In the underground shopping malls of Tokyo or Seoul, as a male subject I am often disappointed of myself, because men are supposed to have a better sense of direction than females. Yet, I am pretty hopeless and lose my way ever so often. If I go shopping in these underground labyrinths with a female companion, the latter inevitably remembers unerringly the way to the fashion store, the snack bar, the place I call “the-useless-stuff-shop” and, ultimately, the way out. Is this superior orientation related to turning reactions that have been explored so well with arthropods like woodlice, centipedes and insects?
A common experiment in practicals for the “Comparative Physiology & Behaviour” class, is to let some arthropods crawl along a tube that has a bend of a certain angle, let’s say 90 degrees, to either the right or the left side. The parcourse may resemble on “L”, in which the long arm is the entrance tube and measures 10 cm and the shorter arm is half that length. Letting, for example, a woodlouse travel along this “L”, which then forces the little animal to change its direction and turn to either the right or the left, one notices that when it emerges from the short arm that it does not run in a straight line away from the end, but exhibits a clear and significant tendency to turn back into the direction it had when in the long entrance arm. If the woodlouse (which is not an insect, but a member of the crustaceans) is forced into a left bend, it would veer towards the right when escaping at the end. If it were forced into a right bend earlier, it would then tend to move to the left later on.
There are numerous modifications to this simple set-up. One can make the entrance arm of the parcourse longer or shorter and do the same with the exist arm, one could choose different angles for the test arthropod to turn, and one could try and see whether the direction of the light has any effect or whether painting one eye (either the left or the right) interferes with the turning response (actually the latter manipulation does). But a longer entrance or exit tube does that too and shows that the angle to restore the original orientation gets increasingly smaller as the distances the arthropod has to cover in the arms either before or after reaching the bend (where it is forced to turn) increases. If the angle in the bend is made smaller than 90 degrees the correcting angle made by the woodlouse upon leaving the exist, also becomes smaller. What does that show us?
One earlier suggestion was that the test animal “remembers” that it really wanted to crawl in a straight line, but couldn’t because of the forced turn to the right or left. When coming to the end of the exit tube, the test animal “remembered” that it now was facing the wrong direction and consequently took action to return to its originally intended pathway. It does seem, however, that what the little test animal’s correction reaction is based on, is an imbalance of the steps between the legs on the right and the left side of its body. Turning to the right, for example, would force the woodlouse to make more and bigger steps with its left legs than with those on its right and to reach equilibrium again once the exit is reached, the side that experienced fewer and smaller steps now catches up. A kind of rebound effect.
This may sound reasonably plausible, but it does not explain how the muscles of the legs “know” what to do. Muscles, especially those involved in as complex an action as “walking” or “crawling” need a nervous input from motor neurons. How would the latter know when and to what extent the leg muscles need to be stimulated? Results of this seemingly simple experiment lead to a lot of deeper thoughts on basic orientation mechanisms and memory involved in path recovery. It also led me to think whether my female shopping companion’s memory of the twists and turns in the underground shopping labyrinth was more similar to the behaviour of a woodlouse than my lack of orientational memory.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
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