[Paper Review] Modelling the Evolution of Spatially Distributed Populations in the Uniformly Changing Environment - Sympatric Speciation

Wojciech Waga, Marta Zawierta+1 more|ArXiv.org|Nov 4, 2009

Evolution and Genetic Dynamics19 references3 citations

TL;DR

This study models sympatric speciation in spatially distributed, age-structured populations under fluctuating environmental conditions using Monte Carlo simulations on a lattice. By simulating environmental shifts that toggle gene functionality, the model shows that reduced recombination rates and population bottlenecks from environmental stress enhance inbreeding and accelerate genetic divergence, leading to rapid sympatric speciation—particularly at population expansion fronts.

ABSTRACT

We have simulated the evolution of age structured populations whose individuals represented by their diploid genomes were distributed on a square lattice. The environmental conditions on the whole territory changed simultaneously in the same way by switching on or off some requirements. Mutations accumulated in the genes dispensable during a given period of time were neutral, but they could cause a genetic death of individuals if the environment required their functions again. Populations survived due to retaining some surplus of genetic information in the individual genomes. The changes of the environment caused the fluctuations of the population size. Since the simulations were performed with individuals spatially distributed on the lattice and the maximal distance between mating partners was set as a parameter of the model, the inbreeding coefficient in populations changed unevenly, following the fluctuation of population size and enhancing the speciation phenomena.

Motivation & Objective

• To investigate how environmental fluctuations influence sympatric speciation in spatially structured populations.
• To examine the role of genetic redundancy and neutral mutation accumulation in population survival during environmental shifts.
• To assess how spatial distribution and limited mating range affect inbreeding and genetic divergence.
• To evaluate the impact of recombination rate and population size fluctuations on speciation dynamics.
• To model the evolutionary consequences of gene inactivation during neutral environmental periods and reactivation during functional demand.

Proposed method

• Simulates diploid, age-structured populations on a 2D square lattice with spatially restricted mating (maximal partner distance as a parameter).
• Implements environmental changes by toggling gene functionality requirements (0 = required, 1 = neutral) over time, with stochastic or periodic switching.
• Tracks mutations in non-essential genes during neutral periods; these become deleterious when environmental requirements are reactivated.
• Uses Monte Carlo simulations to model reproduction, mutation, and survival over generations, with fitness determined by functional gene complementation.
• Applies a genetic complementation mechanism: individuals die if they carry defective alleles for genes required by the current environment.
• Analyzes population structure, inbreeding coefficients, and genetic relatedness across generations using lineage tracing back to the fifth generation.

Experimental results

Research questions

• RQ1 Can sympatric speciation emerge in spatially distributed populations without geographical isolation under fluctuating environmental conditions?
• RQ2 How does the rate of genetic recombination influence the likelihood of sympatric speciation under environmental stress?
• RQ3 What is the effect of population bottlenecks caused by environmental shifts on inbreeding and genetic divergence?
• RQ4 How do neutral periods of gene inactivity lead to accumulation of deleterious mutations and subsequent population collapse upon environmental reactivation?
• RQ5 To what extent does spatial clustering of genetically similar individuals accelerate speciation in fluctuating environments?

Key findings

• Populations subjected to cyclic environmental changes exhibited higher survival rates when recombination rates were low, contrary to classical population genetics expectations.
• Environmental shifts caused population size fluctuations, with severe bottlenecks increasing inbreeding and accelerating genetic divergence.
• Surviving populations formed spatial clusters of genetically related individuals, indicating the emergence of distinct genetic lineages.
• Genetic lineages traced back to the fifth generation confirmed that clustered individuals shared functional gene sets aligned with current environmental demands.
• Speciation was significantly accelerated under periodically or randomly changing environments compared to constant environments, especially at low recombination rates.
• The fraction of originally required environmental functions that remained unchanged over time dropped exponentially, with 2% of functions remaining neutral for over 2000 Monte Carlo steps.