ABSTRACT
Taura syndrome virus (TSV) is an important virus infecting penaeid shrimp in the western hemisphere. Genetic variation and immunohistochemical differences of 20 TSV isolates collected from the USA, Taiwan, Mexico and Nicaragua were compared. Capsid protein genes CP1 (546 bp) and CP2 (584 bp) were amplified by RT-PCR and the cDNAs were sequenced. Pairwise comparison of nucleotide sequences showed a 0-2.4% difference in CP1 and a 0-3.5% difference in CP2. Phylogenetic analyses clustered the TSV isolates into two groups: one contained USA, Taiwan and some Mexican isolates, the other contained Mexican isolates only. Immunohistochemical analysis using a TSV-specific monoclonal antibody produced positive results for the USA and Taiwan isolates but negative results for the Mexican and Nicaraguan isolates. Molecular and immunohistochemical data suggest the existence of at least two TSV strains, one of which might have evolved following contact with a new penaeid host, Penaeus stylirostris.
Subject(s)
Capsid Proteins/genetics , Capsid Proteins/metabolism , Genetic Variation , Penaeidae/virology , RNA Viruses/classification , RNA Viruses/isolation & purification , Americas , Amino Acid Sequence , Animals , Capsid Proteins/chemistry , Immunohistochemistry , Molecular Sequence Data , Phylogeny , RNA Viruses/genetics , RNA Viruses/metabolism , Reverse Transcriptase Polymerase Chain Reaction , TaiwanABSTRACT
Random amplified polymorphic DNA (RAPD) fingerprints of two shrimp populations (Litopenaeus stylirostris) were compared to find genetic marker(s) that may be associated with infectious hypodermal and hematopoietic necrosis virus (IHHNV) resistance or susceptibility. Of the 100 10-mer random primers and 100 intersimple-sequence repeat (ISSR) primers screened, five provided markers specific to the Super Shrimp population and three provided markers specific to the wild caught population. The two populations were further characterized for relative viral load (reported as cycle threshold, CT) using real-time quantitative PCR with primers specific to the IHHNV genome. The beta-actin gene was amplified to serve as a control for normalization of the IHHNV viral load. The mean viral load was significantly lower (C(T) = 34.58; equivalent to 3.3 x 10(1) copies of IHHNV genome/ng DNA) in Super Shrimp than in the wild caught population (CT = 23.49; equivalent to 4.2 x 10(4) copies/ng DNA; P < 0.001; CT values are inversely related to viral load). A preliminary prediction model was created with Classification and Regression Tree (CART) software (Salford Systems, San Diego, Calif.), where the resultant decision tree uses the presence or absence of seven RAPD markers as predictors of the relative viral load.
Subject(s)
Densovirinae/physiology , Penaeidae/genetics , Penaeidae/virology , Random Amplified Polymorphic DNA Technique , Animals , DNA Fingerprinting , Genetic Markers , Polymerase Chain Reaction , Viral LoadABSTRACT
Molecular techniques provide powerful tools for studying the geographic structure of hybrid zones and the dynamics of gene exchange between incipient species. We examined allozyme variation at five loci (PGM, GPI, MDH-1, MDH-2, and LDH) for 27 populations of Palaemonetes kadiakensis from the central, coastal, and eastern regions of Texas. Central Texas populations of P. kadiakensis exhibited highly significant linkage disequilibrium and departures from Hardy-Weinberg genotype proportions. In populations with linkage disequilibrium, allelic differences at GPI defined two types of P. kadiakensis, designated A and B. Both types existed in central Texas with little or no evidence of interbreeding, whereas the populations from all other localities showed complete introgression of type B alleles into the type A gene pool. We also examined ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) variation in a subset of populations, chosen to cover a range of geographic locations and levels of linkage disequilibrium. Two groups of mtDNA haplotypes and two restriction fragment patterns for the rDNA corresponded to allozyme type A and B individuals in populations exhibiting linkage disequilibrium. In populations with ongoing hybridization, all hybrid animals (N= 15) exhibited type A mtDNA. Exhibition of type A mtDNA indicated that type A females had mated successfully with type B males, but type B females had not mated successfully with type A males. Genotype distributions suggest reduced reproduction by hybrid offspring in central Texas populations. These patterns are consistent with a mosaic model of hybrid zone dynamics.
