While the flash might draw attention, the female of the species looks for substance over show – at least for fireflies.
Initially, female Photinus fireflies are very picky and respond – via a flash – to those males with the most attractive bioluminescent courtship flashes. But once the lights go out, females chose mates with the largest ‘nuptial gift’ – a high protein sperm package that helps females produce more eggs.
However, females are likely to mate again the next night – so which males are successful in passing their genes along to the next generation?
“Lots of people don’t realise that sexual selection is happening not only before mating, but also during and even after mating,” said Sara Lewis, Professor of Biology at Tufts University. “Focusing on what happens after contact, we wanted to examine how much a male’s success – in both mating and fathering offspring – depended on his flashes or on his nuptial gift offering.”
The researchers set up an experiment using infrared video and paternity testing based on firefly DNA. They used LED lights programmed to make two kinds of flashes to attract the females – some only saw artificial flashes, while others saw unattractive flashes. The males were also split into two – virgins with larger nuptial gifts, and those who mated the previous night.
After several minutes flashing, the fireflies were paired up and their close-up courtship – illuminated under infrared – recorded. Analysis revealed that once a female was in close quarters with a male, she was more likely to mate with those with a larger nuptial gift.
“We were surprised to discover that attractive flashes only seem to benefit males during the early stages of firefly courtship,” said Adam South, co-author of the paper published in Proceedings of the Royal Society – Biological Sciences.
“Initially flashes are important. Female fireflies preferentially respond to males based on temporary flash characteristics. Once males make physical contact, however, females switch to an alternative cue – one that’s related to male nuptial gift size. What makes this especially intriguing is that females have no way to directly evaluate gift size, since it’s created and transferred internally.”
When females mated sequentially with more than one male, paternity testing showed that males with larger nuptial gifts fathered more offspring compared with rivals.