My broad interests include the molecular evolutionary genetics and biochemistry of marine organisms, from the theoretical to the applied (aquaculture and conservation genetics). I am currently involved in three major projects, a molecular evolutionary study of bay scallops supported by the National Science Foundation, a collaborative effort with the Genomics Groups of Brookhaven National Laboratory to develop and apply new tools to study differential gene expression, and a collaborative investigation of the genetic identity of green sea turtles captured in Long Island waters.
The first project, "Molecular evolution of the glucose phosphate isomerase (Gpi) locus in bay scallops, Argopecten irradians" seeks to understand how genetic variation for a metabolic enzyme can potentially translate into biochemical, physiological and fitness differences among individuals. Virtually every animal and plant species exhibits genetic variation for a variety of enzymes involved in the control of metabolism. Only a few studies have clearly established the relationships among genetic variation for a specific enzyme, the mechanistic, biochemical expression of that variation, and its relevance to the physiology and phenotype of the whole organism. My research attempts to establish a causal explanation for observations of a strong relationship between genotype for the enzyme glucose phosphate isomerase (Gpi) and production-related traits in the bay scallop. The specific project I'm working on now examines DNA sequence variation for the Gpi gene. cDNAs from scallops with different Gpi protein variants are being sequenced, and the resulting patterns of nucleotide polymorphism will be analyzed for evidence for or against natuual selection shaping the evolution of this gene and protein . The results ultimately address questions regarding the biochemical genetic basis of quantitative variation and the relative influence of evolutionary forces shaping genetic variation, and begin to address the functional relevance of nucleotide sequence variation.
Natural populations of eastern oysters, Crassostrea virginica experience heavy mortalities along much of the eastern Atlantic seaboard due to disease. Infections by two protozoan parasites, MSX disease, caused by Haplosporidium nelsoni infection, and Dermo disease, the result of infection by Perkinsus marinus, are prevalent in mid-Atlantic oyster populations and have severely impacted oyster aquacultural efforts and fisheries since the 1950s. Selective breeding programs at Rutgers University and the Virginia Institute of Marine Science have produced oyster lines that are resistant to MSX disease. Resistant lines do not completely escape infection or mortality, rather these lines experience far lower mortality rates than susceptible or wild stock The mechanism by which oysters resist or delay infection by Haplosporidium nelsoni is not clear, although it is known that infections in resistant oysters are localized while those in susceptible oysters become systemic and lethal. Traditional pathological studies have failed to identify the resistance mechanism against MSX, but very recently developed molecular techniques can be used to help characterize the biochemical basis for MSX resistance. Physiological and biochemical responses to disease are accompanied by corresponding changes in gene expression, the production of messenger RNA (mRNA) from DNA and the ultimate synthesis of protein. By examining differences in gene expression between diseased and noninfected individuals, mRNA and proteins unique to diseased individuals can be identified that represent cellular products produced in response to infection. The expression of resistance to MSX, reflected by localized instead of systemic infection, is clearly associated with the expression of some gene or genes that produce proteins that somehow convey resistance. In other words, resistant and susceptible oysters are predicted to express a different suite of genes in response to MSX infection. Those genes expressed only in resistant (and infected) individuals are likely to be directly involved in the resistance mechanism. In collaboration with Dr. Susan Ford, Rutgers University, I am beginning to develop and apply a method to identify differentially expressed genes in MSX - resistant and susceptible oysters that carry MSX infection. The identification of differentially expressed nucleotide sequences may lead to an understanding of the biochemical mechanism(s) of resistance and a better understanding of the metabolic effects of MSX infection. Originally, differential display polymerase chain reaction (ddPCR) was proposed as the method to identify uniquely expressed genes in MSX resistant oyster lines. Attempts to adapt this technique using nonradioactive detection methods have been problematic. Alternatively, I propose to develop SAGE (Serial Analysis of Gene Expression) libraries to identify informative expression tags which can then be used to isolate and identify differentially expressed genes. This work will be done in collaboration with the Genomics Group at Brookhaven National Laboratory.
"Natal origins of Green Turtles (Chelonia mydas) feeding in New York waters" is a project performed in collaboration with Sam Sadove of CRESLI. We are using molecular genetic markers, specifically mitochondrial DNA sequence data and microsatellite DNA variation, to characterize the origins of green sea turtles captured in feeding grounds near Long Island. Because female green turtles return to their tropical natal beach to nest with remarkable fidelity, populations of turtles originating from a single breeding population have grown to be genetically distinct over evolutionary time. Most of these surviving populations of green sea turtles are listed as threatened or endangered by the UN, but their management is made extremely difficult by the fact that the turtles migrate incredible distances to feed. Some green sea turtles migrate up the East Coast as juveniles and feed in Long Island's rich waters in the late summer and early fall. These animals are often incidentally captured in pound nets and are exposed to a number of potentially lethal factors. By characterizing DNA from turtles captured while feeding near Long Island, as well as from turtles from nesting populations in Florida, the Caribbean, and Mexico, we should be able to determine the origin of Long Island turtles. A fragment of mitochondrial DNA is being sequenced from every captured individual, and these data along with natal population sequences will be analyzed using a mixed stock analysis. This analysis will provide an estimate of the proportion of Long Island turtles that originate from each of several potential natal beaches in Florida and the Caribbean, and should tell us whether or not most turtles derive from populations with endangered or threatened status. This information is critically important for refining the Recovery Plan for the green turtle and for the overall conservation of this species.
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