Population Connectivity and Phylogeography of a Coastal Fish, Atractoscion aequidens (Sciaenidae), across the Benguela Current Region: Evidence of an Ancient Vicariant Event

Abstract

Contemporary patterns of genetic diversity and population connectivity within species can be influenced by both historical and contemporary barriers to gene flow. In the marine environment, present day oceanographic features such as currents, fronts and upwelling systems can influence dispersal of eggs/larvae and/juveniles/adults, shaping population substructuring. The Benguela Current system in the southeastern Atlantic is one of the oldest upwelling systems in the world, and provides a unique opportunity to investigate the relative influence of contemporary and historical mechanisms shaping the evolutionary history of warm-temperate fish species. Using the genetic variation in the mitochondrial DNA Control Region and eight nuclear microsatellite DNA loci, we identified the presence of two highly divergent populations in a vagile and warm-temperate fish species, Atractoscion aequidens, across the Benguela region. The geographical distributions of the two populations, on either side of the perennial upwelling cell, suggest a strong correlation between the oceanographic features of the system and the breakdown of gene flow within this species. Genetic divergence (mtDNA φ ST = 0.902, microsatellite F ST = 0.055: probability of genetic homogeneity for either marker = p<0.001), absence of migrants (less than 1% per generation) between populations and coalescent estimates of time since most recent common ancestor suggest that the establishment of the main oceanographic features of the system (2 million years ago), particularly the strengthening and position of the perennial upwelling cell, is the most likely mechanism behind the observed isolation. Concordance between mitochondrial and nuclear genetic markers indicates that isolation and divergence of the northern and southern Benguela populations of A. aequidens occurred deep in the past and has continued to the present day. These findings suggest that the Benguela Current system may constitute an ancient and impermeable barrier to gene flow for warm-temperate fish species.

Molecular genetic, life‐history and morphological variation in a coastal warm‐temperate sciaenid fish: evidence for an upwelling‐driven speciation event

“…aequidens is composed of two allopatric populations situated within the warm‐temperate boundaries of the northern and southern Benguela regions, and present day isolation and breakdown of gene flow between the two populations has been confirmed by Henriques et al . (). The potential temporal variability in the complex oceanographic features of the BUS and their effectiveness as a barrier to dispersal of marine species makes this an interesting system to: (1) examine the long‐term permeability of such a barrier to gene flow and population connectivity in a migratory, warm‐temperate coastal fish such as At.…”

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

“…Ocean gyres and the strong Lüderitz upwelling cell have been linked to genetic breaks in the equatorial Atlantic (Norton and Goetze, 2013) and in the Benguela current region (Henriques et al, 2014), respectively. On the other hand, genetic connectivity may be enhanced by poleward flowing undercurrents, which have been associated with the transport of C. natalis diapause stages and fish larvae along the West African coast (John et al, 1998(John et al, , 2000.…”

Genetic analyses of overfished silver kob Argyrosomus inodorus (Scieanidae) stocks along the southern African coast

“…Atractoscion aequidens (Henriques et al, 2014a) and between South African and Angolan stocks of the coastal Lichia amia (Henriques et al, 2012). Nevertheless, contrasting mitochondrial population genetic structuring patterns have been found in the two Cape hake species co-occurring in Namibian and South African waters, with Merluccius capensis showing no genetic differentiation, while adult (3-4 years old) M. paradoxus showing significant segregation between these two main regions (von der Heyden et al, 2007).…”