Fleeing cockroaches: unpredictable but not random
A team of researchers from Italy, the UK and Puerto Rico have found that when cockroaches flee their predators, they make a seemingly random choice from a set of four preferred escape routes. The findings, which are published online in the journal Current Biology, provide insight into animal evolution and advance our understanding of predator-prey relationships. In nature, any organism gravitates towards a positive stimulus (cake, for example) but flees a negative one, such as a predator. But if an animal always uses the same escape route, its predator will be able to learn the route, predict it and win. Cockroaches are particularly successful in eluding their predators because their escape routes are highly variable, which makes them an ideal subject for study. 'If you model animal behaviour, you'll find there's always an optimal escape strategy,' explained Dr Paolo Domenici of Italy's Institute for Coastal Marine Environment of the National Research Council (CNR-IAMC). 'You can always devise a mathematical model that shows the best way to escape. But if you repeat it, a predator is going to learn it and will catch you. So you need to find a way to increase the variability.' Following this idea to its natural conclusion, selecting an escape route at random would seem to provide ultimate unpredictability. But a truly random choice would sometimes result in the animal running towards its predator, which doesn't actually happen. The researchers sought to create a model of the cockroaches' escape trajectories to establish the insects' true behaviour. The researchers used an existing animal model to test the reactions of cockroaches to various threats (puffs of wind were blown at the bugs from different directions while they walked), but looked at the results using a 'circular' (rather than the traditional Cartesian) statistical model. They used the same statistical model to reanalyse data from several previously published studies and compared the results with their new study. They found that in all studies, cockroaches under threat chose from a set of four preferred escape routes (although these routes weren't exactly the same in all cases) and varied their choice in such an unpredictable way as to keep their predators guessing. According to Dr Domenici, the results show that unpredictable behavioural patterns in nature can actually be quite structured; animals that may seem to be carrying out a single behaviour pattern with wide variation could instead be choosing between multiple strategies. The neural mechanisms underlying the cockroaches' successful unpredictability have yet to be determined. The researchers suggest that further study in this area would be beneficial, and also recommend applying their model to the study of other animals in order to establish a general theory of how animals generate unpredictable escape trajectories. 'The significance of creating a 'blueprint' of what the animals are really doing under normal circumstances is that you can determine when the system is malfunctioning,' Dr Domenici told CORDIS News. 'If you have a real working model, you can analyse the effect of environmental variation, like changes in temperature due to climate change. You can then see whether environmental changes reduce their efficiency.' Plagued by the little pests? If you're inspired to try and predict the escape route of a cockroach, shoe in hand, the authors said that their group of bugs most often chose an escape path directed at a 90 to 180 degree angle from the attack. 'This is where squashing could be aimed,' said Dr Domenici, 'although we like cockroaches and would recommend no squashing.'
Countries
Italy, Puerto Rico, United Kingdom, United States