Mitochondrial, nuclear and morphological differentiation in the swimming crab Liocarcinus depurator along the Atlantic-Mediterranean transition

12 pages, 4 figures, 1 table, supplementary information https://doi.org/10.1038/s41598-024-69883-6.-- Data availability: Haplotype COI sequences were deposited in GenBank under accession numbers (JN564801-JN564803; JN564806; JN564808; JN564809; JN564819; JN564821; JN564825; JN564827; JN564828; KU941957-KU941974; OR414606-OR414631). Individual base data for COI, SSR and RW are available in SI Appendix

Environmental gradients in the sea may coincide with phenotypic or genetic gradients resulting from an evolutionary balance between selection and dispersal. The population differentiation of the swimming crab, Liocarcinus depurator, an important by-catch species in the Mediterranean Sea and North-East Atlantic, was assessed using both genetic and morphometric approaches. A total of 472 specimens were collected along its distribution area, and 17 morphometric landmarks, one mitochondrial gene (COI) and 11 polymorphic microsatellite markers were scored in 350, 287 and 280 individuals, respectively. Morphometric data lacked significant differences, but genetic analyses showed significant genetic differentiation between Atlantic and Mediterranean populations, with a steeper gradient in COI compared to microsatellite markers. Interestingly, nuclear differentiation was due to an outlier locus with a gradient in the Atlantic-Mediterranean transition area overlapping with the mtDNA gradient. Such overlapping clines are likely to be maintained by natural selection. Our results suggest a scenario of past isolation with local adaptation and secondary contact between the two basins. Local adaptation during the process of vicariance may reinforce genetic differentiation at loci maintained by environmental selection even after secondary contact

This study was funded by the project MarGech (PID2020-118550RB) funded by MCIN/AEI/https://doi.org/10.13039/501100011033. The authors are part of the research groups SGR2021-01271 and SGR2021-00405 of the Generalitat de Catalunya. This work acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S) funded by AEI https://doi.org/10.13039/501100011033. CLIFISH CTM2015-66400-C3-3-R, MINECO/FEDER

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