Genetic divergence at the synaptophysin (Syp I) locus among Norwegian coastal and north‐east Arctic populations of Atlantic cod

Abstract

Several nuclear RFLP loci have been discovered recently that exhibit extensive allele frequency variation among Norwegian coastal and north-east Arctic populations of Atlantic cod Gadus morhua. One of these polymorphisms was detected by hybridizing an anonymous cDNA clone (GM798) against genomic DNA digested with the restriction enzyme DraI. This cDNA clone has now been sequenced and identified as synaptophysin (Syp I), an integral synaptic vesicle membrane protein. Primers were constructed that amplify an intron of the Syp I gene that is polymorphic for the DraI site, thus making it possible to use a PCR-based assay to score the polymorphism. A total of 965 individuals sampled from the Barents Sea, coastal areas and fjords in northern Norway have been analysed for this polymorphism. The results confirm that highly significant differences exist between NE Arctic and coastal cod at the Syp I locus. A cluster analysis revealed a deep split between coastal and Arctic populations and hierarchical F-statistics indicated that about 40% of the total variation was attributable to differences between Arctic and coastal groups. The temporal stability of allele frequencies was assessed by comparing Syp I allele frequencies among samples of juveniles (0 group) captured at specific locations in fjords in consecutive years and among samples of adults and juveniles collected from the same fjord. Samples of juveniles collected in 1994 and 1995 in Malangen were genetically indistinguishable whereas juveniles sampled from Dønnesfjord and Ullsfjorden over the same 2-year period exhibited significant differences. Adults and 0-group individuals collected from the same fjord were found to be genetically indistinguishable in Malangen, but not in Balsfjorden. In addition to detecting large differences among Arctic and coastal groups, the Syp I locus suggests that genetic heterogeneity exists among resident populations of cod in different fjords and that gene flow among populations throughout northern Norway may be considerably lower than previously believed. 1997 The Fisheries Society of the British Isles 1997 The Fisheries Society of the British Isles

Sub-populations of coastal cod with different behaviour and life-history strategies

“…The North Atlantic cod (Gadus morhua L.) consists of many populations and sub-populations with different life histories, which are distributed on the west and east coast of the North Atlantic (Mork et al 1985, Brander 1994b, Bentzen et al 1996, Svåsand et al 1996, Fevolden & Pogson 1997, Ruzzante et al 1998, Jonsdottir et al 2002. Populations in warm water grow faster and mature earlier than those in colder water (Hutchings et al 1993, Brander 1994b.…”

Extreme male-skewed sex ratios on spawning grounds for Atlantic cod Gadus morhua with typical coastal cod signatures of the Pan I (pantophysin) locus

“…The ability of the Pan I locus to distinguish between the 2 major stocks of Atlantic cod that occur in coastal and offshore waters in northern Norway was first demonstrated 2 decades ago , Fevolden & Pogson 1997. In the early days of using this locus as a genetic marker some debate arose due to its selective mode, but this was before the advantage of using markers with selective adaptability in revealing population divergences was fully acknowledged.…”

“…DNA was extracted from ethanol-preserved gill tissue sampled from each fish onboard the ship immediately after each catch. DNA from samples up until 2007 was extracted by a modified salt lysis extraction method (Fevolden & Pogson 1997). DNA from the 2013 sample was isolated using the E-Z 96 Tissue DNA Kit (OMEGA Biotek) following the manufacturer's instructions.…”

“…The 2-allelic-class (A and B) Pan I locus (Pogson & Fevolden 2003) is in itself an SNP, since a 1-nucleotide substitution decides the presence or absence of a Dra-1 restriction site. The locus was analysed by a PCRbased method (Fevolden & Pogson 1997). The 2013 sample was analysed including Pan I on a multiplex of microsatellites and genotyped upon fragment analyses on an ABI 3130XL sequencer (Applied Biosystems) according to Stensvik et al (2006).…”

“…NEAC and NCC were first included in a transAtlantic study using this locus (termed GM798 at the time) by Pogson et al (1995), and shortly after in a comparison between cod caught in several fjords and those caught offshore in northern Norway (Fevolden & Pogson 1997; locus then termed Syp I). During the almost 2 decades that have since passed, a series of papers have included Pan I in comparative studies of these 2 stocks (see Fevolden et al 2012 for the most recent overview).…”