Evidence that sensory traps can evolve into honest signals

The gender trap The evolution of male ornaments is a puzzle, as they seem to ignore natural selection, which favours economy. They are usually explained as badges of genetic quality, or an arbitrary link to more functional female preferences. Experiments in Goodeinae, a small fish from central Mexico, show that the initial phase of ornament elaboration can be guided by sexual conflict in the form of a ‘sensory trap’ exploiting a pre-existing female bias. Females later learn to differentiate between model and ornament, then drive ornament elaboration through classic sexual selection. The male ornament in the goodeids, worm-like patterns on the tail fins, first evolved because females reacted to it with feeding behaviour (the sensory trap) but as tails grew more conspicuous (and costly), females began to respond with sexual behaviour.