Cephalopods as Predators: A Short Journey among Behavioral Flexibilities, Adaptions, and Feeding Habits

Projected ocean temperatures impair key proteins used in vision of octopus hatchlings

Global warming is one of the most significant and widespread effects of climate change. While early life stages are particularly vulnerable to increasing temperatures, little is known about the molecular processes that underpin their capacity to adapt to temperature change during early development. Using a quantitative proteomics approach, we investigated the effects of thermal stress on octopus embryos. We exposed Octopus berrima embryos to different temperature treatments (control 19°C, current summer temperature 22°C, or future projected summer temperature 25°C) until hatching. By comparing their protein expression levels, we found that future projected temperatures significantly reduced levels of key eye proteins such as S-crystallin and retinol dehydrogenase 12, suggesting the embryonic octopuses had impaired vision at elevated temperature. We also found that this was coupled with a cellular stress response that included a significant elevation of proteins involved in molecular chaperoning and redox regulation. Energy resources were also redirected away from non-essential processes such as growth and digestion. These findings, taken together with the high embryonic mortality observed under the highest temperature, identify critical physiological functions of embryonic octopuses that may be impaired under future warming conditions. Our findings demonstrate the severity of the thermal impacts on the early life stages of octopuses as demonstrated by quantitative proteome changes that affect vision, protein chaperoning, redox regulation and energy metabolism as critical physiological functions that underlie the responses to thermal stress.

Climate-Change Impacts on Cephalopods: A Meta-Analysis

Aside from being one of the most fascinating groups of marine organisms, cephalopods play a major role in marine food webs, both as predators and as prey, while representing key living economic assets, namely for artisanal and subsistence fisheries worldwide. Recent research suggests that cephalopods are benefitting from ongoing environmental changes and the overfishing of certain fish stocks (i.e., of their predators and/or competitors), putting forward the hypothesis that this group may be one of the few "winners" of climate change. While many meta-analyses have demonstrated negative and overwhelming consequences of ocean warming (OW), acidification (OA), and their combination for a variety of marine taxa, such a comprehensive analysis is lacking for cephalopod molluscs. In this context, the existing literature was surveyed for peer-reviewed articles featuring the sustained (≥24 h) and controlled exposure of cephalopod species (Cephalopoda class) to these factors, applying a comparative framework of mixed-model meta-analyses (784 control-treatment comparisons, from 47 suitable articles). Impacts on a wide set of biological categories at the individual level (e.g., survival, metabolism, behavior, cell stress, growth) were evaluated and contrasted across different ecological attributes (i.e., taxonomic lineages, climates, and ontogenetic stages). Contrary to what is commonly assumed, OW arises as a clear threat to cephalopods, while OA exhibited more restricted impacts. In fact, OW impacts were ubiquitous across different stages of ontogeny, taxonomical lineages (i.e., octopuses, squids, and cuttlefish). These results challenge the assumption that cephalopods benefit from novel ocean conditions, revealing an overarching negative impact of OW in this group. Importantly, we also identify lingering literature gaps, showing that most studies to date focus on OW and early life stages of mainly temperate species. Our results raise the need to consolidate experimental efforts in a wider variety of taxa, climate regions, life stages, and other key environmental stressors, such as deoxygenation and hypoxia, to better understand how cephalopods will cope with future climate change.

Fatty acids and organohalogen contaminants in seafood from the Pearl River Estuary, China: Risk-benefit analyses of seafood consumption

Seafood has long been considered a healthy food choice, but it is also an exposure source of contaminants that may bring potential health risks to humans. Here, 80 organohalogen contaminants (OHCs) and 36 fatty acids (FAs) were analyzed in 22 (n = 211) and 19 fishery species (n = 176) from the eastern- and western Pearl River Estuary (PRE), respectively, for risk-benefit analysis. The average concentrations of total FAs in seafood from the eastern- and western PRE were 26.0 ± 2.14 and 21.3 ± 1.66 mg g-1 wet weight, respectively. Seafood from the eastern PRE exhibited higher levels of OHCs than those from the western PRE, highlighting the spatial heterogeneity of OHC contamination within the PRE. Species occupying higher trophic levels (TLs) typically demonstrated higher levels of OHC accumulation, indicating the biomagnification potential of these contaminants in the PRE ecosystem. Significant negative correlations were observed between TLs and the proportions of monounsaturated fatty acids and polyunsaturated fatty acids, presumably attributed to the ability of fish to synthesize these FAs decreases with increasing TLs. Our benefit-risk quotient (BRQ) analyses revealed that, as far as OHCs are concerned, all seafood species had a BRQ∑OHCs value <1, except for one-spot snapper and daggertooth pike conger, which had BRQ values of 1.03 and 1.14, respectively. The findings indicate that most marine species here analyzed may not pose significant health risks to consumers as a result of OHC exposure. However, considering that many other pollutants and nutrients are not analyzed here, the results of our risk assessments should be treated as preliminary, not final. Future data collection is essential to enhance the comprehensiveness of this type of analysis.

Switching by cuttlefish of preying tactics targeted at moving prey

Previous studies have demonstrated that the size of the prey relative to the cuttlefish is important to the choice between tentacular strike and jump-on tactics. In the present study, we investigated the decision-making in the cuttlefish's tactical switch when preying on the same size prey. A servomotor system controlling the movement of a shrimp was used to elicit the cuttlefish's preying behavior. The success rate of prey capture and the kinematics of visual attack were examined systematically. The results showed that the jump-on behavior appeared mostly after a miss attack by previous tentacular strike on a moving shrimp. Compared with a visual attack with tentacles, the jump-on tactic has over a shorter attacking distance and wider attacking angles. Thus, these two different preying tactics have different operating ranges relative to the prey. More importantly, the cuttlefish can adjust their preying tactics adaptively depending on their prior preying experience.

Aquatic and Terrestrial Invertebrate Welfare

Invertebrates are a diverse group of animals that make up the majority of the animal kingdom and encompass a wide array of species with varying adaptations and characteristics. Invertebrates are found in nearly all of the world's habitats, including aquatic, marine, and terrestrial environments. There are many misconceptions about invertebrate sentience, welfare requirements, the need for environmental enrichment, and overall care and husbandry for this amazing group of animals. This review addresses these topics and more for a select group of invertebrates with biomedical, economical, display, and human companionship importance.

The neural basis of visual processing and behavior in cephalopods

Coleoid cephalopods (octopuses, squids and cuttlefishes) are the only branch of the animal kingdom outside of vertebrates to have evolved both a large brain and camera-type eyes. They are highly dependent on vision, with the majority of their brain devoted to visual processing. Their excellent vision supports a range of advanced visually guided behaviors, from navigation and prey capture, to the ability to camouflage based on their surroundings. However, their brain organization is radically different from that of vertebrates, as well as other invertebrates, providing a unique opportunity to explore how a novel neural architecture for vision is organized and functions. Relatively few studies have examined the cephalopod visual system using current neuroscience approaches, to the extent that there has not even been a measurement of single-cell receptive fields in their central visual system. Therefore, there remains a tremendous amount that is unknown about the neural basis of vision in these extraordinary animals. Here, we review the existing knowledge of the organization and function of the cephalopod visual system to provide a framework for examining the neural circuits and computational mechanisms mediating their remarkable visual capabilities.

Understanding the interactions between cephalopods and marine litter: A research evaluation with identification of gaps and future perspectives

Litter is known to negatively affect numerous marine organisms, but the extent of such impacts is not well known for several groups, including cephalopods. Considering the ecological, behavioral and economic importance of these animals, we reviewed the types of interactions between cephalopods and litter in the scientific literature, to evaluate impacts and knowledge gaps. We found 30 papers, which included records of microplastic ingestion and the transfer of synthetic microfibers along the food web. The largest number of records involved litter use as shelter, and the common octopus was the most frequent species. At first sight, litter use as shelter could appear to be a potential positive effect, but it is necessary to clarify the implications of this choice and its long-term consequences. Regarding ingestion and trophic transfer, further research is needed to elucidate its occurrence and impacts on cephalopods and their predators, including humans.

General and species-specific recommendations for minimal requirements for the use of cephalopods in scientific research

Here we list species-specific recommendations for housing, care and management of cephalopod molluscs employed for research purposes with the aim of contributing to the standardization of minimum requirements for establishments, care and accommodation of these animals in compliance with the principles stated in Directive 2010/63/EU. Maximizing their psychophysical welfare was our priority. General recommendations on water surface area, water depth and tank shape here reported represent the outcome of the combined action of the analysis of the available literature and an expertise-based consensus reached - under the aegis of the COST Action FA1301 - among researchers working with the most commonly used cephalopod species in Europe. Information on water supply and quality, environmental conditions, stocking density, feeding and handling are also provided. Through this work we wish to set the stage for a more fertile ground of evidence-based approaches on cephalopod laboratory maintenance, thus facilitating standardization and replicability of research outcomes across laboratories, at the same time maximizing the welfare of these animals.

De novo transcriptome reconstruction in aquacultured early life stages of the cephalopod Octopus vulgaris

Cephalopods have been considered enigmatic animals that have attracted the attention of scientists from different areas of expertise. However, there are still many questions to elucidate the way of life of these invertebrates. The aim of this study is to construct a reference transcriptome in Octopus vulgaris early life stages to enrich existing databases and provide a new dataset that can be reused by other researchers in the field. For that, samples from different developmental stages were combined including embryos, newly-hatched paralarvae, and paralarvae of 10, 20 and 40 days post-hatching. Additionally, different dietary and rearing conditions and pathogenic infections were tested. At least three biological replicates were analysed per condition and submitted to RNA-seq analysis. All sequencing reads from experimental conditions were combined in a single dataset to generate a reference transcriptome assembly that was functionally annotated. The number of reads aligned to this reference was counted to estimate the transcript abundance in each sample. This dataset compiled a complete reference for future transcriptomic studies in O. vulgaris.

Measurement(s)	Transcriptome sequencing assay
Technology Type(s)	RNA-seq assay (Illumina)
Sample Characteristic - Organism	Octopus vulgaris
Sample Characteristic - Environment	Ocean
Sample Characteristic - Location	NW Spain (Ría de Vigo, Galicia)

Octopus bimaculoides' arm recruitment and use during visually evoked prey capture

Octopus' limb hyper-redundancy complicates traditional motor control system theory due to its extensive sensory inputs, subsequent decision-making, and arm coordination. Octopuses are thought to reduce flexibility control complexity by relying on highly stereotypical motor primitives (e.g., reaching^1-4 and crawling⁵) and multi-level processes to coordinate movement,^6,7 utilizing extensive peripheral nervous system (PNS) processing.^2,8,9 Division of labor along the anterior-posterior axis¹⁰ and limb specialization of the four anterior arms in T-maze food retrieval¹¹ further simplify control. However, specific arm recruitment and coordination during visually guided reaching behavior remains poorly understood. Here, we investigated visually evoked Octopus bimaculoides' prey capture capabilities^12,13 by eliciting and examining prey-specific arm recruitment. When striking crabs, octopuses preferred synchronous arm recruitment, while sequential arm recruitment with a characteristic swaying movement is employed for shrimp. Such behavioral selection aligns with specific prey escape strategies and the octopus' flexible arm biomechanical constraints. Although side bias existed, we found significant bilateral symmetry, with one side being functionally a mirror of the other rather than anterior arm use being functionally equal and differing to posterior arm use. Among arms, the second limb is unequivocally dominant for goal-directed monocularly driven prey capture. Although the eight arms share gross anatomy and are considered equipotential,^10,14 such arm use for specific actions could reflect subtle evolutionary adaptations. Finally, we quantitatively show, corroborating earlier observations,^10,15 that octopuses employ a dimension reduction strategy by actively deciding to recruit adjacent arms over other available arms during either sequential or synchronous visually evoked prey attack.

Methodological considerations in studying digestive system physiology in octopus: limitations, lacunae and lessons learnt

Current understanding of cephalopod digestive tract physiology is based on relatively “old” literature and a “mosaic of data” from multiple species. To provide a background to the discussion of methodologies for investigating physiology we first review the anatomy of the cephalopod digestive tract with a focus on Octopus vulgaris, highlighting structure-function relationships and species differences with potential functional consequences (e.g., absence of a crop in cuttlefish and squid; presence of a caecal sac in squid). We caution about extrapolation of data on the digestive system physiology from one cephalopod species to another because of the anatomical differences. The contribution of anatomical and histological techniques (e.g., digestive enzyme histochemistry and neurotransmitter immunohistochemistry) to understanding physiological processes is discussed. For each major digestive tract function we briefly review current knowledge, and then discuss techniques and their limitations for the following parameters: 1) Measuring motility in vitro (e.g., spatiotemporal mapping, tension and pressure), in vivo (labelled food, high resolution ultrasound) and aspects of pharmacology; 2) Measuring food ingestion and the time course of digestion with an emphasis on understanding enzyme function in each gut region with respect to time; 3) Assessing transepithelial transport of nutrients; 4) Measuring the energetic cost of food processing, impact of environmental temperature and metabolic rate (flow-through/intermittent respirometry); 4) Investigating neural (brain, gastric ganglion, enteric) and endocrine control processes with an emphasis on application of molecular techniques to identify receptors and their ligands. A number of major knowledge lacunae are identified where available techniques need to be applied to cephalopods, these include: 1) What is the physiological function of the caecal leaflets and intestinal typhlosoles in octopus? 2) What role does the transepithelial transport in the caecum and intestine play in ion, water and nutrient transport? 3) What information is signalled from the digestive tract to the brain regarding the food ingested and the progress of digestion? It is hoped that by combining discussion of the physiology of the cephalopod digestive system with an overview of techniques and identification of key knowledge gaps that this will encourage a more systematic approach to research in this area.

Impact of squid predation on juvenile fish survival

Predation is a major source of mortality during the early life stages of marine fishes; however, few studies have demonstrated its impact—especially that of squid predation—on survival processes. Here, we examined the feeding habits and predation impacts of swordtip squid on a major prey fish, juveniles of jack mackerel, in the East China Sea. Otoliths of the juveniles extracted from the squid stomach were used to reconstruct the age–length relationship and the growth trajectory of the consumed juveniles, and they were compared to those of juveniles collected with a net using a newly developed statistical framework. The juveniles consumed by squid had significantly shorter body lengths and smaller body sizes during the late larval and early juvenile stages than the netted juveniles, suggesting that smaller juveniles with slower growth rates have a higher probability to be selected. The body mass ratio of the predator squid to prey juveniles (predator–prey mass ratio, PPMR) ranged from 7 to 700, which was remarkably lower than the PPMR reported in various marine ecosystems based on analyses of fishes. Our findings demonstrate that squid predation can significantly impact the early life survival of fish and the trophodynamics in marine ecosystems.

Host phylogeny, habitat, and diet are main drivers of the cephalopod and mollusk gut microbiome

Background

Invertebrates are a very attractive subject for studying host-microbe interactions because of their simple gut microbial community and host diversity. Studying the composition of invertebrate gut microbiota and the determining factors is essential for understanding their symbiotic mechanism. Cephalopods are invertebrates that have similar biological properties to vertebrates such as closed circulation system, an advanced nervous system, and a well-differentiated digestive system. However, it is not currently known whether their microbiomes have more in common with vertebrates or invertebrates. This study reports on the microbial composition of six cephalopod species and compares them with other mollusk and marine fish microbiomes to investigate the factors that shape the gut microbiota.

Results

Each cephalopod gut consisted of a distinct consortium of microbes, with Photobacterium and Mycoplasma identified as core taxa. The gut microbial composition of cephalopod reflected their host phylogeny, the importance of which was supported by a detailed oligotype-level analysis of operational taxonomic units assigned to Photobacterium and Mycoplasma. Photobacterium typically inhabited multiple hosts, whereas Mycoplasma tended to show host-specific colonization. Furthermore, we showed that class Cephalopoda has a distinct gut microbial community from those of other mollusk groups or marine fish. We also showed that the gut microbiota of phylum Mollusca was determined by host phylogeny, habitat, and diet.

Conclusion

We have provided the first comparative analysis of cephalopod and mollusk gut microbial communities. The gut microbial community of cephalopods is composed of distinctive microbes and is strongly associated with their phylogeny. The Photobacterium and Mycoplasma genera are core taxa within the cephalopod gut microbiota. Collectively, our findings provide evidence that cephalopod and mollusk gut microbiomes reflect host phylogeny, habitat, and diet. It is hoped that these data can contribute to future studies on invertebrate–microbe interactions.

Contact chemoreception in multi-modal sensing of prey by Octopus

Octopuses have keen vision and are generally considered visual predators, yet octopuses predominantly forage blindly in nature, inserting their arms into crevices to search and detect hidden prey. The extent to which octopuses discriminate prey using chemo- versus mechano-tactile sensing is unknown. We developed a whole-animal behavioral assay that takes advantage of octopuses' natural searching behavior to test their ability to discriminate prey from non-prey tastes solely via contact chemoreception. This methodology eliminated vision, mechano-tactile sensing and distance chemoreception while testing the contact chemosensory discriminatory abilities of the octopus arm suckers. Extracts from two types of prey (crab, shrimp) and three types of non-prey (sea star, algae, seawater) were embedded in agarose (to control for mechano-tactile discrimination) and presented to octopuses inside an artificial rock dome; octopuses reached their arms inside to explore its contents - imitating natural prey-searching behavior. Results revealed that octopuses are capable of discriminating between potential prey items using only contact chemoreception, as measured by an increased amount of sucker contact time and arm curls when presented with prey extracts versus non-prey extracts. These results highlight the importance of contact chemoreception in the multi-modal sensing involved in a complex foraging behavior.

Cephalopod Behavior: From Neural Plasticity to Consciousness

It is only in recent decades that subjective experience - or consciousness - has become a legitimate object of scientific inquiry. As such, it represents perhaps the greatest challenge facing neuroscience today. Subsumed within this challenge is the study of subjective experience in non-human animals: a particularly difficult endeavor that becomes even more so, as one crosses the great evolutionary divide between vertebrate and invertebrate phyla. Here, we explore the possibility of consciousness in one group of invertebrates: cephalopod molluscs. We believe such a review is timely, particularly considering cephalopods' impressive learning and memory abilities, rich behavioral repertoire, and the relative complexity of their nervous systems and sensory capabilities. Indeed, in some cephalopods, these abilities are so sophisticated that they are comparable to those of some higher vertebrates. Following the criteria and framework outlined for the identification of hallmarks of consciousness in non-mammalian species, here we propose that cephalopods - particularly the octopus - provide a unique test case among invertebrates for examining the properties and conditions that, at the very least, afford a basal faculty of consciousness. These include, among others: (i) discriminatory and anticipatory behaviors indicating a strong link between perception and memory recall; (ii) the presence of neural substrates representing functional analogs of thalamus and cortex; (iii) the neurophysiological dynamics resembling the functional signatures of conscious states in mammals. We highlight the current lack of evidence as well as potentially informative areas that warrant further investigation to support the view expressed here. Finally, we identify future research directions for the study of consciousness in these tantalizing animals.

Seahorse Predation by Octopuses in the Caribbean and the West Pacific

There is much documentation about seahorses (Hippocampus spp.) being threatened by habitat degradation and overfishing, but relatively few published studies mention their natural predators. The present study documents three cases in which seahorses are being caught by octopuses. In one case, the seahorse was partly consumed. These observations made at Bonaire (Caribbean Netherlands) and New South Wales (Australia) suggest that predation on seahorses by octopuses may be more widespread and common than previously thought.

Imaging Arm Regeneration: Label-Free Multiphoton Microscopy to Dissect the Process in Octopus vulgaris

Cephalopod mollusks are endowed with an impressive range of features that have captured the attention of scientists from different fields, the imaginations of artists, and the interests of the public. The ability to spontaneously regrow lost or damaged structures quickly and functionally is among one of the most notable peculiarities that cephalopods possess. Microscopical imaging techniques represent useful tools for investigating the regenerative processes in several species, from invertebrates to mammals. However, these techniques have had limited use in cephalopods mainly due to the paucity of specific and commercially available markers. In addition, the commonly used immunohistochemical staining methods provide data that are specific to the antigens studied. New microscopical methods were recently applied to vertebrates to investigate regenerative events. Among them, multiphoton microscopy appears promising. For instance, it does not depend on species-related epitopes, taking advantage of the specific characteristics of tissues and allowing for its use in a species-independent way. Here, we illustrate the results obtained by applying this label-free imaging technique to the injured arm of Octopus vulgaris, a complex structure often subject to injury in the wild. This approach allowed for the characterization of the entire tissue arm architecture (muscular layers, nerve component, connective tissues, etc.) and elements usually hardly detectable (such as vessels, hemocytes, and chromatophores). More importantly, it also provided morpho-chemical information which helped decipher the regenerative phases after damage, from healing to complete arm regrowth, thereby appearing promising for regenerative studies in cephalopods and other non-model species.

A phylogenomic look into the systematics of oceanic squids (order Oegopsida)

Oceanic squids of the order Oegopsida are ecologically and economically important members of the pelagic environment. They are the most diverse group of cephalopods, with 24 families that are divergent morphologically. Despite their importance, knowledge of phylogenetic relationships among oegopsids is less than that among neritic cephalopods. Here, we provide the complete mitogenomes and the nuclear 18S and 28S ribosomal genes for 35 selected oceanic squids, which were generated using genome skimming. We performed maximum likelihood and Bayesian inference analyses that included 21 of the 24 oegopsid families. In our analyses, the architeuthid, chiroteuthid and enoploteuthid family groups, which have been proposed previously based on morphological and natural history characteristics, were retrieved as monophyletic. The morphologically divergent Cranchiidae formed a well-supported clade with families Ommastrephidae and Thysanoteuthidae, with a unique mitochondrial gene order. The family Lycoteuthidae was revealed as paraphyletic and contained Pyroteuthidae. Thus, the two lycoteuthid subfamilies are herein elevated to family level, increasing the number of oegopsid squid families to 25. In order to describe the diversity and evolutionary trends of oegopsid squids accurately, the superfamilies Architeuthoidea, Chiroteuthoidea, Cranchioidea and Enoploteuthoidea are resurrected from the literature, and the superfamilies Cycloteuthoidea, Octopoteuthoidea and Pholidoteuthoidea are proposed. The phylogenetic positions of Gonatidae, Histioteuthidae and Onychoteuthidae were not stable in our phylogenetic analyses and are not assigned to a superfamily. This study supports the utility of genome skimming to solve the phylogenetic relationships of oceanic squids.

Assessments of metallic contents in rare cephalopods from the Canary Islands: relationships with depth habitat and body size

This study investigated 20 elements in the muscle of 11 cephalopod species caught in the Canary Islands inhabiting from coastal to meso-bathypelagic habitats. Among them, trace element contents from large and elusive cephalopods such as Architeuthis dux, Taningia danae, Lepidoteuthis grimaldii, and Haliphron atlanticus were determined. Statistically significant differences in element concentration were found among class sizes and habitat. Large species that are inhabiting in deepest waters such as Loligo forbesii, A. dux, T. danae, H. atlanticus, and L. grimaldii showed a high load and variability in Fe and Al, while coastal species were characterized by a homogeneous element composition, being the Zn loads highest than other elements. Metal contents in large and elusive cephalopod species were dominated by Fe, Ni, Al, Zn, and Sr, with these species being able to carry important amounts of these elements to predators such as deep-diving odontocetes that reside around the Canary waters.

A Mysterious World Revealed: Larval-Adult Matching of Deep-Sea Shrimps from the Gulf of Mexico

The identification of deep-sea (>200 m) pelagic larvae is extremely challenging due to the morphological diversity across ontogeny and duration of larval phases. Within Decapoda, developmental stages often differ conspicuously from their adult form, representing a bizarre and mysterious world still left to be discovered. The difficulties with sampling and rearing deep-sea larvae, combined with the lack of taxonomic expertise, argues for the use of molecular methods to aid in identification. Here, we use DNA barcoding combined with morphological methods, to match larval stages with their adult counterpart from the northern Gulf of Mexico and adjacent waters. For DNA barcoding, we targeted the mitochondrial ribosomal large subunit 16S (16S) and the protein coding cytochrome oxidase subunit 1 (COI). These data were combined with previous sequences to generate phylogenetic trees that were used to identify 12 unknown larval and two juvenile species from the infraorder Caridea and the suborder Dendrobranchiata. Once identified, we provide taxonomic descriptions and illustrations alongside the current state of knowledge for all families. For many groups, larval descriptions are missing or non-existent, so this study represents a first step of many to advance deep-sea larval diversity.

Research Trends in Octopus Biological Studies

Simple Summary

Octopuses represent model studies for different fields of scientific inquiry. We provide a bibliometric analysis on biological research trends in octopuses studies by using bibliometrix, a new and powerful R-tool. The analysis was executed from January 1985 to December 2020 including scientific products reported in Web of Science (WoS) database. The main results showed an increasing effort in research involving octopuses with a greater number of journals reporting research on these animals, as well as countries, institutions, and researchers involved. Some research themes lost importance over time, while some new themes appeared recently. Current data provide significant insight into the evolving trends in octopuses studies.

Abstract

Octopuses represent interesting model studies for different fields of scientific inquiry. The present study provides a bibliometric analysis on research trends in octopuses biological studies. The analysis was executed from January 1985 to December 2020 including scientific products reported in the Web of Science database. The period of study was split into two blocks (“earlier period” (EP): 1985−2010; “recent period” (RP): 2011−2020) to analyze the evolution of the research topics over time. All publications of interest were identified by using the following query: ((AK = octopus) OR (AB = octopus) OR (TI = octopus)). Data information was converted into an R-data frame using bibliometrix. Octopuses studies appeared in 360 different sources in EP, while they increased to 408 in RP. Sixty countries contributed to the octopuses studies in the EP, while they were 78 in the RP. The number of affiliations also increased between EP and RP, with 835 research centers involved in the EP and 1399 in the RP. In the EP 5 clusters (i.e., “growth and nutrition”, “pollution impact”, “morphology”, “neurobiology”, “biochemistry”) were represented in a thematic map, according to their centrality and density ranking. In the RP the analysis identified 4 clusters (i.e., “growth and nutrition”, “ecology”, “pollution impact”, “genes, behavior, and brain evolution”). The UK with Ireland, and the USA with Canada shared the highest number of publications in the EP, while in the RP, Spain and Portugal were the leading countries. The current data provide significant insight into the evolving trends in octopuses studies.

Potential evidence of peripheral learning and memory in the arms of dwarf cuttlefish, Sepia bandensis

CREB (cAMP response element-binding) transcription factors are conserved markers of memory formation in the brain and peripheral circuits. We provide immunohistochemical evidence of CREB phosphorylation in the dwarf cuttlefish, Sepia bandensis, following the inaccessible prey (IP) memory experiment. During the IP experiment, cuttlefish are shown prey enclosed in a transparent tube, and tentacle strikes against the tube decrease over time as the cuttlefish learns the prey is inaccessible. The cues driving IP learning are unclear but may include sensory inputs from arms touching the tube. The neural activity marker, anti-phospho-CREB (anti-pCREB) was used to determine whether IP training stimulated cuttlefish arm sensory neurons. pCREB immunoreactivity occurred along the oral surface of the arms, including the suckers and epithelial folds surrounding the suckers. pCREB increased in the epithelial folds and suckers of trained cuttlefish. We found differential pCREB immunoreactivity along the distal-proximal axis of trained arms, with pCREB concentrated distally. Unequal CREB phosphorylation occurred among the 4 trained arm pairs, with arm pairs 1 and 2 containing more pCREB. The resulting patterns of pCREB in trained arms suggest that the arms obtain cues that may be salient for learning and memory of the IP experiment.

Fossilized leftover falls as sources of palaeoecological data: a 'pabulite' comprising a crustacean, a belemnite and a vertebrate from the Early Jurassic Posidonia Shale

Especially in Lagerstätten with exceptionally preserved fossils, we can sometimes recognize fossilized remains of meals of animals. We suggest the term leftover fall for the event and the term pabulite for the fossilized meal when it never entered the digestive tract (difference to regurgitalites). Usually, pabulites are incomplete organismal remains and show traces of the predation. Pabulites have a great potential to inform about predation as well as anatomical detail, which is invisible otherwise. Here, we document a pabulite comprising the belemnite Passaloteuthis laevigata from the Toarcian of the Holzmaden region. Most of its soft parts are missing while the arm crown is one of the best preserved that is known. Its arms embrace an exuvia of a crustacean. We suggest that the belemnite represents the remnant of the food of a predatory fish such as the shark Hybodus.

Distraction sinking and fossilized coleoid predatory behaviour from the German Early Jurassic

Exceptional fossil preservation is required to conserve soft-bodied fossils and even more so to conserve their behaviour. Here, we describe a fossil of a co-occurrence of representatives of two different octobrachian coleoid species. The fossils are from the Toarcian Posidonienschiefer of Ohmden near Holzmaden, Germany. The two animals died in the act of predation, i.e. one had caught the other and had begun to nibble on it, when they possibly sank into hypoxic waters and suffocated (distraction sinking). This supports the idea that primitive vampyromorphs pursued diverse feeding strategies and were not yet adapted to being opportunistic feeders in oxygen minimum zones like their modern relative Vampyroteuthis.

Early Exposure to Water Turbidity Affects Visual Capacities in Cuttlefish (Sepia officinalis)

In La Manche (English Channel) the level of turbidity changes, not only seasonally and daily in seawater but also along the coast. As a consequence, vision in marine species is limited when based only on contrast-intensity. It is hypothesized that polarization sensitivity (PS) may help individuals detect preys and predators in turbid environments. In the cuttlefish, Sepia officinalis, to date, all behavioral studies have been conducted on animals reared in clear water. But the cuttlefish sensory system is adapted to a range of turbid environments. Our hypothesis was that rearing cuttlefish in clear water may affect the development of their visual system, and potentially affect their visually guided behaviors. To test this, newly-hatched cuttlefish, from eggs laid by females brought in from the wild, were reared for 1 month under three different conditions: clear water (C group), low turbidity (0.1 g / l of clay, 50–80 NTU, LT group) and high turbidity (0.5 g / l of clay, 300–400 NTU, HT group). The visual capacities of cuttlefish were tested with an optomotor apparatus at 7 days and at 1 month post-hatching. Optomotor responses of juveniles were measured by using three screen patterns (black and white stripes, linearly polarized stripes set at different orientations, and a uniform gray screen). Optomotor responses of juveniles suggest that exposure to turbid water improves the development of their PS when tested in clear water (especially in LT group) but not when tested in turbid water. We suggest that the use of slightly turbid water in rearing systems may improve the development of vision in young cuttlefish with no detrimental effect to their survival rate. Future research will consider water turbidity as a possible factor for the improvement of cuttlefish well-being in artificial rearing systems.

A novel metabarcoding primer pair for environmental DNA analysis of Cephalopoda (Mollusca) targeting the nuclear 18S rRNA region

Cephalopods are pivotal components of marine food webs, but biodiversity studies are hampered by challenges to sample these agile marine molluscs. Metabarcoding of environmental DNA (eDNA) is a potentially powerful technique to study oceanic cephalopod biodiversity and distribution but has not been applied thus far. We present a novel universal primer pair for metabarcoding cephalopods from eDNA, Ceph18S (Forward: 5'-CGC GGC GCT ACA TAT TAG AC-3', Reverse: 5'-GCA CTT AAC CGA CCG TCG AC-3'). The primer pair targets the hypervariable region V2 of the nuclear 18S rRNA gene and amplifies a relatively short target sequence of approximately 200 bp in order to allow the amplification of degraded DNA. In silico tests on a reference database and empirical tests on DNA extracts from cephalopod tissue estimate that 44-66% of cephalopod species, corresponding to about 310-460 species, can be amplified and identified with this primer pair. A multi-marker approach with the novel Ceph18S and two previously published cephalopod mitochondrial 16S rRNA primer sets targeting the same region (Jarman et al. 2006 Mol. Ecol. Notes. 6, 268-271; Peters et al. 2015 Mar. Ecol. 36, 1428-1439) is estimated to amplify and identify 89% of all cephalopod species, of which an estimated 19% can only be identified by Ceph18S. All sequences obtained with Ceph18S were submitted to GenBank, resulting in new 18S rRNA sequences for 13 cephalopod taxa.

Invertebrate Behavior for the Exotic Pet Practitioner

Invertebrate animals comprise more than 95% of the animal kingdom's species and approximately 40 separate phyla. Yet, invertebrates are an artificial taxon, in which all members simply possess a single negative trait: they lack a vertebral column (backbone). In fact, some invertebrates are more closely related to vertebrates than to their "fellow" invertebrates. For the purpose of this veterinary article, we have elected to review a handful of important groups: Coelenterates, Gastropods, Cephalopods, Chelicerates, Crustaceans, Insects, and Echinoderms. We have primarily included behaviors that may have an impact on clinical case outcome, or be of interest to the veterinary clinician.

Putative Antimicrobial Peptides of the Posterior Salivary Glands from the Cephalopod Octopus vulgaris Revealed by Exploring a Composite Protein Database

Cephalopods, successful predators, can use a mixture of substances to subdue their prey, becoming interesting sources of bioactive compounds. In addition to neurotoxins and enzymes, the presence of antimicrobial compounds has been reported. Recently, the transcriptome and the whole proteome of the Octopus vulgaris salivary apparatus were released, but the role of some compounds—e.g., histones, antimicrobial peptides (AMPs), and toxins—remains unclear. Herein, we profiled the proteome of the posterior salivary glands (PSGs) of O. vulgaris using two sample preparation protocols combined with a shotgun-proteomics approach. Protein identification was performed against a composite database comprising data from the UniProtKB, all transcriptomes available from the cephalopods’ PSGs, and a comprehensive non-redundant AMPs database. Out of the 10,075 proteins clustered in 1868 protein groups, 90 clusters corresponded to venom protein toxin families. Additionally, we detected putative AMPs clustered with histones previously found as abundant proteins in the saliva of O. vulgaris. Some of these histones, such as H2A and H2B, are involved in systemic inflammatory responses and their antimicrobial effects have been demonstrated. These results not only confirm the production of enzymes and toxins by the O. vulgaris PSGs but also suggest their involvement in the first line of defense against microbes.

Genomic and transcriptomic landscapes and evolutionary dynamics of molluscan glycoside hydrolase families with implications for algae-feeding biology

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Genome-wide characterization of GH families is conducted for Mollusca.

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GH9, GH10, GH18 and GH20 families are remarkably expanded in molluscs.

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The wide adoption of CBMs likely facilitates the hydrolysis of polysaccharides.

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Hepatopancreas is the main organ for the prominent expression of GH families.

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Functional divergence of GH families possibly contributes to their adaptive roles.

The hydrolysis of sugar-containing compounds by glycoside hydrolases (GHs) plays essential roles in many major biological processes, but to date our systematic understanding of the functional diversity and evolution of GH families remains largely limited to a few well-studied terrestrial animals. Molluscs represent the largest marine phylum in the animal kingdom, and many of them are herbivorous that utilize algae as a main nutritional source, making them good subjects for studying the functional diversity and adaptive evolution of GH families. In the present study, we conducted genome-wide identification and functional and evolutionary analysis of all GH families across major molluscan lineages. We revealed that the remarkable expansion of the GH9, GH10, GH18 and GH20 families and the wide adoption of carbohydrate-binding modules in molluscan expanded GH families likely contributed to the efficient hydrolysis of marine algal polysaccharides and were involved in the consolidation of molluscan algae-feeding habits. Gene expression and network analysis revealed the hepatopancreas as the main organ for the prominent expression of approximately half of the GH families (well corresponding to the digestive roles of the hepatopancreas) and key or hub GHs in the coexpression gene network with potentially diverse functionalities. We also revealed the evolutionary signs of differential expansion and functional divergence of the GH family, which possibly contributed to lineage-specific adaptation. Systematic analysis of GH families at both genomic and transcriptomic levels provides important clues for understanding the functional divergence and evolution of GH gene families in molluscs in relation to their algae-feeding biology.

Functional traits explain trophic allometries of cephalopods

Individual body size strongly influences the trophic role of marine organisms and the structure and function of marine ecosystems. Quantifying trophic position-individual body size relationships (trophic allometries) underpins the development of size-structured ecosystem models to predict abundance and the transfer of energy through ecosystems. Trophic allometries are well studied for fishes but remain relatively unexplored for cephalopods. Cephalopods are important components of coastal, oceanic and deep-sea ecosystems, and they play a key role in the transfer of biomass from low trophic positions to higher predators. It is therefore important to resolve cephalopod trophic allometries to accurately represent them within size-structured ecosystem models. We assessed the trophic positions of cephalopods in an oceanic pelagic (0-500 m) community (sampled by trawling in a cold-core eddy in the western Tasman Sea), comprising 22 species from 12 families, using bulk tissue stable isotope analysis and amino acid compound-specific stable isotope analysis. We assessed whether ontogenetic trophic position shifts were evident at the species-level and tested for the best predictor of community-level trophic allometry among body size, taxonomy and functional grouping (informed by fin and mantle morphology). Individuals in this cephalopod community spanned two trophic positions and fell into three functional groups on an activity level gradient: low, medium and high. The relationship between trophic position and ontogeny varied among species, with the most marked differences evident between species from different functional groups. Activity-level-based functional group and individual body size are best explained by cephalopod trophic positions (marginal R²  = 0.43). Our results suggest that the morphological traits used to infer activity level, such as fin-to-mantle length ratio, fin musculature and mantle musculature are strong predictors of cephalopod trophic allometries. Contrary to established theory, not all cephalopods are voracious predators. Low activity level cephalopods have a distinct feeding mode, with low trophic positions and little-to-no ontogenetic increases. Given the important role of cephalopods in marine ecosystems, distinct feeding modes could have important consequences for energy pathways and ecosystem structure and function. These findings will facilitate trait-based and other model estimates of cephalopod abundance in the changing global ocean.

Can Cephalopods Vomit? Hypothesis Based on a Review of Circumstantial Evidence and Preliminary Experimental Observations

In representative species of all vertebrate classes, the oral ejection of upper digestive tract contents by vomiting or regurgitation is used to void food contaminated with toxins or containing indigestible material not voidable in the feces. Vomiting or regurgitation has been reported in a number of invertebrate marine species (Exaiptasia diaphana, Cancer productus, and Pleurobranchaea californica), prompting consideration of whether cephalopods have this capability. This "hypothesis and theory" paper reviews four lines of supporting evidence: (1) the mollusk P. californica sharing some digestive tract morphological and innervation similarities with Octopus vulgaris is able to vomit or regurgitate with the mechanisms well characterized, providing an example of motor program switching; (2) a rationale for vomiting or regurgitation in cephalopods based upon the potential requirement to void indigestible material, which may cause damage and ejection of toxin contaminated food; (3) anecdotal reports (including from the literature) of vomiting- or regurgitation-like behavior in several species of cephalopod (Sepia officinalis, Sepioteuthis sepioidea, O. vulgaris, and Enteroctopus dofleini); and (4) anatomical and physiological studies indicating that ejection of gastric/crop contents via the buccal cavity is a theoretical possibility by retroperistalsis in the upper digestive tract (esophagus, crop, and stomach). We have not identified any publications refuting our hypothesis, so a balanced review is not possible. Overall, the evidence presented is circumstantial, so experiments adapting current methodology (e.g., research community survey, in vitro studies of motility, and analysis of indigestible gut contents and feces) are described to obtain additional evidence to either support or refute our hypothesis. We recognize the possibility that further research may not support the hypothesis; therefore, we consider how cephalopods may protect themselves against ingestion of toxic food by external chemodetection prior to ingestion and digestive gland detoxification post-ingestion. Reviewing the evidence for the hypothesis has identified a number of gaps in knowledge of the anatomy (e.g., the presence of sphincters) and physiology (e.g., the fate of indigestible food residues, pH of digestive secretions, sensory innervation, and digestive gland detoxification mechanisms) of the digestive tract as well as a paucity of recent studies on the role of epithelial chemoreceptors in prey identification and food intake.

Assessing the Morphological Impacts of Ammonoid Shell Shape through Systematic Shape Variation

A substantial body of research has been accumulated around ammonoids over several decades. A core aspect of this research has been attempting to infer their life mode from analysis of the morphology of their shells and the drag they incur as that shell is pushed through the water. Tools such as Westermann Morphospace have been developed to investigate and scaffold hypotheses about the results of these investigations. We use computational fluid dynamics to simulate fluid flow around a suite of 24 theoretical ammonoid morphologies to interrogate systematic variations within this space. Our findings uphold some of the long-standing expectations of drag behavior; conch inflation has the greatest influence over ammonoid drag. However, we also find that other long-standing assumptions, such as oxyconic ammonoids being the best swimmers, are subject to substantial variation and nuance resulting from their morphology that is not accounted for through simple drag assessment.

Embracing Their Prey at That Dark Hour: Common Cuttlefish (Sepia officinalis) Can Hunt in Nighttime Light Conditions

Cuttlefish are highly efficient predators, which strongly rely on their anterior binocular visual field for hunting and prey capture. Their complex eyes possess adaptations for low light conditions. Recently, it was discovered that they display camouflaging behavior at night, perhaps to avoid detection by predators, or to increase their nighttime hunting success. This raises the question whether cuttlefish are capable of foraging during nighttime. In the present study, prey capture of the common cuttlefish (Sepia officinalis) was filmed with a high-speed video camera in different light conditions. Experiments were performed in daylight and with near-infrared light sources in two simulated nightlight conditions, as well as in darkness. The body of the common cuttlefish maintained a velocity of less than 0.1 m/s during prey capture, while the tentacles during the seizing phase reached velocities of up to 2.5 m/s and accelerations reached more than 450 m/s² for single individuals. There was no significant difference between the day and nighttime trials, respectively. In complete darkness, the common cuttlefish was unable to catch any prey. Our results show that the common cuttlefish are capable of catching prey during day- and nighttime light conditions. The common cuttlefish employ similar sensory motor systems and prey capturing techniques during both day- and nighttime conditions.

Global biodiversity of the genus Ommastrephes (Ommastrephidae: Cephalopoda): an allopatric cryptic species complex

Cryptic speciation among morphologically homogeneous species is a phenomenon increasingly reported in cosmopolitan marine invertebrates. This situation usually leads to the discovery of new species, each of which occupies a smaller fraction of the original distributional range. The resolution of the taxonomic status of species complexes is essential because species are used as the unit of action for conservation and natural resource management politics. Before the present study, Ommastrephes bartramii was considered a monotypic cosmopolitan species with a discontinuous distribution. Here, individuals from nearly its entire distributional range were evaluated with mitochondrial DNA (cytochrome c oxidase subunit I and 16S rRNA). Four distinct species were consistently identified using four molecular species delimitation methods. These results, in combination with morphological and metabolic information from the literature, were used to resurrect three formerly synonymized names (Ommastrephes brevimanus, Ommastrephes caroli and Ommastrephes cylindraceus) and to propose revised distributional ranges for each species. In addition, diagnostic characters from the molecular sequences were incorporated in the species description. At present, only one of the four newly recognized species (Ommastrephes bartramii) is commercially exploited by fisheries in the North Pacific, but it now appears that the distributional range of this species is far smaller than previously believed, which is an essential consideration for effective fisheries management.

Fatty Acids of Marine Mollusks: Impact of Diet, Bacterial Symbiosis and Biosynthetic Potential

The n-3 and n-6 polyunsaturated fatty acid (PUFA) families are essential for important physiological processes. Their major source are marine ecosystems. The fatty acids (FAs) from phytoplankton, which are the primary producer of organic matter and PUFAs, are transferred into consumers via food webs. Mollusk FAs have attracted the attention of researchers that has been driven by their critical roles in aquatic ecology and their importance as sources of essential PUFAs. The main objective of this review is to focus on the most important factors and causes determining the biodiversity of the mollusk FAs, with an emphasis on the key relationship of these FAs with the food spectrum and trophic preference. The marker FAs of trophic sources are also of particular interest. The discovery of new symbioses involving invertebrates and bacteria, which are responsible for nutrition of the host, deserves special attention. The present paper also highlights recent research into the molecular and biochemical mechanisms of PUFA biosynthesis in marine mollusks. The biosynthetic capacities of marine mollusks require a well-grounded evaluation.

mTOR as a Marker of Exercise and Fatigue in Octopus vulgaris Arm

Cephalopods are highly evolved marine invertebrates that colonized almost all the oceans of the world at all depths. This imposed the occurrence of several modifications of their brain and body whose muscle component represents the major constituent. Hence, studying their muscle physiology may give important hints in the context of animal biology and environmental adaptability. One major pathway involved in muscle metabolism in vertebrates is the evolutionary conserved mTOR-signaling cascade; however, its role in cephalopods has never been elucidated. mTOR is regulating cell growth and homeostasis in response to a wide range of cues such as nutrient availability, body temperature and locomotion. It forms two functionally heteromeric complexes, mTORC1 and mTORC2. mTORC1 regulates protein synthesis and degradation and, in skeletal muscles, its activation upon exercise induces muscle growth. In this work, we characterized Octopus vulgaris mTOR full sequence and functional domains; we found a high level of homology with vertebrates’ mTOR and the conservation of Ser²⁴⁴⁸ phosphorylation site required for mTORC1 activation. We then designed and tested an in vitro protocol of resistance exercise (RE) inducing fatigue in arm samples. We showed that, upon the establishment of fatigue, a transient increase in mTORC1 phosphorylation reaching a pick 30 min after exercise was induced. Our data indicate the activation of mTORC1 pathway in exercise paradigm and possibly in the regulation of energy homeostasis in octopus and suggest that mTORC1 activity can be used to monitor animal response to changes in physiological and ecological conditions and, more in general, the animal welfare.

Prospective severity classification of scientific procedures in cephalopods: Report of a COST FA1301 Working Group survey

Cephalopods are the first invertebrate class regulated by the European Union (EU) under Directive 2010/63/EU on the protection of animals used for scientific purposes, which requires prospective assessment of severity of procedures. To assist the scientific community in establishing severity classification for cephalopods, we undertook a web-based survey of the EU cephalopod research community as represented by the participants in the European COoperation on Science and Technology (COST) Action FA1301, CephsInAction'. The survey consisted of 50 scenarios covering a range of procedures involving several cephalopod species at different life stages. Respondents (59 people from 15 countries) either allocated a severity classification to each scenario or indicated that they were unable to decide (UTD). Analyses evaluated score distributions and clustering. Overall, the UTD scores were low (7.0 ± 0.6%) and did not affect the severity classification. Procedures involving paralarvae and killing methods (not specified in Annexe IV) had the highest UTD scores. Consensus on non-recovery procedures was reached consistently, although occasionally non-recovery appeared to be confused with killing methods. Scenarios describing procedures above the lower threshold for regulation, including those describing behavioural studies, were also identified and allocated throughout the full range of severity classifications. Severity classification for scenarios based on different species (e.g. cuttlefish vs. octopus) was consistent, comparable and dependent on potentially more harmful interventions. We found no marked or statistically significant differences in the overall scoring of scenarios between the demographic subgroups (age, sex, PhD and cephalopod experience). The COST Action FA1301 survey data provide a basis for a prospective severity classification for cephalopods to serve as guide for researchers, project assessors and regulators.

Cephalopod Brains: An Overview of Current Knowledge to Facilitate Comparison With Vertebrates

Cephalopod and vertebrate neural-systems are often highlighted as a traditional example of convergent evolution. Their large brains, relative to body size, and complexity of sensory-motor systems and behavioral repertoires offer opportunities for comparative analysis. Despite various attempts, questions on how cephalopod 'brains' evolved and to what extent it is possible to identify a vertebrate-equivalence, assuming it exists, remain unanswered. Here, we summarize recent molecular, anatomical and developmental data to explore certain features in the neural organization of cephalopods and vertebrates to investigate to what extent an evolutionary convergence is likely. Furthermore, and based on whole body and brain axes as defined in early-stage embryos using the expression patterns of homeodomain-containing transcription factors and axonal tractography, we describe a critical analysis of cephalopod neural systems showing similarities to the cerebral cortex, thalamus, basal ganglia, midbrain, cerebellum, hypothalamus, brain stem, and spinal cord of vertebrates. Our overall aim is to promote and facilitate further, hypothesis-driven, studies of cephalopod neural systems evolution.

Deep pelagic food web structure as revealed by in situ feeding observations

Food web linkages, or the feeding relationships between species inhabiting a shared ecosystem, are an ecological lens through which ecosystem structure and function can be assessed, and thus are fundamental to informing sustainable resource management. Empirical feeding datasets have traditionally been painstakingly generated from stomach content analysis, direct observations and from biochemical trophic markers (stable isotopes, fatty acids, molecular tools). Each approach carries inherent biases and limitations, as well as advantages. Here, using 27 years (1991-2016) of in situ feeding observations collected by remotely operated vehicles (ROVs), we quantitatively characterize the deep pelagic food web of central California within the California Current, complementing existing studies of diet and trophic interactions with a unique perspective. Seven hundred and forty-three independent feeding events were observed with ROVs from near-surface waters down to depths approaching 4000 m, involving an assemblage of 84 different predators and 82 different prey types, for a total of 242 unique feeding relationships. The greatest diversity of prey was consumed by narcomedusae, followed by physonect siphonophores, ctenophores and cephalopods. We highlight key interactions within the poorly understood 'jelly web', showing the importance of medusae, ctenophores and siphonophores as key predators, whose ecological significance is comparable to large fish and squid species within the central California deep pelagic food web. Gelatinous predators are often thought to comprise relatively inefficient trophic pathways within marine communities, but we build upon previous findings to document their substantial and integral roles in deep pelagic food webs.

The Current State of Cephalopod Science and Perspectives on the Most Critical Challenges Ahead From Three Early-Career Researchers

Here, three researchers who have recently embarked on careers in cephalopod biology discuss the current state of the field and offer their hopes for the future. Seven major topics are explored: genetics, aquaculture, climate change, welfare, behavior, cognition, and neurobiology. Recent developments in each of these fields are reviewed and the potential of emerging technologies to address specific gaps in knowledge about cephalopods are discussed. Throughout, the authors highlight specific challenges that merit particular focus in the near-term. This review and prospectus is also intended to suggest some concrete near-term goals to cephalopod researchers and inspire those working outside the field to consider the revelatory potential of these remarkable creatures.

Predatory flying squids are detritivores during their early planktonic life

Cephalopods are primarily active predators throughout life. Flying squids (family Ommastrephidae) represents the most widely distributed and ecologically important family of cephalopods. While the diets of adult flying squids have been extensively studied, the first feeding diet of early paralarvae remains a mystery. The morphology of this ontogenetic stage notably differs from other cephalopod paralarvae, suggesting a different feeding strategy. Here, a combination of Laser Capture Microdissection (LCM) and DNA metabarcoding of wild-collected paralarvae gut contents for eukaryotic 18S v9 and prokaryotic 16S rRNA was applied, covering almost every life domain. The gut contents were mainly composed by fungus, plants, algae and animals of marine and terrestrial origin, as well as eukaryotic and prokaryotic microorganisms commonly found in fecal pellets and particulate organic matter. This assemblage of gut contents is consistent with a diet based on detritus. The ontogenetic shift of diet from detritivore suspension feeding to active predation represents a unique life strategy among cephalopods and allows ommastrephid squids to take advantage of an almost ubiquitous and accessible food resource during their early stages. LCM was successfully applied for the first time to tiny, wild-collected marine organisms, proving its utility in combination with DNA metabarcoding for dietary studies.