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Overall Goals and Emphasis
In the broadest sense, I am interested in
basic and applied questions about the evolution and ecology of aquatic
species and communities. My current research focuses on the evolution
of life history (especially early life history), and its consequences
for genetic divergence and speciation. Recent advances in molecular
genetic techniques and theory, coupled with intensive ecological study
have the potential to reveal how different processes affect genetic
diversity. I use theoretical, molecular (microsatellites, nuclear and
mtDNA sequence data, SSCPs), and field ecological methods to ask
questions about the impact of dispersal, mortality, life history and
phylogenetic and geological history on genetic diversity and
speciation. My primary study group is North American fishes.
Discriminating Historical and
Ongoing Processes
Ongoing processes that shape biodiversity
cannot be fully understood without an understanding of the history of
the study organisms. A large component of my research is focused on
gathering molecular systematic data and using these data to test
hypotheses about the evolution of key characters. My research focuses
on analytical methods for generating phylogenies, and statistical
approaches for incorporating phylogenies in comparative studies.
Ultimately I seek to understand how evolutionary innovations in
morphology and life history influence species diversity. For example, I
conducted a comparative study of gene flow and life history in a
monophyletic group of stream fishes (darters). Population genetic data
and early and adult life history information were compared using a
molecular phylogeny. This study revealed that life history plays an
important role in the magnitude of genetic flow at all spatial scales
(e.g., among local populations and across wide biogeographic
boundaries).
Theoretical and Applied Population
Genetics
My current work addresses applied and basic questions about the
distribution and maintenance of genetic diversity in natural
populations of fresh and salt-water fishes. My focus is decoupling
recent historical effects (e.g., changes in population size) from
ongoing processes (e.g., migration), an important theoretical and
applied problem in population genetics. I am conducting a comparative
study of demography, life history, and temporal genetic variability
among Rio Grande fishes that differ in these attributes. I will
evaluate the genetic effective population size to census size ratio in
these species and ask how empirical measures of this ratio differ from
theoretical expectation. There is good reason to believe that
deviations from theoretical expectation (sometimes observed in species
with type III survivorship) may be tied to life history and demographic
differences among species. I will test this notion through intensive
ecological and genetic study of four species with different life
histories. This research is motivated, in part, by pressing
conservation issues in the Rio Grande and in the southwestern US in
general. I am also actively studying temporal patterns of genetic
variation in a commercially important, estuarine-dwelling fish, the red
drum ( Sciaenops ocellatus ). Red drum suffered population
declines related to overfishing in the early to mid 1980s. I am
interested in how such declines have affected genetic diversity in this
species and more generally, the potential consequences of overfishing
to genetic diversity. To address this problem, I use a combination of
empirical analysis and simulation modeling to understand the behavior
of molecular genetic markers under various non-equilibrium conditions.
Historical Changes in the Rio Grande
Ecosystem using Stable Isotopes and the MSB Fish Collection
 One of the most challenging
questions to restoration biologists is what aspects of the ecosystem
are we trying to restore? The answer is complicated because we often do
not know how the historical (pre-impacted) community functioned, and
there is little opportunity to identify pristine systems for
comparison. My student, Melanie Edwards, and I are currently developing
a novel method to address the problem of reconstructing community
function in the Middle Rio Grande, that is, to identify the role of the
changing river environment for altering nutrient cycling through the
riverine food web. We are using stable isotope signatures obtained from
museum preserved and present-day fishes to compare historical and
current fish communities in the Middle Rio Grande system. The long-term
research plan aims to answer the following questions: Does the
present-day community function similarly to historical community? What
kinds of environmental changes have altered food web dynamics in the
Rio Grande? What effects have species invasions/extinctions had on
ecosystem function? The answers to these questions are fundamental to
successful restoration of the Rio Grande ecosystem, and will provide a
case study for the implementation of stable isotope techniques to
characterize other historical ecosystems.
Molecular Biogeography of South
American fishes
The most diverse freshwater fish fauna in
the world resides in South America, but our understanding of
biogeographic and ecological forces that influence fish species
diversity there is rudimentary. Kirk Winemiller (Texas A&M
university) and I are studying phylogeographic patterns in a family
(Characiformes: Prochilodontidae) of highly migratory species to
understanding the relative roles of ecological and historical processes
for shaping diversity in the Orinoco River basin. All species in the
comparison share life history and migration features in common, but
some species are restricted to heterogeneously distributed black water
and others are found only in more widely distributed white water
habitats. We are using this system to study the roles of habitat
heterogeneity and historical river drainage pattern for determining
genetic (and biological) diversity in this system.
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