Octopus and squid senses linked to human brain evolution

The vast oceans are home to some of the most intriguing and mysterious creatures. Among these are octopuses and squids, known as cephalopods, which have developed unique sensing capabilities to navigate their underwater worlds. 

Octopuses explore the seafloor with their eight arms, using highly sensitive suckers in a “taste by touch” approach, while squids employ a starkly different tactic, patiently hiding until they ambush their prey in swift bursts. 

A recent pair of research studies led by scientists from the University of California San Diego and Harvard University delves into the evolutionary adaptations of these sensing abilities, revealing connections to human brain receptors.

These groundbreaking studies, published in the journal Nature, were conducted by researchers from Ryan Hibbs’ newly established laboratory at UC San Diego (formerly based at the University of Texas Southwestern Medical Center) and Nicholas Bellono’s lab at Harvard. 

The research teams adopted a comprehensive approach, examining cephalopods from atomic-level protein structures to the entire functional organisms. They focused on sensory receptors as a key site for evolutionary innovation, intersecting ecology, neural processing, and behavior.

The investigation of how octopuses and squids sense their marine environments led to the discovery of new sensory receptor families, and the experts determined how these receptors drive distinct behaviors in the environment. 

They employed cryo-electron microscopy technology, which uses cryogenic temperatures to capture biological processes and structures in unique ways, demonstrating that adaptations can help propel new behaviors.

“Cephalopods are well known for their intricate sensory organs, elaborate nervous systems and sophisticated behaviors that are comparable to complex vertebrates, but with radically different organization,” said Hibbs, a professor in the Department of Neurobiology. Hibbs brings expertise on the structure of a family of proteins in humans that mediate communication between brain neurons and other areas such as between neurons and muscle cells. “Cephalopods provide striking examples of convergent and divergent evolution that can be leveraged to understand the molecular basis of novelty across levels of biological organization.”

First study findings

In one of the Nature studies, the scientists described for the first time the structure of an octopus chemotactile receptor, which octopus arms use for taste-by-touch exploration. These chemotactile receptors are similar to human brain and muscle neurotransmitter receptors, but have evolved to help evaluate potential food sources in the marine environment.

“In octopus, we found that these chemotactile receptors physically contact surfaces to determine whether the animal should eat a potential food source or reject it,” said Hibbs. “Through its structure, we found that these receptors are activated by greasy molecules, including steroids similar to cholesterol. With evolutionary, biophysical and behavioral analyses, we showed how strikingly novel structural adaptations facilitate the receptor’s transition from an ancestral role in neurotransmission to a new function in contact-dependent chemosensation of greasy environmental chemicals.”

Second study findings

The second Nature study focused on squids and their distinct ambush strategy for capturing food. The researchers combined genetics, physiology, and behavioral experiments to discover a new class of ancient chemotactile receptors and determined one structure within the class. 

They also conducted an evolutionary analysis to link adaptations in squid receptors to more elaborate expansions in octopus receptors. By placing chemotactile and ancestral neurotransmitter receptors on an evolutionary timeline, the researchers were able to describe how evolutionary adaptations drove the development of new behaviors.

“We discovered a new family of cell surface receptors that offer a rare lens into the evolution of sensation because they represent the most recent and only functionally tractable transition from neurotransmitter to environmental receptors across the entire animal kingdom,” said Hibbs. “Our structures of these unique cephalopod receptors lay a foundation for the mechanistic understanding of major functional transitions in deep evolutionary time and the origin of biological novelty.”

Hibbs says the pair of new studies offers an excellent example of how curiosity in interesting creatures can lead to insights important for all of biology, namely how proteins – life’s building blocks – adapt to mediate new functions and behaviors. 

“These studies are a great example of what being a scientist is all about – wonder, exploration and understanding how things work,” he said.

The findings not only shed light on the fascinating underwater lives of cephalopods, but also reveal a deeper understanding of the complex web of evolutionary connections that tie together the living world, including our own brains.

More about octopuses

Octopuses are fascinating marine creatures that belong to the class Cephalopoda, which also includes squids, cuttlefish, and nautiluses. They are widely known for their remarkable intelligence, problem-solving abilities, and exceptional camouflage skills. Here are some more interesting facts about octopuses:

1. Anatomy: Octopuses have a soft, flexible body with no internal or external skeleton, which allows them to squeeze through tight spaces. They have eight arms lined with suckers, a bulbous head, and a mantle that houses their internal organs. The mouth, located at the center of their arms, has a beak-like structure and a radula, a tongue-like organ with rows of teeth, to break down food.
2. Intelligence: Octopuses are considered the most intelligent invertebrates. They display complex problem-solving abilities, can solve puzzles, unscrew jars to obtain food, and even use tools. They are also known for their escape artistry, sometimes escaping from their tanks in captivity.
3. Camouflage: Octopuses are masters of disguise, thanks to their ability to change their color, pattern, and texture to blend in with their surroundings. They achieve this with specialized cells called chromatophores, which contain pigments, and iridophores and leucophores, which reflect and scatter light. This camouflage helps them avoid predators and sneak up on prey.
4. Locomotion: Octopuses primarily move by crawling along the seafloor using their arms. However, they can also swim by expelling water from their mantle cavity through a funnel-like structure called the siphon, propelling them backward in a form of jet propulsion.
5. Reproduction: Octopuses have a unique reproductive process. The male octopus transfers a sperm packet to the female using a specialized arm called the hectocotylus. After fertilization, the female lays thousands of eggs and guards them until they hatch, often not eating during this time. Most octopus species have a short lifespan, with some living only a few months to a couple of years. The female usually dies soon after the eggs hatch.
6. Venom: Most octopuses produce venom to subdue and immobilize their prey. The venom of some species, like the blue-ringed octopus, can be extremely potent and dangerous to humans.
7. Regeneration: Octopuses have the ability to regenerate lost arms. A new arm can grow back within a few weeks, complete with functional suckers and nerve connections.
8. Size and habitat: Octopus species vary greatly in size, from the tiny Octopus wolfi, which measures only about an inch in length, to the giant Pacific octopus, with an arm span of up to 30 feet. They inhabit various marine environments, from shallow tide pools to deep ocean trenches, and are found in all the world’s oceans.

These captivating creatures continue to be a subject of fascination for scientists and the public alike, as researchers uncover more about their unique biology, behaviors, and adaptations to life in the ocean.

More about squids

Squids are intriguing marine animals belonging to the class Cephalopoda, which also includes octopuses, cuttlefish, and nautiluses. They are known for their streamlined bodies, impressive swimming abilities, and bioluminescence. Here are some more interesting facts about squids:

1. Anatomy: Squids have a distinctive body structure with a torpedo-shaped mantle, eight arms, and two longer tentacles. Their arms and tentacles are equipped with suckers or hooks for capturing prey. Squids have a sharp, parrot-like beak used to tear and consume food. Inside the mantle, they possess a pen or gladius, a remnant of an internal shell, which provides support and aids in streamlining their body.
2. Locomotion: Squids are fast and agile swimmers. They use jet propulsion to move through the water by forcefully expelling water through a funnel-like structure called the siphon. This technique allows squids to move quickly, making them efficient predators and enabling them to escape from threats.
3. Vision: Squids have large, well-developed eyes that allow them to see clearly in low-light conditions. Their eyes are adapted for detecting motion and can perceive the polarization of light, which helps them locate transparent prey and navigate their environment.
4. Camouflage and bioluminescence: Like octopuses, squids can change their color and pattern using specialized cells called chromatophores. Some squid species also have bioluminescent organs called photophores, which emit light, allowing them to communicate, attract prey, or deter predators.
5. Predation: Squids are carnivorous and primarily feed on fish, crustaceans, and other cephalopods. They use their tentacles to catch prey and then pull it towards their beak to consume it.
6. Reproduction: Squid reproduction involves the male transferring sperm packets, called spermatophores, to the female using a modified arm called the hectocotylus. The female then lays eggs in clusters, which are often attached to the seafloor or other underwater structures. Depending on the species, the female may guard the eggs or abandon them to develop on their own. After hatching, the young squids, called paralarvae, are usually planktonic and undergo several developmental stages before reaching adulthood.
7. Size and habitat: Squid species range in size from the tiny Idiosepius, measuring only about an inch in length, to the colossal squid, which can grow up to 46 feet in length, including the tentacles. Squids inhabit various ocean environments, from shallow coastal waters to the deep sea, and are found in all the world’s oceans.
8. Importance to humans: Squids are not only ecologically important as a part of the marine food web, but they also hold cultural and economic significance. They are a popular food source in many cuisines and are commercially fished worldwide. Squids also play a role in scientific research, particularly in the fields of neuroscience and biomechanics.

The fascinating biology, behaviors, and adaptations of squids continue to captivate scientists and the public alike, as researchers uncover more about their complex lives in the ocean’s depths.

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