Tyrone B. Hayes

Tyrone Hayes leaning against a tree

Associate Dean for Diversity, Equity and Inclusion, Judy Chandler Webb Distinguished Chair for Innovative Teaching and Research, and Professor

Email: tyrone@berkeley.edu
Phone: (510) 643-1055

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Research Description

My research focuses on the role of steroid hormones in amphibian development and I conduct both laboratory and field studies in the U.S. and Africa. The two main areas of interest are metamorphosis and sex differentiation, but I am also interested in growth (larval and adult), immune function, and hormonal regulation of reproductive behavior. My work addresses problems on several levels including ecological, organismal, and molecular questions. My work on sex differentiation involves the African clawed frog (Xenopus laevis) and several other species. My main goal is to synthesize ecological/evolutionary, organismal/physiological, and biochemical/molecular studies to learn how an animal translates changes in its external environment to internal changes, how these internal changes are coordinated, what molecular mechanisms are involved, and in turn, how changes at the molecular level affect an animal's ability to adapt to the changes in its external environment. 

I also have a strong interest in examining environmental contaminants that interfere with hormone production and action (e.g. endocrine disruptors). Much of my work in this area has focused on the herbicide and endocrine disruptor, atrazine. Atrazine chemically castrates and feminizes exposed male amphibians, thereby negatively impacting reproductive potential. Though many factors likely contribute to amphibian declines, pesticides (such as atrazine) likely play an important role even in populations that appear to decline for other reasons. Pesticides like atrazine are ubiquitous, persistent contaminants and, though more pronounced in amphibians, the effects described above occur in all vertebrate classes (fish, amphibians, reptiles, and mammals) examined, via common mechanisms. These observations demonstrate the critical impact that pesticides have on environmental health. Furthermore, reproductive cancers and birth defects associated with exposure to many of these same chemicals (e.g. atrazine) via identical mechanisms demonstrate that the impact on environmental health is an indicator of a negative impact on public health. In particular, ethnic minorities and lower socio-economic communities are at risk: More likely to live in contaminated communities, work in occupations that increase hazard exposure and less likely to have educational and healthcare access. Given the importance of this science and relevance to public health, there is a strong need to translate this information and provide public access to this knowledge.

Selected Publications


Hayes, T.B., A. Collins, M. Lee, M. Mendoza, N. Noriega, A.A. Stuart, and A. Vonk, Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses. Proc. Natl. Acad. Sci. USA, 2002. 99: p. 5476-5480.

Hayes, T.B., K. Haston, M. Tsui, A. Hoang, C. Haeffele, and A. Vonk, Feminization of male frogs in the wild. Nature, 2002. 419: p. 895-896.

Hayes, T.B., V. Khoury, A. Narayan, M. Nazir, A. Park, T. Brown, L. Adame, E. Chan, D. Buchholz, T. Stueve, and S. Gallipeau, Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis). Proc. Natl. Acad. Sci. USA, 2010. 107    (10): p. 4612-4617.

Hayes, T.B. and M. Hansen, From silent spring to silent night: Pesticides in the Anthropocene. 2017 Elementa-Science of the Anthropocene 5:57.


Hayes, T.B. Diversifying the Biological Sciences: Past Efforts and Future Challenges. Molecular Biology of the Cell. 2010. 21: 3767–3769.

Barber, P.H., T.B. Hayes, T. Johnson, and L. Marquez-Magaña. Systemic racism in higher education (Letter). 2020 Science 369(6510): 1440-1441.