Observational learning in Octopus vulgaris

Running head: OBSERVATIONAL LEARNING IN OCTOPUS

Jennifer Floyd

INTRODUCTION

Introduction The present study seeks to further investigate the phenomenon of observational learning in Octopus vulgaris. The extraordinary finding that O. vulgaris chose to attack either a red or white ball, based on observation of a conditioned octopus attacking either a red or white ball (Fiorito & Scotto, 1992), is highly intriguing considering not only that octopodes are invertebrates, but that they are also predominantly solitary animals.

Background Although most cases of social learning are noted in social vertebrates, there is growing evidence of such accomplishment in a wide variety of invertebrates (Webster & Fiorito, 2001), some of which do not fall under the social category (Coolen, Dangles & Casas, 2005). These studies suggest that social learning is conditioned upon ecological rather than taxonomic determinants. While it may seem an odd theory to pursue under light of the notoriously asocial and even aggressive behavior of octopodes, there have been quite a few reports of aggregation/ tolerance in a shared environment (Butterworth, 1982; Forsythe & Hanlon, 1988; Guerra, 1981; Kayes, 1974; pers. obs. R.T. Hanlon, 1991; Mather, 1982, 1985; Moynihan & Rodaniche, 1982; Rodaniche, 1991). Non-altruistic group living in other asocial, aggressive species has been reported before (Giovanetti, 2005; Uetz & Burgess, 1979), although it is not known whether these results are due to habitat and resource restrictions, or some form of loose “social” organization. Further, territoriality in octopodes is as of yet unproven (Altman, 1967; Ambrose, 1988; Aronson, 1986; Butterworth, 1982; Hanlon & Messenger, 1996; Kayes, 1974; Mather, 1982; Mather & O’Dor, 1991; Yarnall, 1969), and observations rather indicate den defense

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Running head: OBSERVATIONAL LEARNING IN OCTOPUS

Jennifer Floyd

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(Hartwick, Breen & Tulloch, 1978; Kyte & Courtney, 1978), although there has even been the occasional anecdote of dens occupied by more than one octopus (Moynihan & Rodaniche, 1982; Rodaniche, 1991). These aggregations and other factors such as the relative defenselessness of octopodes, and long- term memory (Hochner, Brown, Langella, Shomrat & Fiorito, 2003), appeal to the idea of observational learning being adaptive (Coolen, van Bergen, Day & Laland, 2003), yet the lack of generation overlap and unstable environment (Galef & Whiskin, 2004) would suggest otherwise. This study looks to either corroborate the findings of Fiorito and Scotto (1992), or to address possible flaws in the study design (Biedermann & Davey, 1993) that may have mistakenly led to the conclusion that octopodes are capable of observational learning.

Significance The significance of this line of research lays in the notion of evolutionary convergence, platform-independent intelligence, and the evolution of social behavior.

GOALS The specific question this study seeks to shed light upon is whether or not O. vulgaris is capable of learning through observation of a conspecific.

METHODS Subjects This study will involve a total of 15 subjects. The species O. vulgaris was decided upon for multiple reasons. O. vulgaris was one of the species that was observed living in a nonrandom distribution (Guerra, 1981; Kayes, 1974). It is also a shallow water species that is diurnally active 30 percent of the time in its juvenile stage (Mather, 1988), which is important as cephalopods’ dependence on sight is an unusual characteristic among invertebrates, and is more similar to vertebrates where socially guided behavior is highly developed. There are also many

Running head: OBSERVATIONAL LEARNING IN OCTOPUS

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studies that verify O. vulgaris’s high activity level and curiosity (Meisel, Byrne, Kuba, Griebel & Mather, 2003), and despite color-blindness (Messenger, 1977), the ability to visually discriminate stimuli by size, shape, orientation, brightness, and plane of polarization (Boycott & Young, 1957; Messenger, 1981; Moody & Parriss, 1961; Sutherland, 1957).

Age of subjects is another potentially important factor for this study. Some cephalopods have shown lack of retention in learning exercises until reaching the age of 16 weeks (Messenger, 1973; Wells, 1962) and senescent cephalopods show similar disabilities (Chichery & Chichery, 1992), so wild caught subjects will be carefully selected to control for developmental variables. This is preferable to laboratory-reared octopodes as there has been speculation that they are slower to learn, which possibly suggests that their natural environment facilitates learning (Boal, 1991).

Other subject features that will be attended to are size of the demonstrator octopodes- as there has been suggestion that successful (large or mature) individuals are more likely to be copied in certain species (Galef & Laland, 2005), and gender of subjects (female) in order to avoid any possible sexual distraction (Warden & Jackson, 1935).

Facilities Subjects will be housed in individual, isolated glass tanks (1.0 x 0.6 x 0.5 m) during intertrial periods. The semi-natural environment will consist of a sandy bottom with rocks and shells suitable to build a den, and a day-night lighting cycle provided by neon lights with a daylight emission spectrum. Live shrimp, mussels, and crabs will be provided during intertrial periods. Water temperature will be kept at 22 degrees celsius, with a turnover rate of 24 times per day (Meisel, Byrne, Kuba, Griebel & Mather, 2003; Vaz-Pires, Seixas & Barbosa, 2004).

Procedures

Running head: OBSERVATIONAL LEARNING IN OCTOPUS

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This question will be addressed in a manner that closely resembles the methods used in the study by Fiorito & Scotto (1992), but with significant changes in design that should control better for alternative explanations of the subject’s behavior. The study will consist of five different groups. Phase I will not begin until the subjects have acclimated to captivity.

Phase I: Group 1 will consist of three octopodes who will one at a time be exposed to one of three naïve octopodes that is undergoing operant conditioning to attack a white ball and not a black ball (brightness discrimination) that will be simultaneously, rather than successively (Sutherland & Muntz, 1959), presented by a mechanical device. This machine will use strings to bob the plastic weighted balls (5cm diameter) in an up and down motion in order to entice action, with position of the stimuli reversed in trials by random fashion. The observer octopus will watch the conditioning of the “demonstrator” who will receive a piece of fish that will be dispensed from the machine for every trial that they attack the white ball. This observation will start one hour after the observer and demonstrator have been placed into adjacent tanks that are isolated from view of all other subjects, and it will go on until the demonstrator attacks the white ball on four consecutive trials. Group 2 will consist of three octopodes who will undergo the same procedure, only their demonstrators will be conditioned to chose the black ball and not the white ball. This portion of the experiment differs from that of Fiorito & Scotto (1992) in that the observers will be able to watch their demonstrators picking the correct and incorrect stimuli and the ensuing reinforcement. This change will serve to counter claims of “rapid imitation” in that observers will also see demonstrators attack the incorrect stimuli as well as the correct one. However, it is the author’s belief that goal-directed, reflective imitation (as opposed to instinctive imitation) is a valid form of observational learning regardless. Groups 3 and 4 are also very important additions

Running head: OBSERVATIONAL LEARNING IN OCTOPUS

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to this procedure. Both Group 3 and Group 4 will each consist of three octopodes who will be exposed, not to a demonstrator, but simply to either a white ball (Group 3), or a black ball (Group 4), bobbing up and down in an adjacent tank for half an hour. It is possible that Groups 1 and 2 may be inadvertently directed to the correct stimuli as the demonstrator octopodes improve with conditioning and increasingly choose the correct stimuli and ignore the incorrect one.

Groups 3 and 4 will serve as controls regarding stimulus enhancement and the exposure effect.

Stimulus enhancement occurs when an individual is attracted to a certain object after observing its manipulation by another individual, but does not necessarily attend to the actions of the other individual (Roberts, 1941). And the exposure effect has shown that a preference for a stimulus can come about from mere familiarity with it (Zajonc, 1968). A somewhat similar type of control played an essential role in the only other study that has been published to date on observational learning in cephalopods (Boal, Wittenberg & Hanlon, 2000). It was found that compared to a control group, na誰ve Sepia Officinalis who observed an experienced conspecific preying on a crab were more successful on their first hunting attempt. Although this would seemingly point to observational learning, it was also found that S. Officinalis that had only previously observed or smelt a crab with no conspecific present, also had higher success on their first hunting attempt compared with the control group. These findings argue against observational learning, although they are not conclusive. Group 5 in the experiment will be a basic control group of three octopodes that is exposed neither to conspecifics in training, nor to stimuli alone. This will serve to provide any evidence of innate stimuli preference (Boycott & Young, 1957; Fiorito & Scotto, 1992; Messenger & Sanders, 1972).

Phase II:

Running head: OBSERVATIONAL LEARNING IN OCTOPUS

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In this phase, subjects from groups 1-5 will all undergo the same testing. One hour after completing phase I, subjects will be moved into individual tanks that are isolated from view of all other subjects as well as researchers, and be exposed to five trials of the white and black ball.

These trials will be conducted in the same manner that was used to condition the demonstrator octopodes, only there will be no reinforcement.

Phase III: This phase will be carried out identically to phase II, only these trials will be engaged two days after the completion of phase II to test retention.

Running head: OBSERVATIONAL LEARNING IN OCTOPUS

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