Although Mars is quite dry and inhospitable today, our rovers continue to search for evidence of a past Mars that could have sustained life. A recent study suggests that, at least in Gale Crater, the opportunities for life to flourish may have been short-lived. In particular, the team looked at carbonates found by the Curiosity rover. These minerals contain varying amounts of carbon and oxygen isotopes that can hint at the conditions the carbonates formed under. The team found a high proportion of heavier isotopes, which suggest one of two possible formation paths. In the first, Gale Crater underwent wet-dry cycles that alternated between more- and less-habitable conditions for life. The second possibility is a cryogenic past, where most of the local water was locked in ice, and life would have had to survive — if possible — in small pockets of extremely salty water. Neither possibility is a great one for the kinds of life we’re accustomed to. (Image credit: NASA; research credit: D. Burtt et al.; via Gizmodo)
Tag: biology
“Last Breath of Autumn”
On a rainy autumn day, Agorastos Papatsanis headed to the forest in search of fungi. There he captured this fairytale-like scene with falling rain and drifting spores. Near the forest floor, any breeze is slight, so mushrooms use their own humidity to move air and spread their spores. As water evaporates from the mushroom’s cap, it cools the air nearby, causing it to spread outward. Since that water vapor is lighter than air, it rises, too, carrying the mushroom’s spores along with it. (Image credit: A. Papatsanis; via Wildlife PotY)
“Immersion”
Some seabirds, including gannets and boobies, feed by plunge diving. From high in the air, they fold their wings and dive like darts into the water, impacting at speeds around 24 m/s to help them reach the depths where their prey swim. With their narrow beaks and necks, the critical moments in this feat come when the bird’s head is submerged but its body remains out of the water. At this point, the bird’s head is decelerating quickly and its body is still moving at full speed; if the neck cannot withstand this combination of forces, it will buckle.
But plunge divers, it turns out, have a secret weapon that helps them handle impact: their head shape. A study of water entry dynamics using 3D-printed models of birds’ heads found that plunge divers have a shape that increases the amount of time it takes to enter the water. The impact forces stretch out over that longer period of contact, which also stretches out the time it takes for the bird to reach its maximum deceleration. The end result? That extended contact time protects birds from unsafe levels of deceleration, just like a crumple-zone in a crashing car keeps its occupants from experiencing the worst decelerations. (Image credit: K. Zhou/BPOTY; research credit: S. Sharker et al.; via Colossal)
Swimming With Cilia
Like most microswimmers, these Synura uvella algae use cilia to swim. Cilia are tiny, hair-like appendages that flap to produce thrust. Even under a microscope, the cilia are hard to see because they are so thin and move quickly in and out of the microscope’s narrow focus. A cilia’s stroke is always asymmetric — no simple back-and-forth motions for them — because, at the algae’s scale, symmetric motion won’t move you anywhere. This is a peculiar feature of small swimmers in viscous fluids. At the human scale, we can mimic the same physics by mixing and unmixing fluids like corn syrup. (Video and image credit: L. Cesteros; via Nikon Small World in Motion)
Synura uvella algae swimming under magnification. 
Pterosaur Tail Vanes
Among vertebrates, pterosaurs were the first to achieve powered flight. Early pterosaurs have tail vanes — similar in appearance to the frills seen on some lizards — but later species lost this feature. Whether the tail vanes helped in flight or served a display purpose is an open question among paleontologists. One group, in a recent pre-print, studied the vanes’ fossilized interior structure and found a cross-linked lattice that provided internal tension to the vanes. That means the vanes could potentially be held stiff, even in the face of aerodynamic forces that would cause untensioned surfaces to flutter. The result suggests that the tail vanes could have helped early fliers steer, even if evolution later moved that function (along with display) to other parts of the body. (Image credit: Sviatoslav-SciFi; research credit: N. Jagielska et al.; via jshoer)
Catching Krill With Bubble Nets
On their own and in groups, some humpback whales enclose their prey in bubbly columns before feeding. The whales build these bubble nets intentionally, swimming in a ring at a constant speed while producing bursts of air from their blowhole. After observing hundreds of bubble nets created by dozens of whales, researchers concluded that whales actively tune the nets, using more rings, closer bubble spacing, or deeper extents to suit their needs. Once they’ve completed the net, whales lunge up through the center, mouth open, collecting their food.
In their study, the team found that building bubble nets is no more energy intensive for whales than typical lunge-feeding. However, the prey concentration in a bubble net means that hunting there nabs more food per lunge. The authors argue that the way humpback whales build and use bubble nets qualifies them as tool users on par with many fellow mammals, as well as some birds, fish, and insects. (Image credit: C. Le Duc; research credit: A. Szabo et al.; via Gizmodo)
Synchronizing Cilia
Just like human swimmers, microswimmers have to coordinate their motion to swim. But unlike humans, swimmers like the freshwater alga Chlamydomonas reinhardtii doesn’t have a brain to help it synchronize its cilia. To investigate how these microswimmers manage their stroke, researchers built a biorobot with mechanically linked segments that mimic the alga’s swimming once a motor sets the robot vibrating.
When the robot’s base is allowed to rotate, the cilia synchronize in the freestyle-like R-mode. When allowed to move along an axis, the biorobot’s cilia synchronize in the X-mode, which resembles the breaststroke. The researchers found two strokes that mirrored the real-life alga. In one, allowing the robot’s base to rotate produced a freestyle-like stroke they called R-mode. The other came from allowing the robot’s base to move forward and backward, which created a breaststroke-like X-mode. In the wild, only the X-mode provides helpful motion, but, oddly enough, the researchers found this mode was the most energy intensive. (Image credit: top – J. Larson, others – Y. Xia et al.; research credit: Y. Xia et al.; via APS Physics)
“Plants That Explode”
We often think of plants as passive and stationary, but the truth is that some plants move faster than we can even see. In this “True Facts” video, Ze Frank takes a look at a whole host of fast-moving plants, including horsetail plant spores that walk and jump, trebuchet-like bunchberry dogwood, vortex-ring-shooting moss, and moisture-driven self-digging seeds. These plants all use clever mechanisms that leverage water to spread the plant’s reproductive material at little to no energy cost to the plant itself. (Video and image credit: Z. Frank)
“The Art of Flying”
Like schools of fish, starlings gather in massive undulating crowds. Known as murmurations, these gatherings are a type of collective motion. Scientists often try to mimic these groups through simulations and lab experiments where individuals in a swarm obey simple rules that depend only on observing their neighbors. It requires very little, it turns out, to form swarms that move in this beautiful manner! (Video and image credit: J. van IJken; via Colossal)
Saving Energy By Following a Leader
Scientists have long suspected that birds save energy by following a leader — think of the V-shaped flight formation used by geese — but a new study captures that savings directly. The team studied starlings, flying singly or in groups of two or three, in a special wind tunnel. Each bird wore a tiny backpack with sensors and lights that captured its motion and helped researchers identify it individually in videos. And, using before and after metabolic measurements, the researchers could pin down exactly how much energy each bird used when flying.
They found that birds who spent most of the flight in a “follower” position used up to 25% less energy than they did when flying solo. That’s a major incentive to follow someone else. Interestingly, they also found that the most efficient solo fliers were the birds most likely to take on the “leader” position. The team notes that these “leaders” tend to use a lower wing-flapping frequency, but a full explanation of how they save energy will require a follow-up study. (Image credit: R. Gissler and S. Hao; research credit: S. Friman et al.; via Physics World)
