The talking crab.

A study focused on the acoustic behaviour of the paddle crab Ovalipes trimaculatus (De Haan, 1833) in relation to its reproductive status and behaviour. Paired male with female (pre-copulatory behaviour) and solitary animals were collected a few hundred metres from the coast of Puerto Madryn (Patagonia, Argentina) and kept in indoor tanks. Synchronized acoustic and video monitoring systems were used to collect the acoustic signals and other behaviours of single and grouped specimens in an experimental tank. The acoustic data were analysed to characterize the crab sounds (duration, pulse number and pulse rate, first and second peaks frequency ([1pkf, 2pkf], amplitude of the 1pkf and 2pkf and bandwidth) and were counted as behavioural events. The video data were analysed to count the behavioural events (i.e. agonistic fight, chela spread) and status (locomotor indices, inter-crab distance). O. trimaculatus produced wide frequency band multi-pulse signals with significant differences between males and females: males showed a lower 1pkf, with a higher amplitude and a higher bandwidth. The sound emission rate was significantly higher in grouped animals than in single individuals. Sound emissions are not an accidental event that are correlated with locomotor activities. In the trials with females in a pre-copulatory status, the total number of sounds increased significantly compared to the trials with control females, and the sounds were not correlated with the agonistic events between males. Our data indicate that in O. trimaculatus sound emissions play a role in the intraspecific communication related to sexual attraction.

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