Conspecific Recognition and Host Choice in a Pea Crab, Pinnixa chaetopterana (Brachyura: Pinnotheridae)

The pea crab Pinnixa chaetopterana (Brachyura: Pinnotheridae) lives in the tubes of the host polychaetes Chaetopterus variopedatus and Amphitrite ornata. While attraction to host odor cues is common in symbiotes, P. chaetopterana resident in Chaetopterus tubes apparently show no attraction to water-borne cues from either host. Because crabs resident in Amphitrite tubes are significantly reduced in their maximum body size and thus clutch size, switching between hosts should occur. We therefore tested the hypothesis that the crabs use odor cues from conspecifics or from the competing crab Polyonyx gibbesi (Anomura: Porcellanidae) when locating a new host. Crabs collected from Amphitrite are significantly attracted to Chaetopterus hosts which contain a mixed sex pair of conspecifics. Females show a strong tendency to avoid hosts containing Polyonyx, but males do not. Neither sex is attracted to unoccupied Chaetopterus or Amphitrite hosts, but both are significantly attracted to isolated conspecifics. This attraction could serve as a reliable means of locating suitable new hosts when switching hosts in the field. Attraction to conspecific odors would also increase the chances of finding a suitable mate already present in a new host.