Multiple phase transitions in an agent-based evolutionary model with neutral fitness

Authored by Dawn M King, Adamd Scott, Sonya Bahar

Date Published: 2017

DOI: 10.1098/rsos.170005

Sponsors: James S. McDonnell Foundation

Platforms: MATLAB

Model Documentation: Other Narrative

Model Code URLs: https://github.com/DawnMKing/Royal-Society-Open-Science-EvolutionSimulation

Abstract

Null models are crucial for understanding evolutionary processes such as speciation and adaptive radiation. We analyse an agent-based null model, considering a case without selection-neutral evolution-in which organisms are defined only by phenotype. Universal dynamics has previously been demonstrated in a related model on a neutral fitness landscape, showing that this system belongs to the directed percolation (DP) universality class. The traditional null condition of neutral fitness (where fitness is defined as the number of offspring each organism produces) is extended here to include equal probability of death among organisms. We identify two types of phase transition: (i) a non-equilibrium DP transition through generational time (i.e. survival), and (ii) an equilibrium ordinary percolation transition through the phenotype space (based on links between mating organisms). Owing to the dynamical rules of the DP reaction-diffusion process, organisms can only sparsely fill the phenotype space, resulting in significant phenotypic diversity within a cluster of mating organisms. This highlights the necessity of understanding hierarchical evolutionary relationships, rather than merely developing taxonomies based on phenotypic similarity, in order to develop models that can explain phylogenetic patterns found in the fossil record or to make hypotheses for the incomplete fossil record of deep time.

Tags

Agent-based model Diversity Biodiversity Clustering Phase transition patterns speciation sympatric speciation Extinction Neutral theory Morphological disparity