This is an unusual (i.e. most people would not think of this as an) example of gene-environment interactions. The environmental stimulus is density and space for movement; how the organisms (ants, in this case) respond to this environmental stimulus of course involves genetic and behavioral networks. Many organisms (e.g. herds of migrating wildebeests, swarms of insects and bacteria, flocks of starlings, shoals of fish, crowds of pedestrians) take part in flow-like collective movements. In most cases, all individuals cruise along the same path in a unique direction — which enables incredible coordination among large numbers of individuals.
The task of maintaining smooth and efficient movement becomes more challenging — when individuals travel in opposite directions and are likely to collide. As well as humans driving vehicles on the highway, ants are one of the rare animals in which collective movements are bidirectional. Ants are “central-place foragers”, which entails a succession of individual journeys between their nest and their foraging site. When exploiting large food sources, many species lay chemical trails (environmental signals), along which individuals commute back and forth. Flow of individuals on these trails can reach several hundred ants per minute; yet, ants seem to fare better than humans, when it comes to traffic management. ☹ However, until this study [see attached article], there was a lack of direct experimental evidence, showing that ants at high density do not get “stuck in traffic jams.”
Authors [see attached] designed experiments to investigate whether ants can maintain a steady stream of traffic — when their path to food gets more crowded. This involved manipulating the density of ants, using a combination of different-sized colonies (ranging from 400 to 25,600 Argentine ants) and changing the width of the bridge connecting the ants to their food source. The experiment was repeated 170 times, and data were collected on traffic flow, speed of ant movement, and number of collisions. For pedestrians and vehicular traffic, the flow of movement will slow down — if occupancy levels (density) reach more than 40% — whereas for ants, the flow of traffic showed no signs of declining, even when bridge occupancy reached 80%. The experiments revealed that ants do this by adjusting their behavior to their circumstances: they speed up at intermediate densities, avoid collisions at large densities, and avoid entering overcrowded trails.
This study [see attached article] embraces molecular biology, statistical physics, and telecommunications. It may also have relevance for managing human traffic, particularly as scientists develop autonomous vehicles that might be programmed to work together cooperatively as ants do. Efficient transportation is crucial for urban mobility, cell function, and survival of certain animal groups. From humans driving on the highway, to ants running on a trail, the main challenge — faced by all collective systems — is how to prevent traffic jams in crowded environments. How many years will it take, until car companies design vehicles that are as efficient as ants in traffic under crowded conditions…?? 😉
eLife 2019; 8: e48945 (2019)