The males of certain species of fish have a yellow band on the tailfin. Females seem uncontrollably drawn to it — and sometimes, a new study suggests, that can be their downfall.
Pregnant females, it seems, can mistake the band for a tasty worm or a damselfly, becoming so distracted by the yellow that their foraging abilities are diminished.
“You can imagine a female trying to feed on damselfly or worm, but a male passes by and she is distracted,” said Constantino Macías Garcia, a behavioral ecologist at the National Autonomous University of Mexico, who led the study. “The female doesn’t have interest in mating at this point but is attracted and instead loses a feeding opportunity.”
The yellow-banded species they studied all belong to a family of North American fish known as Goodeidae. Even in species where females have evolved to learn that the band is not food, they are still drawn to it, the researchers found.
The researchers found that when plant material was available to the females, the effect of males’ being nearby was reduced, which hints that the ability to eat plants may have evolved over time. “We cannot say that it became herbivorous because it was costly to be responding all the time to the males,” Dr. Macías Garcia said. “But it is a likely explanation.”