The chemosensors on the suction cups of the eight octopus arms provide the animals with an accurate "taste by touch" picture of their marine environment or their potential prey through methodical exploration. Behind this is a highly developed nervous system: "Cephalopods are known for their sophisticated sensory organs, well-developed nervous system and advanced behavior comparable to that of complex vertebrates," explains Ryan Hibbs from the University of California at San Diego. “However, the organization of their nervous system is radically different. This makes cephalopods a fascinating example of convergent and divergent evolution.”
Hibbs and his team have now for the first time described the structure of the chemotactile receptors of California two-spot octopuses - the sensory organs that the animals use to explore their surroundings through touch and "taste". With the help of cryo-electron microscopy, the team was able to elucidate the structure of the proteins down to the atomic level. From the exact structure it can be deduced that the receptors are activated by fat molecules such as steroids.
The scientists conclude that the sensors are an evolutionary result of the development of neurotransmitters into environmental receptors. In the course of evolution, the sensory organs of the octopus have adapted to the assessment of possible food sources and have thus created an ecological niche for themselves. Other ten-armed squid species, on the other hand, have different receptors and also pursue a different hunting tactic: They hide and attack their prey from ambush. Ancient chemoreceptors that resemble human neuronal acetylcholine receptors have been found in these species.
These new findings on the tactile and chemoreceptors of the squid provide valuable insights into the evolutionary development of the sensory organs. "Our structural elucidation of these unique cephalopod receptors provides the basis for understanding the mechanisms behind major functional changes in such organs over the course of evolution and also how biologically new functions emerge," says Hibbs.