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

Dawn M King,Sonya Bahar,Adam D Scott

doi:10.1098/rsos.170005

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.

Highlights

Neutral theories of ecology and of evolution via genetic drift have been contentious topics among evolutionary biologists [1,2,3], owing to these theories’ assumption that selective forces may not need to act upon fitness differences between organisms [4] or genomes [5,6] in order to drive ecological2017 The Authors
This work has presented a version of the model that incorporates neutral fitness conditions and an individual death probability that is uniform for all organisms at every generation, and we have shown that the existence of a non-equilibrium, continuous phase transition as this parameter is varied
Any model that is in agreement with the directed percolation (DP) conjecture, and undergoes an RD process of A → 2A, A + A → A and A → Ø should belong to the DP universality class [37,38,39]

Summary

Introduction

Neutral theories of ecology and of evolution via genetic drift have been contentious topics among evolutionary biologists [1,2,3], owing to these theories’ assumption that selective forces may not need to act upon fitness differences between organisms [4] or genomes [5,6] in order to drive ecological2017 The Authors. Neutral theory has continued to thrive 2 in the academic literature [7,8], and it can be a useful tool for uncovering underlying mechanisms of evolutionary processes. Its emergence in the agent-based modelling community has unravelled the minimal necessary mechanisms for speciation to occur, while providing a null hypothesis against which models of selection can be tested. In a 2005 review, DeAngelis & Mooij [11] categorized more than 900 agent-based models of ecological and evolutionary processes into seven major types (such as collective motion, foraging, population dynamics and speciation). In contrast with the widespread acceptance among population geneticists of genetic drift as a meaningful baseline model, many of the ecological models categorized by DeAngelis & Mooij did not investigate neutral evolution

Methods

Results

Conclusion