Evolving increased vertebral counts: Developmental mechanisms underpinning phenotypic evolution in the Lake Malawi cichlid radiation.

One of the fundamental and most longstanding questions in biology is how phenotypes evolve to generate the incredible diversity of forms that surround us in the natural world. Vertebrate body shape is a good example of this, with species’ forms ranging from the rounded ocean sunfish to elongated snakes, and everything in between. The evolution of vertebrate body shapes has been accompanied by significant variation to the axial skeleton and the vertebrae that compose it, which can vary in size and morphology, but crucially also in number, ranging from less than 10 to several hundred. In COUNTS I propose an inter-disciplinary approach to uncover the developmental drivers of phenotypic diversity in vertebrates by using Lake Malawi cichlid fishes as a model system to investigate the evolution of increased vertebral counts.The diverse morphology, conserved genomes, close-relatedness, and ability to hybridise of these fishes makes them the ideal system in which to study how the evolutionary modification of developmental mechanisms has led to phenotypic diversity, in this case by evolving increased vertebral counts. The COUNTS project will combine state-of-the-art experimental embryology, single cell technologies, microscopy, and mathematical modelling to ask how developmental processes differ in three Lake Malawi cichlid species that have convergently evolved increased vertebral counts, and two that retain ancestral numbers. Specifically, we will characterise differences in two developmental processes known to play important roles determining total vertebral counts - gastrulation and somitogenesis - and use data-driven mathematical modelling to ask how these differences might have evolved. COUNTS will increase our fundamental understanding of how phenotypic diversity is generated, informing how phenotypes might evolve when faced with a rapidly changing climate and potentially contributing to practical applications such as organoid design for regenerative medicine.