Genetic homogeneity of the European squid Loligo vulgaris across the eastern Adriatic Sea: New evidence from the Southern Adriatic

Abstract

The European squid Loligo vulgaris supports an economically important fishery throughout the Adriatic Sea. Previous genetic analyses revealed a lack of population structure in the Northern and Central eastern Adriatic, but the absence of Southern Adriatic samples prevented a basin-wide assessment. Here, we analysed mitochondrial cytochrome c oxidase subunit I (COI) sequences from 39 L. vulgaris individuals collected in the Southern Adriatic and combined them with 121 previously published sequences, generating the first COI dataset covering all three eastern Adriatic sub-basins. The Southern Adriatic population showed high haplotype diversity (Hd = 0.742) and low nucleotide diversity (π = 0.00308), consistent with recent demographic expansion. Genetic differentiation among the Northern, Central, and Southern Adriatic sub-basins was low and non-significant (Φ_ST = 0.01396, p = 0.062), with negligible divergence even between the geographically most distant Northern and Southern populations. Most Southern Adriatic haplotypes were shared with Northern and/or Central Adriatic populations, and the star-shaped network was retained across the basin. No spatial genetic structure was detected with COI among the sampled eastern Adriatic sub-basins. If confirmed by studies with broader spatial and temporal sampling and nuclear markers, these results would support the management of L. vulgaris in the eastern Adriatic as a single stock unit.