Getting to the Root of Flexible Stems: The Primary Cilia as a Proximate Mechanism of Plasticity and Evolution of the Cichlid Jaw

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How biodiversity arises and is maintained over time remains an important area of study. Adaptive radiations represent extreme instances of morphological evolution in response to discrete ecological shifts, and are thought to have made significant contributions to biodiversityon this planet. This research seeks to identify and characterize the genetic and cellular mechanisms that promote adaptive radiations, and thus to provide novel insights into the origins of biodiversity. This highly interdisciplinary project provides a rich intellectual landscape to train students in various methods and theories. It also offers an explicit framework to develop pedagogical tools for conveying evolutionary principals to the public. This will be part of on-going efforts to develop a series of animated and interactive evolutionary "origin stories" that detail the genetic mechanisms that underlie the development and evolution of notable traits, including turtle shells, bat wings, and limb loss in whales. Here the team proposes a new chapter-- Making faces: How the fish changes its skull.A focal point of this project is phenotypic plasticity, which refers to the ability of an organism to change its appearance in response to a change in the environment. The ability of an individual to change its phenotype in different environments may increase its fitness in changing and/or fluctuating environments, which suggests that plasticity may be adaptive and therefore subject to selection itself. It is predicted that species that live in fluctuating environments will maintain a high degree of plasticity. Conversely, species that live in more stable environments are predicted to loose the ability to mount a plastic response, and exhibit fixed phenotypes. Unfortunately, a strict genetic basis for phenotypic plasticity has remained elusive, and thus the evolutionary potential for this trait remains largely unknown. The goal of this research is to characterize the molecular basis for phenotypic plasticity of the teleost jaw. An emphasis on the jaws has direct ecological consequences, as different jaw shapes will determine where a fish lives and what it feeds on. Mutant and transgenic zebrafish will be used to assess the degree to which key molecules involved in bone formation, including those that underlie the primary cilia and Hedgehog signaling, are necessary to promote phenotypic plasticity in the skull and jaws. The molecular mechanisms that underlie plasticity will then be compared to patterns of genetic evolution in a textbook adaptive radiation, East African cichlid fishes, which exhibit extensive diversity in the shape of their jaws. It is predicted that the genes that underlie plasticity of the feeding apparatus, also underlie evolution of the jaws. This is because genetic variation that leads to plasticity is predicted to become "fixed" as populations adapt to new environments over time. In all, research under this award will facilitate a better understand of how the genome and environment interact to promote biodiversity.