Meeting Abstract
Species vary enormously in their locomotory ability. For shell-bearing organisms, like hermit crabs and gastropods, locomotion may be strongly constrained by the architectural properties of shells, which represent ‘dead weight’ that must be carried wherever the organism travels. Here we contrasted movement behavior in the wild, across three shell-bearing species: marine gastropods (Nerita scabricosta), marine hermit crabs (Calcinus obscurus), and terrestrial hermit crabs (Coenobita compressus). All three species use the same shells (originally derived from gastropod N. scabricosta); but only terrestrial hermit crabs architecturally remodel these shells through niche construction, creating lighter weight, more portable homes. We hypothesized that niche constructed shells are built for locomotion and therefore would facilitate enhanced travel by terrestrial hermit crabs, relative to the other two species, which use unremodeled shells. In field experiments, we released individuals of all three species into both marine and terrestrial environments, tracking their movement for 20 min. Both in the sea and on land, terrestrial hermit crabs traveled significantly further than either of the other two species, with displacements of over 50 m. In contrast, marine hermit crabs and gastropods showed no difference in displacement, and never exceeded 2 m from their starting point. Additionally, terrestrial hermit crabs traveled significantly further when starting on land vs. in the sea; whereas marine hermit crabs and gastropods showed no difference between environments. Terrestrial hermit crabs thus attain superior mobility using niche constructed shells, which are arguably more adaptive to a highly mobile life style on land in which resource availability is spatially unpredictable.
