Genetic diversity, population genetic structure and demographic history of two actiniarian species ( <i>Anthopleura xanthogrammica</i> and <i>Diadumene lineata</i> ) along the Chinese coastline

Anthopleura xanthogrammica and Diadumene lineata have considerable pharmaceutical potential, but their distribution and population genetics along the Chinese coastline remain poorly understood. We collected 162 samples of the two species based on external morphology from nine intertidal sites. Subsequent analyses of the mitochondrial COI segment (607 bp) confirmed 143 A. xanthogrammica individuals across all nine localities, and only 19 D. lineata individuals restricted to three localities. For A. xanthogrammica, genetic diversity, phylogenetic relationships, population structure and demographic history were analyzed using combined mitochondrial segments (COI + 16S rRNA: 1,055 bp) and nuclear segments (28S rRNA: 316 bp; ITS: 658 bp). This species showed high genetic polymorphism. Mitochondrial DNA data (neutrality tests, mismatch distributions, haplotype network) suggested a historical and mild population expansion, while phylogenetic and molecular variance analyses indicated limited gene flow and high genetic differentiation among geographic populations. Population structure supported three management units for the conservation of this species. For D. lineata, we attempted genetic diversity and neutrality tests using the same molecular markers, but the results were unreliable due to the small sample size. Future studies should identify more suitable sampling sites and use a larger sample size to assess its genetic polymorphism and population structure.