How self-organization can guide evolution

2017

PLoS Comput Biol

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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 second-order 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.

Section: Discussionmentioning

confidence: 97%

Self-organised criticality in the evolution of a thermodynamic model of rodent thermoregulatory huddling

2017

PLoS Comput Biol

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“…A Monte Carlo algorithm has recently been shown to capture the statistics of huddling behaviour [ 20 ], i.e. the distribution of groups of pups in contact, as predicted by more elaborate models of the underlying physical interactions between littermates (see [ 18 , 19 , 47 ]). The idea is to iteratively reconfigure the distribution of pups between groups by choosing pairs of pups at random from the litter and either joining together the groups to which they belong, or isolating one from its group.…”

Section: Modelsmentioning

confidence: 99%

“…The individual behaviour from which rodent huddling emerges has been described formally as ‘homeothermotaxis’; turning in the direction that brings the body temperature closer to a preferred temperature [ 18 , 19 ]. As such, individuals act like the magnetic spins in an Ising model, or the particles in a Vicsek model from statistical physics, attracted or repelled by the relative body temperatures of their littermates [ 20 ].…”

Section: Introductionmentioning

confidence: 99%

Modelling the emergence of rodent filial huddling from physiological huddling

2017

R. Soc. open sci.

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Huddling behaviour in neonatal rodents reduces the metabolic costs of physiological thermoregulation. However, animals continue to huddle into adulthood, at ambient temperatures where they are able to sustain a basal metabolism in isolation from the huddle. This ‘filial huddling’ in older animals is known to be guided by olfactory rather than thermal cues. The present study aimed to test whether thermally rewarding contacts between young mice, experienced when thermogenesis in brown adipose fat tissue (BAT) is highest, could give rise to olfactory preferences that persist as filial huddling interactions in adults. To this end, a simple model was constructed to fit existing data on the development of mouse thermal physiology and behaviour. The form of the model that emerged yields a remarkable explanation for filial huddling; associative learning maintains huddling into adulthood via processes that reduce thermodynamic entropy from BAT metabolism and increase information about social ordering among littermates.

“…In what might be thought of as a zero-dimensional model, the litter were described using a single equation, allowing the effects of huddling on the evolution of a population of litters to be investigated in simulation [18]. In what might be thought of as a one-dimensional model, the litter were described as a system of magnetic spins fixed in position on a lattice, allowing the thermodynamics of huddling interactions to be understood with reference to the theory of Ising spinglass models and statistical physics [10].…”

Section: Discussionmentioning

confidence: 99%

Self-organising Thermoregulatory Huddling in a Model of Soft Deformable Littermates

Biomimetic and Biohybrid Systems

2017

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Abstract. Thermoregulatory huddling behaviours dominate the early experiences of developing rodents, and constrain the patterns of sensory and motor input that drive neural plasticity. Huddling is a complex emergent group behaviour, thought to provide an early template for the development of adult social systems, and to constrain natural selection on metabolic physiology. However, huddling behaviours are governed by simple rules of interaction between individuals, which can be described in terms of the thermodynamics of heat exchange, and can be easily controlled by manipulation of the environment temperature. Thermoregulatory huddling thus provides an opportunity to investigate the effects of early experience on brain development in a social, developmental, and evolutionary context, through controlled experimentation. This paper demonstrates that thermoregulatory huddling behaviours can selforganise in a simulation of rodent littermates modelled as soft-deformable bodies that exchange heat during contact. The paper presents a novel methodology, based on techniques in computer animation, for simulating the early sensory and motor experiences of the developing rodent.