Isolation by distance and selection effects on genetic structure of sardines Sardina pilchardus Walbaum

Abstract

Allozyme data were used to analyse the genetic structure of Sardina pilchardus populations. Fifty samples from 15 locations between the North Sea and Mauritania, including samples from the Azores, Madeira and the Mediterranean Sea, were surveyed. A weak but significant structure was found between all samples (F ST ¼ 0.057, P < 0Á001). This structure results from a change in the most common allele of SOD* between the North African and the Azores populations separated by the greatest distance. This locus seemed to be under selective pressure according to the test of neutrality, and the variations in allele frequencies may be explained due to isolation by distance (IBD) of coastal populations (from Mauritania to the North Sea) (r ¼ 0Á86, P < 0Á001). When SOD* was removed from the analyses, IBD was not observed in coastal populations (r ¼ 0Á236, P > 0Á05) but was observed over the whole range (r ¼ 0Á321, P ¼ 0Á05). The genetic structure of S. pilchardus is driven by both IBD and selective processes.

Evidence for microsatellite hitchhiking selection in European sardine (<i>Sardina pilchardus</i>) and implications in inferring stock structure

“…The results of these studies, though not completely congruent, suggest a very weak genetic structure, with the exception of the allozymic locus SOD*, which could be subject to selection (Chlaida et al 2006;Laurent et al 2007).…”

“…There have been a number of studies addressing the genetic structure of sardine in different parts of its global distribution, using different molecular markers such as allozymes (Spanakis et al 1989, Chlaida et al 2006, Laurent et al 2007, Chlaida et al 2009), mitochondrial DNA (Tinti et al 2002, Atarhouch et al 2006 and microsatellites (Gonzalez and Zardoya 2007a). The results of these studies, though not completely congruent, suggest a very weak genetic structure, with the exception of the allozymic locus SOD*, which could be subject to selection (Chlaida et al 2006;Laurent et al 2007).…”

“…One of the loci (Sp22) appeared to be under selection and exhibited a geographic pattern that closely resembles that of allozymic locus SOD* (Laurent et al 2007). We further checked for correlation between genetic variation and environmental factors (latitude, longitude, temperature and salinity).…”

Searching for a stock structure in <i>Sardina pilchardus</i> from the Adriatic and Ionian seas using a microsatellite DNA-based approach

“…This phenomenon has commonly been reported for marine species of both invertebrates (Zouros and Foltz 1984) and fish (Waldman andMcKinnon 1993, Maggio et al 2009) and was often observed in pelagic fish (Laurent et al 2007, Gonzalez and Zardoya 2007a, Zarraonaindia et al 2009, André et al 2011. A homozygote excess may be explained as a consequence of evolutionary or technical processes, such as i) inbreeding; ii) selection; iii) the effect of mixing between different sub-populations (Wahlund effect); and iv) genotyping errors (i.e.…”

“…In addition, this fish species is one of the most abundant and one of the commercially most important in the Adriatic Sea (Santojanni et al 2005) and accounts annually for over US $32 million, with a peak of 90000 t landed in the early 1980s (Cingolani et al 2004). All the studies on sardine population genetics have shown low levels of genetic differentiation (Spanakis et al 1989, Laurent et al 2007, Gonzales and Zardoya 2007a, Kasapidis et al 2012, mainly suggesting the existence of differentiation between the Atlantic Ocean and the Mediterranean Sea (Atarhouch et al 2006). However, the Adriatic Sea seems to show differences in specific hydrological and oceanographic features (i.e.…”