Cephalopods: Ambassadors of an alternate evolutionary path?
Ellie Kravets
Cephalopods (a class of molluscs including octopuses, cuttlefish, and squid) are widely considered to be the most intelligent of the invertebrates, yet much debate exists over the extent of their cognitive and learning capabilities. Their ability to solve simple problems, such as finding their way through mazes and opening jars, is well documented, but the validity of these claims have been the subject of debate: some scientists suggest that cephalopods represent clear coevolution with vertebrates while others deny their ability to compete in intelligence with vertebrates. Within the last 60 years or so, however, the debate has strengthened. Suddenly studies on cephalopod behavior found behavioral links to higher-order vertebrates that had never been previously observed or noticed. In recent years, cephalopods have been observed exhibiting mammalian-like REM sleep cycles and problem solving methods, further blurring the once-distinct line between invertebrate and vertebrate cognition. Some researchers are beginning to question the extent to which cephalopods represent clear coevolution with vertebrate mammals and birds.
To start, it is important to review the well-documented instances of the simple problem solving abilities in cephalopods. These types of studies litter the field of cephalopod research, and have been the bread-and-butter of cephalopod cognition studies. A representative example of such a study was done by Fiorito et al. in the early 1990s (Fiorito et al., 1990). At its core, the 1990 study was classic: octopuses were offered a jar containing food, and their responses were observed and the time taken to solve the puzzle was recorded. Of the 20 specimens of octopus, 19 were able to solve the jar puzzle in a single initial attack. Five months after the trial had concluded, octopuses were tested one last time and still remembered how to solve the jar puzzle, indicating the octopuses’ ability to imprint behavioral memory (Fiorito et al., 1990). The study concluded that octopuses have the capability for integrated learning, based on three observed trends: (1) A decrease in the number of errors made by the octopuses over time and repetition of the challenge, (2) the presence of exploratory behavior, and (3) the decline in the time needed for the octopuses to complete the task (Fiorito et al, 1990). It should be noted, however, that this study is recent enough to discuss potential indicators for higher-level cephalopod cognitive abilities; earlier versions of this type of study offer no such generosity.
Another advance toward recognizing cognitive similarities between vertebrates and cephalopods came in 2006. For the first time, octopuses were noted as having REM-type sleep cycles like those only typically seen in high order mammals and birds (Brown et al., 2006). Classically, distinct res-activity sleep cycles are only associated with vertebrate sleep cycles, as it is usually assumed to be an indicator of an animal’s ability to learn new behaviors. (The brain needs to “turn off” for a period in order to be “ready” to learn new tasks.) Octopuses observed in the study, when housed in tanks that closely mimic their natural environment, were observed entering a sleep-like state during the night hours, followed by active periods at dawn and dusk. When the light cycles were altered to deny the octopuses their normal resting periods, their ability to complete challenges and tasks set to them dropped drastically (Brown et al, 2006). The study concluded that octopus brains must undergo similar periods of activity and rest in order to maintain high levels of overall function, similar to the brains of higher order vertebrates.
Not much debate exists that cephalopods are extraordinarily intelligent when compared to other invertebrates. The real question that researchers have struggled over is to what extent cephalopod intelligence matches or rivals that of some vertebrates. As such, the more recent research trends concerning intraspecial communication of cephalopods has sparked incredible debate among researchers. The history of cephalopods’ intraspecial communication really started in 1982, when a study by Moynihan and Rodaniche claimed that Caribbean reef squids have a fully functional visual language, complete with nouns, verbs, and descriptors (qtd. in Barbado et al., 2007). While serious concern has been raised about the 1982 study’s viability, its conclusions were the start of a long-running split in the field, with half of the researchers trying to find alternative methods of proving Moynihan’s conclusions and the other half using more conventional methods to disprove them (Mather, 2008).
In 1996, a study was published concerning cuttlefish’s use of the long-known but seldom talked-about ability to sense and display polarized light. Under observation, the cuttlefish seemed to emit the strongest wavelengths and most distinct patterns of polarization when becoming alert (Shashnar et al., 1996). For example, when the cuttlefish were clearly camouflaging on the bottom of the tank, their polarization patterns were faint. When they were alert on the bottom, or swimming around the tank, their the patterns became much stronger. The patterns also changed with the nature of the interactions between cuttlefish. When presented with a mirror that accurately reflected the cuttlefish’s polarization pattern, the specimen usually responded by retreating and camouflaging at the bottom of the enclosure. When the same cuttlefish were presented with a mirror that distorted the polarization of the animal, no such retreat occurred (Shashnar et al., 1996). From the data gathered during the study, then, it seems that the polarization patterns of the cuttlefish may very well be used as a conspecific (or species to same-species) indicator and method of information exchange. Further evidence of the visual communication of cephalopods came to surface during a 2007 study by Barbato et al. Continuing on the theory that cephalopods can communicate by selectively polarizing their skin, the 2007 study found evidence to suggest that cephalopods do not just communicate signals to one another (ie, “predator here, prey there”) but also may lie to one another using their skin signals (ie, “don’t worry; I am a noncompetitive female”).
On the other side of the cephalopod debate, however, are studies such as Huang and Chiao’s 2012 study, which concluded that cuttlefish were incapable of observational learning. a hallmark of higher-order intelligence, specifically with primates and parrots. Implicit in their argument, however, is that true intraspecial communication between cuttlefish can’t exist when they claim cuttlefish lack self-awareness, citing the inability of most cuttlefish to recognize their reflection as a reflection and not another individual (Huang and Chaio, 2012). To classical interpreters, it becomes difficult to imagine true communication without self-awareness, as the lines between “self” and “non-self” are murky if not non-existent (Mather and Kuba, 2013). There is only so far, however, that classical approaches will advance our understanding of cephalopods. The Huang and Chiao study follows a procedure to test observational learning based on procedures used with Rhesus monkeys. Immediately, then, their methodology and theory are both flawed. Their definition of “observational learning” and “imitation” (which they claim to be all that cephalopods have been shown to do) is based very heavily on a bias toward highly-social mammals. Cuttlefish, as representatives of the highly-asocial cephalopods, would have little reason to develop the “observational learning” skills that are central to primate behavioral development, thus the study is inconclusive.
In 2013, Jennifer Mather and Michael Kuba wrote an article that all but outlined the case for approaching cephalopod behavioral studies differently than other animals. The decentralized brain of the cephalopods allows for decision making at several levels, and to all indication probably indicates a type of cognition that is alien to the centralized problem-processing centers of other advanced animals. Mather’s 2013 article argues that the cephalopods represent an alternative evolutionary model to those of mammals and birds for the development of complex brain systems. As such, many of the obviously complex behavioral trends of cephalopods seem to not quite match up to many scientist’s mammalian view of intelligence. As a group of animals, they evolved under different selective pressures: Modern mammals and birds, according to current thought, selected to become highly intelligent as a result of their intensely social lifestyle. Cephalopods are minimally social at best, and therefore their intelligence may have arose from a need to outcompete other species for their ecological niche (Mather and Kuba, 2013).
Mather just touched the problem with cephalopod research, however. The classic methods are only of limited use, but many of the studies conducted in the field (on both sides) follow the same formula that was created 60+ years ago. There will always be debate over cephalopod cognitive capabilities: in many ways, cephalopod research touches a nerve not often acknowledged in zoology. There is an unspoken hierarchy in the way many researchers view animals, and cephalopods—as invertebrates, and therefore one of the “lowest” forms of life—defy that hierarchy. There will always be researchers that are uncomfortable placing them on an intellectual level with “higher order” vertebrates. Regardless, until a solid majority of scientists studying cephalopods are willing to contemplate that potential, the field will stay relatively stagnant. Two things need to change in the way cephalopods are studied: (1) researchers need to leave preconceptions at their lab door, and be open to accepting a model which places cephalopod intelligence on par with some vertebrates. (2) They need to redesign experimental setups and try to study cephalopod intelligence in terms of cephalopod intelligence, not in terms of mammalian intelligence or avian intelligence. There is plenty of evidence to suggest that the brains of cephalopods evolved under drastically different pressures than vertebrate brains. Future research, then, needs to take what is likely a fundamentally different type of intelligence into account.
Works Cited
Barbato, Maria, Marco Bernard, Luciana Borrelli, Graziano Fiorito. (October 2007). Body patterns in cephalopods: “Polyphenism” as a way of information exchange. Pattern Recognition Letters, 28 (14), 1854-1864. http://dx.doi.org/10.1016/j.patrec.2006.12.023.
Brown, Euan R., Stefania Piscopo, Rosanna De Stefano, and Antonia Giuditta. (May 2006). Brain and behavioural evidence for rest-ectivity cycles in Octopus vulgaris. Behavioural Brain Research, 172, 355-359. http://dx.doi.org/10.1016/j.bbr.2006.05.009.
Fiorito, Graziano, Christoph von Planta, Pietro Scotto. (March 1990). Problem solving ability of Octopus vulgaris lamarck (Mollusca, Cephalopoda). Behavioral and Neural Biology, 53(2), 217-230. http://dx.doi.org/10.1016/0163-1047(90)90441-8.
Mather, Jennifer A. (March 2008). Cephalopod consciousness: Behavioral evidence. Consciousness and Cognition, 17(1), 37-48. http://dx.doi.org/10.1016/j.concog.2006.11.006.
Huang, Kuan-Ling and Chuan-Chin Chiao. (October 2012). Can cuttlefish learn by observing others? Animal Cognition, 16(3), 313-320. http://dx.doi.org/10.007/s10071-012-0573-2.
Mather, Jennifer A. and Michael J. Kuba. (2013). The cephalopod specialties: complex nervous system, learning, and cognition. Canadian Journal of Zoology, 91, 431-449. http://dx.doi.org/10.1139/cja-2013-0009.
Shashar, Nadav, Phillip S. Rutledge, and Thomas W. Cronin. (May 1996). Polarization vision in cuttlefish—a concealed communication channel? The Journal of Experimental Biology, 199, 2077-2084.