Everyone knows clownfish are pretty. Almost everyone knows they live among the tentacles of anemones. But I’m willing to bet fewer people know that clownfish are noisy.
Fishes make noises for the same sorts of reasons that other animals make noise. Sometimes, it’s to say, “This is what species I am!” Sometimes, it’s to say, “Listen to how big I am!” All kinds of important signals can be contained in sounds. Such behaviours can become important drivers in evolution. Certain kinds of sounds might be considered “sexy” in different groups, and start driving differences in mate choice, and ultimately speciation.
The team of Colleye and colleagues listened to 14 different species of clownfish, most of which were in the genus Amphiprion (A. ocellaris and A. frenatus are shown here). They predicted that if these sound signals were important in the evolution of this group of fishes, they should see lots of diversification in the signals, and not much overlap between them.
This turned out not to be the case. The sounds were quite similar, perhaps because clownfish all make sounds by snapping their jaws together.
The sounds clownfish make are excellent signals of fish size. Big fish make longer and lower sounding pulses in their calls than small fish. The correlations are tighter than most that you see in biology. (The r values are 0.98 and -0.99! See here for more on correlations.)
This doesn’t support the idea that the sounds are important as way to isolate different species, except incidentally if the species differ in size.
But these signals could be critical to the dynamics between individuals within a group a clownfish, because breeding in groups is dependent on size. If you are the biggest clownfish in your group, you are a reproductive female. If you are the second biggest fish in your group, you are a reproductive male. If you are the third biggest fish in your group... you are a male who doesn’t get to reproduce until one of of the top two go missing. (Yes, clownfish undergo sex changes.)
When your reproductive success depends on size, being able to recognize the information about size in other group members could be critical.
Colleye O, Vandewalle P, Lanterbecq D, Lecchini D, & Parmentier E. 2011. Interspecific variation of calls in clownfishes: degree of similarity in closely related species BMC Evolutionary Biology 11(1): 365. DOI: 10.1186/1471-2148-11-365
Amphiprion ocellaris by Joachim S. Müller on Flickr; Amphiprion frenatus by brian.gratwicke on Flickr; both used under a Creative Commons license.