Miao 1 Anti predator behavior of Octopus vulgaris Emily Miao Department o f Ecology and Evolutionary Biology University o f Cali f ornia, Los Angeles EAP Tropical Biology and Conservation Program, Fall 2016 1 6 December 2016 ABSTRACT Cephalopoda is a varied and unusual class that has occupied oceanic habitats all over the world for millions of years. One species in particular, Octopus vulgaris or the common octopus has a nearly global range. Because o f their so f t bodies and lack o f hard, protective ou ter covering octopu ses are highly vulnerable to numerous predators However, octopuses have evolved to compensate for this loss with a number of other anti predator defenses namely camouflage and substrate hiding Camouflage allows the octopuses to alter their appearance into a variety of colors, textures and shapes as they move through their environments, hiding in plain sight from predators. Substrate hiding allows octopuses to use their surroundings to their advantage, as they squeeze their malleable bo dies into spaces in the substrate that are inaccessible to most predators. My study seeks answer whether or not there is a species wide manner in which octopus display anti predator behaviors or if there is individual variability in these behaviors My results showed that individual octopus react differe ntly in both their rate of camouflage and the types of camouflage displayed when exposed to the same stimuli. This variability in their reactions is reflective of their ability to thrive in the wide range of habitats they occupy throughout the world. In contrast, three distinct behavioral phenotypes emerged with respect to substrate hiding; octopus either spent all their time hiding, all their time exposed, or half their time hiding and half their time exp osed. These shared phenotypes show that substrate hiding does not need to be highly varied between individuals in order to be effective against a wide range of predators. My experiment highlights the importance and effectiveness of these behaviors in allow ing the octopus to avoid, deter and escape predators all over the world, contributing to its global success. Comportamiento antidepredador de Octopus vulgaris RESUMEN Cephalopoda es una Clase variada e inusual que ha ocupado los ocÂŽanos alrededor del mundo durante millones de aÂ–os. Una especie en particular, Octopus vulgaris conocido como el pulpo comÂœn, tiene una gama casi global. Debido a sus cuerpos blandos y la falta de una cubierta externa protectora, los pulpos son altamente vulnerables a nu merosos depredadores. Sin embargo, durante la evoluciÂ—n los pulpos han desarrollado estrategias para compensar esta pÂŽrdida con una serie de defensas anti depredador como el camuflaje y ocultarse entre el sustrato. El camuflaje permite que los pulpos alter en su aspecto en una variedad de colores, texturas y formas mientras se mueven a travÂŽs de su ambiente, ocultÂ‡ndose a la vista de los depredadores. El sustrato permite a los pulpos utilizar su entorno a su ventaja, ya que pueden calzar sus cuerpos maleable s en espacios que son inaccesibles para la mayorÂ’a de depredadores. Mi estudio busca responder si existen o no comportamientos anti depredadores especÂ’ficos o si
Anti predator behavior of Octopus vulgaris Miao 2 hay variabilidad individual en estos comportamientos. Mis resultados mostraron que los pulpos reaccionan individualmente de manera diferente tanto en su tasa de camuflaje como en los tipos de camuflaje mostrados cuando se exponen a los mismos estÂ’mulos. Esta variabilidad en sus reacciones es un reflejo de su capacidad para prosperar en la amplia ga ma de hÂ‡bitats que ocupan en todo el mundo. En contraste, tres fenotipos distintos de comportamiento surgieron cuando se estaban ocultando en el sustrato: pasar todo su tiempo escondido, todo su tiempo expuesto, o la mitad de su tiempo escondido y la mitad de su tiempo expuesto. Estos fenotipos compartidos muestran que el ocultarse en el sustrato no necesita ser muy variado entre los individuos con el fin de ser eficaz contra una amplia gama de depredadores. Mi experimento destaca la importancia y la eficac ia de estos comportamientos al permitir que el pulpo evite y escape de los depredadores en todo el mundo, contribuyendo a su ÂŽxito global. Camouflage in octopuses is made possible by small sacs of pigment in the ir skin known as chromatophores (Messeng er et al 2001) By relaxing or contracting the radial muscles surrounding these chromatophores octopuses can control networks of chromatophores to modif y the color and patterns on their skin and the specific spatial distribution of those elements ( ibid ) These muscles are connected directly to motor centers in the brain, with no synapses interrupting the link between the muscle and brain ( Hanlon et al 2007 ). Three more sets of muscles are devoted to manipulating papillae in the octopus' skin surface in 3 D allowing them to match both the color and texture of their surroundings (Allen et al 2013). Dynamic manipulation of these muscles in tandem with alteration of the overall body shape is what allows the octopus to assume an assortment of colors, te xtures, and shapes. Despite the range o f g uises the octopus can take, variation in visual phenotypes can be sorted into three main classes of camouflage: uniform, mottled a nd disruptive (Hanlon et al 2007 ). Uni f orm coloration lacks clear partitioning o f colors or patterns, while the mottled phenotype contains distinct elements o f colors and/or patterns. Octopuses use these two phenotypes mainly to match their backgrounds and mimic elements of their surroundings (Barbosa et al 2007). Disruptive camouflage incorporates f eatures that break up the outline o f the octopus, or distract f rom the overall shape o f the organism (ibid) None of these phases are mutually exclusive; different elements from each can be combined, demonstrating the range o f phenotypes in the octopus' arsenal In addition to camou f lage, another anti predator behavior exhibited by octopus is substrate hiding. The octopus' so f t body and lack o f a hard outer covering allows it to f it into spaces inaccessible to most predators. Octop uses spend most o f their time hiding in their dens secure crevices in the substrate chosen care f ully by the octopuses, that protect them f rom a variety o f threats (Hanlon et al 1999 ) They return to these dens a f ter a night o f hunting in order to seek re f uge a nd sa f ety (ibid) Octopuses will also opportunistically use their surroundings to hide, squeezing their highly malleable bodies into sa f e spaces. Substrate hiding allows the octopus to use its environment to avoid its multitude o f predators. Many studie s have focused on the physiological mechanisms ( Allen et al 2013, DeMartini et al 2013, Mathger et al 2008 ) that allow octopus es to camouf lage and hide in the
Anti predator behavior of Octopus vulgaris Miao 3 substrate. However, few studies have investigated the existence of species wide t rends and individual variation in these behaviors. My study aims to answer whether there is a species specific manner in which octopus display anti predator behaviors, or i f there is individual variability in these behaviors. MATERIALS AND METHODS Seven Octopus vulgaris were collected between 18 24 November 2016 in Bahia Santa Elena, close to the town of Cuajiniquil, Guanacaste, Costa Rica. All octopus es were collected by a fisherman named F r eddy Ampie from an area o f rocky substrate near the shore just north west of the mariculture p rojec t Octopuses were named in order to distinguish between individuals. Captured octopuses were held in 9.5 L holding tanks before exposure to various test substrates inside two plastic test tanks, one black and one white. Octopu ses were returned to holding tanks in between exposures to new environments. This is due to the speed with which octopuses can alter their appearance; in order to capture their full naÂ•ve reactions to the different substrates, the octopuses had to be taken out of the tanks while the substrates were being changed. This also prevented injury of the octopus while su bstrate was being arranged i n the tanks. Octopuses were f irst placed in the black test tank to acclimate them to the environment, as well as provide a baseline control' f or their reaction to the tank. F ollowing this initial expo sure, octopuses were exposed to two substrates placed in the bottom of the black test tank in this order: f irst were the f lat, red, sedimentary rock s and second were the tan rock s covered in oyster shells o f approximately 2.5 cm x 1 .0 cm. These s ubstrate s were collected from a rocky shore just southeast of the mariculture project. Following exposure to natural' substrates, octopuses were p laced into the white test tank containing a black and white checkered bottom composed of squares 9cm 2 in area The size of the squares was meant to approximate the size of the octopus' prey. Thus, the natural ba sis of this size was used to create a chec kered pat tern that the octopus assumedly could discern. This pattern was meant to test the octopus' reaction to light and d ark, in the same way that sun light creates alternating patterns of light and dark on the ocean floor albeit this pattern was more regular Al l test substrates are ordered in Figure 1 in the order they were tested.
Anti predator behavior of Octopus vulgaris Miao 4 Octopuses were filmed from their introduction into the test tank to a point deemed as a settling' point at which changes in movement and appearance ceased. Following testi ng, octopuses were r eleased at the location at which they were captured. The process as a whole, from capture to rel ease, took about 45 minutes per octopus. Video was analyzed afterwards using the Photos App for Mac OS X and data was entered into Microsoft Excel. Camouflage I established two parameters of interest as markers of camouflage behavior I first determined the individual rates of d istinct phenotype change s (DPT). I defined a distinct phenotype change as a discernible, obvious change in color, brightness, pattern and/or texture. I 1 2 3 4 Fig. 1. octopus' eye view of the various test substrates (1) Blank black test tank without substrate (2) Flat, red sedimentary rock in black test tank (3) Pteria sterna covered tan/yellow rock in black test tank (4) 9cm 2 checkerboard pattern in white test tank
Anti predator behavior of Octopus vulgaris Miao 5 counted the number of DPT's over all the trials and di vided this value by the total amount of time each octopus was visible in the video. Only footage where the octopus was visible was considered as DPTs could not be recorded when the octopus was not visible. As discussed earlier, anti predator camouflage behavior is n ot confined to just blending into the environment but includes other phenotypic changes that can deter predators. Thus I equated this rate to their rate of camouflage. The second variable I calculated was the percent time each octopus spent in each type of camouflage. This variable was recorded in seconds and divided against the total visible time period. The criteria used to distinguish the class of camouflage f or each octopus was based on definitions in Hanlon (2007) and further clarified by me. Uni f or m camou f lage was classified as coloration in which there were no clearly defined partitions of color. Similar to the way that sand contains multi colored sand grains, but appears to be a single color when viewed from a distance, uniform coloration may be comprised of multiple shades of more than one color, however the distinctions between them are subtle. Areas o f color ot her than the base coloration were no larger than the octopus' eye. Mottled camou f lage was de f ined as the prese nce o f clear, de fined sections of color that were at lea st as large as the octopus' eye While di fferent colors may be present in this phenotype they have distinct boundaries that di ff erentiate them f rom one another I rregular patterns may be incorporated such as spots, stripes and other shapes as seen below in Figure 2 Disruptive camou f lage is de f ined as sections o f color that break up the general f orm and outline of the animal. Patterns may also be present here, however they are more regular and larger than those seen in mottled camouflage. Disruptive camouf lage was defined as areas of high contrast and brightness, and/or large sections of color that break up the general form and outline of the animal. Examples of these three main phenotypes can be seen below in Figure 2. In order to incorporate the fact that the three main camouflage types, Uniform, Mottled and Disruptive are not mutually exclusive, I included the phenotypes Uniform Disruptive, Mottled Disruptive, and Uniform Mottled as well. These in be tween phenotypes were def ined as the presence of the elements of both phenotypes, as described above, in a single octopus. Fig. 2.1 2.3. Examples of different camouflage phenotypes (1) Uniform Note the lack of a clearly defined boundary between the light and dark shades (2) Mottled an example of the spotted patterns that can appear in mottled c amouflage with strong contrast between the tan spots and the red base (3) Disruptive striations on the legs of the octopus as well as the light patch between the eyes and dark patches on either side of the eyes all serve to break up the form of the octopus 1 3 2
Anti predator behavior of Octopus vulgaris Miao 6 Substrate Hiding To analyze substrate hiding behavior I calculated the percent time the octopuses spent hiding and visible respectively Only the red rock substrate and oyster covered substrate o ff ered organisms a choice to hide, thus only f ootage f rom those trials was analyzed. The video was cut t o only when the octopus was known to be within the frame of the camera. Hiding was considered to be when less than 25% of octopus was visible. I f the octopus hid immediately upon introduction to the tank, substrates were moved within the tank in order to c ollect adequate data on the octopus's behavior, however if the octopus was exposed during this time it was not considered visible f or a small amount o f time a f ter exposure. This amount of time was about three seconds, giving the octopus ample time to decid e between remaining visible or hiding. Data collection restarted after this period. The amount of time hidden and visible, respectively were measured in seconds, totaled across all tr ials and divided against the total amount o f time each octopus was f ilmed RESULTS My results show that no one octopus camou f lages in exac tly the same manner as another. H owever t hey also revealed three distinct phenotypes within substrate hiding behavior that were shared between all octopuses The individual rates o f phenotypic changes per minute were highly variable between di ff erent octopuses. The values ranged f rom as f ew as 0.26 changes/min up to up to 1.35 times/min as seen in F igure 3 While calculation o f the upper and lower f ences (1.62 and 0.03 respectively) o f this data set did not yi eld any outliers, there is a great diversity seen between individual rates o f phenotypic change. F ig. 3. Individual Rates of Phenotype Change Average number o f phenotype changes f or each octopus over all f our trials. Mean = 0.80, upper fence = 1.62, lower fence = 0.03, no outliers identified, Max = 1.35 by the individual Suave, Min=0.26 by the individual Chicito, Range = 1.09 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Chiquito! Broken Arm! Pega! Ultima Inky Chicle! Suave! Rate o Phenotype Changes/Min!
Anti predator behavior of Octopus vulgaris Miao 7 An i ndividual preference for a single camouflage phenotype was observed in the individual Broken Arm who displayed, on average, a unif orm pattern 99.2 % of the time over all four trials ( Figure 4 ). This value was significantly higher than that in five other individuals. In most other octopus es usage of t he uniform and mottled patterns dominated, but no two octopus es were the same in terms of the way they partitioned their time between different types of camouf lage (Figure 5) This re presents the varied reactions that different octopus had to the same stimuli throughout the experiment. In all four substrates octopuses displayed mottled and unif ormed patterns and overall, spent the most time in those two classes o f camouflage In trials of the red rock substrate uniformed disruptive, and mottled disruptive phenotypes were also observed (Figure 5 .2 ) The checkered tank also elicited displays of mottled disruptive, and was the only substrate in which one oc t o pus, Chiquito displayed a purely disruptive phenotype. The lack of a consistent distribution of time between camouflage phenotypes among the octopuses in the blank, red rock, and checkered trials indicates that there was no general preference towards a c ertain phe notype, as evidenced by Figure 5 In the oyster trials there seemed to be a preference towards uniform camouflage pattern as five out of the seven octopuses spending over 95% in a uniform pattern (Figure 5.3) In the other substrates octopuses did not show a consistent preference for any one type of camouflage. Overall average amount of time each octopus spent in each camouflage phenotype was un ique to each individual as seen in Figure 6 Fig. 4. Percent time each octopus displayed uniform camouflage over four trials on average. Calculated by averaging percent time uniform cam ouflage was used in every trial for each octopus. Standard deviations are represented by error bars for each octopus. 0 10 20 30 40 50 60 70 80 90 100 Broken Arm! Chicito! Suave! Chicle! Inky Ultima Pega! Percentage of Uniform Camoulage Usage!
Anti predator behavior of Octopus vulgaris Miao 8 F ig. 5.1 5.4 Amount of time each octopus spent in various modes of camouflage in each substrate. (1) Empty Tank (2) Red Rock (3) Oyster Covered Rock (4) Checker Pattern In Figures 5.1, 5.2 and 5 .4 no clear preference show across all octo pus es for any particular mode. In Fig ures 5 .3, five out of seven octopus displayed uniform camouflage for more than 90% of the time. 0 20 40 60 80 100 Broken Arm! Chicito! Chicle! Inky Pega! Suave! Ultima % Time! Disruptive! Uniform-Disruptive! Mottled-Disruptive! Mottled! Uniform! 5.2 5.3 5.4 Fig. 6. Overall Temporal Distribution between all modes o f camou f lage f or each individual 5.1
Anti predator behavior of Octopus vulgaris Miao 9 The red rock and oyster covered rock o ff ered the octopus a choice between hiding under cover and remaining visible. A f ter analyzing the relative proportions o f time each octopus chose to remain visible and hidden, respectively, three distinct phenotypes emerged. Octopus either spent nearly all o f their time hiding, nearly all o f their time visible, or split their time close to 50/50 between the two. Fig. 6.1 6.2 Percentage time each octopus spent hidden and visible in (1) Red Rocks and in (2) Oyster covered Rocks. Pr eference for spending nearly 9 0% of time hiding or visible or about 50/50 distribution between the two distinct behaviors seen in both figures 0 20 40 60 80 100 Broken Arm! Chiquito! Chicle! Inky Pega! Suave! Ultima % Time 0 20 40 60 80 100 Broken Arm! Chiquito! Chicle! Inky Pega! Suave! Ultima % Time! % Time Hidden! % Time Visible! 6.1 6.2
Anti predator behavior of Octopus vulgaris Miao 10 DISCUSSION My experiment showed that octopuses display a high level o f individual variability in camou f lage behavior, yet they con f orm to distinct phenotypes in another anti predator behavior, substrate hiding. The variation in individual phenotypic change rates as seen in Figure 3 reveals that exposing the octopuses to the same environments did not produce one consistent rate o f phen otypic change and thus, e ach octopus responded di ff erently to the same stimulus. This is rein f orced by the range o f reactions seen in Figure 5 and Figure 6 in which the ways that each octopus distributed their time between the various camou f lage behaviors was unique to every individual. I believe that this individual variation is in turn, re f lective o f the variety o f habitats and predators that octopuses are exposed to. Octopus vulgaris is f ound all over the world, in a variety o f habitats f illed with many di ff erent predators that, in turn, exert a variety o f selective pressures upon the octopus. In order f or their camou f lage to be e ff ective in the range o f situations that octopuses may encounter, it is important f or them to have an equally large assortment o f reactions. Additionally, it has been shown that octopus o f ten do not per f ectly match their appearance to their environments, but rather, pick and choose elements o f their surroundings to mimic ( Jose f et al 2012). Di ff erent octopuses may pick di ff erent e lements o f the same environment to imitate, thus individual variation arises f rom individual choice. Theoretically, if all the extraneous variables in my experiment that might affect octopus camouflage were controlled perfectly I would still predict variability between octopuses in their responses to the environment, simply due to the range of responses that are possible. Individual variability in camou f lage behavior is there f ore related to a species wide capacity to respond to a myriad o f predators a nd environments. One example o f this dynamic response was the oc t opus Chicle's disruptive response to the checkered pattern. The checkered pattern replicate s a regular pattern o f light and dark, similar to the way that substrate on the ocean f loor creat es variation, albeit this pattern is more regular. As seen in Figure 2.3, Chicle convincingly replicated this alternating pattern with central patches o f light and dark. Striations o f light and dark on his arms f urther broke up his f orm and helped him to e ff ectively blend into his surroundings. In contra s t to Chicle the octopus who displayed the uni f orm phenotype against t he checkered pattern is very obvious (Figure 2.1), making him easy prey f or a visual predators such as barracudas or mako sharks. Octopuses that display a strong pre f erence f or a certain phenotype, such as Broken Arm who displayed a uni f orm phenotype over 99% o f the time (Figure 4) are likely subject to strong selective pressures as they cannot cope with a wide variety o f environmen ts. This is a good example o f how individual choices in camou f lage can a ff ect individual survival in di ff erent habitats as well as how selective pressures can promote greater individual variation throughout the species Going a step f urther, d i ff erent sel ective pressures in varying environments may lead to f urther speciation o f Octopus vulgaris It is speculated that subspecies already exist within Octopus vulgaris (Guerra et al 2010), however f urther research is needed to corroborate this idea and clari f y the role that individual variation in camou f lage may play in speciation. When considering the tendency o f the octopus to either hide or remain visible two distinct phenotypes emerged. In both the red substrate and oyster covered substrate, octopus
Anti predator behavior of Octopus vulgaris Miao 11 either chose to spend all o f their time hiding or visible, or split their time between the two evenly ( Figure 6) Because octopus es spend much o f their time during the day hiding in their dens, the phenotypes o f 50% hidden and 50% visible as well as nearly 100% visible seem unusual. S o f t bodied animals like octopus es are f ar sa f er contained within their dens than out in the open. However, I believe that hiding within their dens does in f act play into the unusual division in phenotypes observed in these tria ls. D en s o ff er octopus es signi f icant protection f rom many types o f predators thus, choosing a secure spot where octopuses are sa f e f rom these predators is key to their survival While the octopus es were likely not choosing a den during the trials, I believe the inherit selectiveness with which they chose their hiding spot is re f lected in their tendencies to remain visibl e during the experiment. In my observations, o f tentimes when octopuses were visible they were moving actively f rom one hiding spot to another. Thus, longer periods o f time in whic h the octopus were visible were because they were searching f o r a new hiding spot or because none o f the hiding spots were satisfactory Furthermore, the presence o f distinct phenotypes in substrate hiding behavior represent s the general e ff ectiveness o f this behavior against a wide variety o f predators High levels o f variability are not necessary because this behavior is generally e ff ective against any predator too large to f it into spaces within the substrate. The variatio ns in camouflage behavior well a s the distinct phenotypes i n substrate hiding behavior are re f lective o f traits shaped by a huge variety o f selective pressures and environments. Individual variability is key to adaptation to the variety o f environments t hat Octopus vulgaris occupies. An individual's f ixed choice o f camou f lage is likely a strong negative selective pressure as its ability to cope with di ff erent environments is hinde red. Additionally, care f ul selection o f hiding spots allow octopuses to compensate f or the loss o f their protective shells, and can be combined with camou f lage to e ff ectively avoid predators. Further research may include studies on wild behavior, and wheth er octopuses exhibit these same behavioral tendencies in their natural environments Other anti predator behaviors, such as inking, also o ff er more chances to analyze individual variation and search f or species wide trends in octopus anti predator behavior O ctopus es employ a variety o f anti predator strategies that have allowed them to occupy the globe and inhabit a huge range o f environments. ACKNOWLEDGEMENTS First and foremost, I would like to thank to Frank Joyce for his endless advice and support throughout this project. Your pat ience and willingness to answer all my questions (including the irrelevant ones) is much appreciated and I could not have done this without your help. A massive thanks also go es to L a uren Cech and Erica Weed whose excellent cinematography skills, sense s of humor and endless suggestio ns allowed my project to run far smoother than if I h ad been on my own. I also want to thank Minor Lara for always taking us out to our study sites even during the impending hurricane. To the entire Lara family thank you for allowing us to turn your home into a veritable gym/study spot/soccer viewing spot. Last but not least, thank you to Flory Castro for the endless smiles, laughter and delicious m eals during the time that I spent at your home. You and your family helped me understand the meaning be h ind
Anti predator behavior of Octopus vulgaris Miao 12 Pura Vida' and in Cuajiniquil I am truly appreciative of the warmth with which you welcomed me into your home. LITERATURE CITED Allen, J J., G R. R. Bell, A M. Kuzirian, S S. Velankar, and R T. Hanlon. "Comparative Morphology of Changeable Skin Papillae in Octopus and Cuttlefish." Journal of Morphology 275.4 (2013): 371 90. Web. Barbosa, A., L M. Mathger, C. Chubb, C. Florio, C. C. Chiao and R. T. Hanlon. "Disruptive Coloration in Cuttlefish: A Visual Perception Mechanism That Regulates Ontogenetic Adjustment of Skin Patterning." Journal of Experimental Biology 210.7 (2007): 1139 147. W eb. DeM artini, D. G., D. V. Krogstad and D. E. Morse. "Membrane invaginations facilitate reversible water flux driving tunable iridescence in a dy n amic biophotonic system." Proceedings of the National Academy of Sciences 110.7 (2013): 2552 556. Web. Guerra A., Roura A., Gonzalez, A. F., Pascual, S., Cherel, Y., & Perez Losada, M. (2010). Morphological and genetic evidence that Octopus vulgaris Cuvier, 1797 inhabits Amster dam and Saint Paul Islands (southern Indian Ocean). ICES Journal of Marine Science doi:10.10 93/icesjms/fsq040 Hanlon, R.T C. C Chiao, L.m Mathger, A. Barbosa, K.c Buresch, and C. Chubb. "Cephalopod Dynamic Camouflage: Bridging the Continuum between Background Matching and Disruptive Coloration." Philosophical Transactions of the Royal Society B: Biological Sciences 364.1516 (2009): 429 37. Web. Hanlon, Roger. "Cephalopod Dynamic Camouflage." Current Biology 17.11 (2007 ) : n. pag. Web Hanlon, R. "Crypsis, Conspicuousness, Mimicry and Polyphenism as Antipredator Defences of Foraging Octopuses on Indo Pacific Coral Reefs, with a Method of Quantifying Crypsis from Video Tapes." Biological Journal o f the Linnean Society 66.1 (1999): 1 22. Web. Josef N., Amodio, P., Fiorito, G., & Shashar, N. (2012). Camouflaging in a Complex Environment Octopuses Use Specific Features of Their Surroundings for Background Matc h ing. PLoS ONE,7 (5). doi:10.1371/journal.pone.0037579 Luca, D D G Catanese, G Procaccini, and G Fiorito. "Octopus vu lgaris (Cuvier, 1797) in the Mediterranean Sea: Genetic Diversity and Population Struct u re." Plos One 11.2 (2016): n. pag. Web.
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