Host-parasite interactions in marine ecosystems are poorly studied compared to those in terrestrial systems. Many commercially exploited bivalve species experience parasitic diseases, and understanding host-parasite responses to climate change has implications for management of these fisheries. A team from Old Dominion University and Rutgers University will investigate host-parasite relationships in the eastern oyster (Crassostrea virginica), which suffers from two lethal protozoan diseases, MSX and Dermo. The team will integrate a wealth of long-term data on environmental fluctuation in Delaware Bay, the structure of its oyster population and two lethal parasites into coupled biological and oceanographic numerical models to predict how climate change may affect the host-parasite relationship. The result will be improved understanding how host genetics and population dynamics, and environment interact with disease organisms to structure host populations, and how climate change may affect these inter-related processes.
They will focus on: 1) the role of disease refugia, 2) the effect of variability in the number of parents (disease-resistant or not) that reproduce offspring each year, 3) the role of environmentally-modulated selection and transmission processes in producing genetic changes in the host population, and 4) the response of the oyster-parasite interaction to climate change and consequent effects on overall host population genetic structure. Using laboratory and field studies, they will identify additional genes linked to MSX and Dermo disease resistance, and identify possible phenotypic and genotypic differences between oysters from putative refugia and high-disease areas. In addition, they will determine whether disease refugia exist because of low transmission rates or because environment inhibits infection development. Finally, they will assess spatial and temporal variability in the effective size of the spawning populations and whether "sweepstakes" reproductive events occur in oyster populations. The data from these studies will underpin models that include explicit genetic structure, disease processes, and oyster population dynamics. A circulation-biogeochemical model will provide environmental conditions for the oyster models, and allow testing of the effects of parasite and larval transport, and current and future climate conditions on host population structure.
The broader impacts of the project include improved understanding of how diseases structure populations of a commercially important estuarine species. This project will also contribute to training of students in the variety of disciplines (genetics, pathology, genomics, bioinformatics, population modeling) needed to solve many of the important problems facing fisheries. Results from this project will be disseminated through scientific conferences, publication in the peer reviewed literature and web sites, and through ongoing outreach efforts to enhance general science education at local schools.
This project was designed to examine how oyster populations develop disease resistance in the marine environment. The advent of global warming has resulted in the incursion of marine diseases into bivalve populations not previously exposed and this has led to significant declines in bivalve abundances in some areas. Particularly hard hit is the Eastern oyster that suffers from two important diseases caused by protozoan parasites: MSX disease and Dermo disease. In Delaware Bay, oysters have developed resistance to MSX, but not to Dermo. As part of the US National Science Foundation Ecology of Infectious Diseases initiative, a program developed for Delaware Bay has focused on understanding how oyster population genetics and population dynamics interact with the environment and these parasites to influence the host populations. The project took on four challenges: (1) to identify and characterize the genetic basis for disease resistance in the eastern oyster; (2) to determine whether refuges from disease exist in Delaware Bay that might sequester susceptible oysters and thus impede the population’s ability to develop further disease resistance; (3) to implement a coupled hydrodynamic / larval growth model for Delaware Bay to examine the role of larval transport in distributing oyster larvae carrying different disease susceptibilities; and finally (4) to implement a population dynamics model for the oyster to explore the influence of populations of oysters consisting of individuals with varying degrees of disease resistance on the development of disease resistance within the entire population. In pursuit of these objectives, the project has successfully applied four primary research activities. First, laboratory and field studies have been used to identify genes related to MSX and Dermo disease resistance, and the occurrence of disease refugia and the mechanisms that allow them to exist. Second, the resulting data from the foregoing studies have provided the necessary inputs to the development of oyster genetics, population dynamics, and larval growth models. Third, the project has implemented an advanced hydro-dynamic circulation model for Delaware Bay, and has investigated inter-annual changes in circulation, water properties and disease prevalence in the bay over the past 30 years. Finally, the circulation model and larval growth models have been used together to infer transport pathways of oyster larvae and MSX and Dermo disease pathogens. Results from the laboratory, field and modeling studies have provided an understanding of long-term changes in Delaware Bay oyster populations that occur as the oyster population responds to climate, environmental, and biological variability. Project results have been summarized thus far in 18 scientific publications (either published, in press, or presently under review). A total of 21 students and postdoctoral scholars have received training within this project. Lastly, the identification of remote populations and disease status of oyster populations is being shared with the local resource agencies to assist with managing Delaware Bay oyster resources. Information from the EID study will be used this year to develop management advice for the Delaware Bay oyster stock, as part of the assessment process.
