BEHAVIOR OF THE ESTUARINE CRAB HEMIGRAPSUS-CRENULATUS (MILNE-EDWARDS 1837) IN RELATION TO THE PARASITISM BY THE ACANTHOCEPHALAN-PROFILICOLLIS ANTARCTICUS (ZDZITOWIECKI 1985) IN SOUTHERN CHILE

Parasites are able to induce phenotypic changes in intermediate hosts (prey), thus favouring transmission toward definitive hosts (predators ). In this study, we assess the behavior of the estuarine crab Hemigra psus crenulatus (Milne-Edwards 1837) when infected by the acanthocepha lan Profilicollis antarcticus (Zdzitowiecki 1985), in the field and in laboratory settings. In the field, we compared the frequency of infec ted and uninfected crabs that reacted fleeing to a visual menace, that showed differences in the caparace colour, that made use of habitats more or less visible, and their location within or outside the water. In the laboratory we assessed the hydrotaxic and phototaxic behavior o f infected and uninfected crabs. We also assessed the readiness of cra bs to react fleeing when visually menaced and the colour changes of th e caparace induced by experimental infections. Our results showed that , in the field, parasites do not induce behavioral or pigmentation cha nges in the estuarine crab. In the laboratory experiments, crabs inocu lated with cystacanths changed their pigmentation. We suggest that the ratio of crab-parasite body size, the location of the parasite in the host body, the magnitude of parasitism in the intermediate host popul ation and the pathogenicity of the parasite for the definitive host, m ay be determinant in the evolution of the manifestation of morphologic al or behavioral changes in parasitized intermediate hosts.