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    Thomas F. Turner

    Photo Dr. Thomas F. Turner

    Director of MSB and Curator of Fishes
    Associate Professor of Biology
    Ph.D., Florida International University, 1996
    Aquatic Ecology and Fish Evolution

    Phone: +1-505-277-3609
    email: turnert[at]


    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

    Photo of a fish 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

    Tom Turner working with summer REU students 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.


    Curriculum Vita