'Squeaky Curtain' divides Europe’s Eastern and Western mice

Two house mouse subspecies meet again in a hybrid zone strangely reminiscent of the Iron Curtain

Europe's two main house mouse areas. West: M.m. domesticus, east: M.m. musculus

If you're a mouse, Europe is still divided in two, along a divide strangely reminiscent of the Iron Curtain

Image source: Macholán, M., Baird, S.J., Munclinger, P. et al. Genetic conflict outweighs heterogametic incompatibility in the mouse hybrid zone?. BMC Evol Biol 8, 271 (2008) doi:10.1186/1471-2148-8-271
  • The house mouse diverged into two subspecies depending on which humans they followed.
  • The Western and Eastern European house mice can interbreed, but the results are, well, mixed.
  • The continent remains divided between Eastern and Western mice except for a narrow contact zone where hybrids eek out a living.

musculus v. domesticus

Smaller and darker than its western counterpart: an Eastern European house mouse

Image source: George Shuklin, CC BY-SA 1.0

It's been 30 years since the fall of the Berlin Wall, and the Iron Curtain is now a distant and dimming memory. But that's only true if you're a human. In the mouse world, Europe is still divided into East and West. As this map shows, the line that separates both halves of the continent is strangely similar to the Cold War frontier between capitalism and communism.

The "Squeaky Curtain" starts at the Baltic Sea, cutting through Denmark, Germany, and Austria before almost making it to the Adriatic. Instead, the line shadows the formerly Yugoslav coast before swerving east, keeping the southern Balkans in "the West," finally diving into the Black Sea.

West of the line lives the Mus musculus domesticus, the Western European house mouse. To the East roams the Mus musculus musculus, the Eastern European house mouse. On average, the Eastern mouse is smaller and browner, the Western one generally a bit sturdier and usually grey. Both subspecies branched from the same ancestor, some 500,000 years ago in Asia.

What ultimately separated house mice into these two subspecies are the humans they chose to follow. The ones moving through Asia's interior via Russia toward Eastern Europe turned into Eastern European house mice. The ones aiming for the Mediterranean, hitchhiking on ships to reach Western Europe (and eventually also the Americas and Australia) became Western European house mice.

Baltic to Black Seas

The 'Squeaky Curtain', dividing Europe from the Baltic to the Black Seas in two zones, for Western and Eastern house mice.

The 'Squeaky Curtain', dividing Europe from the Baltic to the Black Seas in two zones, for Western and Eastern house mice.

Image source: Macholán, M., Baird, S.J., Munclinger, P. et al. Genetic conflict outweighs heterogametic incompatibility in the mouse hybrid zone?. BMC Evol Biol 8, 271 (2008) doi:10.1186/1471-2148-8-271

When the two subspecies met up again in Europe, is unclear. "It has been suggested that source populations first met in the southern region of the current hybrid zone, and only more recently in Central and Northern Europe, with progressive contact from south to north similar to a zipper being pulled up through Europe," write the authors of Genetic conflict outweighs heterogametic incompatibility in the mouse hybrid zone?, a scientific paper that examines interbreeding between Western and Eastern European house mice (and the origin of this map).

"Progressive contact" isn't necessarily a euphemism for doing the dance with two tails. The long genetic separation means the subspecies have drifted far apart. While males of either subspecies generally don't care whom they mate with, females prefer the company of males of the same subspecies. That limits interbreeding. And hybrid couples usually produce fewer offspring than "pure" Eastern or Western ones. Both factors help explain why interbreeding only occurs in a relatively narrow and stable hybrid zone no more than 10 to 20 km wide.

The reduced capacity for interbreeding may be an indication that the two subspecies are in the process of becoming two separate species, entirely unable to interbreed. Only at the centre of the hybrid zone do hybrid mice occur in significant numbers relative to their Eastern and Western forebears. But not everything is gloomy for the hybrids: they're more resistant to parasite-borne diseases than both Eastern and Western European house mice.

Now you know.

Strange Maps #1000

Map taken from open-access article by Macholán, M., Baird, S.J., Munclinger, P. et al. Genetic conflict outweighs heterogametic incompatibility in the mouse hybrid zone?. BMC Evol Biol 8, 271 (2008) doi:10.1186/1471-2148-8-271

Got a strange map? Let me know at strangemaps@gmail.com.

This is what aliens would 'hear' if they flew by Earth

A Mercury-bound spacecraft's noisy flyby of our home planet.

Image source: sdecoret on Shutterstock/ESA/Big Think
Surprising Science
  • There is no sound in space, but if there was, this is what it might sound like passing by Earth.
  • A spacecraft bound for Mercury recorded data while swinging around our planet, and that data was converted into sound.
  • Yes, in space no one can hear you scream, but this is still some chill stuff.

First off, let's be clear what we mean by "hear" here. (Here, here!)

Sound, as we know it, requires air. What our ears capture is actually oscillating waves of fluctuating air pressure. Cilia, fibers in our ears, respond to these fluctuations by firing off corresponding clusters of tones at different pitches to our brains. This is what we perceive as sound.

All of which is to say, sound requires air, and space is notoriously void of that. So, in terms of human-perceivable sound, it's silent out there. Nonetheless, there can be cyclical events in space — such as oscillating values in streams of captured data — that can be mapped to pitches, and thus made audible.


Image source: European Space Agency

The European Space Agency's BepiColombo spacecraft took off from Kourou, French Guyana on October 20, 2019, on its way to Mercury. To reduce its speed for the proper trajectory to Mercury, BepiColombo executed a "gravity-assist flyby," slinging itself around the Earth before leaving home. Over the course of its 34-minute flyby, its two data recorders captured five data sets that Italy's National Institute for Astrophysics (INAF) enhanced and converted into sound waves.

Into and out of Earth's shadow

In April, BepiColombo began its closest approach to Earth, ranging from 256,393 kilometers (159,315 miles) to 129,488 kilometers (80,460 miles) away. The audio above starts as BepiColombo begins to sneak into the Earth's shadow facing away from the sun.

The data was captured by BepiColombo's Italian Spring Accelerometer (ISA) instrument. Says Carmelo Magnafico of the ISA team, "When the spacecraft enters the shadow and the force of the Sun disappears, we can hear a slight vibration. The solar panels, previously flexed by the Sun, then find a new balance. Upon exiting the shadow, we can hear the effect again."

In addition to making for some cool sounds, the phenomenon allowed the ISA team to confirm just how sensitive their instrument is. "This is an extraordinary situation," says Carmelo. "Since we started the cruise, we have only been in direct sunshine, so we did not have the possibility to check effectively whether our instrument is measuring the variations of the force of the sunlight."

When the craft arrives at Mercury, the ISA will be tasked with studying the planets gravity.

Magentosphere melody

The second clip is derived from data captured by BepiColombo's MPO-MAG magnetometer, AKA MERMAG, as the craft traveled through Earth's magnetosphere, the area surrounding the planet that's determined by the its magnetic field.

BepiColombo eventually entered the hellish mangentosheath, the region battered by cosmic plasma from the sun before the craft passed into the relatively peaceful magentopause that marks the transition between the magnetosphere and Earth's own magnetic field.

MERMAG will map Mercury's magnetosphere, as well as the magnetic state of the planet's interior. As a secondary objective, it will assess the interaction of the solar wind, Mercury's magnetic field, and the planet, analyzing the dynamics of the magnetosphere and its interaction with Mercury.

Recording session over, BepiColombo is now slipping through space silently with its arrival at Mercury planned for 2025.

Learn the Netflix model of high-performing teams

Erin Meyer explains the keeper test and how it can make or break a team.

  • There are numerous strategies for building and maintaining a high-performing team, but unfortunately they are not plug-and-play. What works for some companies will not necessarily work for others. Erin Meyer, co-author of No Rules Rules: Netflix and the Culture of Reinvention, shares one alternative employed by one of the largest tech and media services companies in the world.
  • Instead of the 'Rank and Yank' method once used by GE, Meyer explains how Netflix managers use the 'keeper test' to determine if employees are crucial pieces of the larger team and are worth fighting to keep.
  • "An individual performance problem is a systemic problem that impacts the entire team," she says. This is a valuable lesson that could determine whether the team fails or whether an organization advances to the next level.
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Photo by Martin Adams on Unsplash
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