Evolution: blue whale adaptive cardiac changes (Evolution)

by David Turell , Tuesday, November 26, 2019, 01:52 (1823 days ago) @ David Turell

It is well known from previous whale studies that the bigger whales have slower heart beats. I learned this while still a fellow in cardiology. Thsi study about a blue whale illustrates another of the intense complications a whale designer has to overcome:

https://cosmosmagazine.com/biology/scientists-record-a-blue-whale-s-heartbeat?utm_sourc...

"Scientists have recorded the heart rate of a blue whale (Balaenoptera musculus) in the wild and found considerable extremes in how fast it beats.

"When the whale dove for food, its heart rate dropped as low as two beats per minute, but back at the water’s surface it sped up to nearly 40.

"This suggests it is working at its limit, write Jeremy Goldbogen, from Stanford University,

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"And it could explain why the world’s largest animal – with a heart weighing as much as a car – doesn’t get any bigger. Its heart wouldn’t be able to sustain higher energy needs.

"Body size is intimately related to physiological functions, an observation known as allometry.

"The quest to understand this has led researchers like Goldbogen and colleagues to explore the limits of body mass.

“From the smallest shrews to the largest whales, physiological performance at the extremes may shed light on constraints to body size,” they write.

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"Once they managed to decipher the data, the researchers found the lowest rate averaged four to eight beats per minute, up to 50% lower than predicted. The upper rate averaged 25 to 37 beats, nearly outpacing predictions.

"When blue whales dive for krill, their main food source, their heart slows down to lower the rate of oxygen store depletion as well as its own oxygen needs.

"Goldbogen and colleagues found that the extremely low rate at the bottom of the dive increased by 2.5-fold as the whale powerfully ascended in a feeding lunge, then gradually decreased while it glided to filter the water out from the catch.

"It rose to near maximum capacity when the whale resurfaced to replenish its oxygen stores.
The researchers think this explains why the whale’s heart has a high yielding, stretchy aortic arch, to accommodate blood pumped out by the heart and keep it flowing between beats."

Comment: This is a huge whale. So a huge heart is required. But the circulatory changes in heart rate are vital to this animal's life style. Note the amazingly different aortic arch construction. What is also amazing is that they grew to this size from smaller whales to become the largest animal ever on the planet. Since there are eight to nine stages in whale development from land animals, how did this happen? Those eight to nine stages are fossil gaps. Each larger size required more and more cardiac and circulatory changes. We know humans can adapt to a small degree to deep diving. I presented studies here. Only design can do this. By the way the article notes heart rate is related to body size. A hummingbird's heart can reach 1,000 per minute!