New DNA-based tool shows promise to answer questions behind Cook Inlet beluga's decline
Advances in DNA technology and understanding of molecular biology may help fill an important knowledge gap about the critically endangered and declining Cook Inlet beluga population.
Currently, biologists know very little about the ages and age distribution of the Cook Inlet beluga population because the current method of dating belugas requires analyzing its teeth, which can only be collected after an animal dies.
Now, researchers have charted changes on the Cook Inlet beluga’s DNA that can be used to determine how old the animal is using only a small skin sample.
“With humans we take for granted that we know how old we are, and so when things happen in our life like reproduction or disease or even as we get older and more likely to die, all of that is associated with age and aging. But in the wild when you’re working on a population of whales for example, we don’t know how old each of those individuals are in the population. So if we want to study things like reproduction or disease or toxicology, knowing age can improve our work on all of those other topics and it can also improve our understanding of the population as a whole,” said Ellie Bors, a postdoctoral researcher at the University of Washington.
Bors’ research in the field of epigenetics looks at chemical changes attached to DNA. Specifically, Bors looked at the addition of methyl groups in a process called methylation.
“It’s just adding a chemical group to DNA. And it turns out that in mammals, that level of methylation changes predictably with age. So there was a lot of research in humans that sort of laid the groundwork for this and showed that as we age there are certain places in our genome that get more and more methylated or less and less methylated,” Bors said. “It’s not quite this nice, but let’s say I was looking at a particular place in your genome, a particular spot on your DNA. If it were 10 percent methylated you might be 10 years old. If it were 20 percent methylated you might be 20 years old.”
Bors and a team of researchers at Oregon State, UCLA and NOAA Fisheries began working to find out how to use the method to date Cook Inlet belugas in 2018. Using a collection of tissues taken from Cook Inlet belugas over the span of several years archived at a NOAA facility, Bors was able to determine how to apply epigenetic dating to the Cook Inlet beluga whale.
The development could fill a significant data gap and may help biologists understand why the population is not recovering.
“We hope it’s more accurate than our current methodology, which is aging beluga teeth,” Verena Gill, Cook Inlet beluga whale recovery coordinator for NOAA Fisheries said. “You can age belugas and all mammals by looking at the layers that they put down in teeth. The problem with that is you can’t go yanking teeth from live belugas.”
NOAA biologists are able to use a dart to collect small skin samples for biopsies without harming living whales.
“With this epigenetic methodology if you go out into the population and take biopsies, skin samples from the animals that are alive, then you get an overall idea of the age of the entire populations as opposed to the age of the animals that are dying - which is also important but it doesn’t give you the overall picture of the age of the living population out there,” Gill said.
Beluga whales do not reproduce until they are around 10 years old, and females go through menopause and continue living with the pod after their reproductive contributions are finished. Understanding the age distribution could give valuable insight into why the population continues to decline.
“You’re going to look and see that range of females say 10 to 40 years of age are important reproductive members of the population. How many of those do you have in the population? Do you have an abnormally young population or do you have an abnormally old population, and is the lack of birth the reason for their lack of recovery? Because we’re not completely clear on why they haven’t recovered,” Gill said.
Since the tool is still newly developed it has not yet been applied to determine the ages of the whales currently in the Cook Inlet beluga whale population. Researchers will collect biopsies from the animals next summer.