‘Holy grail’ of naked mole-rat research reveals how queens rule

**Katrina Clark** (0:24)
Welcome back to the Nature Podcast. This time, how a naked mole rat queen maintains dominance.

**Nick Patrick Howe** (0:30)
And the science of how people approach board games. I'm Nick Patrick Howe.

**Katrina Clark** (0:35)
And I'm Katrina Clark. First up on the show this week, reporter Shamini Bundell has been finding out about how a special odor helps keep a naked mole rat queen on her throne.

**Shamini Bundell** (0:56)
Naked mole rats are very unusual creatures. They're neither moles nor rats, but these burrowing rodents do have a number of features that make them stand out among mammals.
They're hairless, wrinkly and almost blind. They're extremely resistant to getting cancer. They live for an extraordinarily long time. They're essentially cold-blooded. The list goes on.
But for Melissa Holmes, and you're a scientist who's worked with naked mole rats for 20 years, there's one feature that's really fascinating.

**Melissa Holmes** (1:25)
For me, it's always been about their social behaviour.

**Shamini Bundell** (1:28)
Their social structure is one of the naked mole rats' strangest features, and it's unique amongst mammals.

**Melissa Holmes** (1:34)
Within the group, there's a reproductive female, and we call her the queen. The queen is the only female who is reproductively active. She has her breeding male, and all other individuals within the colony don't reproduce.

**Shamini Bundell** (1:47)
While the queen produces offspring, the workers do things like forage for food, protect the colony, and care for the queen's many, many babies.
This social structure is often compared to that of social insects like honeybees. However, queen bees are raised to be queens from before they even hatch. In naked mole rat society, any female could theoretically one day become a queen.

**Melissa Holmes** (2:12)
Naked mole rat queens aren't born, they're made, or it's something that is controlled by the social environment. It tells us that there's something happening within the colony that is allowing one female to be a queen and preventing all of the other females from being that. It's not a genetic trait.

**Shamini Bundell** (2:27)
This has been the great mystery of naked mole rat research. What determines which female becomes queen, and what prevents the rest of the colony from doing the same?
In bees, other females are prevented from breeding by pheromones produced by the queens. These volatile compounds waft through the air and stop the ovaries developing in the other bees.
In rodents, pheromones are usually found in urine. So researchers looked at queen mole rat urine. They found nothing. It looked like there was no naked mole rat equivalent of bee pheromones to suppress worker reproduction. And that is where the story ended until now.

**Mohammed Khallaf** (3:07)
We keep more than 450 animals. They live in 16 different colonies. They live in a tunnel system where we give them chambers connected with tunnels to make it similar to the wild.

**Shamini Bundell** (3:19)
This is Mohammed Khalaf from the Max Delbruck Centre in Berlin, Germany. He's part of a team that have a paper out in Nature this week that might have cracked the mole rat mystery.
To do so, he had to collect as many odours as possible associated with mole rats, including the queens, which was easier said than done.

**Mohammed Khallaf** (3:39)
It's hard to find the queen, especially in large colonies, because they sleep on top of each other. Once I open the cage, they will all run away because they smell me.

**Shamini Bundell** (3:52)
However, Mohammed did manage to find them, and he collected samples of all the various smells coming from queens and workers from different colonies.
It turned out there was one compound that was exclusively made by Mollrack Queens, a chemical called isopropyl myristate. Here's Gary Lewin, the head of the lab, who worked with Mohammed and others on this new research to explain what it is.

**Gary Lewin** (4:15)
When you looked at the structure, it didn't look like what we think of as pheromones, right? It's a relatively simple molecule. It's a volatile. The first thing you do is you go in literature and you look up where can you find isopropyl myristate. It turns out that it's a relatively common molecule that's found in many plastics. But what was even better is that we can just buy this stuff for basically $5.
And so that's exactly what we did. And then we can start to do experiments and it was easy peasy.

**Shamini Bundell** (4:42)
Isopropyl myristate is a well-known chemical. It's found in skin creams and even head lice treatments. But what was it doing in naked mole rat colonies? Well, it turned out that this molecule was being produced by the queen and detected by the workers. Brain scans showed that it activated the areas of worker brains associated with smell. When the workers could smell the molecule, it was acting as a form of contraception, preventing females from becoming sexually active and reproducing. If a colony loses a queen, ordinarily other females fight amongst themselves to determine who will take up the mantle and begin breeding. However, when researchers added isopropyl myristate to a colony that had recently become queenless, everything stayed exceptionally peaceful.