Mutation rates in whales are much higher than expected

In a new study published in the journal Science, researchers have revealed that mutation rates in whales are much higher than previously reported, aligning more closely with those of other mammals such as humans. 

This key finding has significant implications for our understanding of evolution, adaptation, and the historical population sizes of whales before the onset of industrial whaling.

Pedigree method 

For the study, an international team of researchers led by the University of Groningen used a novel approach called the pedigree method to estimate mutation rates in wild whale populations. The method involves analyzing the genomes of parent-offspring trios to identify new mutations in the offspring. 

Although the pedigree method has been previously used in zoo animals and a few wild animals, such as a single wolf pair and their cubs, its application in wild populations has been limited. This is due to the challenges associated with obtaining tissue samples from both parents and their offspring.

Marcos Suárez-Menéndez, the study’s first author, noted, “The method has only been used on a handful of animals that are living in the wild… It is uncertain if this reflects the mutation rates in the wild where the conditions are very different.” 

Focus of the study

Nevertheless, the team successfully applied the pedigree method to whales, using skin biopsy samples collected over thirty years of collaboration.

The study’s corresponding author, Per Palsbøll, Professor of Marine Evolution and Conservation at the University of Groningen, emphasized the limitations of the traditional phylogenetic method, which relies on fossil data and DNA comparisons to estimate when species diverged and the number of mutations that have occurred since. “However, the fossil record is not that exact. And some mutations may have disappeared over time,” Palsbøll explained.

What the researchers learned 

The results showed that the mutation rates in whales are similar to the rates seen in smaller mammals such as humans, apes, and dolphins. 

“And just like in humans, most new mutations originate from the father. So, whales are very similar to us in this respect,” said Suárez-Menéndez.

The study’s findings also shed light on the number of humpback whales in the North Atlantic before commercial whaling. 

Using the newly determined mutation rates, the researchers concluded that the pre-whaling population was 86 percent lower than earlier estimates based on the phylogenetic method. 

“Our new mutation rates suggested that some 20,000 humpback whales lived in the North Atlantic before commercial whaling, in contrast to the previous estimate of 150,000,” said Palsbøll.

Moreover, the study provided insights into Peto’s paradox, an observation that the incidence of cancer does not correlate with the number of cells in an organism at the species level. 

Study implications 

The finding that whales have human-like mutation rates contradicts the hypothesis that a slower mutation rate, due to lower metabolic rates in whales, protects these large sea mammals against cancer. 

This suggests that other mechanisms, such as an increased number of copies of the p53 gene, which protects against cancer, may be at play in whales.

“Our study revealed that the mutation rate in whale mitochondrial DNA is also much higher than earlier estimates based on the phylogenetic method,” said Suárez-Menéndez. 

Long-term research projects 

This observation was made possible by using a slightly different maternal pedigree method and four decades of sighting data of humpback cow and calf pairs in the Gulf of Maine, directed by senior author Jooke Robbins at the Center for Coastal Studies.

Ultimately, the study underscores the importance of long-term ecological research projects.

“It is difficult to acquire sustained funding for these kinds of long-term ecological studies,” said Palsbøll. “However, we wouldn’t have been able to do this research without the sustained commitment and dedication of the many colleagues who recorded all the sightings and collected the samples that our study relied on.”

The research not only provides a more accurate estimate of mutation rates in whales and their pre-whaling population sizes but also challenges previous assumptions about cancer protection mechanisms in large mammals. 

Additionally, it demonstrates the feasibility of estimating mutation rates in wild animals, contributing to a broader understanding of genetics, genomics, and conservation.

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