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HIDING BEHAVIORS IN OCTOPUS JOUBINI CUVIER BY BEN KING A Thesis Submitted to the Division of Natural Sciences New College of Florida In partial fulfillment of the requirements for the degree Bachelor of Arts of Marine Biology Under the sponsorship of Dr. Sandra Gilchrist Sarasota, Florida April, 2013
Hiding Behaviors in Octopus joubini 2 Contents Abstra Introdu Meth Result Preliminary Observations of Behav Den/Hiding Discus Conclu ...
Hiding Behaviors in Octopus joubini 3 Acknowledgements I would firstly like to thank New College for the Research and Travel Grant award that helped fund this research project. I would also like to thank Dr. Sandra Gilchrist for her patience with me. I thank my parents Chris and Carmen Kin g, and my little brother, Jacob King, for their support in spite of the rough times our family has gone Morgan McCabe, for carrying me when I could not stand on my own.
Hiding Behaviors in Octopus joubini 4 Abstract Octopus joubini is a species of cephalopod that is not well studied because of its relatively small size for an octopus I t is an ideal subject for behavioral research. T o further understand how the pygmy octopus interacts with it s natural environment, which is inshore sea grass beds, three Octopus joubini were subjected to two choice oriented experiments involving dens. Each octopus was given four diff erent objects in their aquaria to make their dens: a plastic vial, a PVC tube, a flat rock, and half of a bivalve shell. Each octopus chose to live in the PVC tube. Then during a series of fifteen trials, each octopus was forcibly removed from its den and placed into a sparse tank with just the same four den types They were allowed to hide in the den of their choice. Overall, the animals chose to hide in the PVC tube, the shell, and the rock an almost equal number of times, but only one octopus hid in the plastic vial once. This study added to informa tion that can allow analysis of behavioral mechanisms that w ent into this behavior and the way in which it relates to cephalopod cognition. _______________________________________________________________________
Hiding Behaviors in Octopus joubini 5 Introduction Cephalopods have been seen as strange alien creatures whose relatives were thought to sink ships and drown seafarers and whose only redeeming quality was how delicious they were to fry into crunchy appetizers. While still regarded by some to have faces that only their mother would love, popular regard for these animals has certainly come a long way from the mythical monsters of the deep. They have begun to be touted as the most intelligent of all the invertebrates by the media that follows the scientific community (Ste wa rt, 1997) and whether or not this is true, these creatures have been shown to have remarkable abilities that certainly put them near the top of the known candidates. Ironically, these animals were originally believed to be quite stupid by none other t han Aristotle because one could catch them by waving your hands underwater when it was really their innate curiosity drawing them in ( Thompson 1910 ) The class Cephalopoda is a part of the phylum Mollusca all members of which are marine animals They sha re the general body plan of bilateral body symmetry and a foot modified to have arms and tentacles that attach to their head. While there used to be many more subclasses (Figure 1) the remaining two extant subclasses are the Coloidea and the Nautiloidea. The Nautiloidea i s the last cephalopod group to retain an external shell and is called the nautilus and Coloidea includes the remaining groups that either have an internal or reduced shell, the cuttlefish and squid respectively, or no shell at all in the octopods. While all cephalopods are known to perform seemingly intellige nt feats, except for the nautilus ( Callaway, 2008) the octopuses are e specially renowned in this area.
Hiding Behaviors in Octopus joubini 6 Figure 1 : Extant groups of Cephalopoda and one extinct group, Ammonoidea. Provided by eGeology, Blogfa.com. One of the most amazing octopus feats involves a benchmark test that humans often use t o evaluate the cognitive complexity o f themselves and other animals which is the use of tools (Ste r ling, 1999) Before delving into what these animals are capable of, it should be noted what constitutes the actual use of tools imple behaviors such as the use of an object (or objects) as shelter, are not generally regarded as tool use, because the shelter is effectively in use all the time, whereas a tool provides no benefit until it is used for a specific purpose (Finn, 2009) This means that in behavioral situations such as with hermit crabs, the snail shell that they reside in is not considered a tool because it is being used passively all the time. C ertain p rimates have been shown to carry sticks around that they use to extract ants and term ites from their nests but have no purpose otherwise The recorded instance of an
Hiding Behaviors in Octopus joubini 7 nvertebrate using tools. Individuals in Bali were observed to forage for not only split coconut, but mollusk she lls and human garbage such as bottles to use for protection (Finn, 2009) When extracted from their object, they immediately returned to it as soon as the extractor released it. When not in use, the octopus would stack the two halves of the coconut on top of one another, extend its arms out and o ver the edges and use them like but walk along the bottom at the same time (Figure 2 C). As can be seen in Figure 2 it is certainly an odd way to go about your business, wi th the whole body being entirely exposed to predators above and the coconut inhibiting the animal from moving in any efficient manner ye t often traveling over twenty meters in a single march carrying the shells. The only benefit the animal gets is the pote ntial for the objects to be used for protection The fact that the majority of the time the octopus is carrying the shells they are not only totally useless, but an encumbrance on the animal helps define this as tool use. It also differentiates it from their use o f rocks as tools because they do not transport them around but instead use them Figure 2 : A F ree octopus. B Octopus holding coconut shells together for protection. C Octopus carrying coconut shells. Finn 2009
Hiding Behaviors in Octopus joubini 8 when available. Furthermore, the animal is required to assemble the two pieces of the shell together before it can perform its function. It is post ulated that these octopus es m ost likely learned this behavior from doing the same thing with bivalve shells and mere extrapolated this behavior to use on similar objects (Mather 20 10) T his behavior in of itself is related to their cognition and in humans is generally referred to as problem solving, as in using previously learned behaviors and applying it to a new situation. The octopuses were familiar with using the mollusk shells, but when they were probably not available but needed, the animals found the foreign objects, like the c oconuts or bottles, to perform the same function. It may also be behavioral generalization. The popularity and renown for the abilities of the octopus seem to be justified, but what are they really capable of and why? Practically, the animal is very useful as experimental subjects because it take s very little time to acclimate to laboratory environments (Hochner, 2008) This can be visually evident because most octopus es will initially be quite reclusive and display striking crypsis colors in attempts to intimidate or hide, but eventually they tend to become quite personable and intrigued by anything that might be going on in or around its aquarium This is the result of the explorative way that octopus es learn, by automatically in vestigating and grabbing with the arms to judge if something is food or another kind of object (Cousteau, 1978) As such, they can be used to explore a number of different visual discrimination tests using artificial objects of varying size, shape, texture and color. Their bodies also tend to be very resilient to invasive procedures which are necessa ry when trying to determine those pathways that certain sensory nerve impulses take when traveling thr ough the nervous system and the structures that mediate re sponses (Young, 1991)
Hiding Behaviors in Octopus joubini 9 Octopus vulgaris or the common octopus, in particular has been the most widely studied species because, it is very easy to find and not very large. In the wild, they are almost universally solitary animals whose lives basically con sist of hiding in their den during the day and hunting for food at night They are nonetheless explorative individuals with an innate curiosity of new objects, foods, and sights. They exhibit a number of different forms of learning and cognitive phenomenon such as sensitization, habituation, spatial learning, observational learning, and associative learning Learning with visual stimuli have been each studied to varying degrees (Hanlon, 1998) Part of what accounts for the octopuses abilities is the way t heir brain is structured and organized. As opposed to most of their invertebrate relatives whose brains are a chain of ganglia their brains are central nervous system with ganglionated tissues which are much more similar to that of most vertebrates with v ast amounts of organized nerve cells at their disposal. The octopus brain works on a hierarchy of levels of organization with the first most important part being the two optic lobes which can contain 180 million neurons and the arm nervous system which can have 500 million neurons both of which are located outside of the brain capsule ( Hochner, 2004) The large number of neurons in the arm nervous system accounts for their ability to almost move on their own in the correct manner when given the appropriate stimulus. The forty lobed central brain only has about 45 million neurons. Certain structures in their brain show evidence of convergent evolution with that of vertebrates, such as the three cortical layers of the optic lobe in octopus and the three retinal layers in vertebrates (Young, 1971)
Hiding Behaviors in Octopus joubini 10 Figure 3 : Ventral view of Octopus vulgaris b r ain. Marine Ecology Wiki. The octopod peduncle lobe also has granular cells that turn into parallel fibers like the folia in the v ertebrate cerebellum. In regard to the morphological organization of learning and memory the vertical lobe is very close to the vertebrate hippocampus (Wells, 1961 ) Electrophys iological studies performed on these structures point to the fact that conve rgent evolution has created similar pathways and similar synaptic plasticity between the cephalopods and vertebrates as suggested by similar behaviors and modes of life. The importance of these cellular and morphological neural systems at directing these complex forms of learning and memory is exemplified by their evolving in such very differe nt animals (Hardie and Raghu, 2001) However, the vertical lobe is still not basic morphological organization of invertebrate ganglia, with monopolar neurons whose cell bodies are organized in an outer layer and which send their processes into an internal neuropil (Bullock and Ho rr idge 1965) C ell membranes of the vertical lobe cells are more like those of
Hiding Behaviors in Octopus joubini 11 invertebrates Bullock and Horridge suggested that the in which the neurons communicate with e ach other is species specific. T he network structure with a type of activity dependent synaptic plasticity is the most potent form by which memory and learning sys tems may be mediated (Hochner, 2006) Intelligence is the general term used logical manner. Young ( 1991) gives an in depth analysis of the what and whys of octopus cognition. He notes that to respond well to a given stimulus, an animal must be able to classify the stimulus and have some idea of how to react to it, and while an animal may not start off knowing exactly what the appropriate action is the y can learn it given the number of neurons available to them. His research shows that octopus do in fact have nervous systems with large numbers of neurons and that the circuits create mat rices with interlacing axes among different lobes of their brain such as those in Figure 4 Figu re 4 : Scheme to show alternative pathways from the visual feature detectors of an octopus. There are output pathways of attack or retreat. A third pathway leads to the four matrices of the vertical lobe system. Here particular patt erns of visual signals are combined with those of taste to increase the future tendency to attack, or with signals of pain to reduce it. Young, 1991. into familiar catego ries with values that biases it toward performing a particular behavior
Hiding Behaviors in Octopus joubini 12 based on the incoming signals. These matrix system of circuits tend to go ha nd in hand with animals that exhibit sophisticated behaviors by ensuring that a part of the stimulus is alwa ys received, activating the entire set of cells at once. These are indeed present in octopuses as well. T hese matrices form sequences that constitute the arrangements of two systems made up of four lobes each that allow the octopus nervous system to catego rize and utilize visual and tactile memories. It was thought that these two systems acted independently from one another, this however has been shown to be false, in that all eight lobes act together to constitute an example of a distributed memory system that uses a series of networks that does not depend on detailed preformed connections (Young, 1983) .Octopus have shown that that they can recognize the chemical nature and texture of different objects by touch which is mediated by the receptors on the rims suckers and passes through the synaps es in the arms, granted the complete path is unknown still ( Hanlon, 1998 ) Figure 5: Sagittal section of the supraoesophageal lobe of Octopus vulgaris stained with Cajal's silver method. Abbreviations for all figures: ant. bas., anterior basal; b. med., median basal; buc. p., posterior buccal; cer. br. con., cerebrobrachial connective; cer. tr., cerebral tract; lat. inf. fr., lateral inferior frontal; lat. sup. fr., lateral superior frontal; mag., magnocellular, med. inf. fr., median inferior frontal; med. sup. fr., median superior frontal; op., optic; ped., peduncle; post. buc., posterior buccal; plex., plexiform layer; prec., precommissural; pv., palliovisceral; ret., reti na; subfr., subfrontal; sup. buc., superior buccal; subv., subvertical; vert., vertical. (Young, 1991).
Hiding Behaviors in Octopus joubini 13 T o test the animal s learning in regards to touch, they were presented with smooth and rough balls. When the correct ball, whether it be smooth or rough was attacked the animals was given food, but when the incorrect ball was attacked they either received nothing or an electrical shock. They were indeed able to learn which ball gave them food, but to ensure it was being done by touch, they repeated the t nerves severed, to which they still succeeded (Wells, 1965) Figure 6: Diagram of the connections of the tactile memory system of Octopus. The successive matrices are labelled I to 8. In addition, there is some learning capac ity in the suboesophageal centers. (Young, 1991). Afferent fibers in the lips of the suckers are also capable of sensing taste and pass though multiple lobes connected with the second sensory matrix where they weave across the trunks of cell fibers which maximizes the ability of any cell of the lobe to receive signals from more types of input fibers ( Hochner, 2006 ) The basic behavio r caused by this system is the arms to reaching out to grasp unfamiliar objects and reel them in, and if the taste signals fr om the sucker s chemoreceptors indicate the object as food the signals will direct to the lateral inferior frontal lobe to form a competitive learning matrix which bene fits. They also found that while this is true, the system of these inferior frontal lobes
Hiding Behaviors in Octopus joubini 14 will respond by pulling in objects unless pain fibers in the subfrontal complex dendritic field are activated by trauma ( Wells, 1965 ) Figure 7: Diagram of connect ions in the inferior frontal system of an octopus (Young, 1971). Associative learning caused by signals of taste from the inferior frontal lobe is very likely unless stopped by pain. When pain signals are transmitted, they ignore the signal given from touch by modifying synapses of the subfrontal lobe. This was given credence by using lesions to destroy ama crine cells in the subfrontal lobe (Figure 7) and the animal did not learn to avoid objects that gave it electrical shocks (Young, 1991) Even tho ugh octopus es are generally solitary ani mals, there is evidence to suggest that they can exhibit observational learning. A group of octopus es was conditioned to attack colored balls (white and red) when introduced t o a bare environment (Fiorito, 1992) Two groups of animals were trained as demonstrators, with Red Group having the red ball being the correct choice, the choosing of which netted them a piece of fish and the whit e ball giving them an electrical shock when touched. White Group did the same,
Hiding Behaviors in Octopus joubini 15 but reversed with the white ball being correct. The untrained animals quickly showed that they were able to learn the association between the colored balls and the positive or negative reinforcement. Figure 8: Schematic of the experiment apparatus and proto col. An Octopus vulgaris is shown (right side of the figure) attacking a ball (the red one) and acting as demonstrator for the other animal (observer, left side) that is standing outside of its home and watching its conspecific during the whole session thr ough a transparent wall. Each tank had an independent supply of running water. Octopuses were allowed to visually interact for 2 hours before the start of the observation phase performances was 40s and inter trial intervals were set at 5 min. (Fiorito, 1992). It was noted that the attention of the observing octopus significantly increased during the trial when compared with their activity between trials as they could be seen moving to get b etter views of their conspecifics and following them by shifting their eyes in head in their direction. The observers were subjected to the same test with some alterations. The observers were presented with the balls in random locations around the test aquarium but this time no positive or negative stimulaus was given when they attacked a ball. As seen in Table 1 the results of the experiment are quite stark as the observed performed much better than the untrained individuals This type of experiment h as been repeated with cuttlefish (Boal, 2001), and therefore shows that octopus exhibit some form of observational learning This is extremely important, because this is a proven procedure on O. vulgaris it can be seen as a benchmark test for octopus ass ociative learning.
Hiding Behaviors in Octopus joubini 16 Table 1 : Learning retention by observers. Mean standard deviation from five experiments with red and white groups of observers and untrained octopuses (12) at 1 and 5 days after the observational phase. The preference for red in untrained animals during free choice experiments was significant at day 5 (Fiorito, 1992) One of the most distinctive features of octopus is their lack of hard body parts, except for the beak. The adv antage to this is their renowned escape artist like ability to fit t hrough almost any crack or crevi ce. The dis advantage is the necessity that they find a shelter in which they can protect themselves from from predators Shelter is one of the most fundamental factors of survival for most if not all living organisms, with food and breeding being the other two. T hey have little to no biological way to protect their soft bodies othe r than venom, expeling ink and jetting away The population of Octopus briareus in a salt water lagoon was shown to be abundant because of a general lack of predatory fish (Aronson, 1986) but in most other areas, the availability of middens to find safety in became the limiting factor of their popu lation. Moray eels specifically feed on octopuses as part of their main diet and numerous beaks have been found in their stomachs (Randall, 1967) They are especially efficient hunters of these animals b ecause of their anguiliform body that lets them chase through almost as many crevices as their prey. To maximize their ability to survive predation, octopus es continually make alterations to the dens throughout the day, especially those that live on soft sediments ( Hanlon, 1998 ) These areas generally lack l arge formations with many available areas for living, so the octopus often need to piece together their shelters, as such, it was not
Hiding Behaviors in Octopus joubini 17 uncommon to find animals that were holding two shell halves together or living in human garbage like beer bottles (Anderso n et al, 1999) Figure 9: Results of enrichment survey. The mean density at each experimental and control site, before and after the enrichment with artificial dens (pre and post correspondingly) is given. (Katsanevakis, 2004). T o analyze the effects of living in these soft sediment areas on octopus popu lation research team conducted multiple surveys on soft sediment areas with no hard objects and soft sediment areas with a number of hard objects, the e ffects of introd ucing manmade objects to an area with none, and the amount of different types of den construction in the area ( Mather, 2010 ) They first found that there were little to no octopus in areas with no hard substances, especially compared to areas with an abundance of hard substances tha t had high populations of octopus When manmade objects were placed in areas with no previously available shelter, the density of octopus greatly increased, but th e number of octopus changed very little when they were added to areas that already had available hid ing areas In the den survey, five different sediment dug by the octopus with rocks and stones used to reinforce the walls and t he
Hiding Behaviors in Octopus joubini 18 was when the animal digs an inclined hole underneath a large Figure 10: A sketch of the 4 different den types. (Katsanevakis, 2004). rock or stone er of bivalve shells or within gastropod shells. was a solid object littered by humans that fo rmed a cavity like empty bottles plastic cups, buckets, barrels, tires, pots, pipes, cans, shoes, etc. Finally animals that were not recorded in a den of any kind were classified as free (Katsanevakis, 2004) A t the time they were observed, 38.7% of the three hundred and forty four octopus resided in human lit ter Se v en point three percent of them were out and about at the time of observation. They also ran tests to account for variables that may have affect ed the results. The variables were octopus size in the den, the depth fineness of the sand, the local geography, and how far it was from the shore. It showed that large octopus never used s hells. Mainly small individuals were inshore, and mainly large ones in deep waters. Wells were used more commonly in coarse sand areas and human origin dens were used more in finer sand areas. There were fewer rock/stone dens the deeper and further from sh ore they were. However, none of these variables indicate why manmade dens were so commonly used
Hiding Behaviors in Octopus joubini 19 material. (pl.=plastic, al.=aluminum). (Katsanevakis, 2004) The main piece of information to be taken from this study is on soft sediment, the material avai la ble that can be used to make dens is a limiting factor on octopus population. In areas that had no octopus at all, the enrichment of the area with artificial dens allowed octopus to establish a population within a month ( Aronson, 1986 ) This also suggests that immigration by octopus is rather frequent. As the small percentage of animals out and about during the day, this suggested that they make shor t trips during the day and make longer trips, most likely to hunt, at night that may result in them finding new shelters. For Octopus joubini it has been shown that not only is the availability of shelter, or middens, the limiting factor of their populati on size. In Octopus bimaculoides it has been shown that dominant relationships exist between conspecifics based on midden ownership and quality. A number of other animals exhibit this same type of behavior. Marine hermit crabs require the use of mollusk sh ells to survive as the quality of these shells determines how effectively they are able to avoid predation (Angel, 2000)
Hiding Behaviors in Octopus joubini 20 Pagurus bernhardus will often fight over shells if there is either a limited number of them or if shell quality is variable The hermi t crabs are able to recognize whether a weaker individual is occupying a higher quality shell and will fight and evict the individual to gain the advantage (Hazlett, 1967) O ctopus es lack a shell for protection from predators so they must rely on shelters camo u flage, ink and venom It was found that areas with fewer predatory fish had high populations of Octopus briareus and areas with larger numbers of predators had smaller populations. (Mather, 1982) Figure 12: Ethogram of behaviors exhibited during den conflicts and score received if performed. (Mather, 1982) These animals have also shown that they can not only distinguish between middens that will provide more or less protection, but will actively choose to live in the better areas (Katsanevakis, 2 004) Even though territoriality is not a known behavior among octopus, they have been shown to compete with other conspecifics for higher quality dens and will protect these from other octopuses (Cigliano, 1993) T o determine what dens were most naturally preferred, a group of animals were allowed to choose from a number of variable sized PVC tube dens (Mather, 198 2 ) PVC tubes were used because
Hiding Behaviors in Octopus joubini 21 individuals were found to reside in plumbing pipes in the wild. Their initial study results revealed that the an imals preferred the small pipe with a small entrance the most, and a large pipe with a large entrance the least. When introduced into the den scenario with conspecifics, their encounters with one another over dominanc e of the area could be classified as either an attack or withdrawal type encounters (Mather, 2010 ) While both dominant and subordinate animals mainly use full on attack styled aggressive behavior, the domi nant animals used these types of aggression significantly more than subordinates did. of its mantle with the highest rank being Alpha and the lowest being Gamma, with the qualifications for each shown in Figure 13. Table 2 : Size classes of individual octopus and what weight and mantle length they had to be to qualify for them. (Mather, 1982) Over time, the octopus es showed evidence that they were able to recognize one another. instead of holding their ground more often, decided to avoid the encounter altogether, even avoiding at some distances away from one another. octopus greatly correlated with their weight when wet and the len gth of their mantle and the ranks stayed constant throughout testing. While previous studies had shown that dominance relationships were mediated by the size of the octopus involved (Mather,
Hiding Behaviors in Octopus joubini 22 1980) this was the first to show that it also correlated with de n use and availability. Although this might suggest evidence of territoriality in these animals there have been reports of large populations living in close proximity because of restrictions on local availability of living materials but without issue with one another ( Aronson, 1986 ) This has also been shown in laboratory situations where animals are being kept in large groups (Cigliano, 1993) Figure 13 : Diver with Octopus joubini. By dividnk on Tumblr The Atlantic Pygmy Octopus, Octopus joubini represents one of the smallest species of octopus in the world and an uncommon choice for testing the cognitive abilities of cephalopods. Little to no behavioral analysis has been done on these animals which make them prime subjects for performing studies on them. There are a number of factors that make them difficult to work with, one of the most important of which is merely keeping the m alive long enough to test, in addition to the fact that they tend not to be very cooperative Luckily, most of the studi es that have been performed on this species involve their care and rearing. Octopus joubini reach a maximum size of 10 to 15cm, and while this allows them to be kept in much smaller enclosures than most other
Hiding Behaviors in Octopus joubini 23 species, it does not allow the caregiver much r oom for error in terms of their water quailty The nitrogen and ammonia levels of water in parts per million are the most common suspects in aquarium deaths given how easily they fluctuate because of animal excretions, evaporation of water, and decaying le ftovers (Dunlop, 2008) T he simplest way to maintain them is to have a constant supply of fresh, incoming seawater, which is difficult to achieve away from co astal areas, thus limiting the number of institutions that can host experiments on this species L ike all other octopus es O. joubini are carnivores and will feed on most crustaceans, mollusks or fish small enough for them to capture. Octopus joubini are mostly solitary animals however, they exhibit some forms of social interaction. To better study what these interactions are, a group of Octopus joubini were kept in a semi natural environment together and observed This was done to gain a better und erstanding of their time spent i n parts of t he environment and agoni stic behaviors between conspecifics along with how it pertains to dens and if it is similar to other species (Mather, 1980) Figure 14: The tank and apparatus used to observe the octopus. (Mather, 1980) Octopus joubini are nocturnal, thus all observations had to be done at night time when they a re most active with a red light illuminating the aquarium The red light did
Hiding Behaviors in Octopus joubini 24 not disturb their movements, but still made them visible enough to see. It was found that while the a nimals spent more time in their dens than otherwise, each animal mostly stayed within a particular grid square or corner which may suggest that these animals show dominance hierarchies with one another and not territorial behaviors. The more dominant membe rs exclude others from their preferred areas and have priority access to the food when it is available over others. In a territorial scenario, the octopus would each have their own area which they defended from conspecifics, but in this case, all mostly pr eferred to be along the corners and walls, presumably because they judged those areas to be safer than others and do not like to be out in the open. This study a lso showed the prevalence of size of an individual in the dominance hierarchies of a group of o ctopus es Size is a signif i cant which gains them access to the best dens and the most amount of food in the area when competing with conspecifics. While there has been relatively little research performed on the Octopus joubini the large number of studies done on other species of octopus like O. vulgaris and O. briareus may shed light on many aspects of their lives The behavioral similarities between th e Octopus vulgaris social interactions over dens compared to those for O. joubini are evident. However, because of size differences there could be many aspects about O. joubini that make them still quite different from other species The small size o f the pygmy octopus suggests that their preys are going to be much smaller than that of the larger animals likely giving them much different hunting strategy The types of middens chosen by the octopus themselves will also be affected by their size, as so me studies show that larger octopus tend to inhabit human litter when
Hiding Behaviors in Octopus joubini 25 available (Katsanevakis, 2004) The current study will examine the decisions Octopus joubini makes in regards to the den choice in a simulated natural environment and their choice of shelter during an emergency situation. Methods During the first series of tests, the subjects were t hree adol escent Atlantic pygmy octopuses The mantle length of each was about 1.5 centimeters, however their exact age, weight, and sex are unknown T he y were all acquired at the same time during breeding season from Gulf Coast Specimens ( www. gulfspecimen .org/) from the northern Gulf of Mexico Figure 15: A picture of the sea table with the three octopus tanks set up with the water system. B. King Given the fact that octopuses are incredibly sensitive to changes in the chemical levels of a water system (Dunlop, 2008) it was necessary to find the most efficient way to ensure Tanks Water Table Fresh saltwater pipes
Hiding Behaviors in Octopus joubini 26 that the water stayed at the most pure level possible. To achieve this, e ach was isolated in an indiv idual 37.85 liter aquarium with identical layouts, each of which was kept in a sea table getting constant feeds of new water (Figure 15) Given the large surface area of water ex posed to the air, one issue that emerged was a high daily evaporation rate so every night, the sum p needed to be filled with new water Each aquarium had 5 cm of aragonite gravel, a piece of coral skeleton, two pieces of fake sea grass, a small conch sh ell, half a clam shell, and two flat pieces of rock. This type of octopus most commonly resides around and in sea grass beds near the shore and around large natural structures like coral and rock formations. While not nearly a perfect mimic of their natural environment, this setup contained many elements that might be present as well as providing enough possible locations for shelter to give each animal a variety of different possible hiding places from which to choose. Howev er, because these animals need ed to be extracted for experimentation, the objects in the aquarium were chosen to keep the m as comfortable as possible, but also to be easily accessibl e when needed. Octopuses are widely known to be escape artists and have even made the news in cases where they have wreaked havoc on aquariums because of their attempts to gain freedom ( Dell'Amore 2009) This is in large part due to the fact that they can fit through any hole that is large enough to fit their beak through T o combat this phenomenon, all three aquaria were topped with custom fitted plastic grate s covered in mesh and weighed down by rocks and dishes that would simultaneously be difficult to push up to open but difficult to cling to with their suction cups as well.
Hiding Behaviors in Octopus joubini 27 Pilot Experiment Because of their small size and fragile constit ution, subjects were given about a month and a half to acclimatize to their aquaria Because of their small size they were fed the smallest food available until they matured which was live grass shrimp ( Paleomonetes pugio ) They were then fed small crabs and pieces of mullet. T o further ensure the animals accessibility to be extracted, a week b efore pre training beg an the conch shell was removed as it was determined that the animals preferred to live in these They were very difficult to remove once they had retreated into the inner reaches of the shell The pre training began by removing them from their aquarium and placing them in a circular dish filled about fou r centimete r s full with new seawater that was shallow enough to keep the animals on level with the set up but deep enough to provide enough water to breath e for extended periods of time. In this dish, th ey were presented spiral shelled small hermit crabs that were attached to half white and half red plates with their shells stuck in them (Figure 16) The subjects were left alone in the dark to eat for half an hour each. Hermit crabs were used because of the likelihood that they were a common prey item for O. joubini in the wild (Mather, 2010) F or each octopus to complete the pre training successfully they needed to consume the hermit crabs off of the plates for four days, only then would the animals be run through the full experiment to ensure they had been conditioned to associate the two colors with food. If an individual failed to eat the hermit crab in 30 minutes the pre training period for that animal was restarted. A 30 minute trial was used compared to (1992) to give the smaller animals more time to adjust to being removed from their enclosure. For each trial, the octopus were removed from their aquarium and placed in the same shallow dish this
Hiding Behaviors in Octopus joubini 28 time they w ere presented with a circle colored red along with another circle colored white Figure 16: Mockup of preliminary study. Overhead view on the left showing the two squares and the octopus. Eye level view on the right showing the pinned hermit crabs on th e back of the plates. Each plate was cut from a sheet of Sintra plastic to be 2 cms in diameter and painted with the appropriate color before being covered in a water proof sealant. Hermit crabs were attached to the backs of these figures with the points of their shells stuck in them. T o condition the animals to not choose the white circ le, it charged with a 0.5v electrical shock that they would receive on touching it T o incentivize the choosing of the red circle it was left as is and the octopus would be allowed to retrieve food from the back Red and white were used because of the oct s polarized vision as they seem to appear different enough in shade to them as well as being common colors that other octopuses use for communication (Mather, 2010) The locations of each were switched randomly for the next test to prevent them from c onfusing sides with the respective reinforcement. Each individual was subjected to the test twice a d ay for as long as it took for them to perform the task with no errors in a day The octopus were left in the test chamber for half an hou r during each tria l and a success would be counted if they
Hiding Behaviors in Octopus joubini 29 grabbed onto the red plate and retrieved the hermit crab wit hin the half hour. A failure would be counted if the octopus either did nothing for the half hour or only grabbed onto the white circle or grabbed the red disk but did not take the crab For the second round of experiments, a new group of Octopus joubini was used. The new three were also obtained from the northern Gulf of Mexico from the Gulf specimens company ( www. gulfspecimen .org/). These specimens were somewhat older than the previous group, as their mantles were about two centimeters long. Because of the age and size difference, this group was only given a week to acclimatize to their new homes because it was believed that the older individuals would b e hardier than their younger counterparts. Den Experiment In order to determine what sort of den preferences these octopuses had, four different hiding areas were placed in their aquariums prior to introducing them to their aquaria. These potential dens were a rock, a half of bivalve shell, a clear vial, and a 5 cm long length of PVC piping. Normally octopuses will choose where to live based on exploration and evaluation of objects in its environment. Individuals may choose to live in a particular den b ecause it is advantageous for survival given the qualities of the environment around it. Two objects were chosen to represent hiding areas that would almost certainly be encountered at some point in its natural environment, the shell and rock, and the othe r two were chosen to be potentially good hiding areas, but nevertheless vial). Hiding Experiment
Hiding Behaviors in Octopus joubini 30 The final study wa s designed to test what kind of hiding places oc topus will occupy in a situation of mild duress. This experiment puts the animal in a situation that is potentially danger ous as it is being forced out of its home into a relatively foreign environment where it has multiple options in which it can choose t o hide if it does at all and what decisions it chooses to make on the spot and what factors may be mediating that decision making. The same general holding method was used with these octopus es T o help ensure that potential waste such as excretions and ink did not stay in the aquarium to harm them, an isolation aquarium was setup beside each aquarium so the octopus could be easily removed and contained when regular cleanings were conducted. The goal of the this test was to analyze the hiding shelter decisions made by Octopus joubini when provided with multiple options where some were available in the holding aquarium and others were foreign. This was designed to induce a more natural behavioral response in a lab oratory setting that could be quantified. All fifteen runs of the experiment were performed between 7:00pm and 9:00pm EST, between October and November, which was a time that the animals would normally be out hunting and exploring. The experiments were con ducted in the centermost isolation aquarium with the rocks and hiding areas removed and with no substrate on the bottom. Four different hiding areas were placed in a circular formation aligned around the center of the aquarium including a small plastic via l, two and a half inch length PVC tube, a semi flat rock and half a bivalve shell, as seen in Figure 16. Each of these objects was also present within the octopuses home aquarium to determine if familiarity with the objects affected their decision making during the testing. For each test the location of each hiding area was
Hiding Behaviors in Octopus joubini 31 randomly alternated to avoid the animals remembering the spot where the object was and continually going inside the same one. Figure 17: A picture of the 10 gallon tank used in th e experiment. From top to bottom and left to right, the clear vial, the rock, the pvc tube and the shell are visible. The bar in the figure is approximately 5cm long, equal to the tube. B. King Subjects were transferred from their home aquaria to the test aquarium by removing the object in which they resided They were gently prodded out with a pipe cleaner to avoid injury as they were not willing to leave on their own. If the animal inked, the excretion was removed using a handheld, wire mesh sieve. If th e animal inked a great deal, for example, enough to cloud most of the aquarium testing for that animal was aborted for the day and the animal was returned to its home aquarium The whole test aquarium was then emptied and cleaned to prevent poisoning of o ther subjects. Once introduced successfully to the experimental environment, the octopuses were given an arbitrary time of thirty minutes to choose a hiding place in the dark The thirty minute
Hiding Behaviors in Octopus joubini 32 time frame was determined based on the previous experiment as a reasonable time for the animal to acclimate to its new environment and perform. If by the end of the thirty minutes they had yet to choose, it was considered a fail ure It was noted if the ani mal entered a hid ing area but left it shortly after and the hid ing area was noted if they stayed inside for more than thirty seconds as a success as well as the total time it took for them to make their final decision. Generally if an octopus decided not t o stay in a chosen area it would leave within ten seconds, so thirty seconds was allowed to be sure they had made their final decision for occasionally one would seemingly change its mind and switch areas Once completed, the animal was removed from the a quarium and placed back into their respective homes. Precautions were taken to ensure ink or chemicals released by previous subjects did not affect the decisions of the next animal. Multiple sets of hiding areas were used that were all of the same size and physical appearance and were rotated after each test. The water was also changed after each run and all of the equipment was washed once testing ceased for the day. The results of each test were quantified in terms of hiding areas chosen, time taken, and individuals taking part as well as qualified by noting what actions were taken and behavior during the tests. Results Table 3 : Ethogram of relevant octopus behaviors. Behavior Description Hide Animal enters a hide and stays for longer than five seconds. Usually would leave in that time. Examine Wraps arms around object or extends arms forward without moving body. Ink Release a puff of ink. Ink and escape Releases a puff of ink then jets away. Pace Moves back and forth in the same area for more than thirty seconds. Escape Crawls out of the current enclosure. Crypsis change (aggressive) Changes the color of the body between dark red and pale white with black eyes. Or holds the dark red color for more than ten seconds. Drill and envenomate Grasps and envelops a shelled prey such as a hermit crab, bivalve, or gastropod
Hiding Behaviors in Octopus joubini 33 shelled prey will be left intact with small hole. Forcibly remove shel led prey Grasps and envelops shelled prey such as a hermit crab, bivalve, or gastropod and uses muscle power to force open shell or pull out the animal. Shell will be left broken or empty. Preliminary observations of behavior pilot study The first group of three Octopus joubini were about 1.5 2cm long each and arrived in the laboratory in June of 2012. It initially took several weeks to learn their hiding places well enough to be able to find them, as the only evidence they still existed was octopus feces and objects kept being moved around. They were each given numbers to help identify them. From aquarium s left to right their names were: 1, 2, and 3 Each seemed to have certain qu i rks and took to the testing differently ; other researchers have described these quirks as personalities ( Zimmer, 2008 ) One on ly ate from the plate sporadically and often tried to escape the training dish. Three was the only one wh ich learned to feed off the plate consistently during pre training, almost never inked, and always hid in a hole in the piece of dead coral in its aqua rium Number t wo never willingly fed from the pre training plate ; eventually it was hand fe d eating and would sometimes ink during the observation s There were also several weeks where it had to be left out of pre training because it wedg ed itself in a rock from which it removed A common factor found among all subjects was their tendency to hide during the pre training sessions (Figure 18) While best efforts were made to reduce the amount of objects in the test area, subjects found they could effectively hide underneath the food plate itself. The inherent problem found with this pilot experiment is the very basic nature most speci es do during hunts at night like that of O. vulgaris and O. briareus a s side
Hiding Behaviors in Octopus joubini 34 observations have shown and previous observations corroborate, Octopus joubini are wait and ambush predators hiding in their midden and wait ing for an organism to pass by U sing the ir long arms, they will reach out, grab, and reel in their prey to be eaten. This test was thought to be achievable on the assumption that feeding was a basic enough instinct that eventually the animals would perform and be able to learn the conditionin g as seen in other species. Figure 18: Re creation of octopus hiding underneath food plate. T wo of the three subjects refused to go after food on their own when in the experimentation environment. These first three subjects died before further observations and testing could be done. Based on observations of these animals it was confirmed that u nlike most other species O. joubini are wait and ambush predators These animals will generally make thei r homes in bivalve shells that they hold together using their powerful arms. There they wait for an organism to pass by and stretch out their long arms grab their prey, reel them in and use their venom to finish them off. Den Experiment For the second part of the experiment, three different pygmy octopuses were obtained While each octopus was again given its own 37.85 liter aquarium, each also had a separate 18.93 liter isolation aquarium setup next to their home aquarium These were
Hiding Behaviors in Octopus joubini 35 in place to give the octopuses a clean area to be held in while their home was being given necessary maintenance The home aquaria were setup in the same water system as described earlier with the constant inflow of new water being fed into each aquarium an d excess flowing out into the water table to be handled by the filtration system Each aquarium had a substrate of salt water gravel, a fake plant, a few flat rocks, a half of a bivalve shell, a clear plastic vial and a four to 12 centimeter long length of PVC pipe All three of the octopuses chose to live in the PVC tube over the other three hiding areas. Each of the items chosen was done so because they were the same set of items within their home aquariums. This time their diet consisted entirely of the hermit crabs collected in the bay, which were kept in a 37.85 liter holding aquarium Hiding Experiment Table 4 : N umber of times each octopus successfully chose each of the hiding areas during the trials. There is also a total of how many times each hiding place was chosen by all the octopus throughout the experiment. Octopus Rock Shell Vial Tube Failures A 2 3 1 2 7 B 3 2 0 5 5 C 4 5 0 3 3 Total 9 10 1 10 1 5 Octopus A Table 5 : T ime line of each trial and indicates what hide they chose, how long it took for them to decide in minutes and seconds, and any observations made about the animal. Day Choice Time to completion (m:s) Notes 1 PVC Tube 5:36 2 N/A Too stressed by removal. Flashed burgundy and white. Inked a lot. 3 Shell 0:02 Immediately entered shell. 4 Shell 16:14 Explored. 5 PVC Tube 14:45 Explored. 6 N/A Could not be removed from home.
Hiding Behaviors in Octopus joubini 36 7 N/A Could not be found. 8 N/A 29:15 Investigated every hiding area checking the tube upwards of five times before escaping out the back. 9 N/A 30:00 Investigated tube and shell before refusing to move. 10 N/A 30:00 Refused to move from back of aquarium 11 Shell 12:26 12 Vial 2:07 Went in shell first. 13 Rock 18:55 Explored. 14 Rock 14:32 15 N/A 30:00 Octopus A was placed on the farthest left area ( Figure 20) It is notable, that this animal had a slightly larger mantle length than the other two and was overall a little larger than the others. Octopus A chose to h ide in the shell the most often As can be seen on Table 3, a timeline of its success rate by time throughout the trial, it had a seven failures. It commonly either totally resisted all attempts to be removed from its home by either expertly hid i ng using its crypsis abilities or wedging itsel f into a shell or the plant pot. It was not forcibly removed for fear of harming the animal It also occasionally attempted to escape from the test tank altogether Figure 20: Mockup of the aquarium setup de picting which octopus was in which aquarium. It would presumably be too stressed to test at that point. This subject would do a multitude of things while in the test aquarium instead of either investigating the hiding
Hiding Behaviors in Octopus joubini 37 areas or hiding in them at all. The most common behavior observed was a behavior that down and side to side of one of the walls repeatedly. Figure 21: H ow long it took the oc topus to complete or fail the trial for the day of testing indicated. If it took the animal the full 1800s or 0s then that trial was failed. This animal would sometimes do this for upwards of ound the rim of the waterline of the aquarium or to explore the hidin g areas Octopus B Table 6 : T ime line of each trial and indicates what hide they chose, how long it took for them to decide in minutes and seconds, and any observ ations made about the animal. Day Choice Time to completion (m:s) Notes 1 Rock 15:11 Explored back side of aquarium and water line. Repeatedly checked out rock. Moved tube. Methodically examined aquarium walls. 2 Rock 2:04 3 Shell 19:47 4 N/A Too stressed by move. Inked a lot. 5 PVC Tube 0:04 Entered tube immediately after inking a lot. 6 N/A 9:22 Inked when entered aquarium Explored before 336 0 2 974 885 0 0 1755 1800 1800 746 127 1135 875 1800 0 200 400 600 800 1000 1200 1400 1600 1800 2000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Seconds Taken Day of Trials Octopus A
Hiding Behaviors in Octopus joubini 38 attempting to escape. 7 PVC Tube 9:30 8 PVC Tube 3:41 9 N/A Too stressed, inked a lot. 10 N/A Refused to be removed. 11 PVC Tube 26:32 Paced along back wall a great deal 12 N/A Refused to be removed. 13 Rock 13:37 14 Shell 7:26 15 PVC Tube 8:30 B could be described as being in the middle ground in terms of success among the three individuals. It had 66.6% completed trials while taking an average time of about 7.7 minutes to do so. Many of i ts failures were aborted trials due to stress. There were no instances where it refused to perform and merely paced or stayed still This is where the trend of the tendency to choose the tube equally if not more than the natural formed objects can be really seen. While this octopus had the two instances each where it chose to e nter the rock and shell. B y far the hide that it chose to enter the most was the PVC Tube. Figure 22 : Time it took the octopus to complete or fail the trial for the day of testing indicated. If it took the animal the full 1800s or 0s then that trial was failed. 911 124 1187 0 4 562 570 221 0 0 1592 0 812 446 510 0 200 400 600 800 1000 1200 1400 1600 1800 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Seconds Taken Day of Trials Octopus B
Hiding Behaviors in Octopus joubini 39 Octopus C Table 7 : T ime line of each trial and indicates what hide they chose, how long it took for them to decide in minutes and seconds, and any observations made about the animal. Day Choice Time to completion (m:s) Notes 1 Rock 0:04 Immediately inked before hiding. 2 Shell 2:15 Explored water line then quickly hid. 3 Shell 4:26 Inked a little before exploring 4 PVC Tube 0:09 Immediately hid under the rock, but moved to the tube. 5 PVC Tube 0:04 Inked repeatedly then hid. 6 Rock 0:04 Inked then hid. 7 Rock 4:46 8 Shell 4:32 Most of the time it sat still on the wall 9 N/A 30:00 Paced for 9 min before sitting still for the remainder 10 Rock 25:15 Sat still for most of the time 11 N/A Inked too much. 12 Shell 0:04 Immediately hid after inking. 13 N/A Too stressed, inked a lot. 14 Shell 5:13 Inked before hiding. 15 PVC Tube 0:06 Octopus C was the only octopus to not begin the experiment with a length of PVC pipe in its home enclosure. This meant that the most it had to work with in terms of making dens were the shells, the vial, and some rocks. At first, C resided in the half biva lve shell. I t was also most likely the most familiar because the animals were shipped in these shells. The rock seemed to require more effort to get under the larger pieces of gravel needed to be removed from underneath after every time it was removed for the trial. Underneath t he rock was its primary home until we were able to find another section of PVC pipe Once this was in, subject C immediately relocated to the tube for its home just like the other two subjects used in this trial T o combat the potent ial downside of having two openings to this midden, each octopus blocked one end of the tube with gravel and small rocks, but not fully, allowing an escape route Other than its initial lack
Hiding Behaviors in Octopus joubini 40 of tube, C distinct personality trait was its level of skittish ness. Out of all the octopus es whenever it was disturbed, whether that meant having objects in its aquarium moved or being extracted from the aquarium C always inked, sometimes a large amount, and tried to jet away Presumably in the wild this would be a beneficial reaction rather than or a conspecific Because of C run times for the tests out of all three animals, often entering a shell within seconds of being ejected from its tube. This individual appeared to favor the shell slightly more so than the rock and the tube, but all three were similar in the amount of times it chose them, except for the vial which it di d not choose at all. Figure 23 : Time it took the octopus to complete or fail the trial for the day of testing indicated. If it took the animal the full 1800s or 0s then that trial was failed. Discussion Octopus A potentially chose the shell more o ften because its larger size made this somewhat more protective than the other options. It also had the only instance of an 4 135 226 9 4 4 286 272 1800 1515 0 4 0 313 6 0 200 400 600 800 1000 1200 1400 1600 1800 2000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Seconds Taken Day of Trials Octopus C
Hiding Behaviors in Octopus joubini 41 octopus choosing the vial as a hiding spot. Part of the impo rtance of the vial is that it provided only a single entrance that the animal needs to watch for predators getting to it. O. vulgaris ( 2004 ), glass bottles are a common choice for octopus to make their homes in, given that they make it very difficult to animals to get at them within. The bo ttle exhibits many of the same advantages that the plastic vial does in that it makes it very difficult for most fish and crabs to get at them when wedged securely enough into it, but it does little to protect them from other octopuses that might prey upon them. This individual had by far the most failures out of the whole group which could be linked to its tendency to attempt escape. It is clear that there are some individual differences between the three octopus es given the variance in the results of thes per se is significant in the analysis of these animals as individuals. Octopus A therefore could be described as the least cooperative of the group. One trend can be noticed when the time taken vs. trial number is examined (figure 21). Octopus A refused to move and perform during the time and took the full thirty minutes of the test. Octopus B first inked a great deal, thereby becoming to o physically stressed to perform the experiment and the second time resisted all effort to be removed from its home. Over time it has become evident that octopus es have the potential to show behaviors that do not necessarily have a beneficial outcome such as the obtaining of shelter or food. The best examp le is playing (Mather 2008) which these animals have been shown to do. T enter certain dens, the qualities of each should be examined. The rock is potentially the least ideal hiding spot out of either of the natural formed dens as it does provide good
Hiding Behaviors in Octopus joubini 42 protection from above, and often an abrasive deterrent for attack, it does not provide protection from the sides. It leaves the sides open to attack by animals like fish that could push unde rneath the rock to get to the animal (Mather, 2010) The shell on the other hand addresses a number of these deficiencies. They will generally be lying with the open side flat on the ground, thus blocking the only entrance and at the same time, making diff icult to get to it. The downside is the fact that it does have only entrance making escape almost impossible if the need arise s such as if another octopus is in pursuit. Figure 24: Octopus A in the clear vial. This was the only time that one of the octopuses chose the vial. Even with their downsides, these both are acceptable choices for hiding areas as can be seen by the results of octopus A and C since they were chosen two to three times each and given that octopus es in the wild commonly use these objects to make their homes. What is not necessarily a normal occurrence it the much greater tendency for this animal to choose the PVC pipe over the other two as well as for A to choose it nearly as much given that it is an unnatural object. Although, wht her or not the animal recognizes the difference between a natural object and a manmade object requires further testing. It was
Hiding Behaviors in Octopus joubini 43 much as the others. The pipe however has many distinct advantages. It is a totally opaque object, keeping the octopus from being seen within. There are only two openings to it, which while it offers two sides from which it can be attacked, the animal always has a second opening from which it can escape. Even though this octopus chose the tube more so than the other hiding areas it does not mean that all octopus es would consider the tube to be the most superior hide as can be seen by Octopus A which chose it nearly as often While not exactly the same, these qualities of the pipe somewhat mimic those of two bivalve shells held together over the animal or that of a gastropod shell. Upon examining all three sets of data for each octopus together, a few tren ds begin to show through. S tudies showed th at objects of human litter were the most preferred dens and plastic bottles were the most popular (Kats a n e vak i s, 2004; Cigliano 1993) Figure 25 : P ercentage out of the total trials that each hide was chosen. 20% 22.2% 2.2% 22.2% 33.4% Total percentage of Performances Rock Shell Vial Tube Failure
Hiding Behaviors in Octopus joubini 44 The rock, the shell and the tube each represent about one fifth of the total performances. This verifies the acceptability hiding areas to the octopus which is corroborated by Katsanevakis ( 2004) who has shown that Octopus v ulgaris can make sophisticated dens from these objects in the wild. That the plastic PVC tube was chosen almost the same amount as the natural objects by the Octopus joubini when hiding and having chosen it over them for making their actual den is also see n in other species as seen in Figure 26 from the study on O. vulgaris den ecology Figure 26 is very similar in terms of percentages to the results of this study, and even though it was performed on soft sediments and not hard, the unnatural objects were a bout 1/3 of the hiding area choices made by octopus species. Again, while there are differences in species and sediment type between the studies, it shows a similarity that merits further research. This suggests that the animals exhibit some sort of decisi on making in regards to what they are going to hide in that does not discriminate between naturally occurring and foreign objects Figure 26: The relative proportion of the different types of occupied by 344 octopus during a survey. The 4 is used. The octopuses that were found moving far from their den w 2004.
Hiding Behaviors in Octopus joubini 45 While it is unclear from data in the current experiments what systems in the octopus nervous system mediate these kinds of behaviors, there are some definite candidates that could be responsible. Given that octopus es generally investigate objects and their surroundings by reaching out with their arms and grabbing them, it is possible the tactile memory systems are responsible, mediated by the subesophageal lobe of their brain (Hochner, 2006) They have shown that they are capable of learning textures and shapes by touch alone (Wells, 1960) This could mean that, for the shells and rocks at least, the octopus es are familiar with how the objects feel when examined and they may automatically acknowledge that this kind of object can provide a hiding spot. On the other hand, for the tube and the vial they may be able to recognize the shape or layout as being good or bad locations for hiding. The octopus may examine the vial and feel that it is not very deep and only has a single entrance similar to holes or crevices in their natural environme nt. This is a much more complex learning behavior that octopuses have been known to exhibit where they take experiences and apply what they learned to new, but similar situations similar to their jar opening performance (Hanlon, 1998) Their evaluation of their surroundings could also be handled by their visual sensory systems. As seen in Figure 2 7 their optic lobes (opt.) are quite large It could, however, not be learning at a ll and merely be a predisposed reaction that does not care whether the object aquarium, the pipe was, when available, the most unanimously popular den choice. It could again merely be an evaluation of the space based on openings available for entrance and escape, space within, and location rather than based on familiarity with the type of space.
Hiding Behaviors in Octopus joubini 46 Figu re 27 : Dorsal view of the octopus nervous system. Young, 1964 If this were the case, it would be a much more efficient method for evaluating an advantageous situations and benefits. It does create a certain amount of risk though This type of explore and evaluate method could lead them to predators or put them in the way of them. Although it is not clear without further testing whether the visual or tactile systems or both mediate this behavior The pygmy octopus also live, for the most part, in sea grass beds where large objects that make ideal hiding areas are in high demand. It may stand to reason that this affects what types of objects they may be used to and will gravitate toward them. It is also of note that they tend to be able to blend well into this environment (Mather, 2010). Conclusion Octopus joubini is a unique species of octopus to work with for behavioral experiments. When an Octopus joubini is removed from its den and introduced in to a
Hiding Behaviors in Octopus joubini 47 sparse environment containing only a length of PVC, a rock, half a bivalve shell, and a clear vial, the individuals clearly showed that the clear vial was not preferred as an immediate hiding place as it was chosen only once out of 45 test runs. While some individuals preferred to hide in certain objects more than others, overall the remaining three objects, which potentially were better hiding spots than the clear vial, were chosen a relatively equal amount. This suggests that when in an adverse situa tion, like being ejected from the den, O. joubini does not necessarily decide to hide in just natural formations when available. It may indicate that they have some form of evaluative process of their surroundings when in adverse situations that they use t o determine a preferred course to follow. Whether this involves visual or tactile processes or both is unclear as it what sort of mental evaluation they may put their surroundings through. When given the choice of dens to inhabit, O. joubini consistently c hooses to inhabit small lengths of PVC tubing over shells, rocks, and clear vials. Other studies have shown that in general, pieces of human litter are chosen more frequently than natural formations when available by other octopus species. This suggests th at octopus of multiple species consistently perform some sort of evaluation process when choosing dens that is not limited to natural formations and may be grounded in more cognitively vigorous processes. Their choices on what sort of dens and hiding areas are the most acceptable could also stem from their hunting tactics. A den that is very closed up might be less feasible to ambush prey from, but this would require further testing on the relationship between their foraging tactics and den ecology to verif y.
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