Male mice take a cue from Bieber

U. FLORIDA (US) — To get the girl, some male mice have to channel their inner Justin Bieber—wooing the ladies with amazing high-pitched vocals.

Researchers suspect the males’ prowess could give the female mice clues to a potential mate’s physical quality, according to a new study published in the journal Animal Behaviour.

“Elaborate courtship displays require fine coordination of the nervous, neuromuscular, and cardiac systems. There is increasing evidence that females evaluate male skills during these displays to determine their overall vigor,” says Bret Pasch, co-author of the study and a biology doctoral candidate at the University of Florida.

When it comes to singing, it’s easy enough to identify characteristics that make a human excel—an exceptional range, or the ability to hold a high note, for example—but mice have different criteria.

“What makes a great performance is how rapidly males can repeat notes while maintaining a large range of frequencies of each note,” Pasch says. “Female preference seems to be based on how well males perform songs.”

In the study, Pasch and his team demonstrated that, like birds, the Alston’s singing mouse, or Scotinomys teguina, has biomechanical limitations to its trills: The faster it trills, the lower the range of frequencies in each note. Conversely, singing with high frequency bandwidths limits the speed with which it can repeat notes.

Pasch uses a textbook analogy: handclapping. The slower you clap, the louder each clap can be because you have time to pull your hands apart to generate power. As one claps faster, there is less time to generate power. Beyond a certain rate, one cannot clap both loudly and quickly.

The similarity to birds surprised Jeffrey Podos, a biologist specializing in vocal behavior at the University of Massachusetts Amherst.

“Mice and birds sing using completely different vocal mechanisms, and so the similarity in song patterns is very much unexpected,” he explains. “It will be interesting to try to identify similarities in vocal mechanics between birds and mice that could explain the convergent pattern.”

In the second component of the study, Pasch and his team demonstrated that male sex hormones, also called androgens, affect how well mice can sing. By neutering the male mice, then giving synthetic hormones to some of them, the researchers showed that mice without hormones weren’t able to perform as well as their counterparts.

The mice who didn’t receive hormone replacement had slower trill rates, and their notes covered a smaller range of frequencies. The researchers suspect that androgens may act on the jaw musculature and diaphragm to influence the rate of mouth movement and force of respiration. The role of androgens in modulating song performance has not been previously studied, Pasch notes.

Pasch and his team—former University of Florida researchers Andreas George and Steven Phelps, now at the University of Texas at Austin, and Polly Campbell, now at the University of Arizona—also showed that female mice preferred better singers. By taking a normal mouse song and manipulating it electronically to pack in more notes per second, the authors created a song they predicted would appeal to females more than the song at normal speed.

They then isolated female mice in a two-way test chamber, where a speaker at one end played the normal song and the other played the enhanced song with the higher trill rate.

“We found that females approached more quickly and spent more time near the speaker playing the faster trill,” Pasch says. “This suggests that females have the capacity to distinguish slight variations in male motor performance and use that information to guide their behavior.”

Female preference for more difficult songs is notable, Podos says, because it has never before been documented in mammals.

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