To us humans, the concept of social recognition is rather intuitive and tangible, as many of our daily interactions rely heavily on the rapid identification of members of our own species. We have an astounding ability to near-instantly recognize friends, family, and even distant acquaintances—only given a cursory glance. As primarily visual creatures, we have evolved to possess physiology that make these feats possible, but what of animals that live in environments that don’t allow for such a reliance on visual systems? One research lab, stationed at the Monterey Bay Aquarium Research Institute, asked this exact question in an observational study of Hapalochlaena maculosa (blue-ringed octopus).
Blue-ringed octopuses are nocturnal ambush hunters that populate the murky rock pools off the southern coast of Australia. Provided the low visibility in their environment, this species of octopus didn’t evolve to develop the sophisticated visual systems of humans and other vertebrates. Prior works have noted that blue-ringed octopuses are a rather docile, antisocial animal that rarely interacts with other members of the same species. With this in mind, blue-ringed octopuses need to take full advantage of the limited interactions they do have—particularly in the context of mating and reproduction. In this light, social recognition is strongly acted upon by sexual selection, as both male and female octopuses benefit from the ability to discriminate between peers. In a 2022 study, Morse and colleagues aimed to investigate the possibility of chemotactile social recognition in blue-ringed octopuses as a functional, more ecologically valid alternative to visual discrimination. Chemotactile social recognition involves the use of physical touch to detect changes in the environment. The rationale for a tactile alternative is rooted in the notion that blue-ringed octopuses are equipped with thousands of receptors on each of their ~100 suckers. These receptors are highly sensitive to changes in texture and chemical composition, much like the perceptual abilities of our fingertips or the taste buds on our tongues. In the same way that we use our eyes to spot a friend from a distance or use our ears to recognize the voice of a loved one, Morse et al. predicted that blue-ringed octopuses rely on touch to distinguish individuals from one another.
Methodologically, the aforementioned study involved placing the octopuses in controlled aquarium environments and cataloging their behavior with an infrared video recording software. To assess mating behavior, different ratios of male and female octopuses were placed into tanks and observed for trials lasting roughly 3-5 days. The researchers scored the number of interactions per specimen (where any contact with the suckers on the underside of the arm qualifies as an interaction) and noted whether the octopuses either retreated or stayed in contract.
Most interestingly, male octopuses seemed to be able to distinguish prior mates by touch alone, suggesting that these octopuses can use chemotactile sensation to recognize other individuals. The authors propose that male blue-ringed octopuses are able to detect identifying characteristics to recognize specific females. Further, males would flee after interacting with a female with whom they have a mating history. On the surface, this behavior doesn’t seem to make intuitive sense. However, mating has its costs, and males have evolved to optimize their reproductive behavior to maximize genetic diversity. As a reclusive species where mating presents risk of physical harm for females and a steep energy demand for males, the ability to recognize other octopuses in a dark or cloudy environment allows males to preserve their resources for encounters with novel females.
Morse, P., & Huffard, C. L. (2022). Chemotactile social recognition in the blue-ringed octopus, Hapalochlaena maculosa. Marine Biology, 169(8), 99. doi: 10.1007/s00227-022-04087-y
