EFFORTS TOWARDS DEVELOPING A LINKAGE MAP FOR PENAEID SHRIMP

Department of Environmental and Population Health, Tufts University School of Veterinary Medicine, 200 Westboro Road, North Grafton, MA 01536 USA

Emerging viral diseases threaten the sustainability of shrimp aquaculture worldwide. To date, little is known about the cellular and molecular mechanisms involved in the response of the shrimp immune system to viral attack. In the US, the most serious disease threatening the Penaeus vannamei industry is Taura Syndrome Virus (TSV). Efforts are underway to develop a gene map for shrimp (ShrimpMap) that will allow identification of the genes associated with immunity to TSV. The goals of ShrimpMap are to develop highly polymorphic markers, construct a medium density linkage map and identify the QTL for TSV resistance.
We are isolating both Type I (protein coding genes) and Type II markers (microsatellites, RAPD) for linkage and QTL mapping efforts. For Type I markers, we focus on expressed sequence tags (ESTs). The mRNA differential display and cDNA library screening techniques are used to isolate ESTs that are differentially expressed in response to TSV infection. Preliminary results have identified over ninety differentially expressed mRNAs in TSV resistant and susceptible shrimp. For Type II markers, we focus on microsatellites isolated from size-fractionated genomic libraries and RAPD techniques. Around two hundred microsatellites have been developed so far. These markers will be used to genotype a family of ~300 F₂ P. vannamei.
This two-track approach will provide baseline information on gene expression and facilitate future chromosome mapping research aimed at understanding the genetic mechanisms that regulate resistance to viral diseases in shrimp. The highly polymorphic markers obtained so far will be useful not only for mapping economically important traits such as disease resistance and high growth but also as a powerful tool for producing genetically improved stocks in breeding programs, studying interactions between cultured and wild shrimp populations and better managing shrimp resources.