Serenading the ladies.
Many different kinds of birds sing to attract mates, but did you know that some mice do the same thing? Male Alston’s singing mice make a high-pitched trilling noise to call out to the females, “hey, ladies, I’m here, and I’m sexy. Come and get it!” Or, at least, that’s what I imagine they’re saying.
New research headed by Bret Pasch and colleagues at the University of Florida, Gainesville has found the key ingredient for making the best male songs in these mice: testosterone. Without it, they can’t even make it past round 1 of Alston Idol. You can find the paper, published online in the journal Animal Behaviour, here.
Females prefer males that can trill faster and whose notes contain a larger range of frequencies. The authors show that there is likely a trade-off between fast singing and “frequency bandwidth“, or the range of frequencies that can be packed into a single trill. So, they hypothesized that females would prefer males who could do both well.
Why? Well, as we’ve seen before, females of many species only like males who have good skills. The idea is that males with those kind of skills must have good genes, and would therefore make good fathers.
The authors first tested whether testosterone affected singing. Previous work from this group showed that, after castration, males simply didn’t try as hard to sing, were less aggressive, and seemed to kind of suck at singing even when they did try. When they added testosterone back into some of the males, they went back to singing just as often as before castration.
In the new study, the authors asked, “what about song quality?” Sure, the males with testosterone are trying just as hard as before, but are their songs as good as they once were? It turns out that they are, so testosterone not only controls how often they sing, but also how well they sing.
The next part was to see if females really cared about how fast or complex the males’ songs were. To do this, the researchers recorded males singing and then enhanced their songs (kind of like Autotune for mice), making them both super fast and complex–the ultimate mouse song. This was done by shortening the gaps between notes in the recorded songs. The songs could then keep the wide range in frequencies in each note, but would be much faster.
They then let females listen to both the original song (the “slow” song) and the enhanced version (the “fast” song). Females were twice as likely to approach the speaker blaring out the fast song than to go near the slow song. They also moved toward the fast song, well, faster and spent more time near that speaker (<50 minutes near slow songs and >100 minutes near fast songs). Even when comparing only enhanced (fast) songs, the females spent more time near the ones with higher performance scores–those that would have been the most difficult for a real male to sing.
If you want to see some mouse songs in action, check out this video: Singing mice.
Why would females like faster songs? If testosterone really is important for making better songs, it may be that the songs are advertising the male’s fertility. Males low in testosterone are likely to be less fertile, since testosterone is necessary for making sperm.
The next great experiment would be to see if males who sing better are actually more fertile or at least more successful at sealing the deal with an interested female.
Related articles:
- What can singing mice teach us about language? (scientificamerican.com)
Filed under: Sexual selection Tagged: Female choice, Male courtship, male fertility, Scientific literature, testosterone
