Here’s a round-up of recent science headlines we didn’t want you to miss!

Ancient Rivers

Without a smart phone or GPS device, how did early humans find their way out of Africa? A study published last week in PLoS One determines that ancient rivers, now covered by the Sahara Desert, provided habitable routes to follow.

Simulating paleoclimates in the region, the researchers found evidence of three major river systems that likely existed in North Africa 130,000–100,000 years ago, but are now largely buried by dune systems in the desert. When flowing, these rivers likely provided fertile habitats for animals and vegetation, creating “green corridors” across the region.

“It’s exciting to think that 100,000 years ago there were three huge rivers forcing their way across 1000-km of the Sahara desert to the Mediterranean—and that our ancestors could have walked alongside them,” says lead author Tom Coulthard of the University of Hull, UK.

Cosmic Beginnings?

Did life on Earth hail from Mars, as one researcher proposed last month, or comet collisions? Apparently, in both cases, it all has to do with the chemistry. Carl Zimmer, one of our favorite science writers, has a recent New York Times article about the chemistry needed to produce DNA from RNA. And while it doesn’t look like early Earth had those compounds, Mars might have.

Then, earlier this week, a study published in Nature Geoscience finds that the collision of icy comets with planetary bodies could result in the formation of complex amino acids, the building blocks of proteins (and life).

The researchers suggest that this process provides another piece to the puzzle of how life was kick-started on Earth, after a period of time between 4.5 and 3.8 billion years ago when the planet was being bombarded by comets and meteorites.

The team made their discovery by recreating the impact of a comet by firing projectiles through a large high-speed gun. This gun, located at the University of Kent, uses compressed gas to propel projectiles at speeds of 7.15 kilometers per second into targets of ice mixtures, which have a similar composition to comets. The resulting impact created amino acids such as glycine and D- and L-alanine. Sounds like a fun method of discovery…

Speaking of fun collisions, if you want more of them, the Morrison Planetarium at the Academy is featuring Cosmic Collisions in its current show rotation. From the our website:

Creative and destructive, dynamic and dazzling, collisions are a key mechanism in the evolution of the Universe.

Missing Mars Methane

One chemical Mars seems to be missing? Methane. The gas was sought as a possible sign of microbial life currently living on the seemingly barren world. However, despite earlier reports that NASA’s Mars rover, Curiosity, discovered methane on the red planet, NASA reports today in Science that none has been found.

Curiosity’s earlier evidence of methane detection turned out to be within leftover air from Earth. And previous reports of localized methane concentrations up to 45 parts per billion on Mars were based on observations from Earth and from orbit around Mars.

“It would have been exciting to find methane, but we have high confidence in our measurements,” says the report’s lead author, Chris Webster. “We measured repeatedly from Martian spring to late summer, but with no detection of methane.”

But don’t give up on microbial Martians just yet… “This important result will help direct our efforts to examine the possibility of life on Mars,” says NASA’s Michael Meyer. “It reduces the probability of current methane-producing Martian microbes, but this addresses only one type of microbial metabolism. As we know, there are many types of terrestrial microbes that don’t generate methane.”

Looking for extraterrestrial life? Next month’s Brilliant!Science festival can deliver it to you. Visit this page for more information.

Image: the Tunable Laser Spectrometer on-board Curiosity: NASA/JPL-Caltech

Studies of bears and sea lions have enabled us to understand how these mammals reserve energy in the form of fat and blubber, sustaining them through winter or allowing them to travel great distances. And they aren’t alone in facing such physical challenges. Great white sharks also need a way to store energy during their long migrations, but until recently, their specific mechanism was unknown. (Maybe no one wanted to get too close to them…)

Great white sharks migrate between foraging and reproductive areas, traveling over 2,500 miles annually. While they are not known to be picky eaters, there is little food available far out in the Pacific Ocean.

Researchers at Stanford University and the Monterey Bay Aquarium studied how great whites could accomplish such a journey while fasting. But again, because great whites are, shall we say, just a wee bit dangerous, scientists needed to find ways to study the sharks’ lives without risking their own.

“The most difficult thing about this research was finding a way to bring all of the different sources of data together into a coherent and robust story,” said Gen Del Raye, a Stanford undergraduate who initiated the project. He knew that if they succeeded, they might shed light on storage strategies for other ocean mammals.

First the team studied a (well-fed) great white shark living at the Monterey Bay Aquarium. Over time the shark gained mass (but still maintained its flattering, streamline figure) and simultaneously increased in buoyancy.

Next the researchers pulled data from shark archival tags. Shark location information is time-stamped, enabling researchers to focus on one specific behavior, “drift-diving.” Huge marine animals sometimes act like hang gliders—they relax their fins while currents and momentum carry them forward. Drift-diving data provided the final clue to the research team: they established that migrating sharks lost buoyancy over time.

By measuring the rate at which sharks sink during drift dives, the researchers were able to estimate the amount of oil in the animals’ livers, which accounts for up to a quarter of their body weight. Sharks store oil before migration (making them float) then gradually use that energy throughout their journey (making them sink).

“Sharks face an interesting dilemma,” said Sal Jorgensen, a research scientist at the Monterey Bay Aquarium. “They carry a huge store of energy in the form of oil in their massive livers, but they also depend on that volume of oil for buoyancy. So, if they draw on those reserves, they become heavier and heavier.”

The new research paper might not only be used to help solve mysteries about other marine animals, but can also be used to assist conservation efforts around coastal feeding grounds.

“We have a glimpse now of how white sharks come in from nutrient-poor areas offshore, feed where elephant seal populations are expanding—much like going to an Outback Steakhouse—and store the energy in their livers so they can move offshore again,” said researcher Barbara Block, a professor of marine sciences and a senior fellow at the Stanford Woods Institute for the Environment. “It helps us understand how important their near-shore habitats are as fueling stations for their entire life history.”

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: Pterantula (Terry Goss)/Wikipedia

Each fall, monarch butterflies east of the Rockies make the long migration to their overwintering site in Mexico. Scientists have exposed the internal rhythms that tell the butterflies where to go, despite the fact that the site was last visited by their great-grandparents. But how do the butterflies know when it’s time to leave Mexico and head north again?

Researchers at the University of Massachusetts suspected that temperature or daylight had something to do with it, so they collected wild monarchs at the start of their southward fall migration, brought them into the lab, and divided them into three groups. Two of the groups were exposed to the same cooler temperatures they would experience in their overwintering ground in Mexico. In addition, one of these two was also exposed to the same changing light levels they would experience south of the border. For the third group, the temperature remained warm and light levels never changed.

When placed into a flight simulator 24 days later, the first two groups of monarchs began flying northward. The third group, not exposed to cooler temperatures, continued flying southward.

If temperature alone determines when the butterflies start their northward migration, scientists raise concerns about the effects climate change will have on these beauties. “Without this thermal stimulus, the annual migration cycle would be broken, and we could lose one of the most intriguing biological phenomena in the world,” says Steven Reppert. His study, coauthored with Patrick Guerra, appeared last month in Current Biology.

Sadly, on the heels of that study comes a report issued last week on the decline of monarch numbers in Mexico this past winter. The study blames drought in the American southwest and an increase in soy and corn farming. Both are responsible for a loss in the milkweed plants the butterflies rely on for food during their long migrations.

“If people want to help,” says Craig Wilson of Texas A&M University, “they can pick up some milkweed plants right now at local farmer’s cooperative stores and this would no doubt be a big boost to help in their migration journey. It is important to have a national priority of planting milkweed to assure there will be monarchs in the future. If we could get several states to collaborate, we might be able to provide a ‘feeding’ corridor right up to Canada for the monarchs.”

Image: Kenneth Dwain Harrelson/Wikipedia

For years, researchers have suspected that the salmon use the Earth’s magnetic field to get back home, but scientists found little evidence to support this theory. Until now…

Researchers, reporting last week in Current Biology, took 56 years worth of data of salmon migration to and from the Fraser River in British Columbia. They then compared migration routes to the intensity of Earth’s magnetic field at pivotal locations in the salmons’ migratory routes.

See, Earth has a magnetic field at its surface that weakens with proximity to the equator and distance from the poles and gradually changes on a yearly basis. Therefore, the intensity of the magnet field in any particular location is unique and differs slightly from year to year.

The trick for these Fraser River salmon is that to get to the open ocean and back they need to navigate around Vancouver Island. The sockeye can travel north via the Queen Charlotte Strait or from the south via the Juan de Fuca Strait.

The researchers discovered that the intensity of the magnetic field largely predicted which route the salmon used to detour around Vancouver Island; in any given year, the salmon were more likely to take whichever route had a magnetic signature that most closely matched that of the Fraser River years before, when the salmon initially swam from the river into the Pacific Ocean. (See image, above right.)

“These results are consistent with the idea that juvenile salmon imprint on (i.e. learn and remember) the magnetic signature of their home river, and then seek that same magnetic signature during their spawning migration,” says Nathan Putman, a post-doctoral researcher at Oregon State University and the lead author of the study.

Other factors, in addition to Earth’s magnetism, also influence the route, Putman says. Once the salmon reach their home river, they probably use their sense of smell to find the particular tributary in which they were born.

Because salmon populations are so important to Northwest economies, the authors hope this study will aid in forecasting fish movement for better fisheries management and conservation.

Image courtesy of Nathan F. Putman et al.

Gourma elephants (Loxodonta africana) living near Timbuktu, Mali, make an epic journey each year in their quest for food and water. Researchers at Oxford University and the University of British Columbia found that the elephants travel across an area of 32,000 square kilometers (more than 12,000 square miles!) in the desert, marking the largest known elephant range in the world.

The animals’ extreme journey is a product of their tough life. The northernmost population of elephants in the world, wandering over a much larger range than their relatives, they frequently endure sand storms, water shortages, and temperatures over 50 degrees Celsius.

“It’s incredible these elephants have survived. They have a truly stressful life with the lack of water and food, and their giant range reflects that,” says lead researcher Jake Wall of the University of British Columbia and the conservation organization Save The Elephants.

Wall and his colleagues attached GPS collars to nine elephants in the Gourma region in Africa in March 2008 and tracked them over the next two years. In a paper published this month in the journal Biological Conservation they report that the elephants migrate south over a large path that extends into northern Burkina-Faso in West Africa.

The Gourma elephants don’t necessarily travel farther than their East and Southern African cousins, but their movements are spread out over an area 150 percent bigger than those reported in Namibia and 29 percent larger than those in Botswana, the researchers said. Interestingly, scientists also found that males and females often take different routes. In fact, they only share about a quarter of their ranges.

“We think the difference is partly because of their tolerances towards people. Bulls generally take more risks and occupy areas that have higher human densities,” explains Wall. “They also have varying food strategies, and we think that differences in the areas they occupy might be because of different vegetation types in those areas.”

Gourma elephants have been able to beat climate change induced heat and drought in their environment and have historically enjoyed relatively peaceful coexistence with the local Touareg, Fuhlani and Dogon peoples. However researchers warn that the elephants may currently be threatened by political violence in Mali and expanding human settlements.

Currently the Gourma population has an estimated 350 elephants. To prevent extinction of this species, scientists have identified 10 hotspots essential for the survival of these animals. “These elephant hot-spots should be considered conservation priorities,” Wall urges.

Zuberoa Marcos is a former biologist and current science writer based in Barcelona. She writes articles regularly for Science Today.

Un viaje de récord por el desierto

Por Zuberoa Marcos

Los elefantes Gourma (Loxodonta africana) que viven cerca de Tombuctú, Malí, realizan un viaje épico cada año en busca de comida y agua. Investigadores de las universidades de Oxford y British Columbia en Canadá han descubierto que viajan a través de un área de 32,000 kilómetros cuadrados por el desierto, el área de distribución más grande de elefantes conocida en el mundo.

Este viaje extremo es consecuencia de sus duras condiciones de vida. Los Gourma constituyen la población más septentrional de elefantes en el mundo y con frecuencia tienen que soportar tormentas de arena, escasez de agua y temperaturas por encima de 50 grados centígrados.

“Es increíble que estos elefantes hayan sobrevivido. Tienen una vida verdaderamente estresante con la falta de agua y alimentos y su área de distribución gigantesca así lo demuestra”, dijo Jake Wall investigador principal del estudio de la Universidad British Columbia y miembro de la organización de conservación Save the Elephants.

Wall y su equipo colocaron collares con GPS a nueve elefantes en la región africana de Gourma en marzo de 2008 y, después, siguieron sus pasos durante los siguientes dos años. En un artículo publicado este mes en la revista Biological Conservation explican que los elefantes migran hacia el sur a través de un sendero de gran longitud que se extiende hacia el norte de Burkina-Faso en el África Occidental.

Los elefantes de Gourma no hacen viajes más largos que sus primos del Este y del Sur de África, pero sus desplazamientos se extienden sobre un área un 150% mayor que la de los elefantes que viven en Namibia y 29% superior que los que hacen en Botswana. Curiosamente, los investigadores también observaron que los machos y las hembras suelen tomar rutas diferentes. De hecho, sólo comparten una cuarta parte de su área de distribución.

“Creemos que la diferencia se debe en parte a su tolerancia hacia las personas. Los machos generalmente toman más riesgos y ocupan las zonas que tienen mayor densidad humana”, dijo Wall. “Ellos también tienen distintas estrategias alimentarias y creemos que las diferencias en las áreas que ocupan pueden ser debidas a diferentes tipos de vegetación en esas regiones”.

Los elefantes de Gourma han sido capaces de superar el calor y la sequía de su entorno inducidas por el cambio climático y han disfrutado históricamente de una convivencia pacífica con los pueblos locales como los Touareg, los Fuhlani y los Dogon. Sin embargo, los investigadores advierten que, hoy en día, la supervivencia de estos animales está amenazada por la violencia política en Malí y por la expansión de los asentamientos humanos.

Actualmente, se calcula que la población Gourma está formada por unos 350 elefantes. Para evitar su extinción, los científicos han identificado 10 sitios esenciales para la supervivencia de estos animales. Wall insta a que estos lugares sean considerados como prioridades para la conservación de los Gourma.

Zuberoa Marcos es una bióloga retirada y actualmente trabaja como escritora científica desde Barcelona. Escribe de forma regular para Science Today.

Image: Chyulu Smith/Save the Elephants

These particular butterflies have never visited the site in Michoacan before—in fact, their grandparents were likely the last generation there—but somehow the orange and black beauties know exactly where to go.

Circadian clocks in the monarchs’ antennae and brain direct the butterflies in their migration, but researchers at UMass Medical Center wanted to dive deeper. “There must be a genetic program underlying the butterflies’ migratory behavior. We want to know what that program is, and how it works,” explains Steven M. Reppert, MD, chair of neurobiology.

So he and his colleagues sequenced the monarch’s genome. Nature’s newsblog reports:

The 273-million basepair genome is the first of any butterfly and is considerably smaller than—and quite different from—that of the commercial silk moth (Bombyx mori), which has 432 million basepairs, suggesting rapid evolution in the Lepidoptera group, which includes both butterflies and moths.

The entire study is published in a recent edition of the journal Cell.

Within those 273 million basepairs, an estimated set of 16,866 protein-coding genes, comprising several gene families, are likely involved in major aspects of the monarch’s seasonal migration, according to the UMass researchers. These genes influence all of the monarchs’ senses in order to navigate: visual input gathers clues from the sun; monarch-specific expansions of odorant receptors exist for long-distance migration; a full repertoire of molecular components exist solely to support the monarch circadian clock; additional molecular signatures orient flight behavior; and a variant of the sodium/potassium pump underlies a valuable chemical defense mechanism to fend off predators during the migration.

“Dissecting the genetic basis of long-distance migration in the monarch may help us understand these mechanisms not only in monarchs but more generally in other migrants, including migratory birds and sea turtles,” Reppert says.

Image: Sonia Carolina Madrigal Loyola/Wikipedia

A new study, published online today in the journal Science, only adds to the conundrum. From the New York Times:

“This is a huge milestone, but unfortunately it raises more questions than it answers,” said Jeffrey Rose, an archaeologist at the University of Birmingham in England.

The study is based on several stone tools found in the United Arab Emirates. The tools date to around 125,000 years ago.  They are similar to those found  belonging to humans in East Africa. In addition, the area is beyond the known boundaries of Neanderthals. Did these tools belong to modern humans? Were Homo sapiens in Arabia that long ago?

The authors of the study propose that the conditions may have favorable for leaving Africa for the peninsula during this time. From Brian Switek’s blog in Wired:

Lower sea levels may have opened a path, and increased rainfall would have made the Jebel Faya area [in the UAE] less arid than it is today.

No remains were found in the area, so the tool-users cannot be definitively confirmed. And theories of human migration always spark debate. Scientists in varying articles regarding the publication call the study “provocative”, an “audacious claim” and find “not a scrap of evidence” indicating the tools belonged to modern humans. Perhaps Alison Brooks, an archaeologist at George Washington University, puts it best on NPR:

Certainly it’s a very intriguing find, and it should hopefully spur research in all kinds of places and directions that haven’t been undertaken before.

Image: Science /AAAS

But it’s what they do in the water might surprise you. They dive to extraordinary depths for feeding – down to between 1000 and 2600 feet! During their migrations in the Pacific, they will travel the open ocean for several months at a time. According to Dan Costa, Professor of Ecology and Evolutionary Biology at UC Santa Cruz and supervisor of elephant seal research at Año Nuevo, one migration (after they wean their pups) lasts two to three months and the other (after they molt) lasts seven months.

This fact has long puzzled researchers.  How do elephant seals rest while migrating at sea for such long periods of time?

Dr. Costa and other researchers believe they have found the answer to this question, and they published their theory in the April 23^rd issue of Biology Letters.

According to the paper, northern elephant seals rest as they perform drift dives, which resemble a type of scuba diving and allow the seal to drift with the currents.  “We found that seals rolled over and sank on their backs during the drift phase, wobbling periodically so that they resembled a falling leaf… this allows them time to rest, process food or possibly sleep during the descent phase of these dives where they are probably less susceptible to predation.”

These drift dives are slower than their other dives. On average, they may last 25 minutes and reach about 1400 feet below sea level. How often are they making these dives? “Mostly they do it more after a series of feeding dives. A few times a day if things are going well,” according to Dr. Costa via email.

Sounds a little like siestas or catnaps, doesn’t it? Making me sleepy… Yawn.

Creative Commons image by Mike Baird