Male splitfins wriggle about the yellow streak on their tail as part of their mating dance. Females are attracted to the wriggling tail because it looks like their typical prey. There's only one problem: the females then forget to eat.
I suppose there's a certain evolutionary brilliance so that part of your body looks like food. It's maybe not the most dignified way to attract the attention of other members of the species - particularly when it involves a truly shocking amount of tail wriggling - but it plays on one of an organism's most basic needs. If nothing else, it's a lot easier than pretending to be an oxygen bubble or something.
The problem, according to researchers at Mexico's National University, is that female splitfins can't always distinguish between a male's tail and actual prey. This confusion can actually be bad enough that the females forget to eat enough real food, as ScienceNOW reports:
When the researchers presented pregnant (and thus hungry) females from six species of splitfins with both yummy insect larvae and males from two of the most flamboyant splitfin species-the polka-dot splitfin (Chapalichthys pardalis) and the butterfly splitfin (Ameca splendens)-the females from all six species were so distracted by the males' tails that individuals from five of the species lost weight over the 1-week trials.
The fish that lost the least weight - including the one that didn't lose any at all - were from the species whose males have more visually striking tails. This might suggest that some of the fish have evolved to sidestep this food-based trap, instead preferring males that they find the most sexually attractive. It's a process that the authors describe as one big evolutionary battle of the fish sexes:
Male ornaments can evolve through the exploitation of female perceptual biases such as those involved in responding to cues from food. This type of sensory exploitation may lead to confusion between the male signals and the cues that females use to find/recognize food. Such interference would be costly to females and may be one reason why females evolve resistance to the male ornaments...Our results lend support to the model of ornamental evolution through chase-away sexual conflict.