EFFECTS OF THE TOXIC SECRETION OF A CRAB ON OTHER CRAB SPECIES

Aggio, J.F., Freitas, J.C.

Biosciences Institute and CEBIMar, University of São Paulo, Brazil

The digestive secretion of the crab Mithrax hispidus may be released on some conditions and contains neurotoxins, as revealed by sucrose-gap. We investigated its effect in vivo on the cardiac activity of another crab, Hepatus pudibundus and on the feeding activity of the ghost crab, Ocypode quadrata. Animals of both species were immobilized and temporarily blinded, and platinum electrodes were glued in small holes drilled in the carapace. Electrodes were used to monitor cardiac activity (both species) and mandibular muscle activity (burst of action potentials) during eating (O. quadrata). Signals were amplified, digitized and stored in a computer for posterior analysis. Stimuli were applied to the oral region of experimental animals including the antennulae, antennae and mouth parts, which are known to possess chemorreceptors. As control stimuli we used mussel extract (50 mg/ml) and filtered sea water. Both species were clearly able to distinguish between the different stimuli. In H. pudibundus, mussel extract caused a non-beating heart to start beating and it increased the frequency of an already beating one, whereas the digestive secretion had the opposite effect (i.e., stopped a beating heart and did not start a quiescent one). Individuals of O. quadrata were fed with mussel tissue and subsequently stimulated. Sea water and mussel extract had no effect, whereas the digestive secretion caused animals to stop eating altogether or, in some cases, deorganized the rhythmic activity associated with eating. Burst durations were unaltered, but the intervals between them became irregular. Our results suggest that the digestive secretion of M. hispidus affects negatively other animals in the environment, thus being a suitable candidate for a chemical defensive system.

CORRESPONDENCE TO:

Juan Felipe Aggio, Departamento de Fisiologia Rua do Matão Trvessa 14 N 101, Cidade Universitária, São Paulo, SP, CEP: 05508-900 , Brasil, Email: jfaggio@usp.br