Cancer allows life histories with the unicellular bottleneck to dominate despite opposing selection from competition

Sydney Ackermann

University of Toronto

"Cancer allows life histories with the unicellular bottleneck to dominate despite opposing selection from competition"

During evolutionary transitions in individuality, new levels of selection are introduced, and thus, the possibility of discordant selection between levels. Cancer or ‘cheating cells’ comes hand in hand with multicellularity. On a cellular level there is selection for cells that replicate faster, even if it is to the detriment of the organism. Given this phenomenon, what has facilitated and maintained the transition to multicellular life? The unicellular bottleneck (unicellular offspring) has been hypothesized as an adaptation to facilitate cooperation among cells by purging lineages of cheating cells. The evolution of propagule size has been explored previously but here we introduce spatial structure and different modes of dispersal by simulating individuals competing on a lattice. We find that size dependent competition favours binary fragmentation strategies but high mutation rates to cancer cells favours fragmentation modes with more unicellular offspring. Specifically, multiple fission is favoured by global dispersal and the unicellular propagule strategy is favoured by local dispersal. Our simulation sheds light on the evolution of multicellular life cycles and the prevalence of unicellular offspring in multicellular species.
Additional authors: Matthew Osmond

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