So what we did then is collect a series of fish called reef fish that were known to be general predators and examine their reaction to these different organisms.
We collected the fish from a different area where these nudibranchs and flatworms were not normally found. We did this because we wanted "naive predators" that had as little experience with these organisms as possible. First thing we did was subject the flatworms, since we had more of them, to four different species of fishes. Three of the species of fish tried to eat the flatworm and immediately spit it out just like they would a nudibranch that was distasteful and then none of those three species would go near a nudibranch or a flatworm or express any interest in either for the two weeks that we tried this experiment.
One very hardy species of trigger fish showed a particular interest in the flatworm. In fact, it wolfed down a flatworm and then it was after another flatworm and it ate another flatworm. It went through about ten of them in rapid succession. I put the nudibranch in the aquarium with that same individual trigger fish. It tried to eat the nudibranch, it spit it right back out and it would not eat any of the flatworms or the nudibranchs for the entire two week period that we were testing these organisms.
So in this case, with three of those species of fishes that would eat neither of these, this would then be a Mullerian mimicry relationship because both of them were distasteful to those particular three species of fish. In the case of the trigger fish, it's basically a Batesian mimicry because they can feed on this. So, not only do you have to understand how the mimicry complex works, these different species have variable palatability to different potential predators. So, one of the things you have to do is place them in their proper ecological context and there is a different context for each potential predator. Different individuals of the same species of fish may have different tastes. Similarly with humans, we find that we tend to eat food that we're familiar with and are less likely to enjoy things that have a tast with which we are not familiar. That's certainly been shown with a variety of organisms, that basically through experience they gain preferences for things that they're familiar with. So, we know that this is a case of convergent evolution as well and that there is differential palatability with different predators.