Phylogeography highlights two different Atlantic/Mediterranean lineages and a phenotypic latitudinal gradient for the deep-sea morid codling Lepidion lepidion (Gadiformes: Moridae)

Abstract

In spite of our awareness that the biosphere is represented to a greater extent in the oceans than elsewhere, little is still known about the genetic structure and phylogeography of most deep-sea fish species. Here, different questions regarding the phenotypic and genetic diversity of deep-sea morid cod Lepidion lepidion across its distribution area have been investigated. Principal Component Analyses of 17 different morphological measurements indicated no differences between Atlantic Ocean and Mediterranean Sea, but the presence of a latitudinal phenotypic gradient. The genetic analyses comprised three mitochondrial and two nuclear markers. Neutrality tests and mismatch distributions indicated events of demographic expansion in the western Mediterranean Sea and the northeastern Atlantic Ocean that should be interpreted with caution due to the limited sample size. In addition, two different nuclear lineages partially mixed have been detected, suggesting isolation with secondary contact between the Atlantic Ocean and the Mediterranean Sea. Moderate genetic structure was found in Aviles Canyon (NW Iberian Peninsula) showing limitations to gene flow and asymmetric migration, probably due to the oceanographic conditions in the area. The results suggest that genetic connectivity of L. lepidion is probably due to its pelagic stages.