'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.

A landslide is imminent and so is its tsunami

An open letter predicts that a massive wall of rock is about to plunge into Barry Arm Fjord in Alaska.

Image source: Christian Zimmerman/USGS/Big Think
Surprising Science
  • A remote area visited by tourists and cruises, and home to fishing villages, is about to be visited by a devastating tsunami.
  • A wall of rock exposed by a receding glacier is about crash into the waters below.
  • Glaciers hold such areas together — and when they're gone, bad stuff can be left behind.

The Barry Glacier gives its name to Alaska's Barry Arm Fjord, and a new open letter forecasts trouble ahead.

Thanks to global warming, the glacier has been retreating, so far removing two-thirds of its support for a steep mile-long slope, or scarp, containing perhaps 500 million cubic meters of material. (Think the Hoover Dam times several hundred.) The slope has been moving slowly since 1957, but scientists say it's become an avalanche waiting to happen, maybe within the next year, and likely within 20. When it does come crashing down into the fjord, it could set in motion a frightening tsunami overwhelming the fjord's normally peaceful waters .

"It could happen anytime, but the risk just goes way up as this glacier recedes," says hydrologist Anna Liljedahl of Woods Hole, one of the signatories to the letter.

The Barry Arm Fjord

Camping on the fjord's Black Sand Beach

Image source: Matt Zimmerman

The Barry Arm Fjord is a stretch of water between the Harriman Fjord and the Port Wills Fjord, located at the northwest corner of the well-known Prince William Sound. It's a beautiful area, home to a few hundred people supporting the local fishing industry, and it's also a popular destination for tourists — its Black Sand Beach is one of Alaska's most scenic — and cruise ships.

Not Alaska’s first watery rodeo, but likely the biggest

Image source: whrc.org

There have been at least two similar events in the state's recent history, though not on such a massive scale. On July 9, 1958, an earthquake nearby caused 40 million cubic yards of rock to suddenly slide 2,000 feet down into Lituya Bay, producing a tsunami whose peak waves reportedly reached 1,720 feet in height. By the time the wall of water reached the mouth of the bay, it was still 75 feet high. At Taan Fjord in 2015, a landslide caused a tsunami that crested at 600 feet. Both of these events thankfully occurred in sparsely populated areas, so few fatalities occurred.

The Barry Arm event will be larger than either of these by far.

"This is an enormous slope — the mass that could fail weighs over a billion tonnes," said geologist Dave Petley, speaking to Earther. "The internal structure of that rock mass, which will determine whether it collapses, is very complex. At the moment we don't know enough about it to be able to forecast its future behavior."

Outside of Alaska, on the west coast of Greenland, a landslide-produced tsunami towered 300 feet high, obliterating a fishing village in its path.

What the letter predicts for Barry Arm Fjord

Moving slowly at first...

Image source: whrc.org

"The effects would be especially severe near where the landslide enters the water at the head of Barry Arm. Additionally, areas of shallow water, or low-lying land near the shore, would be in danger even further from the source. A minor failure may not produce significant impacts beyond the inner parts of the fiord, while a complete failure could be destructive throughout Barry Arm, Harriman Fiord, and parts of Port Wells. Our initial results show complex impacts further from the landslide than Barry Arm, with over 30 foot waves in some distant bays, including Whittier."

The discovery of the impeding landslide began with an observation by the sister of geologist Hig Higman of Ground Truth, an organization in Seldovia, Alaska. Artist Valisa Higman was vacationing in the area and sent her brother some photos of worrying fractures she noticed in the slope, taken while she was on a boat cruising the fjord.

Higman confirmed his sister's hunch via available satellite imagery and, digging deeper, found that between 2009 and 2015 the slope had moved 600 feet downhill, leaving a prominent scar.

Ohio State's Chunli Dai unearthed a connection between the movement and the receding of the Barry Glacier. Comparison of the Barry Arm slope with other similar areas, combined with computer modeling of the possible resulting tsunamis, led to the publication of the group's letter.

While the full group of signatories from 14 organizations and institutions has only been working on the situation for a month, the implications were immediately clear. The signers include experts from Ohio State University, the University of Southern California, and the Anchorage and Fairbanks campuses of the University of Alaska.

Once informed of the open letter's contents, the Alaska's Department of Natural Resources immediately released a warning that "an increasingly likely landslide could generate a wave with devastating effects on fishermen and recreationalists."

How do you prepare for something like this?

Image source: whrc.org

The obvious question is what can be done to prepare for the landslide and tsunami? For one thing, there's more to understand about the upcoming event, and the researchers lay out their plan in the letter:

"To inform and refine hazard mitigation efforts, we would like to pursue several lines of investigation: Detect changes in the slope that might forewarn of a landslide, better understand what could trigger a landslide, and refine tsunami model projections. By mapping the landslide and nearby terrain, both above and below sea level, we can more accurately determine the basic physical dimensions of the landslide. This can be paired with GPS and seismic measurements made over time to see how the slope responds to changes in the glacier and to events like rainstorms and earthquakes. Field and satellite data can support near-real time hazard monitoring, while computer models of landslide and tsunami scenarios can help identify specific places that are most at risk."

In the letter, the authors reached out to those living in and visiting the area, asking, "What specific questions are most important to you?" and "What could be done to reduce the danger to people who want to visit or work in Barry Arm?" They also invited locals to let them know about any changes, including even small rock-falls and landslides.

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