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

Abstract

SUMMARY:The genetic structure of the European sardine (Sardina pilchardus) was assessed throughout its geographic range using five microsatellite loci. One of the loci seemed to be under hitchhiking selection and exhibited a latitudinal cline along the eastern Atlantic, with abrupt change in allele frequencies from the Alboran Sea to the western Mediterranean and from the east Atlantic coast to the Azores and Madeira. This pattern was very similar to that previously described for the allozymic locus SOD* and these 2 loci could be linked. A Bayesian analysis of environmental factors with the genetic data indicated temperature as a potential selection factor. Selection pressure may be stronger at the southern limit of sardine distribution, because heterozygosity of the non-neutral locus was much lower there. The abrupt change in allele frequencies of the non-neutral locus in certain regions seem to be related more to strong barriers to gene flow, which were not evident for neutral loci, than to abrupt changes in selection pressure. These areas of discontinuity provide a guideline to define and delineate genetic stocks and are generally consistent with areas of phenotypic change in sardine, but they are not in concordance with the currently recognized morphological subspecies.Keywords: sardine, genetic structure, microsatellite DNA, selection, Atlantic, Mediterranean. RESUMEN: Evidencia para selección hitchhiking de microsatélite en sardina europea (Sardina pilcharduS) y las implicaciones para inferir la estructura del stock. -La estructura genética de la sardina europea se evaluó a lo largo de su área de distribución geográfica, con cinco loci de microsatélites. Uno de los loci parecía estar bajo selección por hitchhiking y exhibió una clina latitudinal a lo largo del Atlántico oriental, con el cambio abrupto en las frecuencias alélicas del Mar de Alborán al Mediterráneo Occidental y de la costa Oriental del Atlántico hacia las Azores y Madeira. Este patrón es muy similar al descrito previamente para el locus alozímico SOD*, por lo que estos dos loci podrían estar ligados. Un análisis bayesiano de factores ambientales con los datos genéticos indicó que la temperatura puede ser el factor de selección. La presión de selección puede ser más fuerte en el límite sur de distribución de la sardina, dado que la heterozigosis del locus no neutro fue allí mucho más baja. El abrupto cambio en las frecuencias alélicas de locus no neutro parece estar relacionado más con barreras fuertes al flujo de genes, que no se evidenciaron en el caso de los loci neutrales, que a cambios en la presión de selección. Estas áreas de discontinuidad proporcionan una guía para definir y delinear stocks genéticos y son generalmente consistentes con las áreas de cambio fenotípico de la sardina, pero no están conformes con las subespecies morfológicas actualmente reconocidas.

Differential introgression from a sister species explains highFSToutlier loci within a mussel species

“…This suggests that the oceanographic front itself is not sufficient alone to explain the genetic structure observed in many marine species. When differentiation is observed, it is often highly heterogeneous across loci (Quesada et al, 1995c;Lemaire et al, 2005;Kasapidis et al, 2012), suggesting the barrier to gene flow is not only natural but also genetic (Bierne et al, 2011). Indeed, genetic barriers to gene flow are often semi-permeable (Harrison, 1993) and are expected to coincide with natural barriers to gene flow (Hewitt, 1975;Barton, 1979).…”

Population structure of the chub mackerel (Scomber colias) in the North-east Atlantic inferred from otolith shape and body morphometrics

“…Although molecular markers, namely mtDNA, show weak genetic structure among marine pelagic fish (Chlaida et al 2009;Kasapidis et al 2012;Moreira et al 2019b), a single stock of S. colias has been considered until now for the Northeast Atlantic (Scoles et al 1998;Zardoya et al 2004). However, the present results showed significant regional differences in body geometric morphometrics and otolith-shape analyses of individuals collected in the North-east (ICES IXa and X) and eastern Centre (CECAF 34.1.2) Atlantic fishing areas for the species.…”

Targeted Sequencing of Mitochondrial Genes Reveals Signatures of Molecular Adaptation in a Nearly Panmictic Small Pelagic Fish Species

“…Nuclear genetic variation was investigated with five microsatellites previously described in other sardine studies–SAB07, SAR09, SR15, SAR112, SAR218, and SP17 [ 45 , 46 ]. Amplification and genotyping protocols can be found in Appendix A.1 .…”

“…Additional locus-specific analyses were performed because one of the utilized markers (SAR112) was reported to be the subject of clinal selection along the Mediterranean [ 46 ]. In this context, first, the frequency of HWE deviation across locations for each locus was explored.…”