For some time, scientists have suspected that sharks belong among the growing number of animals known to navigate using Earth's magnetic field. Testing anything with a shark, though, requires some care.
"The reason this question has been withstanding for 50 years is because sharks are difficult to study," says Bryan Keller of the Save Our Seas Foundation. "To be honest, I am surprised it worked."
The key was selecting the right candidate. Keller and his colleagues chose the bonnethead shark, Sphyrna tiburo, a small critter that summers at Turkey Point Shoal off the coast of the Florida State University Coastal and Marine Laboratory with which Keller is affiliated.
Bonnetheads elsewhere have been known to complete 620-mile roundtrip migrations. As the lab's Dean Grubbs puts it, "That's not bad for a shark that is only two to three feet long. The question is how do they find their way back to that same estuary year after year." There's a report of a great white shark migrating between two locations, one in South Africa and another in Australia, year after year.
The research is published in Current Biology.
Shark tank
These are the three places the bonnethead sharks were magnetically fooled into thinking they were located.Credit: Keller et al. / Current Biology
Keller and his team rounded up 20 local juvenile bonnetheads and transported them into a holding tank at the marine lab. For the tests, the researchers simulated three real-world magnetic fields. As the various magnetic fields were activated, the sharks' movements were captured by GoPro cameras and their average swimming orientations calculated by software.
The first simulation, serving as a control, mimicked the magnetic field of the nearby shoal from which the sharks had been captured. When this field was activated, the sharks essentially acted like they were "home," just swimming around as they do.
A second field was the magnetic equivalent of a location 600 kilometers south of the lab within the Gulf of Mexico. When this field was activated, the sharks, apparently mistaking themselves for being far south in the Gulf, began swimming northward toward the shoal.
The opposite occurred with a field standing in for a location in continental North America 600 km north of their home shoal — the sharks began swimming southward.
Suspicion confirmed
"For 50 years," says Keller, "scientists have hypothesized that sharks use the magnetic field as a navigational aid. This theory has been so popular because sharks, skates, and rays have been shown to be very sensitive to magnetic fields. They have also been trained to react to unique geomagnetic signatures, so we know they are capable of detecting and reacting to variation in the magnetic field."
His team's experiments confirm what's long been suspected, Keller says: "Sharks use map-like information from the geomagnetic field as a navigational aid. This ability is useful for navigation and possibly maintaining population structure."
The psychologist William James noted that consciousness did not arrive in the universe fully formed. Phenomena like perception and memory are in no way limited to our own form of consciousness, though humans often pretend we're evolution's crowning achievement. In many reckonings, all timelines end with Homo sapiens. Because of this errant belief, we've both exalted our own kind while treating other species as lesser forms on the road to our greatness.
Good science is not so egotistical. We should study other species, as evolutionary threads can be picked from their development to help us weave the story of ourselves. Such endeavors require imagination. Thomas Nagel succinctly posed the hard problem of consciousness in a 1974 essay in which he wondered aloud what it's like to be a bat, setting off decades of debate over the nature of consciousness.
We can, and arguably should, also wonder what it's like to an octopus—if we can.
Australian science philosopher Peter Godfrey-Smith argues that intelligence is not a straight line to humans, but rather evolved separately in cephalopods (such as octopuses and cuttlefish) and vertebrates, like us. Humans might ponder the hard problem of consciousness, a question that splits fans of emergent phenomena with dualists, but the bottom dweller known as the octopus has no time for such a debate. Godfrey Smith writes,
"In an octopus, the nervous system as a whole is a more relevant object than the brain: it's not clear where the brain itself begins and ends, and the nervous system runs all through the body. The octopus is suffused with nervousness; the body is not a separate thing that is controlled by the brain or nervous system."
Why some angry octopuses punch fish
An octopus body, Godfrey-Smith argues, in some sense transcends the brain-body divide—neither embodied cognition nor disembodied spirit. Rather, it's "all possibility." Nagel, according to Godfrey-Smith, flubbed the question: the octopus is like something, just nothing like a human, therefore making it difficult to even define.
Alas, we can't help but anthropomorphize. Octopuses might maintain a vastly different intelligence, yet like us, they've had to figure out how to survive in challenging environments. As a new study, published in The Scientific Naturalist, shows, they seem to do that, in part, by punching fish.
Our evolutionary success is due in large part to group fitness: we work together well. On occasion, we collaborate with other species to our mutual benefit, as with hunting dogs. The authors of this study point out that ocean life is filled with multispecific collaborative hunting groups, such as moray eels and groupers. Octopuses get in on this action as well.
"Involving active recruitment and referential gestures, the nature of this relationship is mutually beneficial (byproduct mutualism); that is, both can increase their hunting success rate from the presence of the other species, which likely played an important role in the emergence of complex interactions between groupers and eels."
Image sequence depicting the behavioral action of Octopus cyanea punching (white arrows) a yellow‐saddle goatfish (Parupeneus cyclostomus) partner during interspecific multicollaborative hunting.
Coral reef fishes have made bonds with other ocean life, such as octopuses, who chase prey within rocks and coral crevices while bottom-feeders scour the seafloor. Octopuses are known to tail groupers on hunting expeditions. As with any complex social network, however, life is not all mutual benefit. Tensions rise.
Recording instances in Israel in 2018 and Egypt in 2019, the team observed octopuses punching collaborating fish when things got heated. The goal appears to be moving the fish to a less advantageous location or simply telling them to scram.
"Thus, from the octopus's perspective, punching serves as a partner control mechanism, the nature of which is dependent on the ecological context of the interaction, and on how the octopus benefits from inflicting costs on fish partners."
As Godfrey-Smith writes, octopus arms are partly self and partly non-self—each arm is, in a sense, autonomous. To extend a metaphor, breathing is autonomic yet we can also control it. So too each octopus arm travels on its own but also coordinates with the rest of the body. The central brain, he continues, is like a conductor, with each arm being an improvisational jazz player, paying attention to the structure of the song while meandering off when needed.
We will never know what it's like to be an octopus. Nature has branched intelligence in distinctly different directions. Perhaps we share common ground on the hunt for survival. The team believes that research on punching octopuses helps reveal underlying game structures in the deep sea. And maybe, in some form of interspecies solidarity, we can appreciate their method of defending territory.
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Stay in touch with Derek on Twitter and Facebook. His most recent book is "Hero's Dose: The Case For Psychedelics in Ritual and Therapy."
For almost every animal, getting decapitated means certain death. But a new study shows that some species of sea slug are able to not only survive decapitation, but also regenerate entirely new bodies after splitting from their old ones.
The study, published Monday in Current Biology, shows that autotomy is stranger and more extreme in the animal kingdom than previously thought.
Autotomy is an evolved behavior in which animals shed a body part for a strategic purpose. For example, when salamanders are attacked, they'll often shed their tails to distract the attacker. Similarly, African spiny mice are known to automatically release chunks of their skin when attacked by predators, a sacrifice that boosts their odds of slipping away (mostly) intact.
But two species of sacoglossan sea slug take "autotomizing" to the next level. In the recent study, researchers observed that a handful of laboratory-bred slugs began to self-decapitate between 226 to 336 days after hatching. Existing as a severed head, the slugs were able to feed on algae. Within a week, they had regenerated their heart, and after three weeks they had regenerated an entirely new body. One slug even decapitated itself and grew a new body twice.
Credit: S. MITOH AND Y. YUSA/CURRENT BIOLOGY 2021
As for the slugs' discarded bodies? They survived, too, and some were able to move around on their own for months. But they never regrew new heads.
"The bodies gradually shrank and became pale, apparently from losing chloroplasts, and eventually decomposed," the researchers wrote. "The beating of the heart was visible just before the body decomposed."
So, why did some sea slugs evolve this extreme form of autotomy? The researchers still aren't quite sure, but the answer might not be related to escaping predators. That's because it takes hours for the slugs to split their heads from their bodies, meaning it wouldn't be a useful defense mechanism during attacks.
Credit: S. MITOH AND Y. YUSA/CURRENT BIOLOGY 2021
Instead, self-decapitation might be a way for the slugs to protect themselves against parasites. The researchers noted that the several sea slugs which completely shed their body were infected with parasitic crustaceans called copepods. Meanwhile, none of the parasite-free slugs engaged in autotomy.
As for how the slugs can survive self-decapitation, the researchers proposed the answer has to do with the unique way the mollusks obtain energy. Sea slugs eat algae, which contains chloroplasts—structures in which photosynthesis occurs.
When sea slugs eat algae, they incorporate some of the plant's chloroplasts into their body, allowing them to draw energy from the sun. This process is known as "kleptoplasty," and it may be what allows the animals to survive for weeks without bodies.
S. MITOH AND Y. YUSA/CURRENT BIOLOGY 2021
Still, scientists aren't exactly sure how kleptoplasty interacts with autotomy in sea slugs, and the authors noted that more research is needed to confirm what drives autotomy and body regeneration in the sea creatures. But despite the uncertainties, the new study shows that extreme forms of regeneration are possible in the animal kingdom.
As scientists continue to uncover the secrets of autotomy and regeneration in animals, it could pave the way for advances in regenerative medicine, a field that aims to harness the body's natural healing mechanisms.
"One day, patients will have access to regenerative medicine treatments that will circumvent the complications of organ donation," Sharlini Sankaran, executive director of Duke University's Regeneration Next Initiative, told Duke University School of Medicine. "We will be able to use our bodies' own innate repair mechanisms to eliminate the wait time, cost, and limited supply of organ transplantation. Instead of transplanting organs, we will know how to repair our own."
While there are significant differences between mollusks and mammals, the drivers of regeneration in sea slugs could provide clues as to how scientists might use approaches like stem-cell therapies to repair damage to cells, tissue and organs.
The Stanford marshmallow test, an experiment asking kids to hold off on eating one marshmallow for 15 minutes in exchange for two as a reward, was introduced in 1972 by psychologist Walter Mischel. The study checked in on the participants years later and noted that those who could delay their gratification a bit generally turned out better than those who could not.
The study has attracted attention since the day it was published. Attempts to recreate it have confirmed its basic findings, although some of those attempts suggest that how well the kids turn out is partly attributable to factors other than the ability to delay gratification.
While we debate how important the ability to wait for rewards is, science continues to find out which other animals are capable of it. A new variation on the experiment adds cuttlefish to that list.
Proof that some people are less patient than invertebrates
The common cuttlefish is a small cephalopod notable for producing sepia ink and relative intelligence for an invertebrate. Studies have shown them to be capable of remembering important details from previous foraging experiences, and to adjust their foraging strategies in response to changing circumstances.
In a new study, published in The Proceedings of the Royal Society B, researchers demonstrated that the critters have mental capacities previously thought limited to vertebrates.
After determining that cuttlefish are willing to eat raw king prawns but prefer a live grass shrimp, the researchers trained them to associate certain symbols on see-through containers with a different level of accessibility. One symbol meant the cuttlefish could get into the box and eat the food inside right away, another meant there would be a delay before it opened, and the last indicated the container could not be opened.
The cephalopods were then trained to understand that upon entering one container, the food in the other would be removed. This training also introduced them to the idea of varying delay times for the boxes with the second symbol.
Two of the cuttlefish recruited for the study "dropped out," at this point, but the remaining six—named Mica, Pinto, Demi, Franklin, Jebidiah, and Rogelio—all caught on to how things worked pretty quickly.
It was then that the actual experiment could begin. The cuttlefish were presented with two containers: one that could be opened immediately with a raw king prawn, and one that held a live grass shrimp that would only open after a delay. The subjects could always see both containers and had the ability to go to the immediate access option if they grew tired of waiting for the other. The poor control group was faced with a box that never opened and one they could get into right away.
In the end, the cuttlefish demonstrated that they would wait anywhere between 50 and 130 seconds for the better treat. This is the same length of time that some primates and birds have shown themselves to be able to wait for.
Further tests of the subject's cognitive abilities—they were tested to see how long it took them to associate a symbol with a prize and then on how long it took them to catch on when the symbols were switched—showed a relationship between how long a cuttlefish was willing to wait and how quickly it learned the associations.
All of this is interesting, but what use could it possibly have?
A diagram showing the experimental set up. On the left is the control condition, on the right is the experimental condition.
Credit: Alexandra K. Schnell et al., 2021
As you can probably guess, the ability to delay gratification as part of a plan is not the most common thing in the animal kingdom. While humans, apes, some birds, and dogs can do it, less intelligent animals can't.
While it is reasonably simple to devise a hypothesis for why social humans, tool-making chimps, or hunting birds are able to delay gratification, the cuttlefish is neither social, a toolmaker, or is it hunting anything particularly intelligent. Why they evolved this capacity is up for debate.
Lead author Alexandra Schnell of the University of Cambridge discussed their speculations on the evolutionary advantage cuttlefish might get out of this skill with Eurekalert:
"Cuttlefish spend most of their time camouflaging, sitting and waiting, punctuated by brief periods of foraging. They break camouflage when they forage, so they are exposed to every predator in the ocean that wants to eat them. We speculate that delayed gratification may have evolved as a byproduct of this, so the cuttlefish can optimize foraging by waiting to choose better quality food."
Given the unique evolutionary tree of the cuttlefish, its cognitive abilities are an example of convergent evolution, in which two unrelated animals, in this case primates and cuttlefish, evolve the same trait to solve similar problems. These findings could help shed light on the evolution of the cuttlefish and its relatives.
It should be noted that this study isn't definitive; at the moment, we can't make a useful comparison between the overall intelligence of the cuttlefish and the other animals that can or cannot pass some variation of the marshmallow test.
Despite this, the results are quite exciting and will likely influence future research into animal intelligence. If the common cuttlefish can pass the marshmallow test, what else can?
Life finds a way. That way may be uncomfortable, brimming with struggle, and demand an unsightly appendage or two, but as Jeff Goldblum reminds us, "Life will not be contained, life breaks free, it expands to new territories, and it crashes through barriers painfully, maybe even dangerously, but, uh, there it is."
To crash through those barriers, however, creatures must find the requirements for life waiting on the other side: namely, liquid water, a source of energy, and biogenic elements such as carbon and nitrogen. While terrestrial life has found some environments too hostile to call home, it's also evolved mind-boggling adaptations that allow it to access those three essentials in some bizarre places.
For example, the denizens of hydrothermal vents—such as the yeti crabs, scaly-foot gastropods, and Pompeii worms—dwell too deep in the ocean for sunlight to reach. Because their food chains can't rely on photosynthesis, they're supported by microbes that utilize a process called chemosynthesis, which converts chemicals from the vents into sugars and, in turn, useable energy.
Similarly, the Atacama Desert is a place so dry and barren that scientists compared it to the rusty dunes of Mars. Yet, even here, life has found a way in the form of microbes who wait patiently for those fleeting spits of rainfall to replicate.
And a new study, published in Frontiers in Marine Science, has proven Goldblum correct, uh, yes, once again. The study details the discovery of unusual creatures in one of the most unsympathetic environments on Earth's most inhospitable continent.
A cold dark place to call home
The Antarctic sessile creatures photographed on their home boulder.
Credit: Frontiers in Marine Science
Researchers made the discovery while drilling boreholes on the Filchner-Ronne Ice Shelf. Antarctica's ice shelves are giant, permanent floating ice sheets connected to the continent's coastlines, with the Filchner-Ronne shelf being one of the largest. Using a hot-water drill system, they bore through roughly 900 meters of the ice looking for sediment samples. Instead, they discovered a boulder. Two hundred sixty kilometers away from the ice front, the rock was nestled in a world of complete darkness at -2.2°C. And on it, they found sessile organisms.
"This discovery is one of those fortunate accidents that pushes ideas in a different direction and shows us that Antarctic marine life is incredibly special and amazingly adapted to a frozen world," Dr Huw Griffiths, the study's lead author and a biogeographer of the British Antarctic Survey, said in a press release.
Sessile creatures are defined by their inability to move freely. They live their lives anchored to a substrate—in this case, the aforementioned boulder. Common sessile animals found in coastal tide pools include mussels, barnacles, and sea anemones, yet none of these were present beneath the Antarctic shelf. Instead, the researchers discovered a stalked sponge, roughly a dozen non-stalked sponges, and 22 unidentifiable stalked organisms.
Previous boreholes had revealed creatures living in these murky waters, but they had always been free-moving predators and scavengers such as jellyfish and krill. It's not too surprising to find such animals under the ice shelves as their mobility allows them to seek out food that may drift beneath.
But sessile organisms depend on their food to be delivered to them. That's why they are so bountiful in tide pools; tides and currents are the DoorDash of the ocean world. It's also why the researchers found the sponge's Antarctic lodgings so astounding. Because they live 1,500 kilometers upstream from the nearest source of photosynthesis, it's unknown how a food supply reaches these sponges or whether they generate nutrients from some other means, such as glacial melt or carnivorous noshing.
"Our discovery raises so many more questions than it answers, such as how did they get there? What are they eating? How long have they been there? How common are these boulders covered in life? Are these the same species as we see outside the ice shelf or are they new species? And what would happen to these communities if the ice shelf collapsed?" Griffiths added.
To answer those questions, researchers will need to revisit the sponges to collect samples and study them in more depth. We'll also need to explore further the vast reaches of the Antarctic continental shelf. According to the release, counting the previous boreholes, scientists have only studied an area roughly the size of a tennis court to date.
Life will not be contained
As science discovers life in more and more unusual places, it's also considering more and more that life has not been contained to our pale blue dot. For example, the recent discovery of microbial life in the Atacama Desert has reignited hope that evidence of past life will be found on Mars. NASA's Perseverance Rover recently land on Mars to begin analyzing soil samples from the Jezero Crater to test that hypothesis.
Looking to the future, NASA's Dragonfly rotorcraft aims to explore the Saturn moon of Titan. The icy moon has a makeup similar to early Earth's, so the vehicle will study the moon's atmosphere and surface for signs of chemical evidence for life. And the ice-covered surface of Europa could hold twice as much water as Earth and a bevy of hydrothermal activity that could harbor life within our solar system.
Here life is, uh, and there it may be.
