Julian Finn

Dynamic mimicry in an Indo–Malayan octopus

During research dives in Indonesia (Sulawesi and Bali), we filmed a distinctive long-armed octopus, which is new to science. Diving over 24 h periods revealed that the ‘mimic octopus’ emerges during daylight hours to forage on sand substrates in full view of pelagic fish predators. We observed nine individuals of this species displaying a repertoire of postures and body patterns, several of which are clearly impersonations of venomous animals co-occurring in this habitat. This ‘dynamic mimicry’ avoids the genetic constraints that may limit the diversity of genetically polymorphic mimics but has the same effect of decreasing the frequency with which predators encounter particular mimics. Additionally, our observations suggest that the octopus makes decisions about the most appropriate form of mimicry to use, allowing it to enhance further the benefits of mimicking toxic models by employing mimicry according to the nature of perceived threats.

Female impersonation as an alternative reproductive strategy in giant cuttlefish

Out of all the animals, cephalopods possess an unrivalled ability to change their shape and body patterns. Our observations of giant cuttlefish (Sepia apama) suggest this ability has allowed them to evolve alternative mating strategies in which males can switch between the appearance of a female and that of a male in order to foil the guarding attempts of larger males. At a mass breeding aggregation in South Australia, we repeatedly observed single small males accompanying mating pairs. While doing so, the small male assumed the body shape and patterns of a female. Such males were never attacked by the larger mate–guarding male. On more than 20 occasions, when the larger male was distracted by another male intruder, these small males, previously indistinguishable from a female, were observed to change body pattern and behaviour to that of a male in mating display. These small males then attempted to mate with the female, often with success. This potential for dynamic sexual mimicry may have played a part in driving the evolution of the remarkable powers of colour and shape transformation which characterize the cephalopods.

Mitochondrial genome diversity and population structure of the giant squid Architeuthis: genetics sheds new light on one of the most enigmatic marine species

Despite its charismatic appeal to both scientists and the general public, remarkably little is known about the giant squid Architeuthis, one of the largest of the invertebrates. Although specimens of Architeuthis are becoming more readily available owing to the advancement of deep-sea fishing techniques, considerable controversy exists with regard to topics as varied as their taxonomy, biology and even behaviour. In this study, we have characterized the mitochondrial genome (mitogenome) diversity of 43 Architeuthis samples collected from across the range of the species, in order to use genetic information to provide new and otherwise difficult to obtain insights into the life of this animal. The results show no detectable phylogenetic structure at the mitochondrial level and, furthermore, that the level of nucleotide diversity is exceptionally low. These observations are consistent with the hypotheses that there is only one global species of giant squid, Architeuthis dux (Steenstrup, 1857), and that it is highly vagile, possibly dispersing through both a drifting paralarval stage and migration of larger individuals. Demographic history analyses of the genetic data suggest that there has been a recent population expansion or selective sweep, which may explain the low level of genetic diversity.

Revision of the Octopus horridus species-group, including erection of a new subgenus and description of two member species from the Great Barrier Reef, Australia

The tropical Indo-West Pacific region contains a distinctive group of small to moderate-sized octopuses referred to in the past as the Octopus horridus species-group. Member species are found primarily on intertidal reef flats. They possess small bodies, long arms and complex skin sculpture and body patterns enabling excellent camouflage. When attacked, these octopuses are capable of autotomising their arms at the base: the writhing severed arm acting as a decoy to predators and aiding escape. Lost arms regenerate within 2–3 months. Attributes of this group of octopuses are described and the subgenus Abdopus, subgen. nov. is here coined to define this group. Historically, many members of this subgenus have been incorrectly identified as Octopus horridus, a distinct large-egg species known only from the Red Sea and the northwest Indian Ocean. Seven species are here recognised as belonging in Abdopus, subgen. nov. Two member species from Great Barrier Reef waters (Octopus aculeatus d’Orbigny, 1834 and Octopus capricornicus, sp. nov.) are described. A number of additional, as yet undescribed, species occur throughout the Indo-West Pacific region. Certain earlier works have linked other octopus genera and species with members of this subgenus on the grounds of long arms and arm autotomy. Significant differences occur in the morphologies of these taxa and the nature of the arm autotomy processes. It is proposed that these groups have evolved independently and that arm autotomy has arisen more than once amongst the octopuses. The restriction of the subgenus Abdopus to the tropical Indo-West Pacific region suggests relatively recent origins and radiation.

Preparing the Perfect Cuttlefish Meal: Complex Prey Handling by Dolphins

Dolphins are well known for their complex social and foraging behaviours. Direct underwater observations of wild dolphin feeding behaviour however are rare. At mass spawning aggregations of giant cuttlefish (Sepia apama) in the Upper Spencer Gulf in South Australia, a wild female Indo-Pacific bottlenose dolphin (Tursiops aduncus) was observed and recorded repeatedly catching, killing and preparing cuttlefish for consumption using a specific and ordered sequence of behaviours. Cuttlefish were herded to a sand substrate, pinned to the seafloor, killed by downward thrust, raised mid-water and beaten by the dolphin with its snout until the ink was released and drained. The deceased cuttlefish was then returned to the seafloor, inverted and forced along the sand substrate in order to strip the thin dorsal layer of skin off the mantle, thus releasing the buoyant calcareous cuttlebone. This stepped behavioural sequence significantly improves prey quality through 1) removal of the ink (with constituent melanin and tyrosine), and 2) the calcareous cuttlebone. Observations of foraging dolphin pods from above-water at this site (including the surfacing of intact clean cuttlebones) suggest that some or all of this prey handling sequence may be used widely by dolphins in the region. Aspects of the unique mass spawning aggregations of giant cuttlefish in this region of South Australia may have contributed to the evolution of this behaviour through both high abundances of spawning and weakened post-spawning cuttlefish in a small area (>10,000 animals on several kilometres of narrow rocky reef), as well as potential long-term and regular visitation by dolphin pods to this site.

Evidence of mimicry of gelatinous zooplankton by anguilliform leptocephali for predator avoidance

Leptocephali are the transparent larvae of eels and their relatives, whose laterally compressed bodies contain gelatinous material. Although abundant throughout the world’s oceans, leptocephali are rarely observed in their natural environment. Video recordings of leptocephali in surface waters at night at Osprey Reef in the Coral Sea revealed that 6 of 21 larvae filmed displayed a distinct shape-change behavior of curling up into fully or partially coiled shapes. Their transparency and gelatinous consistency results in the coiled leptocephali resembling the typical body shapes and consistency of gelatinous zooplankton such as jellyfish, ctenophores, siphonophores, and salps. Due to either stinging defenses or low food value, many fishes avoid consuming gelatinous zooplankton, so the curling behavior in response to threatening situations may result in mimicry of these organisms. This could provide leptocephali with higher survival rates compared with flight from pelagic predators that are close enough to detect them.

The argonaut shell: gas-mediated buoyancy control in a pelagic octopus

Argonauts (Cephalopoda: Argonautidae) are a group of rarely encountered open-ocean pelagic octopuses with benthic ancestry. Female argonauts inhabit a brittle ‘paper nautilus’ shell, the role of which has puzzled naturalists for millennia. The primary role attributed to the shell has been as a receptacle for egg deposition and brooding. Our observations of wild argonauts have revealed that the thin calcareous shell also functions as a hydrostatic structure, employed by the female argonaut to precisely control buoyancy at varying depths. Female argonauts use the shell to ‘gulp’ a measured volume of air at the sea surface, seal off the captured gas using flanged arms and forcefully dive to a depth where the compressed gas buoyancy counteracts body weight. This process allows the female argonaut to attain neutral buoyancy at depth and potentially adjust buoyancy to counter the increased (and significant) weight of eggs during reproductive periods. Evolution of this air-capture strategy enables this negatively buoyant octopus to survive free of the sea floor. This major shift in life mode from benthic to pelagic shows strong evolutionary parallels with the origins of all cephalopods, which attained gas-mediated buoyancy via the closed-chambered shells of the true nautiluses and their relatives.

Taxonomy and biology of the argonauts (Cephalopoda: Argonautidae) with particular reference to Australian material

Argonauts (Argonautidae: Cephalopoda) are a family of pelagic octopuses that inhabit tropical and temperate oceans of the world. Argonauts are most commonly recognised by the beautiful white shells of females (known as “paper nautiluses”) that wash up on beaches throughout the world. Historically, taxonomic delineation of the group has relied on features of these shells—structures not homologous to true molluscan shells and prone to extreme variability. As a consequence, more than 50 species names have been coined worldwide to date. This study constitutes the first thorough examination of argonauts from Australian waters. All argonaut material housed in Australian museums was examined using modern octopus taxonomic methodology and compared to material from key museums throughout the world. Three argonaut species are identified from Australian waters: Argonauta nodosus, Argonauta hians and Argonauta argo. All species can be separated based on morphological characters of males and females, and features of the shells of females. Detailed diagnoses, synonymies, maximum size records, distributional records, nomenclature corrections and biological information are included for each species. Details of the east Pacific Argonauta nouryi, the only other species recognised worldwide, are included for comparative purposes.

Dynamic Skin Patterns in Cephalopods

Cephalopods are unrivaled in the natural world in their ability to alter their visual appearance. These mollusks have evolved a complex system of dermal units under neural, hormonal, and muscular control to produce an astonishing variety of body patterns. With parallels to the pixels on a television screen, cephalopod chromatophores can be coordinated to produce dramatic, dynamic, and rhythmic displays, defined collectively here as “dynamic patterns.” This study examines the nature, context, and potential functions of dynamic patterns across diverse cephalopod taxa. Examples are presented for 21 species, including 11 previously unreported in the scientific literature. These range from simple flashing or flickering patterns, to highly complex passing wave patterns involving multiple skin fields.

Liquid sand burrowing and mucus utilisation as novel adaptations to a structurally-simple environment in Octopus kaurna Stranks, 1990

Cephalopods are often celebrated as masters of camouflage, but their exploitation of the soft-sediment habitats that dominate the ocean floor has demanded other anti-predator strategies. Previous research has identified a small number of cephalopods capable of burying into sand and mud, but the need to directly access the water column for respiration has restricted them to superficial burying. Here, we report on the first known sub-surface burrowing in the cephalopods, by Octopus kaurna, a small benthic species that uses advanced sand-fluidisation and adhesive mucus for sediment manipulation. This burrowing strategy appears linked to easily fluidised sediments as shown in experimental trials in three size-grades of sediment. While the selective pressures that drove evolution of this behaviour are unknown, its identification enriches our understanding of the possible life-history traits and functional role of mucus in other benthic octopus species living in soft-sediment environments.