Absence of Host-Seeking Chemotaxis in a Commensal Crab

Abstract:

The pea crab, Dissodactylus mellitae, is a commensal symbiote that can be found on the sand dollar species Mellita quinquiesperforata, a species common in the Tampa Bay Area in Florida. As symbiotes, pea crab populations are fragmented across multiple hosts, and therefore they must be able to switch hosts to locate suitable mates or avoid competition. Detection of chemical cues is often used in host location, and pea crabs have been shown in prior work to select hosts based on odor cues released from sand dollars in Y-tube experiments. We conducted laboratory experiments using a gravity-fed flow tank, as well as ex-situ observations to verify this mechanism. We expected for crabs to exhibit the same active host-seeking behavior reported in previous literature. However, preliminary results have shown no preference between a water source with sand dollar pheromones and water without. Crabs were also observed to not actively seek out hosts in the same environment and instead wait until the hosts approached them before attaching. Our findings contradict the previous literature but, given our choice of methods, may be more representative of the behavior of this species in the wild. Considering the habitat these crabs reside in and the density of hosts in the field, it may be more advantageous for them to implement a lie-in-wait strategy rather than active host-seeking. 

For more information contact ljgunder@eckerd.edu or ollord@eckerd.edu