The biogeography of the stripped Venus clam, Chamelea gallina, in the Mediterranean Sea indicates limited gene flow and shows evidence of local adaptation.

Abstract

AimTo assess how biogeographic barriers and environmental heterogeneity shape connectivity and local adaptation in the striped Venus clam (Chamelea gallina), a commercially exploited bivalve in the Mediterranean Sea. LocationNortheast Atlantic (Gulf of Cadiz) and Mediterranean Sea (Alboran, Balearic, Tyrrhenian and Adriatic regions). TaxonChamelea gallina (Bivalvia: Veneridae). MethodsWe analysed genome-wide single nucleotide polymorphisms (SNPs) from 226 individuals sampled across six regions (Gulf of Cadiz, Alboran Sea, Balearic Sea, Ebro Delta, Tyrrhenian Sea and Adriatic Sea) using a seascape genomic framework. Population structure was inferred using both putatively neutral and adaptive loci. Genotype-environment associations were tested against key oceanographic variables, including sea surface temperature, salinity and nutrient availability. ResultsNeutral loci revealed weak genetic differentiation, consistent with substantial gene flow across most of the species range. In contrast, putatively adaptive loci uncovered pronounced genetic structure that corresponded closely to major Mediterranean biogeographic regions, particularly the Adriatic Sea, the Gulf of Cadiz and western-central Mediterranean basins. Significant associations were detected between genetic variation and environmental gardients, with several candidate adaptive SNPs located within coding regions, suggesting functional responses to spatially heterogeneous conditions. Main conclusionsOur results demonstrate that local adaptation can generate biologically meaningful population structure in C. gallina despite high levels of connectivity inferred from neutral markers. This decoupling between neutral and adaptive variation highlights the importance of integrating adaptive genomic information into biogeographic inference. Recognizing environmentally driven genetic differentiation is essential for defining robust management units and for improving the long-term sustainability and resilience of C. gallina fisheries under increasing anthropogenic pressure and climate change.