The effects of loose, firm, fine, and coarse substrates on the movement of the red flour beetle

Movement plays a crucial role in animal behavior. However, despite the prevalence of uneven terrains in nature, many movement studies are conducted in arenas with smooth substrates. This discrepancy raises questions about the ecological validity of such experiments. To address this gap, we investigated the effect of rough substrates on movement properties using the red flour beetle (Tribolium castaneum) as a model organism. Our findings revealed significant variations in movement behavior between rough and smooth substrates. Notably, beetles traveled longer distances on smooth surfaces compared to sandpaper and loose sand. Moreover, variations in step size were influenced by substrate treatment, with the highest values observed on sand and sandpaper treatments. The proportion of time spent standing still also showed sensitivity to substrate conditions. The interaction between substrate properties and beetle sex further influenced several movement properties. Even the spatial configuration of rough and smooth areas in the arena had an impact on beetle movement, with areas along the arena perimeter exhibiting a stronger effect. These results highlight the impact of uneven terrain on beetle movement, underscoring the importance of considering environmental conditions when designing experimental setups. Here, this refers to the substrate on which animals move, but it may refer to other conditions, such as the test arena size and shape, temperature, humidity, and illumination. Failure to account for these background environmental conditions may result in inadvertently examining the interaction of the tested animals with these conditions, rather than focusing on the effect of the treatments applied in the experiment.