Male treefrogs get the jump on rivals
The inconsistent sexual signals of male treefrogs have made it more difficult for females to find a quality mate, according to a new study by a researcher at The University of Western Australia.
The study, published in Science Advances, found that when males behaved inconsistently, females were unable to choose between them based on differences in how fast they call. This meant that males with unattractive, low call rates could succeed in mating despite female preferences for faster call rates.
Dr. Jessie Tanner from UWA's Centre for Evolutionary Biology measured the call rates of a species of treefrog that use the sound of their calls to choose appropriate mates during the breeding season.
As calling uses a lot of energy, call rate is a useful way for females to gauge the suitability of various males as mates. But producing high call rates consistently is difficult, and male call rates are often inconsistent, sometimes speeding up and slowing down dramatically over a period of minutes.
Dr. Tanner said unattractive males may use this to their advantage, calling at high rates for short bursts of time to deceive females into believing that they consistently call at higher rates.
"In general, wild males that called at faster average call rates also produced more consistent call rates," Dr. Tanner said.
"However, males that produced slower average call rates occasionally produced brief sound bites of faster call rates. It seems that treefrog males might be able to occasionally subvert female decision-making with these sound bites."
Dr. Tanner said the background noise of the frog chorus also made it difficult for females to choose the preferred, faster call.
"As breeding ponds host many calling male frogs of multiple species, this mate choice happens against a backdrop of loud noise that can impair females' ability to discriminate among males."
Dr. Tanner said the findings suggested that animals were sometimes unable to effectively use communication signals to make optimal mating decisions because of the natural inconsistency and the noisy communication environment.
"We showed that when inconsistency in call rate and loud chorus noise are present, females are less likely to choose the males they would prefer under ideal conditions," Dr. Tanner said.
"As a result, signals are likely evolving more slowly in Cope's gray treefrog and, more broadly, in animals that communicate acoustically, than previously thought.
"Future research should repeat the experiment in other animals that use acoustic signals, such as other frogs, singing insects, and songbirds, as well as animals that signal visually, to better understand how communication behaviours evolve."