Experimental arena settings might lead to misinterpretation of movement properties

Abstract

Movement is an important animal behavior contributing to reproduction and survival. Animal movement is often examined in arenas or enclosures under laboratory conditions. We used the red flour beetle (Tribolium castaneum) to examine here the effect of the arena size, shape, number of barriers, access to the arena's center, and illumination on six movement properties. We demonstrate great differences among arenas. For example, the beetles moved over longer distances in clear arenas than in obstructed ones. Movement along the arena's perimeter was greater in smaller arenas than in larger ones. Movement was more directional in round arenas than in rectangular ones. In general, the beetles stopped moving closer to the perimeter and closer to corners (in the square and rectangular arenas) than expected by chance. In some cases, the arena properties interacted with the beetle sex to affect several movement properties. All these suggest that arena properties might also interact with experimental manipulations to affect the outcome of studies and lead to results specific to the arena used. In other words, instead of examining animal movement, we in fact examine the animal interaction with the arena structure. Caution is therefore advised in interpreting the results of studies on movement in arenas under laboratory conditions and we recommend paying attention also to barriers or obstacles in field experiments. For instance, movement along the arena's perimeter is often interpreted as centrophobism or thigmotaxis but the results here show that such movement is arena dependent.

Flour beetles prefer corners over walls and are slowed down with increasing habitat complexity

“…[75]). An additional methodological implication strengthens the conclusion of our previous study demonstrating strong effects of the test arena's shape on a variety of movement characteristics [35]. Whereas in round arenas movement along the perimeter is frequent (greater than 80% of the time), there is a strong preference in square arenas, like the one used here, for corners, and movement along the perimeter (or walls) is less frequent than expected by chance.…”

“…This contradicts to some extent the common assumption that males are better in solving spatial tasks than females and that males are more sensitive to the microhabitat's shape than females [ 64 , 65 ]. Past studies on the red flour beetle disagreed on whether individuals of one sex move more than the other (females move more than males [ 51 , 66 ]; males move more than females [ 53 , 67 ]; no difference [ 35 , 68 ]). Whereas males may move over longer distances in search of females, females may do so in search of suitable oviposition sites [ 49 ].…”

“…Animal behaviour in corners may differ from the behaviour along walls. Furthermore, if there is already a preference for movement in specific parts of the habitat, like movement along the habitat periphery, obstacles in such habitat parts or in front of the target, may have a more significant impact on animals than obstacles in less frequently used habitat parts [ 34 , 35 ].…”

“…Previous studies demonstrated that red flour beetles strongly followed walls, even more than 80% of the time [ 51 , 52 ]. The beetle's preference depends also on arena size and structure, with walls being favoured to a greater extent in smaller and round arenas compared with larger or rectangular ones [ 35 ]. While some tests indicate that females tend to move more than males, this trend does not hold in all cases (cf.…”

“…While some tests indicate that females tend to move more than males, this trend does not hold in all cases (cf. [ 35 , 51 , 53 ]). At least in this species, movement increases after eclosion and then decreases with age, decreases following starvation, but increases after mating [ 51 , 52 , 54 , 55 ].…”