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

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

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

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

A Self-Organising Model of Thermoregulatory Huddling

Endotherms such as rats and mice huddle together to keep warm. The huddle is considered to be an example of a self-organising system, because complex properties of the collective group behaviour are thought to emerge spontaneously through simple interactions between individuals. Groups of rodent pups display two such emergent properties. First, huddling undergoes a ‘phase transition’, such that pups start to aggregate rapidly as the temperature of the environment falls below a critical temperature. Second, the huddle maintains a constant ‘pup flow’, where cooler pups at the periphery continually displace warmer pups at the centre. We set out to test whether these complex group behaviours can emerge spontaneously from local interactions between individuals. We designed a model using a minimal set of assumptions about how individual pups interact, by simply turning towards heat sources, and show in computer simulations that the model reproduces the first emergent property—the phase transition. However, this minimal model tends to produce an unnatural behaviour where several smaller aggregates emerge rather than one large huddle. We found that an extension of the minimal model to include heat exchange between pups allows the group to maintain one large huddle but eradicates the phase transition, whereas inclusion of an additional homeostatic term recovers the phase transition for large huddles. As an unanticipated consequence, the extended model also naturally gave rise to the second observed emergent property—a continuous pup flow. The model therefore serves as a minimal description of huddling as a self-organising system, and as an existence proof that group-level huddling dynamics emerge spontaneously through simple interactions between individuals. We derive a specific testable prediction: Increasing the capacity of the individual to generate or conserve heat will increase the range of ambient temperatures over which adaptive thermoregulatory huddling will emerge

The energetics of nestling birds

The nestling energy budget is examined with particular reference to the Dipper. Dippers showed an adaptive strategy of differential growth allowing premature fledging. Sex-specific differences in energetics and growth dynamics were observed which may result in differential mortality between the sexes. Field thermoregulation costs were lower than laboratory estimates, however heat loss did not obey the 0.67 exponent rule in the Dipper. Adults appear to adjust their brooding behaviour in response to nestling body temperature. Activity costs measured directly were only about 10% of previous indirect estimates. Brood activity costs increased exponentially with increasing brood-size thus offsetting any reduction in thermoregulation costs through huddling; implications of these results are discussed. Time-activity-laboratory estimates of daily energy expenditure provided excellent agreement with field measurements using doubly-labelled water on 'mature* Dipper nestlings. TAL estimates, however, progressively over-estimated daily metabolised energy (DME) in younger nestlings. Sources of this error are evaluated, and a predictive equation for nestling DME presented. Influences of brood DME on parental care are discussed. Energetic implications of hatching asynchrony were examined in the House Martin. Four hypotheses are discussed. (1) Nest failure; (2) Brood reduction; (3) Peak load reduction, and (4) Reduced sibling rivalry. The latter two were modelled and tested in the field. Little evidence was found for the hypotheses considered, lending support to the view that hatching asynchrony is an incidental trait, and moreover one in which costs may outweigh benefits

Sociality in the African woodland dormouse

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy 2017Social systems describe the social organisation, mating system and social interactions of a species, and are revealing of the nature of how animals live and the underlying mechanisms of living alone or in groups. The social system of the African woodland dormice Graphiurus murinus has not been documented. The aim of my study was to investigate sociality, the mechanisms promoting sociality, and to G. murinus along the continuum of sociality in respect of rodents. Investigations on nest sharing in free-living woodland dormice showed that sleeping associations were common in females than males but changed seasonally (females all year round; males in breeding and winter seasons), reflecting the reproductive and thermoregulatory needs. The social structure of these sleeping associations was assessed using association indices and social network analysis. Woodland dormice exhibited a web of relationships between sex and age groups, with adult female groups and juvenile groups forming strong and exclusive relationships, while male groups showed ephemeral and weak relationships. In staged dyadic encounters of same sex dyads in captivity, females were amicable and tolerated unfamiliar females, whereas males displayed low tolerance and aggression towards unfamiliar. The three-chamber paradigm tests for sociability and social preferences revealed that both adult males and females had an intrinsic motivation to be social. However, this motivation differed by sex, with females showing a greater affinity for both strangers and unfamiliar females, whereas males showed an affinity for familiar males. Observations of huddling in female dyads revealed that, under decreasing Ta, females huddled together and combined nest material, thus changing the local microclimate and the insulation capacities of nests. In addition, long-associations were maintained even after Ta was increased, revealing that thermal challenges might promote group formation and enhance familiarity amongst females. Both my field and laboratory data suggest that woodland dormice form small seasonally transient sleeping associations. In females, limited aggression, tolerance, and nest sharing and construction under low temperatures could also lead to prolonged group-living. In males, aggression towards unfamiliar males, possibly maintains intra-sexual territoriality, yet familiarity creates tolerance, leading to group-living. Group-living in this arboreal rodent is mediated by the apparently phylogenetically constrained energetic demands of thermoregulation, coupled with an inherent need to associate with conspecifics. The level of familiarity between conspecifics or the presence of social partners facilitates group formation and is shaped by prevailing ecological conditions.MT 201

Scaffolding layered control architectures through constraint closure : insights into brain evolution and development

The functional organization of the mammalian brain can be considered to form a layered control architecture, but how this complex system has emerged through evolution and is constructed during development remains a puzzle. Here we consider brain organization through the framework of constraint closure, viewed as a general characteristic of living systems, that they are composed of multiple sub-systems that constrain each other at different timescales. We do so by developing a new formalism for constraint closure, inspired by a previous model showing how within-lifetime dynamics can constrain between-lifetime dynamics, and we demonstrate how this interaction can be generalized to multi-layered systems. Through this model, we consider brain organization in the context of two major examples of constraint closure—physiological regulation and visual orienting. Our analysis draws attention to the capacity of layered brain architectures to scaffold themselves across multiple timescales, including the ability of cortical processes to constrain the evolution of sub-cortical processes, and of the latter to constrain the space in which cortical systems self-organize and refine themselves

Climatic, social and reproductive influences on behavioural thermoregulation in a female-dominated lemur

It is well-established that social rank in a large group confers a higher adaptive value to a dominant individual relative to others, though there is scant evidence that members of small social groups either have similar social standing or maintain strict dominance. We aimed to determine whether members of small social groups, using the southern bamboo lemur (Hapalemur meridionalis) as a model, gain rank-related benefits. We first established a dominance hierarchy through a network-based analysis of win-loss interactions, which showed that adult females maintained social dominance within their groups, similar to many strepsirrhine species. To address whether dominant individuals gained rank-related benefits, we then explored how social dynamics may permit access to resting huddles, which provide a physiological benefit. Social thermoregulation, i.e. huddling, is a behavioural energy conservation mechanism, and among many mammals is a direct response to decreasing ambient temperatures. As such, huddling behaviour may have evolved among social animals because of its potential direct and indirect benefits. To examine the effect of dominance rank within small social groups on huddling inclusion, we used generalized linear mixed-effects models to predict the likelihood of huddling to occur during resting bouts from climatic (e.g., temperature, precipitation), social (e.g., affiliation, dominance rank, grooming) and reproductive (e.g., access, infant protection) variables. We found that colder temperatures, especially during shorter resting bouts, increased the likelihood of huddling. Grooming between partners with a high discrepancy in rank increased huddling. Additionally, huddling increased during the reproductive season, potentially offering greater opportunity for males to gain favour with sexually receptive females, and also when new-borns were present, providing essential thermal maintenance and potential anti-predator protection to infants. Taken as a whole, our results suggest that even in small social groups, females gain rank-related benefits by controlling access to huddles, i.e., the intrinsic benefits of social thermoregulation

Animal thermoregulation: a review of insulation, physiology and behaviour relevant to temperature control in buildings

Birds and mammals have evolved many thermal adaptations that are relevant to the bioinspired design of temperature control systems and energy management in buildings. Similar to many buildings, endothermic animals generate internal metabolic heat, are well insulated, regulate their temperature within set limits, modify microclimate and adjust thermal exchange with their environment. We review the major components of animal thermoregulation in endothermic birds and mammals that are pertinent to building engineering, in a world where climate is changing and reduction in energy use is needed. In animals, adjustment of insulation together with physiological and behavioural responses to changing environmental conditions fine-tune spatial and temporal regulation of body temperature, while also minimizing energy expenditure. These biological adaptations are characteristically flexible, allowing animals to alter their body temperatures to hourly, daily, or annual demands for energy. They exemplify how buildings could become more thermally reactive to meteorological fluctuations, capitalising on dynamic thermal materials and system properties. Based on this synthesis, we suggest that heat transfer modelling could be used to simulate these flexible biomimetic features and assess their success in reducing energy costs while maintaining thermal comfort for given building types

Strategies for Hypothermia Compensation in Altricial and Precocial Newborn Mammals and Their Monitoring by Infrared Thermography

Publication history: Accepted - 18 May 2022; Published - 23 May 2022.Thermoregulation in newborn mammals is an essential species-specific mechanism of the nervous system that contributes to their survival during the first hours and days of their life. When exposed to cold weather, which is a risk factor associated with mortality in neonates, pathways such as the hypothalamic–pituitary–adrenal axis (HPA) are activated to achieve temperature control, increasing the circulating levels of catecholamine and cortisol. Consequently, alterations in blood circulation and mechanisms to produce or to retain heat (e.g., vasoconstriction, piloerection, shivering, brown adipocyte tissue activation, and huddling) begin to prevent hypothermia. This study aimed to discuss the mechanisms of thermoregulation in newborn domestic mammals, highlighting the differences between altricial and precocial species. The processes that employ brown adipocyte tissue, shivering, thermoregulatory behaviors, and dermal vasomotor control will be analyzed to understand the physiology and the importance of implementing techniques to promote thermoregulation and survival in the critical post-birth period of mammals. Also, infrared thermography as a helpful method to perform thermal measurements without animal interactions does not affect these parameters.Non

Adaptive Movements And Thermoregulation In Big-Eared Bats

There are a variety of (non-exclusive) reasons to explain the presence of group-living, but clustering or huddling is especially important for small endotherms with high surface-area-to-volume ratios. Clustering is interesting because variations within clustering are seldom investigated despite anecdotal evidence that bat clustering varies widely. I studied a colony of Rafinesque\u27s big-eared bats (Corynorhinus rafinesquii) to learn more about clustering behavior using infrared video. I predicted that temperature would be the primary driver of how and when bats cluster while roosting. The actual relationship was not as predicted by an energetic model. High density clusters of bats were comacross a wide range of ambient and roost temperatures, and substantial clustering variation exists. The bats i captured (79 individuals) shono sign of the causal agent of wns. I found that areas of the roost used by bats were less variable in temperature but not warmer than areas not used. Also presented are preliminary nighttime foraging locations for bats at this roost site. These results provide insight into energetics, clustering behavior, and general ecology for an uncomspecies in a part of its range where it has not been previously studied. These data should be useful for future behavioral and/or energetic investigations as well as for conservation decision-making. Resampling of variation in bat numbers suggested that building roosts require at least 3 visits to confirm bat absence and 16 visits to count the maximum number of bats using the site. Finally, i discuss considerations and ideas for future research