The influence of reproductive mode on resource competition and diversity patterns in Ediacaran early animal communities

The appearance of the oldest known animals during the late Ediacaran (∼574 million years ago [Ma]) ^1–4 was followed by a phase of little change ⁵ . This period, which lasted ∼14 million years, ended with a burst of rapid diversification known as the Ediacaran “Second Wave”. The reasons for these diversity patterns are poorly understood. Here we investigate how reproductive mode mediated community dynamics, and in turn macroevolutionary change, in the Ediacaran. We show that widespread reproduction via stolon (namely via filaments connecting clones) in the first animals limited intra-specific competition among neighbours, leading to inter-specific competition acting at smaller-spatial scales than intra-specific competition, a phenomenon called heteromyopia ⁶ . Heteromyopia enables co-existence of sub-optimal competitors because the dispersal limitation of the dominant species means that they do not inhabit all the optimal habitat, so that lesser competitors can still exist within the same community, operating under reduced selection pressure. We explored the consequences of this dispersal limitation on community diversity using Approximate Bayesian Computation to estimate the posterior distributions of dispersal with a spatially explicit model fitted to the three Ediacaran assemblages and showed that the change from stoloniferous to sexual reproduction that coincided with the Second Wave could explain the sudden increase in alpha diversity observed in the fossil record. We conclude that widespread asexual reproduction via stolon likely constrained early animal evolution, limiting diversification until the onset of mobility and widespread sexual reproduction ^7–9 .