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ASSESSING REGIONAL IMPACTS AT THE
POPULATION-GENETIC LEVEL IN ESTUARINE ANIMALS IMPACTED
BY HURRICANE KATRINA
Research by Dr. Joseph M. Quattro
Department of Biological Sciences/Marine Science Program
Grass shrimp are important resources for
fisheries management. Many coastal sport fish spend at
least part of their life in estuaries where grass shrimp
are a critical food source. The grass shrimp
Palaemonetes pugio is a widely distributed,
ecologically important, crustacean and is often used as
a model organism. Estuarine grass shrimp are an obligate
food source for shrimps, crabs and most estuarine
bottom-feeding fishes. Because of its high natural
densities and ease of culture in laboratories, P.
pugio has become a “sentinel species” in coastal
ecosystems.
 University
of South Carolina researchers have been active in
describing the species and its congeners population
genetic history while forging new multidisciplinary
approaches to toxicological studies using grass shrimp
as model estuarine organisms. To this end, researchers
examined DNA sequence variation from a large number of
animals across the species’ range in an effort to
examine phylogeographic history.
Although Atlantic populations are nearly devoid of
detectable variation at the mitochondrial Cytb locus,
samples from the Gulf of Mexico are highly diverse. Of
particular interest for this project were those
populations characterized genetically that were impacted
by Hurricane Katrina. These samples served as baseline
genetic data to study the immediate and long-term
effects of hurricane activity on grass shrimp population
genetic structure.
Specifically, researchers sought to (1) determine levels
of genetic variation within grass shrimp populations
prior to Hurricane Katrina, (2) sample storm-impacted
areas and assay these samples for levels of genetic
variation, (3) compare levels of genetic diversity
within impacted areas and between impacted/non-impacted
areas, and (4) use these data to assess the impact of
Hurricane Katrina on the population dynamics of an
estuarine- dependent crustacean.
Researchers used mitochondrial DNA sequence data to
assess changes in levels of genetic diversity within and
among populations pre- versus post-Katrina.
Specifically, they examined mitochondrial DNA diversity
in about 200 samples of grass shrimp collected before
and immediately after Hurricane Katrina. The research
team’s previous genetic work suggested significant
population-level genetic subdivision in this species
pre-Katrina, and they were interested in the potential
impacts of this event on genetic differentiation among
coastal populations.
Researchers used an Analysis of Molecular Variance (AMOVA)
that nested pre-Katrina and post-Katrina samples as
regions, (with five impacted, coastal populations
collected from Alabama through Louisiana nested within
these regions) to detect significant genetic
differentiation before as opposed to after the storm.
Their preliminary analyses suggested that a large
significant, but interestingly, negative component of
genetic variance can be attributed to pre- versus
post-Katrina differentiation, a result that can be
attributed to sampling of two rather divergent genetic
lineages in one sample (Cocodrie, Louisiana).
When researchers removed this sample, they found that
genetic differentiation across time (pre- versus
post-Katrina) was small, negative but non-significant,
and a larger proportion of the total genetic variance
was found among samples within any one year. Their
results suggested that Hurricane Katrina has had minimal
impact on the population genetics of this common
estuarine species. This study enhanced researchers’
understanding of the demographic processes at work in
estuarine populations, particularly levels of
connectedness between estuaries. This knowledge allows
for informed management decisions regarding these
biological communities that are important ecological
resources.
Researchers expect federal and state agencies charged
with oversight of coastal areas will benefit from this
work, and they anticipate several avenues of
collaboration. In addition, this work has strengthened
USC researchers’ partnerships with the University of New
Orleans, NMFS, Pascagula, Mississippi, and NOAA,
Charleston, South Carolina. This study also formed an
important component of the Ph.D. dissertation for one
graduate student (MAR). Additionally, one undergraduate
student actively participated in the data collection.
The research results are expected to lead to additional
unique research and mentoring opportunities.
USC researchers anticipate the publication of two
manuscripts to peer-reviewed journals — one describing
the genetic markers for P. pugio and a second
addressing the impact of this hurricane on estuarine
demographics in grass shrimp. This study provides
baseline data for such impacts and forms the basis for
future research.Biography
Dr. Joseph M. Quattro is an associate professor in
the Biological Sciences Department and Marine Science
Program at USC-Columbia. His research involves the
phylogeography of marine and freshwater animals and,
more recently, the effects of natural and anthropogenic
impacts on population-genetic history. Before coming to
USC, Quattro held a Sloan Post-doctoral Fellowship at
Hopkins Marine Station, Stanford University after having
been awarded a Ph.D. in Ecology from Rutgers University. Research Team/Collaborators:
Dr. Joseph Michael Quattro, Professor, USC, and Ph.D.
candidate Mark A. Roberts, USC, provided oversight on
the entire project including sample collection,
preparation and processing, sequence analysis, and
report/manuscript preparation. Dr. T. W. Greig, CCEHBR,
NOAA, aided in technique development and sequence
analysis. Dr. James M. Grady, University of New Orleans,
and Dr. Trey Driggers, NMFS, Pascagula, were responsible
for project oversight and, importantly, logistics,
including access to crucial sampling locations. |
