Animal behaviour and ecological interactions

Psychology

Animal Behaviour

The hypothesis of the article "Sound production in red-bellied piranhas (Pygocentrus nattereri, Kner): an acoustical, behavioural and morphofunctional study" by Millot, Vandewalle & Parmentier (2011), is that piranhas make sounds and these sounds are able to be associated with given behaviors like aggression, intimidation, food competition, and chasing and that these sounds were generated by rapid contractions of sonic muscles that insert on a broad tendon surrounding ventrally the cranial sac of the swimbladder.

Main Conclusion Regarding the Hypothesis

The author's main conclusions were that each kind of sound emitted by piranhas is associated with a specific behavior; the caudal swimbladder does not play a role in sound production; the vibration frequency of the cranial swimbladder corresponds exactly to the sonic muscle contraction rate; the bark sound was produced by sonic muscle contraction at 100?Hz because this frequency brings together the conditions necessary to produce this type of sound; the other sound type might be produced by only one sonic muscle contraction; and the third sound was the result of the jaws snapping.

One strength of the Experimental Design

A strength of the experimental design was that the researchers made direct underwater observations of the feeding and social interactions of red-bellied piranhas. They examined breeding behaviour, described how individual piranhas attacked goldfish and investigated piranha shoaling behaviour in a controlled environment.

One Weakness of the Experimental Design

A weakness of this experimental design was that there was no testing of the vibratory capacities of the cranial and caudal sacs to see if this might have been the source of the sounds being recorded. To date the exact role of both sacs in sound production remains poorly understood and really could use some further research in order to see what role, if any they play in the sound production of piranhas.

Follow up Study to Test the Same Hypothesis

A follow up study that could be done in order to test the same hypothesis would be to test the same type of fish in their natural environment instead of in a tank environment. The same variables of the cranial and caudal sacs would be observed in order to determine if the sounds being produced where indeed coming from these organs or not. It may be that these two organs are either the source of the sound or are in someway related to the sound that these researchers heard during the tank experiment coming from the swimbladder.

Did the newspaper article describe the research article correctly? Explain.