Sockeye salmon put on a lot of miles during their short life
. From the freshwater riverbeds where they hatch and spend their first couple years, juvenile salmon travel some 4,000 miles to the ocean where they fatten up for two years before turning around and retracing their steps.
But salmon can’t leave actual footprints, nor do they have the luxury of dropping waterproof bread crumbs so they can find their way back home. Scientists have long suspected that these big fish instead use the Earth’s magnetism to orient their inner compass. A recent study of 56 years’ worth of migration data presents pretty convincing evidence for this geomagnetic hypothesis and how it works.
Just as Vikings pillaged their way from Norway to Greenland and Iceland 1000 years ago, another group of furry raiders appears to have made a similar trek: common house mice. A new analysis of ancient and modern mouse DNA suggests that the mice in Iceland and Greenland came from Norway.
Scientists began by looking at mitochondrial DNA (mtDNA) extracted from living mice in Iceland and Greenland as well as from mouse bones found in old settlements. The ancient gene sequences were strikingly similar to those of modern mice found in UK and Norway, as well as to modern Icelandic mice, suggesting a common origin in either the UK or Norway. The low genetic diversity in Iceland, to boot, suggests recent colonization by a small number of stowaway mice. These findings have prompted speculation that mice may have arrived in the islands in Viking ships, though there is no evidence that that’s the case.
As scientists continue using human DNA to map our ancestors’ migrations, it’s neat to be reminded that there might be similar patterns of migration in species that tend to live with humans. Perhaps the bones of mice may in the future provide helpful clues for figuring out where ancient humans went and what they brought with them.
[via New Scientist]
From Ed Yong:
In 1996, a loggerhead turtle called Adelita swam across 9,000 miles from Mexico to Japan, crossing the entire Pacific on her way. Wallace J. Nichols tracked this epic journey with a satellite tag. But Adelita herself had no such technology at her disposal. How did she steer a route across two oceans to find her destination?
Nathan Putman has the answer. By testing hatchling turtles in a special tank, he has found that they can use the Earth’s magnetic field as their own Global Positioning System (GPS). By sensing the field, they can work out both their latitude and longitude and head in the right direction.
By testing turtle hatchlings in a tank surrounded by magnets he could control, Putman showed turtles could sense it if he reversed the magnetic field around them and would begin heading in the opposite direction.
For more about the experiment—and how turtles can travel so far at such high stakes with just magnetism to guide them—check out the rest of Ed’s post at Not Exactly Rocket Science.
Not Exactly Rocket Science: Foxes use the Earth’s magnetic field as a targeting system
Not Exactly Rocket Science: Robins can literally see magnetic fields, but only if their vision is sharp
80beats: Did Earth’s Magnetic Field Have a Fast Flip-Flop?
Image: Wikimedia Commons
Leatherback turtles are the wandering type, undertaking far-flung ocean migrations of thousands of miles. What scientists who follow these long-lived creatures didn’t know, though, was just how many different routes they travel, and how far they journey before returning home. These are critical pieces of information for protecting the turtles, whose numbers are dropping. So Matthew Witt says he and his international team affixed trackers to the turtles and revealed the routes of their great sea voyages:
“What we’ve shown is that there are three clear migration routes as they head back to feeding grounds after breeding in Gabon, although the numbers adopting each strategy varied each year. We don’t know what influences that choice yet, but we do know these are truly remarkable journeys.” [The Guardian]
Gabon, in West Africa, is the home base for this largest breeding group of leatherbacks—it’s where they nest and lay their eggs. Witt’s team tracked 25 female turtles, all of whom followed one of those three general routes: out to the middle of the Atlantic and then back, down the African coast to the temperate South, or even all the way across the ocean to South America.
One female was tracked making a 7,563 kilometer (4,699 mile) journey traveling in a straight line across the South Atlantic from Africa to South America, said [Witt]. At a pace of 50 kilometers a day, that trip took about 150 days of consistent swimming, he said. [AP]
When Chrysoula Gubili from the University of Aberdeen compared the DNA of white sharks from around the world, she found a big surprise. The great white is the most genetically diverse shark studied so far but the Mediterranean fish are only distantly related to nearby populations in the North-West Atlantic, or even in South Africa. Their closest kin actually live half a world away in the Indo-Pacific waters of Australia and New Zealand….
Gubili thinks that the European population was set up by a single founding female who got lost. Female great whites undergo long migrations of thousands of kilometres, but they tend to return to the place where they were born. However, it’s possible that some individuals lose the bearings on these monster treks. These navigational problems rarely amount to anything. But if the wayward female is pregnant, she might end up setting up an entirely new splinter group in a far-off corner of the world.
Not Exactly Rocket Science: Prehistoric Great White Shark Had Strongest Bite in History
80beats: In Stereo: Hammerhead Sharks Have Human-Like Vision
80beats: The Secret Lives and Loves of Great White Sharks
Image: flickr / hermanusbackpackers
You know the “out of Africa” story: how our ancestors left the savannas where humanity grew up and trekked outward to other continents. Today in Nature, however, a new study of 40 million-year-old fossils argues that an “into Africa” story predates the other narrative: that the animals that would eventually evolve into apes like us and monkeys came from Asia into Africa.
These fossil teeth found in Libya belong to early anthropoids, according to the scientists. The team found several different species in this location.
The new fossils are about 38 to 39 million years old, and none of the animals would have weighed more than 500 grams [just more than 1 pound], conclude a team led by Jean-Jacques Jaeger, a palaeontologist at the University of Poiters, France. Their diminutive size fits in with previous research suggesting that early anthropoids started small and eventually evolved ever bigger bodies. [Nature]
From Ed Yong:
On 7 August 1999, a lucky photographer snapped a female humpback whale frolicking off the east coast of Brazil. Two years later, on 21 September 2001, the same whale was caught on camera again, by a tourist on a whale-watching boat. But this time, she was a quarter of the world away, off the eastern coast of Madagascar. The two places where she was spotted are at least 9800 kilometres apart, making her voyage the longest of any mammal.
In American terms, that means the adventurous humpback had taken a trip of about 6,000 miles. Read the rest of the post–including info about how scientists are sure they were looking at the same whale both times–at Not Exactly Rocket Science.
80beats: Lady Humpback Whales Make Friends & Meet up for Summer Reunions
80beats: Cacophony in the Oceans May Confuse Whales and Drown Out Their Songs
80beats: Tiny Tern Makes World-Record 44,000-Mile Migration
80beats: Tiny Bird Backpacks Reveal the Secrets of Songbird Migration
80beats: Migrating Marine Animals May Follow Magnetic Fields to Find Their Homes
Two weeks ago we covered the dust-up between eco-groups and the government of Tanzania over the latter’s proposal to build a road through the heart of Serengeti National Park, home to the world-famous annual migrations of wildebeests, zebras, and more. Today in Nature, a group of 27 scientists chimed in on the project. Their verdict: It would be a biodiversity disaster.
Conservationists led by Princeton’s Andrew Dobson … argue the planned 2012 road would stop the yearly migration of 1.3 million wildebeests, the cornerstone species of the park, and harm other animals such as the 1.5 million zebras that yearly migrate as well. [USA Today]
Government and big business try to build a massive industrial project in a protected space. Wildlife defenders rise up to save the threatened reserve. This starkly drawn plot line sounds like the simplistic basis of a hundred Disney films, but in this case the drama is playing out for real in Tanzania.
The government of Tanzania would like to build a highway that connects the commercial activity on the country’s coastal eastern side to the inland and more remote west. That highway, however, would cut right through the plains of Serengeti National Park, and right through the annual migratory path of the millions of gazelles, zebras, and wildebeests that head from Tanzania to Kenya and provide a gorgeous visual staple for nature films.
Crocodiles like to lurk in the shallows, preparing to pounce. They are not, as a general rule, strong enough swimmers to go on extended ocean cruises whenever they feel like it. Despite this, these creatures managed to reach islands across the South Pacific. How?
A group of scientists led by Craig Franklin, and including the late “Crocodile Hunter” Steve Irwin, studied saltwater crocs from the Kennedy River area of Northeastern Australia for about a year for a study forthcoming in the Journal of Animal Ecology. The team tagged 20 animals with receivers to give both their position and body temperature.
They found that eight crocodiles undertook a total of 42 long-distance journeys of more than 10 kilometres [6.2 miles] per day. In 96% of these trips, the reptiles traveled with the current flow. In contrast, the crocodiles were equally likely to travel with and against the current flow when making short journeys [Nature].
The body temperature reading gave the scientists another way to verify this, besides matching croc travel habits to changing ocean currents. When the tide went against the crocs, they just hung out on the beach and their body temperature rose to 90 degrees F as they soaked up the sun. However, when the current became favorable and they went traveling, their temperatures descended to more like 77 degrees.