Concordant patterns of mtDNA and nuclear phylogeographic structure reveal Pleistocene vicariant event in the green crab Carcinus aestuarii across the Siculo-Tunisian Strait

Abstract

. Concordant patterns of mtDNA and nuclear phylogeographic structure reveal Pleistocene vicariant event in the green crab Carcinus aestuarii across the Siculo-Tunisian Strait.

Parapatric genetic divergence among deep evolutionary lineages in the Mediterranean green crab, Carcinus aestuarii (Brachyura, Portunoidea, Carcinidae), accounts for a sharp phylogeographic break in the Eastern Mediterranean

“…The best known oceanographic discontinuities in the Mediterranean are: (1) the Almería-Oran Front as the main genetic breakpoint between the Atlantic Ocean and the Mediterranean Sea [ 4 , 7 ], (2) the transition between the Western and the Eastern Mediterranean, due to unidirectional water flow at the Siculo-Tunisian Strait [ 5 ], and (3) the hydrographic isolation of the Aegean, Ionian and Adriatic seas [ 5 ]. In addition to these oceanographic barriers, the geological history of the Eastern Atlantic and Mediterranean Sea, including the breaking up of the Tethys Sea, the Messinian Salinity Crisis [ 8 ], and the Pleistocene glaciations [ 9 ], might have left marked footprints on the genetic structure of species and made the Mediterranean region a notably dynamic hotspot of diversity [ 10 – 12 ]. For example, intensified modifications to the coastline (sea level regressions) during repeated Pleistocene glaciations could have limited the biotic exchange across physical barriers, such as the Gibraltar Strait [ 13 ] and the Siculo-Tunisian Strait [ 14 ], and strongly influenced the formation of distinct phylogenetic lineages within Mediterranean marine species.…”

“…In this context, the phylogeography of Mediterranean species underwent a common set of processes resulting from fragmentation within glacial refugia, range expansions via postglacial colonisation, and secondary contact zones among historically divergent lineages [ 4 , 12 , 15 – 18 ].…”

“…Both retrieved genetic groups were found to be genetically and morphologically differentiated across the Siculo-Tunisian Strait [ 36 , 37 ]. A more recent investigation by Deli et al [ 12 ], detailing phylogeography and population genetic structure of the Mediterranean green crab across the Siculo-Tunisian Strait, showed concordant patterns of mitochondrial and nuclear divergence among western and eastern Mediterranean populations from northern Africa. The study also revealed a marked divergence between two highly separated haplogroups, suggesting an Early Pleistocene vicariant event in the genetic differentiation of this highly dispersive decapod species [ 12 ].…”

“…These insights, inferred so far from population genetic surveys of C. aestuarii throughout the western and central Mediterranean coasts [ 12 , 23 , 34 – 36 ], trigger the necessity of detailed phylogeographic and population genetic analyses of this species across the poorly investigated Eastern Mediterranean Basin. Sea-level Pleistocene oscillations potentially caused the isolation or partial isolation of the Black Sea, Aegean Sea and Eastern Mediterranean Basin [ 38 ].…”

“…In order to achieve these goals, new mitochondrial Cox1 (cytochrome oxidase subunit 1) sequences were obtained from 76 specimens collected from seven sites across the Eastern Mediterranean Basin, stretching across the Greek and Turkish coasts. This newly generated dataset of sequences was merged with previously examined data by Ragionieri and Schubart [ 35 ] and Deli et al [ 12 ] for phylogeographic re-analyses.…”