Temporal instability in genetic structure of a marine monocot (Halophila ovalis)

The genetic structure of marine organisms is shaped by different driving forces (i.e. dispersal ability, physical barriers, natural selection) under a range of spatial and temporal scales, therefore, studying both the spatial and temporal genetic structure of focal species could improve understanding on their evolutionary history and po-tential mechanisms driving their genetic structure. Herein, we collected Halophila ovalis (spoon seagrass) plants from 7 locations around Penghu Island for two consecutive years, and employed 7 microsatellite loci to reveal their spatial and temporal genetic structure. The results of Bayesian clustering analysis showed that each pop-ulation represents a unique genetic population across time and space. This phenomenon can neither be fully explained by low dispersal capacity nor fast population turnover. We subsequently used samples collected from 2017 as source populations and samples collected from 2018 as an unknown source to perform the assignment test in order to reveal their possible origin. Surprisingly, most of the samples were assigned to Qitou (QT) where the largest H. ovalis meadow occurs around Penghu Island. Given these findings, we hypothesize that typhoon invasion during the fruiting season may increase the dispersal of propagules and subsequent local adaptation may shape the genetic structure observed in this study. Therefore, we suggest that a protected marine area need to be established at QT to protect the source population of H. ovalis. Meanwhile, a long-term monitoring program to elucidate the population dynamics as well as genetic diversity should be initiated to ensure successful man-agement well into the future.

Automated summary

Studying the genetic structure of marine organisms is crucial for understanding their evolutionary history and potential mechanisms driving their genetic structure. In this study, the spatial and temporal genetic structure of Halophila ovalis was investigated using microsatellite loci. Each population represented a unique genetic population across time and space. Source population assignment analysis showed that most samples originated from the largest H. ovalis meadow in Qitou. Typhoon invasion may enhance propagule dispersal and subsequent local adaptation may shape the observed genetic structure. The establishment of a protected marine area and long-term monitoring program is recommended for the conservation and management of H. ovalis.