Presentation Information
[C01-05]A structured population model for the evolutionary transition from unicellular to filamentous forms in cyanobacteria
*Hikari Kai1, Yuuya Tachiki1 (1. Tokyo Metropolitan University (Japan))
Keywords:
adaptive dynamics,predator-prey system,size preference,evolutionarily stable strategy,evolution of multicellularity
Some strains of cyanobacteria, oxygen-producing photosynthetic bacteria, exhibit a filamentous morphology, in which cells are arranged in a single row. The transition between unicellular and filamentous forms has occurred multiple times across independent lineages. The average filament length varies among strains. Both the evolution of the unicellular-to-filamentous transition and the diversification of filament length can be understood as the evolution of cell-cell adhesion. This is because mutations that cause daughter cells to remain attached after cell division drive the transition to filamentous forms, while filament length is influenced by mutations in genes associated with the cell envelope. However, theoretical studies on the evolution of cell-cell adhesion remain limited.
To address this gap, we developed a structured population model to investigate the evolutionary dynamics of cell-cell adhesion in filamentous cyanobacteria under predation pressure. Our model describes the population dynamics of cyanobacterial filaments of varying lengths and their predators using differential equations. We defined cell-cell adhesion as the probability that daughter cells remain attached after cell division and explored its evolutionary consequences within the framework of adaptive dynamics. Given that growth rates generally decline with increasing body size, we assumed that cell division occurs more slowly in longer filaments. Conversely, increased body size may confer an advantage by reducing predation risk. Zooplankton, major predators of cyanobacteria, exhibit size-selective predation, preferring prey of a certain size depending on their own body size and taxonomic group. The further a prey's size deviates from this preferred range, the less likely it is to be consumed. Accordingly, we incorporated size-selective predation into our model.
As a result, filament length was determined by the balance between reduced cell division rate and avoidance of predation. When predators preferentially targeted filaments of intermediate length, the evolutionary trajectory of cell-cell adhesion depended on initial conditions.
To address this gap, we developed a structured population model to investigate the evolutionary dynamics of cell-cell adhesion in filamentous cyanobacteria under predation pressure. Our model describes the population dynamics of cyanobacterial filaments of varying lengths and their predators using differential equations. We defined cell-cell adhesion as the probability that daughter cells remain attached after cell division and explored its evolutionary consequences within the framework of adaptive dynamics. Given that growth rates generally decline with increasing body size, we assumed that cell division occurs more slowly in longer filaments. Conversely, increased body size may confer an advantage by reducing predation risk. Zooplankton, major predators of cyanobacteria, exhibit size-selective predation, preferring prey of a certain size depending on their own body size and taxonomic group. The further a prey's size deviates from this preferred range, the less likely it is to be consumed. Accordingly, we incorporated size-selective predation into our model.
As a result, filament length was determined by the balance between reduced cell division rate and avoidance of predation. When predators preferentially targeted filaments of intermediate length, the evolutionary trajectory of cell-cell adhesion depended on initial conditions.