalian, China, in 2016 and suggested to be derived from the earlier floating population. Since 2016, floating populations have kept appearing in the adjacent area. The genetic connectivity between this recently established benthic population and the adjacent floating populations remains unclear. In this study, 10 novel informative trinucleotide microsatellite markers were developed through the high throughput sequencing technology, and employed to analyze the genetic structure of the benthic population (DS16 and DS18) and three adjacent floating populations (DL16, BL16, and DL18) sampled in 2016 and 2018, with one floating population collected from Shidao in 2016 (SD16) as reference. Significant genetic differentiation was found to exist between the benthic and floating populations, and among floating populations from different years. Almost no membership of floating populations was detected in the benthic population and vice versa by the Bayesian model–based structure analysis, indicating very limited genetic connectivity between them. Significant excess of heterozygosity, significant multilocus linkage disequilibrium, high frequency of repeated genotypes, and putative clones were detected in all floating populations, indicating that asexual reproduction is likely dominant in them. Inbreeding and founder effect were revealed to be present in the benthic population. Further studies will focus on tracking the dynamics of genetic structure in the recently established benthic population and investigating the exact reproductive means and patterns of floating populations.