All good men know that the way to a woman’s heart is through her stomach, and none more so than the swordtail characin (Corynopoma riisei). Males of this popular tropical aquarium fish take a rather literal approach to getting the girls “eating out of the palm of their hand” by luring them in with an anatomical ornament that looks like their favourite snack. The exact shape varies with diet across different populations - some, for example, take the form of ants where these are the dominant prey. This is an example of what is known as sensory drive, where sensory communication methods evolve by adapting to local environmental conditions. This can lead to speciation - the division of populations to form new species - particularly in cases like this where mate choice is affected. The swordtail characin is one of the few fish that reproduces by internal fertilisation, so by luring the female into close proximity, the male is then better able to position himself for mating to occur.
Ref: Kolm N., Amcoff M., Mann R. P. & Arnqvist G. (2012) Diversification of a food-mimicking male ornament via sensory drive. Current Biology [link]