Molecular genetic studies of Hematodinium sp., a parasitic dinoflagellate of the blue crab, Callinectes sapidus

• Main Author: Lohan, Katrina M. Pagenkopp
• Format: Others
• Language: English
• Published: W&M ScholarWorks 2011
• Subjects: Genetics; Parasitology
• Online Access: https://scholarworks.wm.edu/etd/1539616750; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2317&context=etd

Economically viable fisheries for the American blue crab, Callinectes sapidus, occur in the USA from Delaware Bay to the Gulf of Mexico. Unfortunately, a number of factors, including overexploitation, degraded habitats, and disease, have contributed to the decline of blue crab populations in the USA. In April 2008, the Secretary of Commerce declared the blue crab fishery in the Chesapeake Bay a "commercial fishery disaster." One factor potentially contributing to the decline of blue crab populations in high salinity waters is infection with Hematodinium sp., a parasitic dinoflagellate, which can cause significant mortalities in blue crab populations. Since the first report of this parasite infecting blue crabs in 1975, few studies have used molecular techniques to examine life history characteristics, population structure, geographic range, and host specificity of the species of Hematodinium that infects this host. to examine host specificity, a variety of crustaceans were collected from the Delmarva Peninsula, a region that has high prevalence of Hematodinium sp. in blue crabs. Sequence data obtained from the first internal transcribed spacer (ITS1) region of the ribosomal RNA (rRNA) gene complex from Hematodinium sp. in blue crabs and potential alternate hosts was used to determine that this species of Hematodinium is a host generalist, capable of infecting many decapods and possibly amphipods along the Delmarva Peninsula. Additional sequence data obtained from Hematodinium sp. from infected blue crabs collected from Georgia, the Gulf Coast of Florida, and Texas showed that one species of Hematodinium, the same species found in Virginia, infected blue crabs in all of these locations. Due to the lack of variation observed in the ITS1 region sequences, an enriched microsatellite library was developed using a non-clonal primary culture of Hematodinium sp. from an infected blue crab. From this library, eleven microsatellite markers were identified and optimized for Hematodinium sp. to assess intra-specific variation. Eight microsatellite markers were polymorphic and these were used to genotype Hematodinium sp. from infected blue crabs from six locations along the Delmarva Peninsula. Allele frequencies from these microsatellite markers, along with analyses of the multi-locus genotypes recovered from single genotype infections, indicated that the Delmarva Peninsula contains a single population of this parasite. Microsatellite data also indicate that this parasite is haploid in the hemolymph of the blue crab and that multiple infections are common. The observed genotypic variation was extremely high, indicating that sexual reproduction occurs at some point in the life cycle of this parasite, though the exact life history stage that undergoes sexual reproduction is unknown. This is the first report for evidence of ploidy, multiple infections, population structure, and sexual reproduction for this species of Hematodinium .