Multiple molecular sources reveal possible expansion range of the Egyptian sole in the Mediterranean

In the Mediterranean flatfish are valuable fishery resources, with potential for aquaculture production. The assessment and monitoring of the stocks status are crucial to achieve environment-friendly management. However, the coexistence of two cryptic Solea species, S. solea and S. aegyptiaca, might lead to misidentification of specimens during the collection of fishery data, especially in areas where they live in sympatry. Using recently developed molecular markers, which have enabled their reliable identification, we provide new insights on the evolutionary history of the Mediterranean soles by analyzing species distribution, population structure, demography and inter-specific reproductive interactions with multiple molecular datasets. The analyses reveal a wider distribution of S. aegyptiaca in the Mediterranean Sea than previously described, hence pointing to a possible range expansion. In both species all markers consistently revealed significant population structuring according to a longitudinal gradient and demographic expansion. Despite their sympatric distribution in various regions, nuclear data confirmed the lack of inter-specific hybridization or introgression. Further multidisciplinarity in research (combining morphology, reproductive biology, life history traits analysis with genetics) are needed to unravel the possible range expansion of S. aegyptiaca according to a general hypothesis of Mediterranean tropicalization and its ecological interactions with the sympatric S. solea.