Uncovering the evolutionary history and significance of Fibonacci spirals in vascular plants

Characterising the drivers of biological form over geological time continues to represent one of the grand challenges in evolutionary biology. However, doing so has proved difficult as there are few study systems where it is possible to test the competing roles of selection, constraint and chance. Land plants offer a largely overlooked but ideal study system for tackling these questions because of their excellent fossil record and close relationship between form, function and development. In WhyFib I will leverage all of these benefits to uncover the evolutionary drivers behind one of the key features of land plants, the arrangement of leaves. On theoretical grounds, plant leaves could be positioned on stems in an almost infinite number of possible arrangements. However, they are not. In fact, they are arranged in a very restricted number of discrete patterns, of which by far the most frequent are spirals that are described by integers of the Fibonacci series. Why Fibonacci spirals are so frequent in plants has perplexed scientists for centuries and remains a major unanswered question. In WhyFib I will answer this question by taking a broad evolutionary approach, underpinned by my own interdisciplinary background and new break-through methodologies developed in my lab. To uncover the evolutionary history of Fibonacci spirals I will combine results gained from investigating development in non-seed plants with insights from newly collected fossils, analyses of quantitative trait evolution and quantitative modelling approaches. I will then use these data, representing over 400 million years of evolution, to test the major competing hypotheses for the prevalence of Fibonacci spirals. The results of the project will provide a textbook case study for the drivers of biological form over geological time, while allowing me to solve the mystery of why Fibonacci spirals are so common in plants today.