20
November
2017
|
23:42
Asia/Singapore

Dancing crab keeps losers away

An NUS research team has discovered that a common Southeast Asian mangrove crab engages in a strident victory dance to intimidate losers from initiating a fresh bout. The research was published in Ethology on 12 October.

The research team consisted of Professor Peter Ng from NUS Biological Sciences and the Lee Kong Chian Natural History Museum at NUS; Assistant Professor Roman Carrasco Torrecilla from NUS Biological Sciences; and Dr Paul Chen, formerly a PhD student at NUS Biological Sciences. Using the colourful Perisesarma eumolpe, the biologists investigated the browbeating function of the crabs’ victory display.

Male crabs hand-collected from Pasir Ris Mangrove were randomly paired and placed in a fight arena. In all, the researchers analysed 77 fights which occurred in 27 staged trials. In 55 per cent of the fights observed, the winners did a victory dance. In these instances, losers reinitiated a fight only 35 per cent of the time. But in the absence of a victory display, the losers reinitiated a fight 65 per cent of the time.

Describing the victory display, first author of the study Dr Chen said, “Perisesarma eumolpe, a mangrove species, often performs a victory display after having won an intense fight. Some have likened it to revelling in its recent triumph or as a taunt. It does so by downturning one claw into the ground and rubbing it with the other claw up and down in such quick succession that vibrations are generated.”

The findings suggested that the winners performed victory displays to “browbeat” losers into a more permanent submission. Explaining the role that victory displays played, Dr Chen shared, “Having to engage in less fights, especially if they are unnecessary, could translate to more time for other activities. To our knowledge, this study provides the first empirical evidence that demonstrates this function in victory displays.”

As the Perisesarma eumolpe had a tendency of dropping their claws when threatened, much like how lizards lose their tails in a similar situation, Asst Prof Carrasco’s statistical expertise was indispensable in ascertaining that the observed behaviour was due to the crabs engaging in browbeating when they performed their victory displays.

The researchers also noted that after the victory dance, winners commonly continued to initiate further fights. Further research is required to determine whether such behaviour serves to advertise the recent victory to other crabs in the vicinity as well, and if so, the difference in reaction between male and female crabs.