Subtle population structuring within a highly vagile marine invertebrate, the veined squid Loligo forbesi, demonstrated with microsatellite DNA markers

Abstract

Microsatellite DNA markers were applied for the first time in a population genetic study of a cephalopod and compared with previous estimates of genetic differentiation obtained using allozyme and mitochondrial DNA (mtDNA) markers. Levels of genetic variation detected with microsatellites were much higher than found with previous markers (mean number of alleles per locus=10.6, mean expected heterozygosity (HE)=0.79; allozyme HE=0.08; mtDNA restriction fragment length polymorphism (RFLP) HE=0.16). In agreement with previous studies, microsatellites demonstrated genetic uniformity across the population occupying the European shelf seas of the North East Atlantic, and extreme genetic differentiation of the Azores population (RST/FST=0.252/0.245; allozyme FST=0.536; mtDNA FST=0.789). In contrast to other markers, microsatellites detected more subtle, and significant, levels of differentiation between the populations of the North East Atlantic offshore banks (Rockall and Faroes) and the shelf population (RST=0.048 and 0.057). Breakdown of extensive gene flow among these populations is indicated, with hydrographic (water depth) and hydrodynamic (isolating current regimes) factors suggested as possible barriers to migration. The demonstration of genetic subdivision in an abundant, highly mobile marine invertebrate has implications for the interpretation of dispersal and population dynamics, and consequent management, of such a commercially exploited species. Relative levels of differentiation indicated by the three different marker systems, and the use of measures of differentiation (assuming different mutation models), are discussed.

Genetic structure of the high dispersal Atlanto-Mediterreanean sea star Astropecten aranciacus revealed by mitochondrial DNA sequences and microsatellite loci

“…Similar results have been found in several other studies comparing mtDNA and microsatellite data (e.g., Shaw et al 1999;Krafsur 2002;Diaz-Almela et al 2004;Lemaire et al 2005;Peijnenburg et al 2006). As the effective mitochondrial population size (N e ) is expected to be four times smaller than the nuclear N e , assuming both 1:1 sex ratios and diploidy (Birky et al 1983), there is a higher potential for genetic drift in mtDNA, which leads to a higher θ.…”

“…As the effective mitochondrial population size (N e ) is expected to be four times smaller than the nuclear N e , assuming both 1:1 sex ratios and diploidy (Birky et al 1983), there is a higher potential for genetic drift in mtDNA, which leads to a higher θ. Ratios significantly higher than fourfold can be caused by sex bias in migration, reproduction or population size or by a difference in the mutation rate of the two markers (Turan et al 1998;Shaw et al 1999). The average θ C / θ N ratio in A. aranciacus is slightly higher than fourfold, for which the mentioned possibilities of sex bias or differences in mutation rates, combined or separately, could be partly responsible.…”

“…In this study, we sequenced the complete control region of the mitochondrial DNA, a region that has the highest rate of evolutionary change of any mtDNA region (Aquadro and Greenberg 1983;Parsons et al 1997). As nuclear markers, we used four polymorphic microsatellite loci, which are believed to be neutral and have been shown to be more variable compared to e.g., allozyme data (Shaw et al 1999;Estoup et al 1998;Perez-Losada et al 2002).…”

Evidence for fine-scale genetic structure and estuarine colonisation in a potential high gene flow marine goby (Pomatoschistus minutus)

“…Consequently, the genetic structure of numerous organisms has been assessed using several kinds of estimators, resulting in the discovery of disparate levels of genetic differentiation for different markers (Pogson et al, 1995;Lemaire et al, 2000;but see, Allendrof and Seeb, 2000). Although allozymes are still widely used, microsatellites have gained in importance due to their high levels of polymorphism, which facilitates the discovery of subtle differentiation (Ruzzante et al, 1998;Shaw et al, 1999). In addition, they are useful tools for the inference of historical dispersal and gene flow events, due to molecular insights into the nature of alleles and their mutation models (Balloux and Lugon-Moulin, 2002).…”

Extensive population subdivision of the cuttlefish Sepia officinalis (Mollusca: Cephalopoda) around the Iberian Peninsula indicated by microsatellite DNA variation

“…Microsatellite markers have shown considerable utility for genetic studies of population structure, particularly in organisms exhibiting low variability detectable by other methods (Hughes and Queller, 1993;Estoup et al, 1998). Several recent studies of widespread and abundant marine species (eg, squid, Shaw et al, 1999a;and herring, Shaw et al, 1999b) have indicated the greater capacity of microsatellite vs allozyme markers to detect fine population structure in such species. Microsatellites are also presumed to be neutral markers whereas allozymes have been suggested to be subject to selective forces, a potentially complicating factor when clinal frequency changes are found.…”