Variation was observed during mating displays by stickleback fish
Females do not always trust males who emit strong sexual signals, according to a study by evolutionary biologists.
Researchers from Glasgow and Exeter universities studied mating behaviour in three-spined stickleback fish.
They found "initial flashy displays" by males were not always successful at attracting a mate.
The study said some females waited until sexual signals were more honest as weaker males exhausted themselves with "shows" they could not sustain.
The team, led by Dr Jan Lindström, found that the honesty of mating displays could vary dramatically over time.
Dr Lindström said: "Honesty in males mostly depends on how many opportunities there are to breed.
"If males can breed now but the future promises little in terms of further matings, all males should immediately reveal their 'true colours' - so that the signals they produce are a reliable indication of their quality.
"But if males can potentially breed several times over the course of a breeding season, it pays those in best condition to keep some of their strength in reserve.
"In contrast, those males in poorer condition cannot afford to delay seeking a mate, so must signal as hard as they can - with the result that at the start of the breeding season a female cannot reliably judge a male's quality from his signal.
"However, as time goes on, the poorer condition males must drop out of the competition, leaving only the better ones and making it easier for a female to pick a high quality mate."
The predictions were tested using three-spined sticklebacks, a species of fish in which breeding males develop a red throat in order to attract females.
Sticklebacks can breed several times over the course of the summer, but pay a heavy price since few survive for another year.
Dr Lindström added: "We found that the redness of the males changed over the summer, with all starting out red but only those in good condition being able to sustain their colour.
"As predicted by our model, females seemed to ignore the redness of a male when choosing a mate in early summer, and only developed a preference for redder males later, once it became a more honest signal of a male's quality."
The study was funded by the UK's Natural Environment Research Council. It will be published in the scientific journal, American Naturalist.