Presentation Information
[MS12-06]Phyllotaxis and EVOLUTION (not Growth) of Plants
*Takuya Okabe1 (1. Shizuoka University (Japan))
Keywords:
adaptation,surface-area-to-volume ratio,xylem,Bower hypothesis
In everyday language, "growth" and "evolution" are often used interchangeably, with the difference seen as a matter of degree -- evolution involving more substantial changes over time. However, in biological contexts, these terms describe distinct processes. Growth occurs within an individual organism, whereas evolution refers to inherited genetic changes over successive generations, driven by natural selection. Traits that enhance an organism's survival and reproductive success are more likely to be inherited by future generations, leading to gradual adaptation. Biological phenomena, including phyllotaxis, are products of these evolutionary processes. Mathematical perspectives are essential for understanding phyllotaxis, particularly the characteristic spiral patterns associated with Fibonacci angles. Previous mathematical studies have largely focused on the growth of these Fibonacci patterns within a single generation, often examining the developmental mechanisms driving their formation. It is reasonable to expect that insights gained from these growth studies could be adapted to address fundamental questions about the evolutionary origins of such patterns.
A critical step in understanding the evolutionary basis of phylotaxis is elucidating the selective pressures that have shaped its development. While efficient sunlight capture and reduced competition for resources are frequently proposed as driving forces, they often fail to fully account for the universal prevalence and remarkable precision observed in phylotaxis across a wide range of plant species. Here, we demonstrate a link between the evolution of phylotaxis and the optimization of vascular transport efficiency. Building on Bower's hypothesis, we suggest that plants have evolved to maximize the surface-to-volume ratio of their vascular tissues -- the network responsible for nutrient transport -- thereby enhancing overall fitness and adaptability. Critically, this ratio is intimately dependent on leaf arrangement, and we quantify this relationship using mathematical modeling to explore its evolutionary implications. Our analysis of optimal divergence angles reveals an evolutionary trajectory for phylotaxis that aligns mathematically with the established growth model proposed by Schwendener and van Iterson, suggesting a fundamental connection between developmental patterns and evolutionary optimization.
A critical step in understanding the evolutionary basis of phylotaxis is elucidating the selective pressures that have shaped its development. While efficient sunlight capture and reduced competition for resources are frequently proposed as driving forces, they often fail to fully account for the universal prevalence and remarkable precision observed in phylotaxis across a wide range of plant species. Here, we demonstrate a link between the evolution of phylotaxis and the optimization of vascular transport efficiency. Building on Bower's hypothesis, we suggest that plants have evolved to maximize the surface-to-volume ratio of their vascular tissues -- the network responsible for nutrient transport -- thereby enhancing overall fitness and adaptability. Critically, this ratio is intimately dependent on leaf arrangement, and we quantify this relationship using mathematical modeling to explore its evolutionary implications. Our analysis of optimal divergence angles reveals an evolutionary trajectory for phylotaxis that aligns mathematically with the established growth model proposed by Schwendener and van Iterson, suggesting a fundamental connection between developmental patterns and evolutionary optimization.