Evaluation of the genetic relationship between the farmed populations on a typical kelp farm and the adjacent subtidal spontaneous population of Undaria pinnatifida (Phaeophyceae, Laminariales) in China

Abstract

In our previous study, asymmetric gene flow was revealed between sympatric farmed populations of Undaria pinnatifida and spontaneous ones on the cultivation rafts on a kelp farm in Dalian, China. However, the spontaneous population in the adjacent subtidal zone, which is assumed to be closely related to the spontaneous and farmed populations on the cultivation rafts, was not included in that study, making the whole scenario incomplete. Here, specimens of U. pinnatifida, including the spontaneous populations occurring on the cultivation rafts of U. pinnatifida (UWT-18) and Saccharina japonica (KWT-18), and the farmed population (F1–18) on the same farm and the adjacent subtidal spontaneous population (SW-18), were collected in 2018 and analyzed with the same set of microsatellites. The genetic diversity was highest in UWT-18 and lowest in F1–18 in terms of number of alleles and expected heterozygosity. Analyses of the genetic structure were conducted based on the combined genotypic data from the previous and the present studies. Neighbor-joining cluster analysis based on genetic distance, Bayesian model-based structure analysis, and discriminant analysis of principal components revealed most significant genetic divergence between the farmed populations and the subtidal spontaneous one. SW-18 contained nearly no membership from the farmed populations and vice versa, suggesting that the reciprocal gene flow between them was scarce. The population UWT-18 contained mixed membership from both the farmed populations and SW-18. The population KWT-18 contained almost only membership from SW-18, which was likely due to the close distance between them. Combination of the two studies depicts an intact picture about reciprocal impacts between sympatric spontaneous and farmed populations of U. pinnatifida.