Meeting Abstract
As crabs made the evolutionary transition from aquatic to terrestrial environments, they faced a shift in the mechanical challenges imposed on their skeletal support systems. Exacerbating the challenges of transitioning to land is the need to accommodate two fundamentally different modes of skeletal support- rigid and hydrostatic. As the largest arthropods to inhabit both environments and use two distinct skeletons, crabs are an interesting system to examine biomechanical adaptations in skeletal support systems. I hypothesized that terrestrial crabs would have modified morphology to enhance mechanical stiffness in both the rigid and hydrostatic phases, which would provide more support against greater gravitational loading. Using the terrestrial blackback land crab, Gecarcinus lateralis, and the aquatic blue crab, Callinectes sapidus, I measured and compared body mass, merus morphology (dimensions, cuticle thickness, and I) and mechanics (EI, E, critical stress, and hydrostatic pressure) of rigid and hydrostatic stage crabs encompassing a range of sizes (C. sapidus: 1.5-133 g, N ≤ 24; G. lateralis: 22-70 g, N ≤ 15). Results revealed that rigid G. lateralis has similar merus morphology [merus length/merus diameter (L/D) and cuticle thickness/merus diameter (T/D)] and mechanics (EI, critical stress) to C. sapidus. In contrast, hydrostatic land crabs differ from aquatic crabs by having different morphology (thinner cuticle) and mechanics (greater internal pressures). These results suggest that the rigid crab body plan is inherently overbuilt and sufficient to deal with the greater gravitational loading that occurs on land, while mechanical adaptations are important for hydrostatically supported crabs. The hydrostatic skeleton of crabs appears to experience greater challenges with gravity and, as a result, may impose greater constraints to crab growth on land.
