Factors affecting the spatial distribution of natural populations of Octopus joubini robson

Observations were made on the density and distribution of Octopus joubini in its natural environment. The average density of octopuses was 1/33 m² but their distribution was clumped. This distribution correlated significantly with the distribution of molluscan shells in which they hid. In addition, octopuses were attracted to sites that had been enriched with extra empty gastropod shells. Since site stability was not observed and they were not repelled from one another when placed at a high density, octopuses were probably not spaced by social pressure. Small crab species, the normal prey of O. joubini, were at a very high density of 30/m², and food abundance probably did not limit octopus number. The main factor affecting distribution of this population of octopuses may be predator pressure acting through the availability of places to hide.     

Octopus joubini (Mollusca: Cephalopoda): a detailed study of growth through the full life cycle in a closed seawater system

Twenty individual pygmy octopuses, Octopus joubini , were reared at 25°C from hatching to maturity on a quantified diet of live crabs in closed (recirculating) natural seawater systems. At 24 week intervals the animals were narcotized, weighed and measured. There was 85% survival to sexual maturity.
Growth rates were highest during the first four weeks of exponential growth. Beyond four weeks, growth rates steadily declined and growth became logarithmic in form. Female octopuses grew slightly faster than males and attained a larger size at maturity. The length-weight relationship showed male Octopus joubini to weigh more than females at a given mantle length. This species displays slight allometric growth resulting in changing body proportions through the life cycle. Relative food intake is highest at hatching and decreases with age. Mean gross growth efficiency over the life span was approximately 40%.     

Alternative diets for maintaining and rearing cephalopods in captivity

The requirement of live marine prey for cephalopod mariculture has restricted its practicality for inland research laboratories, commercial enterprises and home aquarists. We evaluated acceptability and resultant growth on: (a) frozen marine shrimps, (b) live and frozen marine polychaete worms, (c) live and frozen marine crabs, (d) frozen marine fishes, (e) live adult brine shrimp, (f) live freshwater fish and (g) live freshwater crayfish. The diets were presented for periods of 2 to 11 weeks to octopuses, cuttlefishes or squids and in most trials the results were compared to animals fed control diets of live marine shrimps, crabs or fish. Overall, frozen marine shrimp proved to be the best alternative diet tested. Adult Octopus maya on frozen marine shrimp diets grew as well as those on control diets at 2.8% body weight per day (%/d) compared to 2.0%/d on live freshwater crayfish, 1.4%/d on live marine polychaete worms and 0.8%/d on live freshwater fish (Tilapia sp.). Juvenile Octopus maya and Octopus bimaculoides also grew comparably to controls when fed frozen marine shrimps; growth rates ranged from near 3.0%/d at 3 months of age to nearly 2.5%/d at 6 months of age. Thus, these alternatives are acceptable as the octopuses end their exponential growth phase at an age of 3 - 5 months. Attempts to rear O. maya hatchlings and juveniles (up to 1 month of age) on dead foods resulted in high mortality and slow or negative growth. No live or dead alternative diet has been found yet that will promote good growth and survival in hatchling octopuses. Hatchling F3 generation Sepia officinalis (the European cuttlefish) were reared for 6 weeks exclusively on adult brine shrimp (Artemia salina).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pull or Push? Octopuses Solve a Puzzle Problem

Octopuses have large brains and exhibit complex behaviors, but relatively little is known about their cognitive abilities. Here we present data from a five-level learning and problem-solving experiment. Seven octopuses (Octopus vulgaris) were first trained to open an L shaped container to retrieve food (level 0). After learning the initial task all animals followed the same experimental protocol, first they had to retrieve this L shaped container, presented at the same orientation, through a tight fitting hole in a clear Perspex partition (level 1). This required the octopuses to perform both pull and release or push actions. After reaching criterion the animals advanced to the next stage of the test, which would be a different consistent orientation of the object (level 2) at the start of the trial, an opaque barrier (level 3) or a random orientation of the object (level 4). All octopuses were successful in reaching criterion in all levels of the task. At the onset of each new level the performance of the animals dropped, shown as an increase in working times. However, they adapted quickly so that overall working times were not significantly different between levels. Our findings indicate that octopuses show behavioral flexibility by quickly adapting to a change in a task. This can be compared to tests in other species where subjects had to conduct actions comprised of a set of motor actions that cannot be understood by a simple learning rule alone.     

Fatal penetrating skin ulcers in laboratory-reared octopuses

Young Octopus joubini and O. briareus (35 to 60 days old) that were being reared in high-density groups for biomedical studies developed skin ulcers, whereas octopuses reared in individual containers in the same culture system were disease-free. The ulcers first affected the epidermis of the mantle, and then penetrated downward through the dermis and underlying muscle tissue. Four stages of ulceration were observed. Untreated octopuses with ulcers always died, usually within 4 days. Five species of bacteria were isolated from ulcers: Vibrio alginolyticus, V. damsela, Pseudomonas stutzeri, and Aeromonas caviae from O. joubini; and V. parahaemolyticus, V. damsela, and P. stutzeri from O. briareus. Bacteria were found during all stages of the ulceration. Healthy O. joubini were infected experimentally with four species of bacteria, and V. alginolyticus produced skin ulcers within 2 days. The ulceration was treated with nifurpirinol, and complete healing of the skin occurred within 2 months. The ulcers were probably species-specific because O. maya and O. bimaculoides that were reared in the same culture systems were not affected. The cause of the ulceration was probably an increase in contact among crowded octopuses that produced skin abrasions which were invaded by opportunistic bacteria.     

Some observations of Octopus joubini reared in an inland aquarium

Octopus joubini Robson were hatched and reared in a closed circulating sea-water system. Mortality was greatest during the period of hatching. The longest surviving octopus lived for 128 days—it had increased its weight × 5, from 0·04–0·19 g, mantle length × 3, from 3–9 mm, head width × 2, from 3–5 mm. Observations of (1) general behaviour, (2) feeding behaviour, (3) social behaviour of the newly hatched octopuses (0–3 days) and the three longest surviving octopuses (93–119 days) are described. In particular it was observed that the older octopuses would readily grasp and eat small live crabs when these were made to touch the suckers or arms. On no occasion did the attacks appear to be visually elicited. This result is discussed with reference to the memory and learning experiments using O. vulgaris. Possible reasons for the limited survival are also discussed.     

Two new Aggregata species (Apicomplexa: Aggregatidae) infecting Octopus tehuelchus and Enteroctopus megalocyathus (Mollusca: Octopodidae) in Patagonia, Argentina

During a long-term study carried out between 1981 and 1996 on the biological and fishery aspects of octopuses inhabiting the Gulfs of San Matías, San José, and Nuevo, Patagonia, Argentina, 2 new species of Aggregata (Apicomplexa: Aggregatidae) were found in the digestive tracts of Octopus tehuelchus d'Orbigny, 1834 (prevalence 72%) and Enteroctopus megalocyathus (Gould, 1852) (prevalence 77%). Both species can be distinguished from other congeners on the basis of their hosts, the diameters of sporocysts, and number and length of sporozoites. Despite overlap in the distributions of the two hosts species in the area covered in this study, both Aggregata new species exhibited high host specificity.     

Phylogenetic relationships among major species of japanese coleoid cephalopods (Mollusca: Cephalopoda) using three mitochondrial DNA sequences

Phylogenetic relationships among 36 species of major coleoid cephalopods from Japanese waters were studied using partial sequences of three mitochondrial genes, 16S rDNA, 12S rDNA, and cytochrome c oxidase subunit I gene. Octopoda and Decapoda were monophylic groups. Within Sepioidea, Sepiadariidae and Sepiolidae were not closely related to Sepiidae, but rather related to Teuthoidea. Sepiidae with a distinct calcareous shell formed a single cluster. Myopsida was closely related to Oegopsida. Within Octopoda, Opisthoteuthis depressa and Argonauta argo diverged earlier than Octopodiidae. The common octopuses in Japanese waters were separated into three clusters. The first cluster occupied a basal position, and includes large-sized octopuses, such as Enteroctopus dofleini and Octopus (Paroctopus) conispadiceus from the continental shelf and upper slope. The second cluster consisted of long-armed octopuses, such as O. ornatus, O. minor, and O. sasakii. The third cluster contained small- to medium-sized octopus, such as Amphioctopus fangsiao, A. areolatus, O. cyaneus, and O. vulgaris, in which several species possess ocelli on the web. The second cluster formed the sister group to the third cluster.     

Molecular phylogeny of the benthic shallow-water octopuses (Cephalopoda: Octopodinae)

Octopus has been regarded as a "catch all" genus, yet its monophyly is questionable and has been untested. We inferred a broad-scale phylogeny of the benthic shallow-water octopuses (subfamily Octopodinae) using amino acid sequences of two mitochondrial DNA genes: Cytochrome oxidase subunit III and Cytochrome b apoenzyme, and the nuclear DNA gene Elongation Factor-1alpha. Sequence data were obtained from 26 Octopus species and from four related genera. Maximum likelihood and Bayesian approaches were implemented to estimate the phylogeny, and non-parametric bootstrapping was used to verify confidence for Bayesian topologies. Phylogenetic relationships between closely related species were generally well resolved, and groups delineated, but the genes did not resolve deep divergences well. The phylogenies indicated strongly that Octopus is not monophyletic, but several monophyletic groups were identified within the genus. It is therefore clear that octopodid systematics requires major revision.     

Movement, injuries and growth of members of a natural population of the Pacific pygmy octopus, Octopus digueti

Sampling inadequacies and an inability to distinguish age classes have limited our knowledge of octopus biology in nature. Using an artificial shelter sampling technique (Voight, 1988 a ), and defining mature males by the presence of enlarged suckers (Voight, In press), an intertidal population of Octopus digueti was monitored for one year.
In total, 803 octopuses were narcotized; the mass, sex, arm injuries and reproductive condition of each octopus were recorded. Captures were more frequent in lower intertidal areas offering higher shelter availability and a more moderate environment. Capture rates, assumed to indicate octopus movement, correlated with sea temperature except during full moon periods when they were reduced. Over 26%, of the octopuses handled had damaged arms or arm tips, with dorsal arm pairs more often injured. The overall sex ratio was significantly male biased, probably due to maturity-linked mobility differences between the sexes.
Reproduction occurred throughout the year; reproductively competent adults, brooding females and juveniles were present every month. However, annual temperature oscillations synchronize spring hatching of eggs spawned from winter to early spring, creating a clear spring cohort. Growth and age at maturity of males in the spring and autumn cohorts were estimated. Variance was too high for these parameters to be estimated in the winter cohort. Growth rates of males over 12 weeks of age did not differ from those reported in laboratory rearing studies. Estimated average age at maturity ranged from 20 to 32 weeks, depending on temperature.     

Demographic inference and genetic diversity of <Emphasis Type="Italic">Octopus mimus</Emphasis> (Cephalopoda: Octopodidae) throughout the Humboldt Current System

Climatic and oceanographic events occurring during the last glacial cycle in the Humboldt Current System (HCS) have left genetic footprints in marine invertebrate populations. The objective of this study was to evaluate the effect of the glacial period on Octopus mimus populations found throughout the HCS. This species lays a large number of small eggs which hatch into planktonic paralarvae with the potential to undergo wide dispersal. We sequenced the COIII gene to perform phylogeographic analyses of 197 octopuses sampled from seven localities. The genetic diversity of Octopus mimus was low and decreased towards the southern end of the distribution range, which comprises a single population. The haplotype genealogy and Bayesian Skyride plot suggest that O. mimus underwent a demographic expansion after the last glacial maximum (LGM). This would imply a contraction of the range of this organism toward northern latitudes during the LGM followed by southward expansion and recolonization once the contemporary interglacial period began.     

A second site occupied by Octopus tetricus at high densities,with notes on their ecology and behavior

We report wild octopuses (Octopus tetricus) living at high density at a rock outcrop, the second such site known. O. tetricus are often observed as solitary individuals, with the species known to exist at similar densities and exhibiting complex social behaviors at only one site other than that described here. The present site was occupied by 10–15 octopuses on eight different days. We recorded frequent interactions, signaling, mating, mate defense, eviction of octopuses from dens, and attempts to exclude individuals from the site. These observations demonstrate that high-density occupation and complex social behaviors are not unique to the earlier described site, which had been affected to some extent by remains of human activity. Behavior at this second site confirms that complex social interactions also occur in association with natural substrate, and suggest that social interactions are more wide spread among octopuses than previously recognized.     

Hole boring of crustacean prey by the octopus Eledone cirrhosa (Mollusca, Cephalopoda)

Eledone cirrhosa has been found to make a borehole in the carapace of a high proportion of its crustacean prey. This is the first account of drilling in crustaceans by octopus. The frequency of incidence of the boring behaviour varied between prey species from 17 to 93% of those killed. The incidence of boreholes was higher in crabs killed by small octopuses. Using crabs mainly of the genera Cancer, Carcinus, Corystes and Macropipus , the distribution and orientation of the boreholes was recorded. The boreholes occurred in any part of the carapace but the great majority were found close to the mid-line and in the posterior half. The long axis of the oval penetration was usually aligned with the anteroposterior axis of the crab. The Mediterranean species Eledone moschata was also found to bore crabs, and newly hatched juveniles of this species are capable of boring as early as their second killing of a live crab. No evidence was found that Octopus vulgaris normally bores the carapace of crabs.     

Camouflaging in a complex environment--octopuses use specific features of their surroundings for background matching

Living under intense predation pressure, octopuses evolved an effective and impressive camouflaging ability that exploits features of their surroundings to enable them to "blend in." To achieve such background matching, an animal may use general resemblance and reproduce characteristics of its entire surroundings, or it may imitate a specific object in its immediate environment. Using image analysis algorithms, we examined correlations between octopuses and their backgrounds. Field experiments show that when camouflaging, Octopus cyanea and O. vulgaris base their body patterns on selected features of nearby objects rather than attempting to match a large field of view. Such an approach enables the octopus to camouflage in partly occluded environments and to solve the problem of differences in appearance as a function of the viewing inclination of the observer.     

Autonomous Learning in Maze Solution by Octopus

We tested seven octopuses, Octopus vulgaris, in maze-learning experiments. They tried to reach the goal, so as to get a reward, by using various locomotory actions in the path, and sometimes encountered obstacles. They came to select efficient swimming actions in the path; afterwards less efficient tactile actions (crawling, staying put, and so on: these reduce the speed of movement) gradually increased, while time to detour around the obstacle was reduced. To investigate whether octopuses reduce time spent detouring around obstacles by estimating their actions in the path, we devised a trade-off situation in which octopuses were obliged to use tactile actions even though the set-up also encouraged them to use swimming actions. As a result, we could observe that they reduced the detouring time. In that way, we experimentally constituted a perspective as if octopuses looked around the whole maze and estimated their actions. Such a perspective appeared to be autonomous learning.     

Sexual cannibalism by Octopus cyanea on a Pacific coral reef

Sexual cannibalism is rare in the animal kingdom. Although cannibalism is not uncommon in cephalopods, here we report the first documented case of sexual cannibalism. A large female Octopus cyanea was observed continuously for 2.5 days in Palau, Micronesia, when she was out of her den. On the second day, a small male followed and mated her 13 times during 3.5 h while she continued to forage over 70 m distance. After the 12th mating, she aggressively chased a different small octopus that barely escaped by jetting, inking and swimming upwards. Shortly thereafter, the original small male mated her a 13th time, but subsequently she attacked and suffocated him and spent 2 days cannibalizing him in her den. This sort of intraspecific aggression helps to explain several reports of octopuses mating out in the open, a behaviour that may serve to allow the smaller mate to escape cannibalism.     

Changes in body weight and intake of food by Octopus vulgaris

The changes in body weight of 12 octopuses, fed on fish or crabs, were followed under laboratory conditions for periods of 1 to 7 1/2 months. The food intake was estimated and compared with the changes in body weight of the octopuses; 25 to 55% of the total intake of food appeared to be incorporated. The range of the average increase in weight over the whole observation period of each of the animals was 1.9 to 7.7g per day (1 to 7 1/2 months); the mean value was 4.8g per day. The effect of changing the diet of small octopuses (fish or crab)was followed for four weeks but there was no evidence that alteration of the diet affected the rate of changes in body weight of animals of more than 47g initial body weight.     

Evolution of development type in benthic octopuses: holobenthic or pelago-benthic ancestor?

Octopuses of the family Octopodidae are singular among cephalopods in their reproductive behavior, showing two major reproductive strategies: the first is the production of few and large eggs resulting in well-developed benthic hatchlings (holobenthic life history); the second strategy is the production of numerous small eggs resulting in free-swimming planktonic hatchlings (pelago-benthic life history). Here, we utilize a Bayesian-based phylogenetic comparative method using a robust molecular phylogeny of 59 octopus species to reconstruct the ancestral states of development type in benthic octopuses, through the estimation of the most recent common ancestors and the rate of gain and loss in complexity (i.e., planktonic larvae) during the evolution. We found a high probability that a free-swimming hatchling was the ancestral state in benthic octopuses, and a similar rate of gain and loss of planktonic larvae through evolution. These results suggest that in benthic octopuses the holobenthic strategy has evolved from an ancestral pelago-benthic life history. During evolution, the paralarval stage was reduced to well-developed benthic hatchlings, which supports a “larva-first” hypothesis. We propose that the origin of the holobenthic life history in benthic octopuses is associated with colonization of cold and deep sea waters.     

Bipedal locomotion in Octopus vulgaris: A complementary observation and some preliminary considerations

Lacking an external shell and a rigid endoskeleton, octopuses exhibit a remarkable flexibility in their movements. Bipedal locomotion is perhaps the most iconic example in this regard. Until recently, this peculiar mode of locomotion had been observed only in two species of tropical octopuses: Amphioctopus marginatus and Abdopus aculeatus. Yet, recent evidence indicates that bipedal walking is also part of the behavioral repertoire of the common octopus, Octopus vulgaris. Here we report a further observation of a defense behavior that encompasses both postural and locomotory elements of bipedal locomotion in this cephalopod. By highlighting differences and similarities with the other recently published report, we provide preliminary considerations with regard to bipedal locomotion in the common octopus.