Genetic variability of Crassostrea gigas and Crassostrea corteziensis from a hatchery in northwestern Mexico

Abstract

To evaluate the genetic variability of oysters supplied by the Centro Reproductor de Especies Marinas del Estado de Sonora (Marine Species Hatchery Center of the State of Sonora), allozyme loci of triploid Crassostrea gigas (n = 78) and the F1 generation of a new batch of diploid native oyster Crassostrea corteziensis (n = 78) were analyzed. For the C. gigas sample, 10 enzymatic systems were analyzed, revealing 16 loci of which 12 were polymorphic. For C. corteziensis, 9 enzymatic systems revealed 13 loci, of which 8 were polymorphic. The average expected and observed heterozygosities for C. gigas were 0.350 and 0.309, respectively, with no significant differences between them. These figures are similar to those reported for wild diploid organisms, but lower than those reported for triploids. The average expected and observed heterozygosities for C. corteziensis were 0.294 and 0.065, with significant differences (P = 0.001). The phenotypic frequency analysis of the 12 polymorphic loci of C. gigas demonstrated that only 3 loci (AKP*, EST-2*, and PEP-1*) were in equilibrium according to the Hardy-Weinberg Law, with an average inbreeding of 0.133. For C. corteziensis, the 8 polymorphic loci were found outside of the Hardy-Weinberg Law, reflecting a high inbreeding value of 0.777 because of the large heterozygote deficiency in all loci, suggesting that the source broodstock is genetically eroded. If genetic variability is not considered in the selection of the broodstock, oyster culture in northwest Mexico will become unstable. We recommend a program of selection of diploid lineages of C. gigas with a good genetic variability and a good level of heterozygosis, and for C. corteziensis it is important to choose the wild population with the lowest inbreeding index in order to get a genetically healthy broodstock.

VARIABILIDAD GENÉTICA EN ADN MICROSATÉLITE DE UN NUEVO LINAJE DE OSTIÓN (Crassostrea gigas) EN SONORA

“…Aun cuando el ostión japonés (y otras especies de la familia Ostreidae) es un recurso acuacultural importante, no hay estudios de seguimiento de la estructura genética en generaciones sucesivas de manera equivalente a lo que se ha realizado con el camarón cultivado, sin embargo, hay varios estudios puntuales con alozimas, microsatélites y AFLPs que se han centrado en poblaciones naturales (Ozaki y Fujio, 1985;Yang et al, 2000;Yu et al, 2008 ), ferales (Li et al, 2003) y de cultivo (De la Rosa-Vélez, et al, 1991;Launey y Hedgecock, 2001;Li et al, 2006;Enríquez-Espinoza y Grijalva-Chon, 2010). Debido a que el nivel de la variabilidad genética no es una información que se proporcione por el laboratorio de origen de la semilla de ostión, el objetivo de este estudio fue evaluar la variabilidad genética a nivel de microsatélites de un nuevo linaje de C. gigas adquirido por el CREMES y el seguimiento de la estructura genética en la generación sucesiva con el fin de garantizar la viabilidad y la explotación comercial del mismo.…”

Are 45 years of reproductive isolation enough to prevent the amplification of mitochondrial genes in the Pacific oyster?

“…This variability may reflect the effects of prolonged artificial selection, cumulative inbreeding, divergence from the original source and bottlenecks, since all of the above leads to a loss of the potential for adaptability in populations (Barg, 1992). Studies on the structure and population genetic variability of the Pacific oyster have been carried out with allozymes, microsatellites, AFLP, and mitochondrial DNA sequences in natural (Ozaki & Fujio, 1985;Yang et al, 2000;Yu et al, 2008), feral (Li et al, 2003;Meistertzheim et al, 2013) and cultured populations (De la Rosa-Vélez et al, 1991;Launey & Hedgecock, 2001, Li et al, 2006Enríquez-Espinoza & Grijalva-Chon, 2010). In the study of mitochondrial variability, the non-coding control region has been widely used for analysis of polymorphism and population variability (Ferris & Berg, 1987;Allendorf et al, 2013).…”

“…However, recently the mitochondrial NADH dehydrogenase 5 (ND5) gene has been used successfully for the analysis of the population genetic structure (Makhawi et al, 2013), even in the Pacific oyster (Kawamura et al, 2017). In the case of C. gigas cultivated in Mexico, little has been studied, excepting some research using allozymes (De la Rosa-Velez et al, 1991;Correa et al, 2004;Enríquez-Espinoza et al, 2010), and microsatellites (Cruz et al, 2007;Grijalva-Chon et al, 2013). In order to compare the differences in the genetic variability of the oyster spat that occurs in northwestern Mexico, we aimed to conduct a study of population genetics in the spat produced by the four largest commercial hatcheries in the region.…”