Biologists from the University of Texas at Austin, Louisiana State University Health Sciences Center and the Smithsonian Tropical Research Institute have observed that female cognitive ability can limit how melodious or handsome males become over evolutionary time.
Studying neotropical tungara frogs, they found that females lose their ability to detect differences in male mating calls as the calls become more elaborate.
“We have shown that the female tungara frog brains have evolved to process some kinds of information and not others,” said Mike Ryan, professor of integrative biology at The University of Texas at Austin, “and that this limits the evolution of those signals.”
In tungara frogs, males gather en masse to attract female frogs with a call that is made up of a longer “whine” followed by one or more short “chucks.”
Through a series of experiments conducted in Panama, Ryan and his collaborators found that females prefer male calls with the most chucks, but their preference was based on the ratio of the number of chucks. As males elaborate their call by adding more chucks, their relative increase in attractiveness decreases due to a perceptual constraint on the part of females.
The researchers also studied how the bats respond to additional ‘chucks’ in the male call.
They discovered that bats choose their prey based on chuck number ratio, just as the female frogs do. So, as males elaborate their call by adding chucks, the relative increase in predation risk decreases with each additional chuck.
“What this tells us is that predation risk is unlikely to limit male call evolution. Instead, it is the females’ cognition that limits the evolution of increasing chuck number,” said Karin Akre, lecturer at The University of Texas at Austin
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