Geographical variation in Calanus helgolandicus s. l. (Copepoda, Calanoida) and evidence of recent speciation of the Black Sea population

Abstract

AbstractGeographic analysis was carried out on a small number of morphometric characters and on the occurrence of integumental organs, i.e., supernumerary pores, on the ventral side of urosome segments 2 and 3 in adult females of Calanus helgolandicus s.l. Morphometry indicated the existence of two distinctive populations, one in the Black Sea, the other in the Mediterranean Sea and Atlantic Ocean. Significant differences in the frequency of supernumerary pores, however, indicated a Black Sea population, an east Mediterranean population, and a west Mediterranean-Atlantic population.Limited hydrographic exchange between the Aegean and Black Seas together with directional selection of the Black Sea population adjusting to the unusual properties of its environment appears to have shifted the equilibrium of this gene pool to a position substantially different from that of the Mediterranean. It is argued that the unusually low frequency of supernumerary pores characterizing the east Mediterranean population is...