Rodents such as rats and mice huddle together to keep warm. In a new study published in the open-access journal PLoS Computational Biology, scientists at the University of Sheffield found they could simulate huddling by assuming simply that touching individuals in turn brings their temperatures closer to an ideal body temperature.
Common degus (Octodon degus). Image credit: Arjan Haverkamp / CC BY 2.0.
“Many species of mammals and birds spend a large proportion of their lives in direct contact with conspecifics, engaging in a synergistic pushing, climbing, wriggling, and burrowing behavior referred to as huddling,” the scientists wrote in the study.
“For rodents, huddling begins at birth, when the dam first gathers her litter of around a dozen pups into a single aggregation, and it persists as the frequency and duration of her excursions from the nest increase.”
“Pups aged between two and ten postnatal days reliably orient themselves in the direction of contact with a littermate, and pups that are displaced from the huddle center orient themselves back towards its center, suggesting that individual behaviors actively help to maintain the integrity of the huddle.”
According to the model developed by University of Sheffield researchers, individual behaviors improve the ability of the whole group to regulate its temperature.
The equations of the model suggest that the huddle behaves like a ‘super-organism,’ as if it were one larger animal able to change its shape to retain its heat. This allows the group to better adapt to changes in the outside temperature.
“Our model describes the huddle as a self-organizing system, and reveals how complex group behaviors can emerge from very simple interactions between animals,” said lead author Jonathan Glancy of Sheffield Robotics at the University of Sheffield.
“Huddling is an important example of a self-organizing behavior with a clear evolutionary advantage, because animals that can coordinate their movements to keep warm are more likely to survive.”
A surprising prediction of the study is that effective huddles can only self-organize when individuals contribute some of their own heat for the greater good of the group.
Moreover, the model predicts that the ability of individuals to thermoregulate might actually disrupt huddling.
Future experiments can therefore test the accuracy of the model, and shed light on how evolution might take advantage of useful tricks like huddling.
Glancy and co-authors are now interested to see whether their huddling equations could be used to coordinate movement patterns in teams of cooperating robots, or perhaps even biohybrid teams of robots and animals.
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Glancy J et al. 2015. A Self-Organising Model of Thermoregulatory Huddling. PLoS Comput Biol 11 (9): e1004283; doi: 10.1371/journal.pcbi.1004283
