A recurrent theme in current biology is that of collective behavior at all scales. We have a growing interest in exploring aspects of these collective dynamics in extreme situations, e.g. collective dynamics of cell aggregates, and the behavior of super-organisms exemplified in the life of social insects. A basic question here is not so much the plethora of patterns that they exhibit, but why they do so, and how they are regulated to achieve a modicum of functional efficiency.
Patterns in active systems are a way to harness and control the processing of matter, energy and information, and create micro-niches that are neither completely permeable nor completely insulated. Either extreme will not allow for function. So how and why these collective patterns lead to homeorhesis, a dynamical out-of-equilibrium steady state seen in living systems on all scales, is an important motivation. Social insects are a great example to study these questions because they occupy a range of ecological niches and these natural experiments give us clues about their function. They also are not dissimilar to multicellular organisms with a division of labor, analogs of somatic and germlines, etc. And they can be studied in the lab and the field at multiple scales.
We have worked on termite mounds to understand the morphology, physiology, and ecology of their mound architectures that are a thousand times their size. To understand the functional consequence of their mounds, we carried out fieldwork in India and Namibia, and uncovered the mechanism underlying ventilation in termite mounds , showing that it is driven by diurnal temperature oscillations that lead to convection that reverses once a day, allowing the mound to breathe like a lung. We have also built macroscopic and microscopic models of mound morphogenesis, gently breaking down the artificial boundaries between the physical and biological systems that are tightly integrated here – the environment is modified by behavior and in turn, modifies it.
Working with bee clusters, we have explored how they actively harness the elastodynamics of their clusters to transmit mechanical information and stabilize the system to external loads, how they actively create and harness flows at boundaries to ventilate their nests and hives, and how they actively create and harness the porosity of their hives and clusters to regulate the temperature within clusters.
We are also just beginning to study ant behavior in the context of construction and destruction, and the mechanisms of information transmission and its use via chemical, hydrodynamic and mechanical channels.
And we are also interested in seeing if we can build artificial analogs of these organisms, e.g. bristlebots and r(obotic) ants, to understand what are the minimal rules that drive aggregation patterns and how they might be harnessed to be functional.
H. King, S. Ocko, and L. Mahadevan, Proceedings of the National Academy of Sciences 112, 37, 11589–11593, 2015. [View PDF] [Download PDF]