Genome-wide SNP markers provided insights into the reproductive strategy and genetic diversity of the green tide causative species Ulva prolifera in China.

Ulva prolifera is the causative species of the annually occurring large-scale green tides in China since 2007. Its specific biological features on reproductivity strategies, as well as intra-species genetic diversity, are still largely unknown, especially at the genome level, despite their importance in understanding the formation and outbreak of massive green tides. In the present study, the restriction site-associated DNA genotyping approach (2b-RAD) was adopted to identify the genome-wide single-nucleotide polymorphisms (SNPs) of 54 individual thalli including samples collected from Subei Shoal in 2019 and Qingdao coast from 2019 to 2021. SNPs genotype results revealed that most of the thalli in 2019 and 2020 were haploid gametophytes, while only half of the thalli were gametophytes in 2021, indicating flexibility in the reproductive strategies for the formation of the green tides among different years and the dominance of asexual and vegetative reproductive mode for the floating period. Besides, population analysis was conducted and revealed a very low genetic diversity among samples from Subei Shoal and the Qingdao coast in the same year and a higher divergence among samples in different years. The results showed the efficiency of 2b-RAD in the exploration of SNPs in U. prolifera and provided the first genome-wide scale evidence for the origin of the large-scale green tides on the Qingdao coast. This study improved our understanding of the reproductive strategy and genetic diversity of the green tide causative species and will help in further revealing the biological causes of the green tide in China. [ABSTRACT FROM AUTHOR]