Evolution and development of polyphenisms: a mechanistic model based on bistable switches

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Polyphenisms represent a form of adaptive phenotypic plasticity that gives rise to discrete alternative phenotypes, based on a developmental switch. However, existing models for the evolution of polyphenisms do not consider the role of development and therefore cannot explain how the switching behavior emerges and evolves. In this research project, I aim to reveal how polyphenisms evolve by modeling the evolution of their underlying developmental regulatory architecture. The main research objective is to test the hypothesis that polyphenisms are based on bistable switches in the underlying gene regulatory network (GRN), which usually requires positive feedback and ultrasensitivity. To test this hypothesis, I will develop a theoretical mechanistic model that focuses on the evolution of the GRN responsible for the polyphenism switch. I expect that, under conditions favorable to the evolution of a polyphenism, both positive feedback and ultrasensitivity will emerge in the GRN, giving rise to a polyphenism switch. I will then use the model to investigate the implications of the regulatory architecture for the evolution of polyphenisms. In addition to the general model version, which can be applied to a wide range of polyphenisms, I will also develop a concrete model version specifically tailored to environmental sex determination and employ it to study how evolutionary transitions in sex-determining systems are mediated by the evolution of GRNs. Connecting evolutionary biology and systems biology, this research project should advance our understanding of polyphenisms in several ways. First, the project offers a novel, GRN-based perspective on the developmental basis of polyphenisms. Thus, it is able to explain both the threshold behavior and the phenotypic stability of polyphenisms. Moreover, the approach allows us to address critical yet unexplored questions, and make testable predictions, about the evolution of polyphenisms and how it is contingent upon underlying regulatory conditions.