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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.
If you have comments or suggestions, email me at biomkk@hofstra.edu
