Stomatopod Grooming Behavior: Functional Morphology and Amputation Experiments in Gonodactylus Oerstedii

Abstract

Qualitative and quantitative observations on G. oerstedii show that its grooming behavior consists (in order of decreasing frequency) of antennae (Al and A2), eye, subcarapace, gill, and general body grooming. As in decapod crustaceans, there is an inverse relationship between bout frequency and bout duration of grooming behaviors in this stomatopod. The only appendage observed in grooming, the first maxilliped, has grooming brushes of rasp, multiscaled, and scaled serrate setae; the microstructure of these setae is described and illustrated with SEM. In the Stomatopoda, low diversity of specialized grooming structures reflects a conservative stomatopod body plan, while the high diversity of cleaning characters in the Decapoda reflects the group's high variation in body morphology. Analysis of the functional morphology of G. oerstedii's fifth maxilliped (M5) propodal brush suggests that it is a reduced and vestigial grooming character. It is concluded that a vestigial M5 grooming brush is a synapomorphy that supports the hypothesis by Jacques (1983) that the Gonodactylidae, Odontodactylidae, and Protosquillidae are closely related. Amputation experiments were performed to test the hypothesis that grooming behavior is an antifouling adaptation. Members of the experimental group had the first maxillipeds amputated; in control groups, exopods of the third pereiopods, a nongrooming appendage, were ablated. Experimental and control animals were exposed to fouling on sea-water tables for 2 weeks. Fouling was quantified by counting strands of Leucothrix, a filamentous bacterium. Both gill filaments and antennular aesthestascs of experimental (nongrooming) stomatopods were heavily fouled by Leucothrix and other bacterial growth after 2 weeks, while those of controls remained clean. The low fouling on eyes and lack of fouling on most other body surfaces in experimentals raises the possibility that some parts of the exoskeleton may be protected from microbial fouling by the secretion of antifouling compounds.