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The genetics of L. vannamei in Brazil and in the world

Nearly five years ago we began to study the shrimp genetics. In that time, studies and even researchers interested in that type of approach in this animal group in Brazil were practically inexistent. Nowadays, there are possibly about twenty researchers distributed throughout different laboratories that begin to qualify Brazil among the countries that contribute to the genetic knowledge of shrimp. Genetic studies on our native shrimp species are atill very rare. In one of these few, Gusmão and Solé-Cava (2000) performed a mitochondrial DNA analysis that compared the cytochrome oxidase gene of the shrimp species distributed throughout our coast and that identified two putative cryptic species in the morphological group Farfantepenaeus subtilis. In a second study, Sanchez (2001) partially characterized the nucleotide sequence of the molting hormone ofo Farfantepenaeus paulensis.

Motivated by the advance in the rearing of the exotic L. vannamei in the Brazilian coast, the current genetic studies concentrate on this species. A set of studies using different multiloci molecular markers, such as VNTR (Freitas, 1999; Freitas and Galetti, 2002a) and RAPD (Calgaro, 2002; Freitas and Galetti, 2001), permitted an important diagnostic of the genetic variation found in the various L. vannamei already domesticated broodstocks that are in different laboratories of larvae production, in many States of the federation et al, 2001). The comparison of the genetic distances between these stocks has already made possible the guidance of breedings for the establishment of lineages in these laboratories. These studies are growing (Freitas and Galetti, 2002b; Francisco and Galetti, 2002), and, in the short-term, the knowledge of the entire genetic structure of the rearedL. vannamei (or lineages) available in Brazil is expected, forming a breeding guideline for a genetically sustainable exploitation of these stocks. An important consequence of these studies is the monitoring of the genetic variation along the domestication process, which apparently suffers a significant reduction in an inbreeding lineage submitted to mass selection (Freitas and Galetti, 2001).

In the genomic context and in the search of more efficient markers for population studies, we are developing an extensive work in the search and characterization of microsatellite sequences. Currently, we already possess a few validated microsatellite loci and have initiated the investigation of their polymorphism (Jesus and Galetti, 2002). The microsatellite markers will be extremely useful for physical DNA mapping studies, which will open up to the possiblity of a future marker-assisted selection in genetic improvement programs.

Genetic studies on reared shrimp are also more frequent in other countries, and a lot has been analyzed on the genetic variation identified by molecular markers (Dhar et al., 2000; Alcivar-Warren, 2001; Xu et all., 2001) or analyzed by the phenotypic characters of the animal (Benzieet al., 1997).

However, there are only a few references on the genomic sequencing of shrimp around the world. From a partnership between the Australian Institute of Marine Science and the Commonwealth Scientific and Industrial Research Organisation of Australia, the EST genome project of Penaeus monodon, species commonly reared in that country, is already underway. Up to today, a few hundreds of ESTs have already been isolated and are listed in the webpage Other penaeid species also already possess some isolated and characerized EST sequences, such as Litopenaeus setiferus (Barttlett et al., 2002) e Marsupenaeus japonicus (cited in the page indicated above).

There are also a few citations on the EST isolation of L. vannamei, from libraries of different tissues (Dhar et al., 2000; Alcivar-Warren, 2001; Bartlett et al., 2002). Nearly 700 EST sequences obtained from shrimp exposed to the TSV viral disease are cited in Alcivar-Warren (2001). Therefore, it is clear that the genomics of penaeids has already become of interest to many researchers, but, considering the genome size of these animals and the few ESTs described thus far, there is much more to be done. The concentrated effort that characterizes the shrimp genome network here proposed will certainly represent the greatest gathering of EST knowledge ever performed for this animal.


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