This post is the second in a six post series outlining the evolution of mimicry within the ocean realm. These posts detail various ways in which organisms may copy other organisms in appearance and behavior, and the evolutionary context for how these mimic-model pairings have come to be. The first entry in this series goes over some fundamental introductory concepts and definitions regarding mimicry in general.
A fish that has evolved to mimic a completely different, potentially entirely unrelated species of fish is relatively impressive. It is a testament to the power of natural selection, this honing and whittling down of a creature so that it may converge on the same exact external form for the sake of protection or the easy procurement of food.
But fish all have the same overall “blueprint.” Paired fins, vertically oriented tail fin, eyes in the front, big, snappy mouth, gills behind the eyes, generally sleek and muscular…there are a number of distinctly “fishy” features that evolution doesn’t fuck around with too much. This sort of basic body plan of a taxonomic group is sometimes down as a “bauplan” and its sort of the generic physical shape and scaffolding with which a given lineage of organisms ends up modifying as different branches break off and try out different tweaks and strategies. The “bauplan” for a motor vehicle, for example, is basically four wheels with tires, a broad cabin for passengers resting atop the rolling chassis, windows, engine, headlights, perhaps a trunk in the back. Anyone can tell you that there are many differences between a Chevy Camaro, a Subaru Outback, and a Hummer, but all of them are superficial when you consider the motor vehicle bauplan they all share. Similarly, the alterations and adaptations associated with the evolution of mimicry in these fish are limited by the constraints generated by their overall body plans. A fish can only fake it so far, and imitating another animal with the same bauplan is completely within any developmental constraints.
But there are fish that manage to step outside the “vertebrate box” when it comes to pulling a fast one on their ocean community. There are some fish that are mimics of invertebrates; spineless, squishy, squirmy things that they haven’t shared a common ancestor with for well over 550 million years. These fish convincingly pass themselves off as things that aren’t even remotely built the same way, all through some clever innovation through the prism of evolution.