Ricardo Perez-Enriquez, Fidencio Hernandez-Martinez, Pedro Cruz*, Manuel Grijalva-Chon, Josefina Ramos-Paredes, Fernando Mendoza-Cano
Centro de Investigaciones Bioldel Noroeste, S.C. (CIBNOR)
Mar Bermejo 195, Col. Playa Palo Santa Rita, La Paz, Baja California Sur, Mexico 23090
rperez@cibnor.mx
There is a concern in the Mexican shrimp aquaculture industry that because closed broodstocks have been used in commercial hatcheries for many generations, these would be suffering the effects of low genetic diversity, and hence subject to the effects of inbreeding depression. Since little information is available about the genetic diversity of the Mexican broodstocks, we analyzed the genetic composition and inbreeding levels of six commercial hatcheries in Northwestern Mexico.
We sampled muscle tissue of 50 individuals per lot within each hatchery for DNA extraction and microsatellite analysis. The genetic composition at 6 independent loci (Pvan1758, Pvan1815, TUXMLv8.256, TUXMLv10.312, TUXMLv10.312, and LV5) was obtained and genetic diversity and inbreeding parameters were estimated. Data from the two Pvan microsatellites were compared with three generations of a breeding program at CIBNOR (years 2000-2002). Genetic diversity was also measured based on mtDNA sequences of control region.
The genetic diversity among hatcheries was relatively similar, although two of them showed lower values than the average (Fig. 1). Even though the microsatellite genetic composition was significantly different among hatcheries, the main alleles in all loci were always the same. The main mtDNA haplotypes were also the same in all hatcheries indicating a common origin of the broodstocks.
Even though the comparison between 2000-2002 and 2007 broodstocks did not show a decrease in the number of alleles, a decrease in observed heterozygosity was found. The Fis index showed inbreeding levels of 28%, which might be due not only to inbreeding itself but also to the analysis of mixtured stocks within the hatcheries, or to the overrepresentation of multiple-spawning females.
Management practices for almost 10 generations since the introduction of a single stock from Venezuela to Mexico, had permitted the broodstocks to retain high levels of genetic diversity. Nevertheless, hatchery managers should be aware of the potential inbreeding accumulation, and take crossbreeding measures to decrease the probability of inbreeding depression.
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