Discordant patterns of genetic connectivity between two sympatric species, Mullus barbatus (Linnaeus, 1758) and Mullus surmuletus (Linnaeus, 1758), in south-western Mediterranean Sea

- Two co-occurring species showed divergent connectivity patterns.
- Mullus barbatus samples were genetically homogeneous.
- Mullus surmuletus species showed high spatial heterogeneity.
- Habitat, shelf morphology and currents are potential causes for observed differences.
- MPA can act as genetic reservoirs due to high heterozygosity found inside it.

Population connectivity scales are important tools to achieve a mechanistic understanding of the factors regulating the abundance and distribution of marine populations and therefore support conservation actions to manage fisheries and stocks. We used 10 microsatellites markers on mullets' samples across the Spanish coast to determine the spatial scale of gene flow as well as the origin of post-larvae caught inside two MPAs. Population structure varied from complete homogeneity for Mullus barbatus, to high spatial variability in Mullus surmuletus samples. Differential habitat utilization by species, geomorphological features and oceanographic patterns are discussed as potential causes of patterns observed. Although we were unable to verify the origin of most post-larvae caught inside MPAs we suggest that they may act as genetic reservoirs due to high heterozigosity levels found in adult specimens inside (M. surmuletus) and nearby (both) them. Our results indicate that early life history traits (i.e. larvae) may not be the only determinant on species dispersal capability, suggesting that other mechanisms such as fine scale adult or juvenile movement may have been underestimated as promoting population connectivity.