The rules of the tree cricket world, speaking sexually, are simple.
Perched from the edge of a leaf, males call at night rhythmically rubbing their wings. Females study the soundscape, gravitating toward the stronger, larger males. The small, silent guys drown.
Unless they are cheating the system.
Some male crickets make their own megaphones by cutting wing-sized holes in the center of the leaves. Their crickets trapped in the middle of this vegetative speaker, male crickets Oecanthus henryi can more than double the volume of their calls, allowing naturally quiet males to attract both females and strong males, researchers reported Dec. 16 in Proceedings of the Royal Society B.
It’s a rare example of using insect tools that “really challenges you to think about what it takes to produce complex behavior,” says Marlene Zuk, an evolutionary biologist at the University of Minnesota at St. Louis. Paul who did not participate in the study.
Sign up to receive the latest from Science News
Headlines and summaries of the latest Science News articles, delivered in your inbox
Biologists first saw crickets creating leaf speakers, called baffling, and singing from them, or baffling, in 1975. Since then, baffling behavior has been reported in two other species, but it was unclear exactly how it benefits individual crickets.
Rittik Deb, an evolutionary ecologist now at the National Center for Biological Sciences in Bangalore, India, was stunned when he was bafflingly witnessed by a male O. henryi in 2008. “It was incredibly beautiful,” he says, “he had to understand why he was to happen. "
Deb, then at the Indian Institute of Science in Bangalore, and her colleagues first looked for some common ground among crickets using baffles. Only 25 of 463, or 5 per cent, of the crickets observed and individually marked in the fields outside Bangalore were baffled. On average, baffling males were smaller and called quieter when not baffling. In the field, Deb found that the baffling roughly doubles the call volume of a quiet male, elevating him to the level of the most attractive males.
Cricket wings are essentially resonant structures, reverberating with the vibration caused by friction, like the body of a violin (SN: 30/04/12). When the baffles crawl through a hole in a sheet, align the wings with the sheet, and start singing, they’re essentially expanding this resonant structure, using the sheet “a bit like a speaker or a megaphone,” Deb says.
Do females fall for their inflated calls? Yes, according to laboratory experiments. When chosen, females overwhelmingly prefer the loudest calls, even when they come from baffling males. The baffling essentially equals the playing field, allowing quiet males to attract as many females as stronger males.
The benefits of the baffle don’t stop there.
The climax of cricket mating is the transfer of spermatophore, a protein ball filled with sperm. Females dictate the amount of sperm they accept for how long they retain the spermatophore. With larger males it is about 40 minutes, compared to only 10 minutes for smaller males. But when Deb artificially increased the calls of small, silent males, the females treated them like large males, keeping their spermatophores longer. “That really surprised us,” Deb says. "It's like the females were somehow fooled."
It’s unclear why females don’t seem to notice that they mate with a smaller male, though it’s not necessarily surprising. “They’re not wrapping their little arms around the males to see if they’re big or small,” Zuk says. "Maybe there's something in the song that says 'go ahead and have more of these babies.'"
Whatever the mechanism, O. henryi males have developed a very effective mating strategy, Zuk says. The behavior appears to be innate, unlearned, as laboratory-raised crickets of all sizes can make and use baffles when given leaves. “It makes me really want to know why such a small portion of males really do,” Zuk says.
The baffling may not be worth the extra work for larger males that can already attract many females. But there are many small, silent males who presumably could get huge bewildering rewards, but they don’t. Maybe crickets face a shortage of leaves large enough or perhaps baffling males face compensation: with the antennae blocked by the leaf, the baffler can make crickets ducks so that predators like geckos and spiders attack by behind.
Despite the potential costs, it is clear that these crickets have developed a clever way to bend the natural world to their interests. The use of this type of tool among animals is varied, from primates that crack nuts with stones to puffins that scratch with sticks (SN: 24/06/19; SN: 30/12/19). Although some biologists may argue designating a deflector as a tool in good faith, these crickets demonstrate that sophisticated behaviors are not just for large, complex brains. “That idea really goes through my head,” Deb says.