Integrated Genetic and Statolith Shape Analysis Reveals the Population Structure of Loliolus (Nipponololigo) uyii (Cephalopoda: Loliginidae) in the Coastal Waters of China

Understanding population structure is a priority for evaluating population dynamics of commercially fished cephalopods under fishing pressure and environmental changes. This study employed a multidisciplinary approach to clarify the population structure of Loliolus (Nipponololigo) uyii, a common squid in inshore fisheries. Sampling was conducted multiple times to cover the distribution range across the East China Sea and South China Sea. High haplotype diversity was revealed by three gene markers (COI, 16S and ODH). Two geographical clades with significant genetic differentiation were divided through phylogenetic trees and haplotype networks. The boundary between the two clades is delineated by the Dongshan population in the southern East China Sea. Furthermore, the neutrality tests and mismatch analysis suggested that L. (N.) uyii populations may have undergone population expansion. Correspondingly, statolith differences in lateral dome and posterior indentation, along with high classification success, further supported the genetic division. The overall difference in statolith shape also efficiently identified seasonal groups in the Beibu Gulf lacking genetic differentiation. This result offers new insights into the influence of genetic and environmental factors on statolith shape. The integrated results provide a comprehensive understanding of the population structure of L. (N.) uyii, laying the foundation for resource development and the conservation of the species.