Behavioral compensation masks morphological trade-offs in the locomotion of the terrestrial hermit crab Coenobita compressus

Abstract

The trade-off between protection and mobility is a central principle in functional ecology and is particularly relevant in terrestrial hermit crabs, which depend on gastropod shells for defense while potentially incurring locomotor costs. Under the trade-off hypothesis, heavier or asymmetric shells are expected to impair movement, especially on heterogeneous or uneven substrates. To evaluate this prediction, we examined locomotor behavior in the land hermit crab Coenobita compressus on Coiba Island (Panama), integrating field observations with controlled experimental assays across substrates differing in topography and compaction. Contrary to classical expectations, shell weight and morphology exerted limited effects on locomotor performance. Instead, individuals exhibited substantial behavioral flexibility, adjusting posture and gait across environmental contexts. These findings suggest that C. compressus may buffer mechanical constraints imposed by shell architecture through adaptive behavioral compensation. Our results support an expanded interpretation of the trade-off framework in which behavioral plasticity attenuates, rather than eliminates, functional trade-offs, potentially enhancing performance in dynamic coastal habitats.