Population genetic structure of Calanoides natalis (Copepoda, Calanoida) in the eastern Atlantic Ocean and Benguela upwelling system

Abstract

The population genetic structure of Calanoides natalis (ex Calanoides carinatus; Copepoda, Calanoida), an ecologically important component of African upwelling systems, was studied in order to (i) search for potential cryptic species, (ii) describe spatial patterns in the distribution of genetic variance and (iii) identify potential barriers to gene flow. Samples were obtained in the eastern Atlantic Ocean from the Iberian Peninsula to Namibia. Analysis of mitochondrial (cytochrome c oxidase subunit I; COI) and nuclear (citrate synthase; CS) marker genes revealed a genetically cohesive population of C. natalis with a prevalent shift in allele frequencies. The discovery of a deep split solely present in the mitochondrial dataset does not point to cryptic speciation, but rather suggests the occurrence of nuclear mitochondrial pseudogenes or incomplete reproductive isolation upon secondary contact. Genetic differentiation between the northern and southern hemisphere was significant, which may point to a potential, but permeable barrier close to the equator. No vertical genetic structuring was detected in the northern Benguela implying that horizontal differentiation was more pronounced than vertical structuring. Retention mechanisms and the oxygen minimum zone did not have a strong impact on genetic differentiation of C. natalis in the Benguela region.