- Animal Behavior, Endocrinology, Genetics, Genomics, Molecular Biology, Sex Determination, Sexual Differentiation
I am an integrative biologist at the University of North Dakota. I am best known for my work on temperature-dependent sex determination (or TSD for short). My research has contributed significantly to our understanding of both the mechanistic basis and the adaptive significance of this unusual mode of sex determination. While much of my work has focused on TSD, I am interested in all kinds of sex differences and every aspect of phenotypic plasticity.
As a result of my own training, I value research that spans multiple levels of biological organization from the molecular to the ecological. I first started doing research with Jeffrey Lang when I was an undergraduate at the University of North Dakota. After delving into research, I decided to do a M.S. rather than applying to veterinary school (I had originally wanted to be a veterinarian). After finishing my M.S. in Jeff’s lab, I was hooked on scientific discovery and went on to do a Ph.D. with David Crews at the University of Texas-Austin. I then did postdoctoral work with John Cidlowski at the National Institute of Environmental Health Sciences. Along the way, I developed expertise in evolution, physiological ecology, neurobiology, endocrinology, behavior, quantitative and population genetics, reproductive biology, and molecular biology. I was hired as an Assistant Professor in 2003, promoted to Associate Professor in 2009 and then to Professor in 2016. I have always been open to using tools and concepts from different disciplines to address biological questions in new ways. For example, I was the first to use knowledge about the hormonal basis of TSD to test the leading hypothesis about the evolutionary significance of TSD. I continue to stay up to date on the latest experimental techniques and to incorporate new methods in my research when appropriate.
BIOL 315. Genetics. 3 Credits.
An introduction to genetics, with emphasis on classical genetic analysis and the biochemistry of gene transmission, expression and regulation. Prerequisites: BIOL 150, BIOL 150L, BIOL 151, and BIOL 151L or an equivalent approved by the department. F.
BIOL 338. Animal Behavior. 2 Credits.
Studies in animal social behavior. The influences of environmental factors on behavior is emphasized. Prerequisites: BIOL 150, BIOL 150L, BIOL 151, BIOL 151L or an equivalent approved by the department. S, even years.
BIOL 390. Endocrinology. 3 Credits.
This course focuses on the endocrine system of vertebrates. Students will learn how endocrine glands synthesize and secrete hormones and how hormones regulate gene expression, cell proliferation, cell differentiation, and cell physiology. Students build on these basic ideas to understand endocrine control of important developmental and physiological processes. Examples of positive and negative feedback loops will be presented throughout the semester. This reinforces the idea that endocrine glands and hormones work together as an integrated system to maintain homeostasis and produce complex biological cycles. Common endocrine disorders like diabetes mellitus, obesity, dyslipidemia (abnormal cholesterol levels), osteoporosis, erectile dysfunction, and polycystic ovary syndrome will be discussed. In summary, hormones produced by endocrine glands are required for normal development, survival, and reproduction. Prerequisites: BIOL 150, BIOL 151, and CHEM 122. F.
BIOL 410. Molecular Biology Techniques. 4 Credits.
Applications of DNA and RNA analysis and recombinant DNA technologies, emphasizing practical experience in the laboratory. This class will meet twice a week for 50 minutes in the classroom, and students will be expected to work approximately 4-6 hours a week in the lab during open lab times. Counts as an upper-division laboratory course. Prerequisite: BIOL 315 is recommended. S.
BIOL 491. Seminar. 1 Credit.
Discussion of selected topics in advanced biology, a different topic each semester. Prerequisite: Major or minor in biology. Repeatable to 4 credits. On demand.
BIOL 503. Seminar. 1 Credit.
Discussion of selected topics in advanced biology, a different topic each semester. Repeatable to 6 credits.
BIOL 597. Advanced Topics in Physiology and Development. 1-4 Credits.
Advanced topics in physiology and development. Examples include: Comparative Endocrinology, Vascular Development, Embrionic Physiology, and Neural Physiology. Repeatable when topics vary. Prerequisite: Graduate status or upper division status with consent of instructor. Repeatable. On demand.
I am broadly interested in the evolution of sex differences and organism-environment interactions. I take an interactive approach to study the genetic, epigenetic, cellular, and developmental mechanisms underlying sex differences and how organisms respond to their environment. These topics are intertwined because environmental factors can influence the vital decision to become male or female in many species. Moreover, the environment can have sex-specific fitness effects in species with environmental sex determination or genotypic sex determination.
Sex Determination: My main research focuses on elucidating genetic and epigenetic mechanisms involved in temperature-dependent sex determination (TSD for short). There are two sides to the coin, so to speak, for this research. On one side, we are identifying unique genes that sense and transduce temperature into a biological signal to determine sex (i.e., whether embryos develop ovaries or testes). On the other side, we study aspects of gonad differentiation that are evolutionarily conserved. Many genes that are involved in ovary or testis development are the same across vertebrate groups, from non-avian reptiles (lizards, snakes, turtles, crocodilians) to birds to mammals.
Additional Areas of Interest: I have also carried out research in other areas of biology, including Animal Behavior, Cardiovascular Development, Endocrinology, Evolution, Genetics, Neuroscience, and Reproductive Biology. See curriculum vitae for papers published in these areas.
Significant recent publications (see curriculum vitae for full list of publications):
Ruhr, I., J. Bierstedt, T. Rhen, D. Das, S.K. Singh, S. Miller, D.A. Crossley II, and G.L.J. Galli. Developmental programming of DNA methylation and gene expression patterns is associated with extreme cardiovascular tolerance to anoxia in the common snapping turtle. Epigenetics & Chromatin 14:42 (DOI: 10.1186/s13072-021-00414-7).
Rhen, T., Z. Even, A. Brenner, A. Miller, D. Das, S.K. Singh, R. Simmons. 2021. Evolutionary turnover in Wnt gene expression, but conservation of Wnt signaling during ovary determination in a TSD reptile. Sexual Development 15:47-68 (DOI: 10.1159/000516973).
Das, D., S.K. Singh, J. Bierstedt, A. Erickson, G.L.J. Galli, D.A. Crossley II, and T. Rhen. 2020. Draft genome of the common snapping turtle, Chelydra serpentina, a model for phenotypic plasticity in reptiles. G3: Genes, Genomes, Genetics 10:4299-4314. (DOI: 10.1534/g3.120.401440). Featured article in issue and selected for 2020 Spotlight collection of research and scholarship excellence published in the Genetics Society of America journals.
Singh, S.K., D. Das, and T. Rhen. 2020. Embryonic temperature programs phenotype in reptiles. Frontiers in Physiology 11:35. (DOI: 10.3389/fphys.2020.00035).
Schroeder, A.L., K.J., Metzger, A. Miller, and T. Rhen. 2016. Novel genetic association between cold-inducible RNA-binding protein and temperature-dependent sex determination. Genetics 203:557-571. (DOI: 10.1534/genetics.115.182840). F1000Prime Recommendation by Deborah Charlesworth F1000Prime.com/726190637#eval793517921
University of Texas-Austin, Ph.D. in Zoology
University of North Dakota, M.S. in Biology
University of North Dakota, B.S. in Biology, minor in Chemistry