The physiology of an hourlong mating call

Pacific Midshipman Fish
The bottom-dwelling Pacific midshipman fish produce a mating call in which they contract and relax their muscles up to 360,000 times in 60 minutes.

Over the past few decades, Penn’s Larry Rome, a professor in the Department of Biology in the School of Arts and Sciences, has solved the mystery of how the humble toadfish sustains a mating call that lasts hours and hours with only brief pauses in between. The feat, it turns out, requires careful management of the calcium required to contract and relax muscles.

Now, Rome and colleagues have lent their expertise in understanding superfast muscle contraction to another physiological puzzle, this time investigating the Pacific midshipman fish. These bottom-dwelling creatures produce a mating call arguably more taxing than that of the toadfish: they vibrate the muscles around their swim bladder without pause for an hour, requiring them to contract and relax their muscles up to 360,000 times in 60 minutes.

The findings reveal new information about how organisms regulate and make use of calcium during muscle contraction—information that could have broader implications for other animals.

“By looking at a specialized case, we can see mechanisms that might apply more broadly,” Rome says.

For nearly 30 years, Rome and colleagues have studied the Atlantic toadfish, which also vibrates its swim bladder to generate a mating call. Unlike midshipman, however, the toadfish call has regular pauses in between sounds.

Researchers weren’t sure how the midshipman could sustain their call, involving 100 contractions a second, without pause for so long. Each contraction requires the release of calcium ions from a storage vessel called the sarcoplasmic reticulum. This calcium must then be pumped back in before the next contraction can occur.

In a series of experiments with bundles of midshipman muscle fibers, Rome and colleagues found that the maximum rate of the calcium pump in midshipman was significantly lower than in toadfish.

“The trick they play is that they release tiny amounts of calcium, about one-eighth of the amount of toadfish,” Rome said. “The calcium pumps operate closer to their maximum in midshipman, which allows them to keep up with the tiny calcium releases.” 

With this new understanding in hand, Rome says he’d next like to figure out another question: How do small exchanges of calcium turn the swim bladder muscle on and off?

Originally published on .