Research Interests


Overall Goals and Emphasis

In the broadest sense, I am interested in the evolution and ecology of aquatic species and communities.  I use theoretical, molecular, and field ecological methods to ask questions about the impact of dispersal, mortality, life history and phylogenetic and geological history on the maintenance of genetic diversity in wild populations, and in the speciation and extinction process.  There are two major components to my research program:

 

1) Using theoretical and molecular approaches to understand how evolution of key innovations affects genetic diversity, speciation, and species persistence.

 

2) Integrating long-term studies of ecological systems and population genetics to understand the interplay of ecological and abiotic factors that determine genetic diversity of organisms.

 

These approaches provide perspective on both basic and applied questions in conservation biology, which is a major focus of my research.  Many of the questions we address in my lab are motivated by the need to predict and, in some cases attempt to mitigate, organism responses to severe water shortfalls in the arid southwestern United States.

 

To accomplish the task of obtaining long-term genetic and ecological data, I have integrated my research and curatorial programs in the Museum of Southwestern Biology Division of Fishes.  The benefit is that our natural history collection offers a substantial historical record of changes in aquatic ecosystems (and their components) in the southwest, which helps us pose and test hypotheses about the causes of ecosystem change and species declines in these imperiled systems. 


 

Molecular Ecology and Evolution of Fishes

 

Comparative approaches in population genetics and ecology

 

red shiner – photo by T. Kennedy

 
Cyprinella lutrensis copy.jpgWe are interested in processes that affect distribution and maintenance of genetic diversity in natural populations of freshwater fishes in arid systems in the American southwest.  This research is motivated, in part, by pressing conservation issues in the Rio Grande and other aquatic ecosystems of the southwestern US.   Our focus is decoupling recent historical processes (e.g., changes in population size over time) from ongoing processes (e.g., migration), an important theoretical and applied problem in population genetics.  My lab group is conducting a comparative study of demography, life history, and temporal genetic variability among Rio Grande and Pecos River fishes (Alò and Turner 2005, Moyer et al. 2005, Osborne et al. 2005, Turner et al. 2006) that differ in key life history attributes, especially early life history.  Our research links demographic and genetic processes explicitly by examining the genetic effective population size to census size ratio in fishes to ask how empirical measures of this ratio differ from theoretical expectation. Comparative genetic study has indicated that river fragmentation is probably the most important general factor leading to the loss of genetic variation, thus impacting the long-term probabilities of persistence of fishes in this region.  This finding is important because it suggests that management priorities should focus on mitigating the effects of river fragmentation, rather than investing in other management efforts.  Ultimately, we seek to discover underlying factors that lead to decline and extinction of freshwater fishes in the southwestern US.   

 

Molecular Biogeography of South American fishes

 

coporo, Prochilodus mariae

 

 
mariaeThe 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 patchily-distributed black water and others are found only in more continuously-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 (Turner et al. 2004, Moyer et al. 2005).  One key feature of this research is to conduct phylogeographic analysis on nuclear and mitochondrial genes with multiple focal species.  Using this comparative approach, we have determined that natural selection, demography, and vicariance all play important roles for speciation in neotropical freshwater fish assemblages.  Future work will use an explicit comparative phylogeographic approach to understand the association of habitat heterogeneity and life history and speciation rates.

 

 

Immunogenetics and conservation of small, isolated populations

 

In this project, we are examining the evolution of Major Histocompatibility Complex (MHC) genes in native trout species (Apache and Gila trout, Rio Grande cutthroat trout).   This study takes advantage of genomic information available for the rainbow trout, a model vertebrate organism whose genes involved in adaptive immunity are among the best characterized of teleost (bony) fishes.  Yet, how these genes evolve in small, isolated, populations is poorly understood.  Our aim is to understand patterns of evolution at MHC class II β1 within and among closely-related species of inland trout; (i) rainbow trout, Oncorhynchus mykiss, (ii) Gila trout (Oncorhynchus gilae) and (iii) Apache trout (Oncorhynchus apache).  The latter two species are closely related to rainbow trout and occur in small populations restricted to mountain streams southwestern US.  Native species shared a common ancestor about 10,000 years ago, and diverged from rainbow trout probably 200,000 years ago.  Comparative study among populations and species of these inland trout will provide insights into the role of population genetic processes like local selection, drift, migration, and hybridization for maintaining genetic variation at MHC.  One major goal is to evaluate spatial heterogeneity in pathogen communities to evaluate whether local adaptation may play an important role in shaping diversity at MHC.  We have obtained extensive data using neutral genetic markers for each species to provide and expectation of divergence under a strictly neutral process (Wares et al. 2004, Peters & Turner 2008). 

 

Discriminating Historical and Ongoing Processes

Blue River form of orangebelly darter – photo by T. Turner

 
TFT-06-013-8Ongoing 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 (e.g., Turner 1997). 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 as a framework for analysis.   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) (Turner et al. 1996, Turner and Trexler 1998).  I am also generally interested in the role of evolutionary constraint, and identifying key life history trade-offs (e.g., Charnov et al. 2001) for understanding which characteristics are likely to change over evolutionary time.

 

 


Community Ecology of Arid-Land Rivers: Historical and Contemporary Perspectives

Historical Changes in the Rio Grande Ecosystem using Stable Isotopes and the MSB Fish tomcrewCollection

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 provide a case study for the implementation of stable isotope techniques to characterize other historical ecosystems.

 

Abiotic and Biotic Control of Arid-Land River Foob Webs

 

07-010-7 ASB,NDB,MKT_3.jpgRivers that flow through arid lands provide a limiting resource for human population and economic growth while simultaneously supporting a diverse community of plants and animals. Consequently, these rivers are often targets of intensive restoration activities based, perhaps erroneously, on concepts developed for mesic (wetter) rivers. Arid-land systems differ from mesic counterparts in that they experience enormous variability in flows that range from high floods to being nearly dry. Low flows and river intermittency are common occurrences, and drying events may be important for enhancing species diversity by allowing coexistence of organisms that specialize on high- and low-flow conditions, respectively. However, actual effects of seasonal variability in discharge, especially low flows, on aquatic communities remain largely unknown. To address this gap in knowledge, a field and experimental study will be conducted on the Rio Grande in New Mexico. Changes in biomass and nutrient composition of algae, invertebrates, and fishes that make up the river’s food web will be tracked. Macronutrients, such as carbon, nitrogen, and phosphorus, are used as tracers to understand the dynamics of community changes associated with flow variability and drying in natural river environments. Finally, an experimental study will manipulate key variables that appear to strongly affect species abundance and diversity in drying river environments. The outcomes of this study will aid development of scientifically defensible restoration policies and establishment of minimum flows in arid-land rivers. Development of such policies is of paramount economic importance to arid and semi-arid regions worldwide.

 

 

 

Integrative Research: Environmental and Genetic control of Reproductive Timing in Cyprinid fishes

 

The timing and sequence of fish reproduction differs among species in most temperate rivers, and phenology of reproduction is predicted to strongly influence freshwater fish community structure in arid and semi-arid catchments.   This prediction suggests complex interactions across four levels of ecological hierarchy where abiotic cues (ecosystem properties) initiate spawning (individual properties) and subsequent recruitment success or failure (population and community properties).    Our results suggest that while highly predictable cues (e.g., day length) appear to determine spawning readiness in all species, more variable abiotic cues (e.g., temperature and discharge) probably initiate spawning.  Ultimately, plasticity in spawning time enhances survivorship by surmounting dramatic fluctuations in abiotic conditions, but stable isotope results (Pease et al. 2006, Turner et al. 2010) suggest that timing differences among species are maintained, in part, by interspecific competition.  Intensive ecological study coupled with comparative genomic analyses offers the prospect of closing the loop between environmental signals and genetic control of reproductive timing in Rio Grande fishes.  Such an integrative approach will lead to better predictive models of the effects of global climate change.  We will develop this approach in my laboratory over the next few years; to this end we have established an experimental mesocosm system to evaluate trophic dynamics and interactions of fish larvae, invertebrates, and algae.  We have also developed a number of candidate genes and a microarray approach to identify sensory and regulatory pathways linked to the onset of reproduction in Rio Grande fishes.

 


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Last updated 14 April 2012 © T. Turner