Heat stress from ocean warming harms octopus vision

While climate change has led to an increase in the abundance of octopuses, heat stress from projected ocean warming could impair their vision and impact the survivability of the species.

"We found several proteins important for vision that were affected by thermal stress," says Dr Qiaz Hua, a recent PhD graduate from the University of Adelaide's School of Biological Sciences.

"One of them is a structural protein found in high abundance in animal eye lenses to preserve lens transparency and optical clarity, and another is responsible for the regeneration of visual pigments in the photoreceptors of the eyes.

"The levels of both of these proteins were significantly reduced under projected ocean warming conditions, which suggests that octopus vision is likely to be impaired under thermal stress."

Octopuses are highly visual animals, with 70 per cent of the octopus brain dedicated to vision -- which is 20 per cent more than in humans.

"The primary functions of vision include but are not limited to visual acuity, discrimination of brightness, depth perception, motion detection and polarisation, and it is crucial for detecting predator and prey as well as for communication," says Dr Hua.

"Having impaired vision will affect an octopus's chances of survival in the wild through increased predator risk as well as lower foraging success."

To make this finding, the research team, including academics from the University of South Australia, University of California Davis, and the South Australian Research and Development Institute's aquatic sciences division, exposed Octopus berrima embryos to different temperature treatments, a control 19°C exposure, 22°C to model current summer temperatures, and 25°C to model projected summer temperatures.

"The future-projected temperature was based on the Intergovernmental Panel on Climate Change's projected increase of about 3°C of warming by 2100," Dr Hua says.

In addition to impaired vision, Dr Hua found increased ocean water temperatures would have a negative effect on octopus broods.

"We found a high mortality rate under future warming conditions. Out of three replicate octopus broods, none of the eggs hatched for two of them and less than half of the eggs hatched for the remaining brood," Dr Hua says.

"In the broods where none of the eggs hatched, the mothers died naturally while the eggs were still in early development stages.

"Because maternal care of embryos occurs in octopuses, global warming could have a simultaneous impact on multiple generations, with the low survival rate of the embryos caused by the direct effect of thermal stress as well as the indirect effect of thermal stress on the mothers.

"Our study shows that even for a highly adaptable taxon like octopuses, they may not be able to survive future ocean changes."

Other effects of higher temperatures which have been observed in octopuses include a higher metabolic rate, reduced size at maturity, and even a range shift in the distribution of some species.

"We hope that future research would examine a combination of environmental stressors including ocean acidification, warming, and deoxygenation," Dr Hua says.

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Human cells help researchers understand squid camouflage

Squids and octopuses are masters of camouflage, blending into their environment to evade predators or surprise prey. Some aspects of how these cephalopods become reversibly transparent are still "unclear," largely because researchers can't culture cephalopod skin cells in the lab. Today, however, researchers report that they have replicated the tunable transparency of some squid skin cells in mammalian cells, which can be cultured. The work could not only shed light on basic squid biology, but also lead to better ways to image many cell types.

The researchers will present their results at the spring meeting of the American Chemical Society (ACS).

For many years, Alon Gorodetsky, Ph.D., and his research group have been working on materials inspired by squid. In past work, they developed "invisibility stickers," which consisted of bacterially produced squid reflectin proteins that were adhered onto sticky tape. "So then, we had this crazy idea to see whether we could capture some aspect of the ability of squid skin tissues to change transparency within human cell cultures," says Gorodetsky, who is the principal investigator on the project.

The team at the University of California, Irvine focused their efforts on cephalopod cells called leucophores, which have particulate-like nanostructures composed of reflectin proteins that scatter light. Typically, reflectins clump together and form the nanoparticles, so light isn't absorbed or directly transmitted; instead, the light scatters or bounces off of them, making the leucophores appear bright white.

"We wanted to engineer mammalian cells to stably, instead of temporarily, form reflectin nanostructures for which we could better control the scattering of light," says Gorodetsky. That's because if cells allow light through with little scattering, they'll seem more transparent. Alternatively, by scattering a lot more light, cells will become opaque and more apparent. "Then, at a cellular level, or even the culture level, we thought that we could predictably alter the cells' transparency relative to the surroundings or background," he says.

To change how light interacts with cultured cells, Georgii Bogdanov, a graduate student in Gorodetsky's lab who is presenting the results, introduced squid-derived genes that encoded for reflectin into human cells, which then used the DNA to produce the protein. "A key advance in our experiments was getting the cells to stably produce reflectin and form light-scattering nanostructures with relatively high refractive indices, which also allowed us to better image the cells in three dimensions," says Bogdanov.

In experiments, the team added salt to the cells' culture media and observed the reflectin proteins clumping together into nanostructures. By systematically increasing the salt concentration, Bogdanov got detailed, time-lapse 3D images of the nanostructures' properties. As the nanoparticles became larger, the amount of light that bounced off the cells increased, consequently tuning their opacity.

Then, the COVID-19 pandemic hit, leaving the researchers to wonder what they could do to advance their investigation without being physically in the lab. So, Bogdanov spent his time at home developing computational models that could predict a cell's expected light scattering and transparency before an experiment was even run. "It's a beautiful loop between theory and experiments, where you feed in design parameters for the reflectin nanostructures, get out specific predicted optical properties and then engineer the cells more efficiently -- for whatever light-scattering properties you might be interested in," explains Gorodetsky.

On a basic level, Gorodetsky suggests that these results will help scientists better understand squid skin cells, which haven't been successfully cultured in a laboratory setting. For example, previous researchers postulated that reflectin nanoparticles disassemble and reassemble to change the transparency of tunable squid leucophores. And now Gorodetsky's team has shown that similar rearrangements occurred in their stable engineered mammalian cells with simple changes in salt concentration, a mechanism that appears analogous to what has been observed in the tunable squid cells.

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Octopus lures from the Mariana Islands found to be oldest in the world

An archaeological study has determined that cowrie-shell artifacts found throughout the Mariana Islands were lures used for hunting octopuses and that the devices, similar versions of which have been found on islands across the Pacific, are the oldest known artifacts of their kind in the world.

The study used carbon dating of archaeological layers to confirm that lures found on the Northern Mariana Islands of Tinian and Saipan were from about 1500 B.C., or 3,500 years ago.

"That's back to the time when people were first living in the Mariana Islands. So we think these could be the oldest octopus lures in the entire Pacific region and, in fact, the oldest in the world," said Michael T. Carson, an archaeologist with the Micronesian Area Research Center at the University of Guam.

The study, titled "Let's catch octopus for dinner: Ancient inventions of octopus lures in the Mariana Islands of the remote tropical Pacific," is published in World Archaeology, a peer-reviewed academic journal. Carson, who holds a doctorate in anthropology, is the lead author of the study, assisted by Hsiao-chun Hung from The Australian National University in Canberra, Australia.

The fishing devices were made with cowrie shells, a type of sea snail and a favorite food of octopuses, that were connected by a fiber cord to a stone sinker and a hook.

They have been found in seven sites in the Mariana Islands. The oldest lures were excavated in 2011 from Sanhalom near the House of Taga in Tinian and in 2016 from Unai Bapot in Saipan. Other locations include Achugao in Saipan, Unai Chulu in Tinian, and Mochom at Mangilao Golf Course, Tarague Beach, and Ritidian Beach Cave in Guam.

Known artifacts, unknown purpose -- until now

"The artifacts have been known -- we knew about them. It just took a long time considering the possibilities, the different hypotheses, of what they could be," Carson said. "The conventional idea -- what we were told long ago from the Bishop Museum [in Honolulu] -- was that these must be for scraping breadfruit or other plants, like maybe taro. [But] they don't look like that."

The shells didn't have the serrated edge of other known food-scraping tools. With their holes and grooves where the fiber cord would have been attached as well as the stone sinker components, they appeared a closer match to octopus lures found in Tonga from about 3,000 years ago, or 1100 B.C.

"We're confident they are the pieces of octopus lures, and we're confident they date back to 1500 B.C.," Carson said.

An invention of the ancient CHamorus?

Carson said the question now becomes: Did the ancient CHamoru people invent this adaptation to their environment during the time when they first lived in the islands?"

That's a possibility, he said, the other being that they brought the tradition with them from their former homeland; however, no artifacts of this kind have yet been discovered in the potential homelands of the first Marianas settlers.

If the CHamoru people did invent the first octopus lures, it provides new insight into their ingenuity and ability to problem solve -- having to create novel and specialized ways to live in a new environment and take advantage of an available food source.

"It tells us that […] this kind of food resource was important enough for them that they invented something very particular to trap these foods," Carson said. "We can't say that it contributed to a massive percentage of their diet -- it probably did not -- but it was important enough that it became what we would call a 'tradition' in archaeology."

The next question to look at, Carson said, is whether there are similar objects anywhere else from an older time.

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Rubbery camouflage skin exhibits smart and stretchy behaviors

The skin of cephalopods, such as octopuses, squids and cuttlefish, is stretchy and smart, contributing to these creatures' ability to sense and respond to their surroundings. A Penn State-led collaboration has harnessed these properties to create an artificial skin that mimics both the elasticity and the neurologic functions of cephalopod skin, with potential applications for neurorobotics, skin prosthetics, artificial organs and more.  

Led by Cunjiang Yu, Dorothy Quiggle Career Development Associate Professor of Engineering Science and Mechanics and Biomedical Engineering, the team published its findings on June 1 in the Proceedings of the National Academy of Sciences. 

Cephalopod skin is a soft organ that can endure complex deformations, such as expanding, contracting, bending and twisting. It also possesses cognitive sense-and-respond functions that enable the skin to sense light, react and camouflage its wearer. While artificial skins with either these physical or these cognitive capabilities have existed previously, according to Yu, until now none has simultaneously exhibited both qualities -- the combination needed for advanced, artificially intelligent bioelectronic skin devices.  

"Although several artificial camouflage skin devices have been recently developed, they lack critical noncentralized neuromorphic processing and cognition capabilities, and materials with such capabilities lack robust mechanical properties," Yu said. "Our recently developed soft synaptic devices have achieved brain-inspired computing and artificial nervous systems that are sensitive to touch and light that retain these neuromorphic functions when biaxially stretched."  

To simultaneously achieve both smartness and stretchability, the researchers constructed synaptic transistors entirely from elastomeric materials. These rubbery semiconductors operate in a similar fashion to neural connections, exchanging critical messages for system-wide needs, impervious to physical changes in the system's structure. The key to creating a soft skin device with both cognitive and stretching capabilities, according to Yu, was using elastomeric rubbery materials for every component. This approach resulted in a device that can successfully exhibit and maintain neurological synaptic behaviors, such as image sensing and memorization, even when stretched, twisted and poked 30% beyond a natural resting state.  

"With the recent surge of smart skin devices, implementing neuromorphic functions into these devices opens the door for a future direction toward more powerful biomimetics," Yu said. "This methodology for implementing cognitive functions into smart skin devices could be extrapolated into many other areas, including neuromorphic computing wearables, artificial organs, soft neurorobotics and skin prosthetics for next-generation intelligent systems."

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