Genetic variation and population structure of wild white shrimp (Litopenaeus vannamei) from 4 geographic locations from Mexico to Panama were investigated using 5 microsatellite DNA loci. The genetic diversity between populations was indicated by the mean number of alleles per locus and mean observed heterozygosity, which ranged from 7.4 to 8.6 and from 0.241 to 0.388, respectively. Significant departures from Hardy-Weinberg equilibrium were found at most locations at each locus, with the exception Guatemala at Pvan0013, and were caused by high heterozygote deficiencies. Genetic differences between localities were detected by pairwise comparison based on allelic and genotypic frequencies, with the exception of locus Pvan1003. Significant pairwise F (ST) values between locations and total F (ST) showed that the white shrimp population is structured into subpopulations. However, population differentiation does not follow an isolation-by-distance model. Knowledge of the genetic diversity and structure of L.vannamei populations will be of interest for aquaculture and fisheries management to utilize and preserve aquatic biodiversity.

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Genetic diversity in a shrimp-breeding program was monitored for 2 generations by microsatellite DNA markers (Pvan1578 and Pvan1815) to establish levels of variation and proceed with a selection program. An increase in the number and frequencies of some alleles in both microsatellite loci from G0 to G2 was induced by foreign sire contributions. Most common alleles and high heterozygosities (around 70% in both loci) were maintained through the generations, indicating that there had not been a significant loss of genetic variability in the breeding program. However, when compared with variability in other wild and cultured stocks, the presence of 4 main alleles at both loci may be an indication that a certain reduction in variability already was present in the line used as founder stock (G0). Therefore, it is recommended that additional genetic variability be introduced to the breeding stock by crossing it with a different line.

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