ABSTRACT
Very few studies of sound production in the Brachyura have simultaneously identified the type of individuals (e.g., sex) producing acoustic signals, the structures involved in making sound and the social context. The emission and type of sound signals in Neohelice granulata were previously characterized, but the sex and the body structures involved in the sound production mechanism were not determined. In the present study, experiments conducted in the laboratory demonstrated that acoustic signals were produced by males through an up-down movement of the cheliped by rubbing the merus against the pterygostomial area of the carapace. The micromorphology of the merus showed that it has a ridge of tubercles which may act as a plectrum, while the pterygostomial area bears tubercles and might function as the pars stridens. Acoustic signals were displayed more frequently in the presence of receptive females. Agonistic encounters among males also occurred more often in the presence of receptive females. The authors propose that Neohelice granulata males use their chelipeds to produce sound signals in a mating context, probably to attract the receptive female and/or to repel other males when a receptive female is present. Thus, the display might have a reproductive function influencing mate choice.
ABSTRACT
In semi-terrestrial crabs, the production of sounds has been recognized to be related to courtship communication dynamics. The present study aimed to assess if the crab Neohelice granulata (Varunidae) was able to emit acoustic signals and if they played a role in the crab's behaviour. We also assessed the locomotor behaviours to examine these parameters in different mating contexts of crabs. The study was divided into two different experimental conditions: 'solitary experiment' (consisting of three combination layouts with male, unreceptive and receptive females alone) and 'group experiment' (consisting of mixed combinations layouts of males, unreceptive, and receptive females). Synchronized acoustic and video monitoring systems were used to record the acoustic signals and locomotor behaviours of alone and grouped specimens. The greatest values of locomotor behavioural parameters were observed in layouts with receptive females alone and with 2 males plus 1 receptive female, probably related to courtship behaviour. N. granulata produced two distinct signals, a multi-pulse rasp signal (highest numbers were recorded in layouts with male alone and with 2 males plus 1 receptive female) and a single rasp signal. These results may suggest that males use the multi-rasp signal to advertise their presence to other males or to attract receptive females.
