Fine‐scaled geographical population structuring in a highly mobile marine species: the Atlantic cod

Abstract

Compared with many terrestrial and freshwater environments, dispersal and interbreeding is generally much less restricted in the marine environment. We studied the tendency for a marine species, the Atlantic cod, to be sub-structured into genetically differentiated populations on a fine geographical scale. We selected a coastal area free of any obvious physical barriers and restricted sampling to a 300-km region, well within the dispersal ability of this species. Screening 10 polymorphic microsatellite loci in 6 samples we detected a weak, but consistent, differentiation at all 10 loci. The average FST over loci was small (0.0023) but highly significant statistically, demonstrating that genetically differentiated populations can arise and persist in the absence of physical barriers or great distance. We found no geographical pattern in the genetic differentiation and there was no apparent trend of isolation by distance along the coastline. These findings lend support to the notion that low levels of differentiation are due to passive transport of eggs or larvae by the ocean currents rather than to adult dispersal, the latter being strongly dependent on distance.

Fine-scale spatial and temporal genetic structure of Atlantic cod off the Atlantic coast of the USA

“…Skarstein et al 2007, Pampoulie et al 2008a. In the present study, we also found differences among discrete populations within a spawning complex (F ST = 0.0039 to 0.0061) that were consistent with fine-scale differences documented among nearby fjords (separated by 60 to 300 km) in Norway (F ST = 0.0013 to 0.0054, PanI not used, Knutsen et al 2003) and among cod in Icelandic waters (F ST = 0.0030, excluding PanI, Pampoulie et al 2006). Weak genetic differentiation may be a result of the recent origin of cod populations (Pampoulie et al 2008a).…”

“…Yet, recent research shows that larval recruitment for some marine organisms, including cod, may occur on a local scale. In Atlantic cod, local recruitment has been linked to fine-scale habitat associations (Bradbury et al 2008) and egg and larval retention has been hypothesized as a mechanism promoting fine-scale genetic structure (Knutsen et al 2003, Jorde et al 2007). Norwegian cod may select spawning sites within sheltered fjords to minimize advection of pelagic larvae ).…”

“…While cod population structure has been the subject of extensive study in the northeast Atlantic (e.g. Hutchinson et al 2001, Knutsen et al 2003, Nielsen et al 2003, Jorde et al 2007) and in Canadian waters (Ruzzante et al 1996b, 1998, Beacham et al 2002, it has received much less attention in US waters (Lage et al 2004, Wirgin et al 2007). Much of the genetic diversity in this species may reside in smaller sedentary populations that may be particularly vulnerable to overharvest (Robichaud & Rose 2004).…”

Phylogeographic mitogenomics of Atlantic cod Gadus morhua: Variation in and among trans‐Atlantic, trans‐Laurentian, Northern cod, and landlocked fjord populations

“…Extensive mtDNA analyses have found little or no structure in waters off the coasts of eastern North America (Carr, Snellen, Howse, & Wroblewski, 1995), Iceland (Árnason, Pálsson, & Arason, 1992; Árnason, Petersen, Kristinsson, Sigurgíslason, & Pálsson, 2000), the Faroe Islands (Sigurgíslason & Árnason, 2003), Norway (Árnason & Pálsson, 1996), and the Baltic Sea (Árnason, Petersen, & Pálsson, 1998). In contrast, microsatellite studies suggest range‐wide isolation by distance (O'Leary, Coughlan, Dillane, McCarthy, & Cross, 2007), and significant structure in waters off North America (e.g., Flemish cap, Bentzen, Taggart, Ruzzante, & Cook, 1996; inshore vs. offshore, Ruzzante, Taggart, Cook, & Goddard, 1996; Arctic populations, Hardie, Gillett, & Hutchings, 2006), Norway (Knutsen, Jorde, André, & Stenseth, 2003), and the North Sea (Hutchinson, Carvalho, & Rogers, 2001). Furthermore, genome scans of nuclear SNP markers have suggested the presence of local adaptation and temperature gradients at both large and small scales (Árnason & Halldórsdóttir, 2015; Berg et al., 2016; Bradbury et al., 2010, 2013; Nielsen et al., 2009).…”

Population structure and persistence of Pacific herring following the Great Tohoku earthquake

“…Such stable but high gene flow population structures were found in Atlantic herring in Swedish waters (F ST = 0.002-0.003, Larsson et al 2010) Jørgensen et al 2005). Temporally stable and significantly differentiated structures with high gene flow were also found in major Atlantic cod (Gadus morhua) populations (F ST = 0.0012-0.0400, Poulsen et al 2006) even over small geographic scales (F ST = 0.0023, Knutsen et al 2003) as reviewed by Hauser and Calvalho (2008). Chemical marking of otoliths previously revealed that 53-70% of herring that migrate to Miyako Bay for spawning were hatcheryreared progeny of wild herring that migrated to Miyako Bay and were released at a TL of 5 cm in Miyako Bay .…”