Three mitochondrial lineages and no Atlantic-Mediterranean barrier for the bogue Boops boops across its widespread distribution

Abstract

Marine species exhibiting wide distributional ranges are frequently subdivided into discrete genetic units over limited spatial scales. This is often due to specific life-history traits or oceanographic barriers that prevent gene flow. Fine-scale sampling studies revealed distinct phylogeographic patterns in the northeastern Atlantic and the Mediterranean, ranging from panmixia to noticeable population genetic structure. Here, we used mitochondrial sequence data to analyse connectivity in the bogue Boops boops throughout most of its widespread distribution. Our results identified the existence of three clades, one comprising specimens from the Azores and eastern Atlantic/Mediterranean, another with individuals from the Canary Islands, Madeira and Cape Verde archipelagos, and the third with samples from Mauritania only. One of the branches of the northern subtropical gyre (Azores Current) that drifts towards the Gulf of Cádiz promotes a closer connection between the Azores, southern Portugal and the Mediterranean B. boops populations. The Almería-Oran Front, widely recognised as an oceanographic barrier for many organisms to cross the Atlantic-Mediterranean divide, does not seem to affect the dispersal of this benthopelagic species. The southward movement of the Cape Verde Frontal Zone during the winter, combined with the relatively short duration of the pelagic larval stage of B. boops, may be potential factors for preventing the connectivity between the Atlantic oceanic archipelagos and Mauritania shaping the genetic signature of this species.

Figure 1

Sampling sites across the distributional range of Boops boops in the Northeastern Atlantic and the Mediterranean. Location codes in Table 1. Circles size proportional to samples sizes. Figure generated using the worldHires (http://CRAN.R-project.org/package=mapdata) function implemented in R language. URL https://www.R-project.org/) (version 3.3.1), which uses publicly available coastline coordinates from the NOAA National Geophysical Data Center (http://www.ngdc.noaa.gov/mgg/shorelines/shorelines.html).

Figure 2

Haplotype network for the mitochondrial control region of Boops boops showing the existence of three main groups. The green shade highlights the group including samples from the Canary Islands, Cape Verde and Madeira Islands. The purple shade represents the clade corresponding to the group including individuals from Mauritania. The third group corresponds to samples from the Atlantic/Mediterranean and the Azores. Colours refer to sampling locations. The area of the circles is proportional to each haplotype frequency. In the case where haplotypes are shared among sampling locations, filling is proportional to the frequency of the haplotype in each sampling location.

Figure 3

Heatmap and dendrogram based on pairwise distances based on Kimura (1980) for the mitochondrial control region of Boops boops. The heatmap and the associated dendrogram were generated using the pheatmap R-package (https://cran.r-project.org/web/packages/pheatmap/index.html).