Self-organised criticality in the evolution of a thermodynamic model of rodent thermoregulatory huddling
Authored by Stuart P Wilson
Date Published: 2017
DOI: 10.1371/journal.pcbi.1005378
Sponsors:
No sponsors listed
Platforms:
C++
Python
Model Documentation:
Other Narrative
Mathematical description
Model Code URLs:
https://journals.plos.org/ploscompbiol/article?rev=2&id=10.1371/journal.pcbi.1005378#sec009
Abstract
A thermodynamic model of thermoregulatory huddling interactions between
endotherms is developed. The model is presented as a Monte Carlo
algorithm in which animals are iteratively exchanged between groups,
with a probability of exchanging groups defined in terms of the
temperature of the environment and the body temperatures of the animals.
The temperature-dependent exchange of animals between groups is shown to
reproduce a secondorder critical phase transition, i.e., a smooth switch
to huddling when the environment gets colder, as measured in recent
experiments. A peak in the rate at which group sizes change, referred to
as pup flow, is predicted at the critical temperature of the phase
transition, consistent with a thermodynamic description of huddling, and
with a description of the huddle as a self-organising system. The model
was subjected to a simple evolutionary procedure, by iteratively
substituting the physiologies of individuals that fail to balance the
costs of thermoregulation (by huddling in groups) with the costs of
thermogenesis (by contributing heat). The resulting tension between
cooperative and competitive interactions was found to generate a
phenomenon called self-organised criticality, as evidenced by the
emergence of avalanches in fitness that propagate across many
generations. The emergence of avalanches reveals how huddling can
introduce correlations in fitness between individuals and thereby
constrain evolutionary dynamics. Finally, a full agent-based model of
huddling interactions is also shown to generate criticality when
subjected to the same evolutionary pressures. The agent-based model is
related to the Monte Carlo model in the way that a Vicsek model is
related to an Ising model in statistical physics. Huddling therefore
presents an opportunity to use thermodynamic theory to study an emergent
adaptive animal behaviour. In more general terms, huddling is proposed
as an ideal system for investigating the interaction between
self-organisation and natural selection empirically.
Tags
Competition
behavior
Social interactions
Temperature
Small mammals
Rat pups
Thermally advantageous positions
Newborn domestic rabbits
Litter
huddle
Brown fat