|Social status and its effects in some hermit crabs (Decapoda, Anomura)|
Mainardi, D.; Rossi, A.C. (1972). Social status and its effects in some hermit crabs (Decapoda, Anomura), in: Battaglia, B. (Ed.) Fifth European Marine Biology Symposium. pp. 317-326
In: Battaglia, B. (Ed.) (1972). Fifth European Marine Biology Symposium. Piccin Editore: Padova. 348 pp., more
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VLIZ: Proceedings 
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Most aggressive interactions between 2 hermit crabs lead to the development of social orders. Groups of 2 isospecific crabs, belonging to the 3 species, were analyzed through proper experimental devices. The results of a comparative study of the social interactions, at the level of dominance-subordinance relationships, are reported. Clibanarius erythropus surely is the most gregarious species of the 3 studied as it appeared from a large number of observations in the laboratory and in the field. In this species, social contacts seem to occur through highly ritualized optical and tactile signstimuli which are very hard to detect and interpret by an observer. In the slightly less gregarious species Diogenes pugilator real fights are less frequent and the submissive posture, as the other displays, less dramatic but more effective in comparison with the analogous behaviour patterns of Dardanus arrosor. In D. pugilator physical injuries are exceptional, particularly against the harmless molting crabs. On the contrary, in lab conditions, the molting Dardanus is always killed by its opponent, whether dominant or subordinated, and every fight leads to effective physical damage of the loser crab. Our experimental results suggest that D. arrosor is the least social species of the 3 studied. The dominant crab, which is usually the larger of the 2 opponents, obtains the preferred shell and more food; as a consequence its molting is far more frequent than for the subordinated crab. All the investigated species present interesting behaviour patterns such as threat displays, ritualized fighting and different submissive signals, which probably evolved as adaptive compensations for aggressive behaviour. The behavioural interactions of the members of a developed social set are strongly affected by their social status and, in some cases, by their latest social experiences. The rate of evolution of the signals, which develop and maintain a hierarchy, reducing physical aggressions, depends on the degree of sociality of the species.