A review of reproductive strategies in cephalopods

Let's talk about sex: Mechanisms of neural sexual differentiation in Bilateria

In multicellular organisms, sexed gonads have evolved that facilitate release of sperm versus eggs, and bilaterian animals purposefully combine their gametes via mating behaviors. Distinct neural circuits have evolved that control these physically different mating events for animals producing eggs from ovaries versus sperm from testis. In this review, we will describe the developmental mechanisms that sexually differentiate neural circuits across three major clades of bilaterian animals-Ecdysozoa, Deuterosomia, and Lophotrochozoa. While many of the mechanisms inducing somatic and neuronal sex differentiation across these diverse organisms are clade-specific rather than evolutionarily conserved, we develop a common framework for considering the developmental logic of these events and the types of neuronal differences that produce sex-differentiated behaviors. This article is categorized under: Congenital Diseases > Stem Cells and Development Neurological Diseases > Stem Cells and Development.

The Fecundity Characteristics and Spawning Strategy of Uroteuthis edulis in the East China Sea

The fecundity characteristics and spawning strategy of Uroteuthis edulis in the East China Sea were investigated by observing the potential fecundity (PF), relative fecundity by dorsal mantle length (PFML) and relative fecundity by body weight (PFBW). The relationship between fecundity and a single biological indicator was measured, and generalized additive models (GAMs) were fit by adding environmental variables to help better understand this comprehensive relationship. The long diameter and short diameter of the ovarian oocytes ranged from 0.72 mm to 4.74 mm and from 0.46 mm to 3.67 mm, respectively. The long and short diameters of oviducal eggs ranged from 0.61 mm to 5.12 mm and from 0.39 mm to 3.81 mm, respectively. The egg diameter had a unimodal distribution. The PF, PFML and PFBW ranged from 540 to 13,743 cells, 5 to 86 cells/mm and 6 to 53 cells/g, respectively. Three fecundity indicators were unimodally distributed, and the PFBW was more stable than the PFML (δ2PFBW < δ2PFML). The fecundity and single biological indicators were fitted, and it was found that the PF and PFML were positively correlated with dorsal mantle length (ML) and body weight (BW). The generalized additive model (GAM) fitting showed that when considering the interaction between dorsal mantle length and sea surface height (M13), the deviation explanation rate of the PF and PFML was the highest. Studies have shown that the ovary oocytes of U. edulis mature in batches, and then the eggs are laid in batches. The dorsal mantle length (ML), water temperature at 25 m depth (T25) and sea surface height (SSH) are important indicators to measure the fecundity of U. edulis. These findings allow for a deeper understanding of the U. edulis population dynamics for the future management of this economically and ecologically important species.

A retrospective study of pathologic findings in cephalopods (extant subclasses: Coleoidea and Nautiloidea) under laboratory and aquarium management

This retrospective study examines pathologic findings in 593 captive cephalopods (340 octopuses, 130 cuttlefish, 33 squid, and 90 nautiluses; 22 species in total) submitted to International Zoo Veterinary Group Pathology between May 2003 and August 2022. Common octopus, European common cuttlefish, hummingbird bobtail squid, and chambered nautilus were the most numerous species from the included orders of Octopoda, Sepiida, Sepiolida, and Nautilida, respectively. Commonly identified conditions included coccidiosis and renal dicyemid mesozoan infection in octopuses, amebiasis in squid, bacterial infections in cuttlefish, and idiopathic multisystemic inflammatory disease in nautiluses. Coccidiosis was most frequent in common octopuses, giant Pacific octopuses, and California 2-spot octopuses (present in 68.4%, 46.3%, and 23.8% of these species, respectively) and was the attributed cause of death in 32.3%, 36.0%, and 60.0% of such cases, respectively. Ulcerative dermatitis (UD) was common, affecting squid, cuttlefish, and octopuses, while many nautiluses exhibited black shell disease and/or UD. Notable differences in the prevalence of UD were detected between laboratory and aquaria-housed decapodiforms; 52.2% for laboratory squid versus 20.0% in aquaria; 51.3% in laboratory cuttlefish versus 11.0% in aquaria. All octopuses and nautiluses in the study were derived from aquaria. Semelparity-associated death in Coleoidea species was identified in 22.4% of octopuses, 11.5% of cuttlefish, and 6.1% of squid. This report aims to provide an overview and reassessment of species-specific disease patterns under aquarium and laboratory management as a starting point for future developments in husbandry and disease investigation.

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.

First Evidence of Microplastics in the Yolk and Embryos of Common Cuttlefish (Sepia officinalis) from the Central Adriatic Sea: Evaluation of Embryo and Hatchling Structural Integrity and Development

Once they reach the aquatic environment, microplastics (MPs) are accidentally ingested by aquatic biota, thus entering the food chain with possible negative effects. The present study investigated, for the first time, MP presence in cuttlefish (Sepia officinalis) eggs and their association with embryonic development. Cuttlefish eggs were sampled from four different sites along the Marche region (Senigallia, Ancona, Numana, and San Benedetto del Tronto). Embryo and hatchling biometric parameters were evaluated and the internal structural integrity was examined through histological analysis. MPs were detected and characterized in embryos and yolk samples. MPs were identified in all sites (size < 5 µm), however, their presence has not been associated with an impairment of either embryo or hatchling internal structures. Noteworthy, the highest number of MPs (in both yolk and embryo samples) were found in Numana (37% of the total amount), where the lowest hatchling size was observed. On the other hand, the highest embryo mantle length was associated with the lowest number of MPs detected (9%) in Ancona. Overall, only MP fragments and sphere types (74 and 26%, respectively) were observed, and the most frequent polymers were Polyvinyl chloride (52%), Polypropylene, and Cellulose acetate (15% both). Further studies are needed to assess the possible MP effects on the yolk quality and assimilation.

Strategy of spawning in the tropical squid females, Lolliguncula diomedeae: Allocation of energy, senescence, and influence of Aggregata coccidians

Although the squid Lolliguncula diomedeae Hoyle, 1904 is of commercial and ecological importance in the Gulf of Tehuantepec (southeastern Mexico), this is the first study to examine female spawning strategy. Information on reproductive indicators was used to assess the impact of spawning behavior on growth rates and the condition of somatic tissue, since energy for reproduction is derived mainly from somatic tissue and from consumed food. Additionally, oocyte storage patterns were examined to determine the type of spawning that characterizes this species. A total of 1,347 females, ranging between 27.3 to 90.0 mm dorsal mantle length (ML) and 0.1 to 25.6 g of total weight, were examined. Statolith analysis indicates that the life cycle of L. diomedeae is 212 days. Allometric growth was observed during the female life cycle. The size at maturity was at 68.54 mm ML, with synchronous ovulation (by groups) and intermittent spawning. The results show that L. diomedeae is an energetically efficient squid species that feeds during all of its reproductive life stages, thus ensuring the occurrence of partial spawning events, and that feeding ends when senescence begins. However, its life cycle could be affected by the presence of coccidian parasites, mainly during senescence.

Length weight relationships of coleoid cephalopods from the eastern Mediterranean

Length-weight relationship (LWR) studies have been widely conducted for fish. They are important because they provide information about the growth of the fish, its general wellbeing, and fitness in a marine habitat. In comparison, relatively few LWR studies have been conducted on cephalopods. A total of 13,474 specimens belonging to 28 cephalopod species was investigated to define their length–weight relationship status and Fulton’s condition factors, and compared with previous studies to evaluate life history traits and test comparability of LWR values. Isometry was found in 8 species including 2 teuthids, 2 sepiids and 4 octopods, and positive allometry was found in 2 squid species. Other species showed negative allometry. Four orders of the class Cephalopoda distributed in the Mediterranean Sea were also compared in respect of their coefficient b values, and a clear distinction was found between the orders reflecting their characteristic body types and thus lifestyles. Coefficient b values of mature animals were found lower than that of maturing ones that reflects growth of semelparous cephalopods stops or at least slows down when they reach maturity. Some extreme condition factor values were calculated for especially octopods that one of them reached to 140.91 in a deep-sea octopus Pteroctopus tetracirrhus. It suggests that there are many factors that might affect the calculations. Some of them were: different body structure and growth type in cephalopods than that of fish, different length measurement method applied in cephalopods, different body parts that might have different growth rates, and preservation methods that could affect the body shape and weight in soft bodied animals.

Behavioral changes in senescent giant Pacific octopus (Enteroctopus dofleini) are associated with peripheral neural degeneration and loss of epithelial tissue

Most species of octopus experience extreme physical decline after a single reproductive bout which extends over a period of days, weeks, or months before eventual death. Although outward indicators of senescence are widely recognized, comparatively little is known about physiological and neural changes accompanying terminal decline in octopuses. Here, we measured changes in behavioral response to nociceptive stimuli across the lifespan in giant Pacific octopus (GPO), Enteroctopus dofleini, held in public aquariums in the USA. Post-euthanasia, tissue was collected from arm tips, and neural and epithelial cell degeneration was quantified and compared with biopsies of arm tips from healthy, pre-reproductive GPOs. Behavioral assays showed significant changes both in low threshold mechanosensory responses and nociceptive behavioral responses beginning early in senescence and extending until euthanasia. Histology data showed that while the ratio of apoptotic cells to total cell number stayed constant between healthy and senescent GPOs, overall neural and epithelial cell density was significantly lower in terminally senescent octopuses compared with healthy controls. Our data provide new insight into the time-course and causes of sensory dysfunction in senescent cephalopods and suggest proactive welfare management should begin early in the senescence phase, well before animals enter terminal decline.

Genetic mechanisms of aging in plants: What can we learn from them?

Plants hold all records in longevity. Their aging is a complex process. In the presented review, we analyzed published data on various aspects of plant aging with focus on any inferences that could shed a light on aging in animals and help to fight it in human. Plant aging can be caused by many factors, such as telomere depletion, genomic instability, loss of proteostasis, changes in intercellular interaction, desynchronosis, autophagy misregulation, epigenetic changes and others. Plants have developed a number of mechanisms to increase lifespan. Among these mechanisms are gene duplication ("genetic backup"), the active work of telomerases, abundance of meristematic cells, capacity of maintaining the meristems permanently active and continuous activity of phytohormones. Plant aging usually occurs throughout the whole perennial life, but could be also seasonal senescence. Study of causes for seasonal aging can also help to uncover the mechanisms of plant longevity. The influence of different factors such as microbiome communities, glycation, alternative oxidase activity, mitochondrial dysfunction on plant longevity was also reviewed. Adaptive mechanisms of long-lived plants are considered. Further comparative study of the mechanisms underlying longevity of plants is necessary. This will allow us to reach a potentially new level of understanding of the aging process of plants.

Ontogeny, evolution and palaeogeographic distribution of the world's largest ammonite Parapuzosia (P.) seppenradensis (Landois, 1895)

The world’s largest ammonite, Parapuzosia (P.) seppenradensis (Landois, 1895), fascinated the world ever since the discovery, in 1895, of a specimen of 1.74 metres (m) diameter near Seppenrade in Westfalia, Germany, but subsequent findings of the taxon are exceedingly rare and its systematic position remains enigmatic. Here we revise the historical specimens and document abundant new material from England and Mexico. Our study comprises 154 specimens of large (< 1 m diameter) to giant (> 1m diameter) Parapuzosia from the Santonian and lower Campanian, mostly with stratigraphic information. High-resolution integrated stratigraphy allows for precise cross-Atlantic correlation of the occurrences. Our specimens were analysed regarding morphometry, growth stages and stratigraphic occurrence wherever possible. Our analysis provides insight into the ontogeny of Parapuzosia (P.) seppenradensis and into the evolution of this species from its potential ancestor P. (P.) leptophylla Sharpe, 1857. The latter grew to shell diameters of about 1 m and was restricted to Europe in the early Santonian, but it reached the Gulf of Mexico during the late Santonian. P. (P.) seppenradensis first appears in the uppermost Santonian- earliest Campanian on both sides of the Atlantic. Initially, it also reached diameters of about 1 m, but gradual evolutionary increase in size is seen in the middle early Campanian to diameters of 1.5 to 1.8 m. P. (P.) seppenradensis is characterized by five ontogenetic growth stages and by size dimorphism. We therefore here include the many historic species names used in the past to describe the morphological and size variability of the taxon. The concentration of adult shells in small geographic areas and scarcity of Parapuzosia in nearby coeval outcrop regions may point to a monocyclic, possibly even semelparous reproduction strategy in this giant cephalopod. Its gigantism exceeds a general trend of size increase in late Cretaceous cephalopods. Whether the coeval increase in size of mosasaurs, the top predators in Cretaceous seas, caused ecological pressure on Parapuzosia towards larger diameters remains unclear.

Episodic-like memory is preserved with age in cuttlefish

Episodic memory, remembering past experiences based on unique what–where–when components, declines during ageing in humans, as does episodic-like memory in non-human mammals. By contrast, semantic memory, remembering learnt knowledge without recalling unique what–where–when features, remains relatively intact with advancing age. The age-related decline in episodic memory likely stems from the deteriorating function of the hippocampus in the brain. Whether episodic memory can deteriorate with age in species that lack a hippocampus is unknown. Cuttlefish are molluscs that lack a hippocampus. We test both semantic-like and episodic-like memory in sub-adults and aged-adults nearing senescence (n = 6 per cohort). In the semantic-like memory task, cuttlefish had to learn that the location of a food resource was dependent on the time of day. Performance, measured as proportion of correct trials, was comparable across age groups. In the episodic-like memory task, cuttlefish had to solve a foraging task by retrieving what–where–when information about a past event with unique spatio-temporal features. In this task, performance was comparable across age groups; however, aged-adults reached the success criterion (8/10 correct choices in consecutive trials) significantly faster than sub-adults. Contrary to other animals, episodic-like memory is preserved in aged cuttlefish, suggesting that memory deterioration is delayed in this species.

A review of sperm storage methods and post-copulatory sexual selection in the Cephalopoda

In many animal phyla, females have a unique sperm storage organ (SSO). Post-copulatory sexual selection is a powerful driving force of SSO evolution. SSOs are generally considered to have evolved through sexual antagonistic coevolution between male genitalia and the SSO and/or cryptic female choice (CFC). In cephalopods, sperm transfer and fertilization are conducted through complex processes, and sperm storage methods show inter-species variation. In some species, males implant spermatangia superficially under the female skin, and then sperm released from the spermatangia are transferred into a seminal receptacle (SR). Deep-sea cephalopods, which lack a SR, have instead evolved a deep-implanting method by which the spermatangium is embedded deep in the musculature of the mantle wall of the female. In some species, the female stores whole spermatangia within a spermatangium pocket. Because the males of most species do not insert an intromittent organ into the female when transferring sperm, SSO evolution may have been influenced by CFC alone. This review summarizes the sperm storage methods and the mechanisms of post-copulatory sexual selection in cephalopods and it is proposed that these diverse methods evolved as adaptive mechanisms through post-copulatory sexual selection.

Another lesson from beautiful monsters: the case of 'sex reversals' in the Ammonoidea and their significance

BACKGROUND

Expression of sexual dimorphism is recognised in various fossil groups of molluscs such as the Ammonoidea, an extinct group of shelled cephalopods. During the Mesozoic, the best-documented sexual dimorphic examples are seen in the Jurassic superfamily Perisphinctoidea. It is usually expressed by distinct adult size and apertural modifications between the antidimorphs. Putative males (otherwise referred to as microconch) are small in size and develop lappets at the end of the shell while the females (macroconch) are larger and bear a simple peristome. Dubious cases are, however, known in that superfamily, which often relate to taxonomic biases or lack of diagnostic characters, and some others expose ontogenetic anomalies illustrated by 'sex reversals' in the shell morphology and ornamentation.

RESULTS

The discovery of two specimens of the Callovian Aspidoceratidae Peltoceras athleta (Phillips), having both female and male features, questions the significance and causes of 'sex reversals' in the Ammonoidea. The two specimens have started with the macroconch ontogeny of Peltoceras athleta and show an apparent change toward maleness in the adult, as illustrated by their rounded whorl section, ribs retroversion, fading of the tubercles and lappets typical of the microconchs. Few other cases of female-to-male, as well as male-to-female 'sex reversal', are known in the fossil record, all belonging to the Jurassic Perisphinctoidea (families Perisphinctidae or Aspidoceratidae). Since all Jurassic Perisphinctoidea are strictly gonochoristic, these 'sex reversals' are pathological in nature and are herein referred to as a new forma-type pathology: namely "forma hermaphrodita".

CONCLUSIONS

In the absence of any clear evidence of injury or parasitism, we hypothesize that such "forma hermaphrodita" individuals illustrate pathologic cases of intersexuality. Little is known about the ammonoid soft parts, and it is not possible to determine which internal sexual organs occur in specimens having both male and female external shell features. Abnormal feminisation and/or masculinisation also occur in modern cephalopods, the latter also grouping only gonochoric species. This phenomenon is similarly illustrated by a change in the adult body size and a mixing of both female and male structures. In that case, intersexuality is either advantageous in the population or caused sterility. The causes of intersexuality are not clearly established but environmental pollutants are evoked in modern cephalopods because they act as endocrine disrupters. 'Sex reversals' and/or non-functional reproductive abnormalities have also been caused by endocrine disrupters in various gonochoric gastropods species, but infestation, genetic abnormalities, temperature fluctuations or viruses are multiple causes, which can stimulate or inhibit neural-endocrinal activity by direct gonadal influence, and ultimately lead to feminisation or masculinisation in fishes, isopods, crustaceans, and gastropods as well. Regardless of whether "forma hermaphrodita" is due to an exogenic or endogenic cause, the record of intersex Perisphinctoidea in the Jurassic can be explained by the ready recognition of dimorphic pairs, and the easy collection of large and sufficiently preserved fossil palaeopopulations in which intersex specimens have statistically more chance to be found.

In situ recordings of large gelatinous spheres from NE Atlantic, and the first genetic confirmation of egg mass of Illex coindetii (Vérany, 1839) (Cephalopoda, Mollusca)

In total, 90 gelatinous spheres, averaging one meter in diameter, have been recorded from ~ 1985 to 2019 from the NE Atlantic Ocean, including the Mediterranean Sea, using citizen science. More than 50% had a dark streak through center. They were recorded from the surface to ~ 60–70 m depth, mainly neutrally buoyant, in temperatures between 8 and 24°C. Lack of tissue samples has until now, prohibited confirmation of species. However, in 2019 scuba divers secured four tissue samples from the Norwegian coast. In the present study, DNA analysis using COI confirms species identity as the ommastrephid broadtail shortfin squid Illex coindetii (Vérany, 1839); these are the first confirmed records from the wild. Squid embryos at different stages were found in different egg masses: (1) recently fertilized eggs (stage ~ 3), (2) organogenesis (stages ~ 17–19 and ~ 23), and (3) developed embryo (stage ~ 30). Without tissue samples from each and every record for DNA corroboration we cannot be certain that all spherical egg masses are conspecific, or that the remaining 86 observed spheres belong to Illex coindetii. However, due to similar morphology and size of these spheres, relative to the four spheres with DNA analysis, we suspect that many of them were made by I. coindetii.

Cerebrotypes in Cephalopods: Brain Diversity and Its Correlation With Species Habits, Life History, and Physiological Adaptations

Here we analyze existing quantitative data available for cephalopod brains based on classical contributions by J.Z. Young and colleagues, to cite some. We relate the relative brain size of selected regions (area and/or lobe), with behavior, life history, ecology and distribution of several cephalopod species here considered. After hierarchical clustering we identify and describe ten clusters grouping 52 cephalopod species. This allows us to describe cerebrotypes, i.e., differences of brain composition in different species, as a sign of their adaptation to specific niches and/or clades in cephalopod molluscs for the first time. Similarity reflecting niche type has been found in vertebrates, and it is reasonable to assume that it could also occur in Cephalopoda. We also attempted a phylogenetic PCA using data by Lindgren et al. (2012) as input tree. However, due to the limited overlap in species considered, the final analysis was carried out on <30 species, thus reducing the impact of this approach. Nevertheless, our analysis suggests that the phylogenetic signal alone cannot be a justification for the grouping of species, although biased by the limited set of data available to us. Based on these preliminary findings, we can only hypothesize that brains evolved in cephalopods on the basis of different factors including phylogeny, possible development, and the third factor, i.e., life-style adaptations. Our results support the working hypothesis that the taxon evolved different sensorial and computational strategies to cope with the various environments (niches) occupied in the oceans. This study is novel for invertebrates, to the best of our knowledge.

Recent advances in heteromorph ammonoid palaeobiology

Heteromorphs are ammonoids forming a conch with detached whorls (open coiling) or non-planispiral coiling. Such aberrant forms appeared convergently four times within this extinct group of cephalopods. Since Wiedmann's seminal paper in this journal, the palaeobiology of heteromorphs has advanced substantially. Combining direct evidence from their fossil record, indirect insights from phylogenetic bracketing, and physical as well as virtual models, we reach an improved understanding of heteromorph ammonoid palaeobiology. Their anatomy, buoyancy, locomotion, predators, diet, palaeoecology, and extinction are discussed. Based on phylogenetic bracketing with nautiloids and coleoids, heteromorphs like other ammonoids had 10 arms, a well-developed brain, lens eyes, a buccal mass with a radula and a smaller upper as well as a larger lower jaw, and ammonia in their soft tissue. Heteromorphs likely lacked arm suckers, hooks, tentacles, a hood, and an ink sac. All Cretaceous heteromorphs share an aptychus-type lower jaw with a lamellar calcitic covering. Differences in radular tooth morphology and size in heteromorphs suggest a microphagous diet. Stomach contents of heteromorphs comprise planktic crustaceans, gastropods, and crinoids, suggesting a zooplanktic diet. Forms with a U-shaped body chamber (ancylocone) are regarded as suspension feeders, whereas orthoconic forms additionally might have consumed benthic prey. Heteromorphs could achieve near-neutral buoyancy regardless of conch shape or ontogeny. Orthoconic heteromorphs likely had a vertical orientation, whereas ancylocone heteromorphs had a near-horizontal aperture pointing upwards. Heteromorphs with a U-shaped body chamber are more stable hydrodynamically than modern Nautilus and were unable substantially to modify their orientation by active locomotion, i.e. they had no or limited access to benthic prey at adulthood. Pathologies reported for heteromorphs were likely inflicted by crustaceans, fish, marine reptiles, and other cephalopods. Pathologies on Ptychoceras corroborates an external shell and rejects the endocochleate hypothesis. Devonian, Triassic, and Jurassic heteromorphs had a preference for deep-subtidal to offshore facies but are rare in shallow-subtidal, slope, and bathyal facies. Early Cretaceous heteromorphs preferred deep-subtidal to bathyal facies. Late Cretaceous heteromorphs are common in shallow-subtidal to offshore facies. Oxygen isotope data suggest rapid growth and a demersal habitat for adult Discoscaphites and Baculites. A benthic embryonic stage, planktic hatchlings, and a habitat change after one whorl is proposed for Hoploscaphites. Carbon isotope data indicate that some Baculites lived throughout their lives at cold seeps. Adaptation to a planktic life habit potentially drove selection towards smaller hatchlings, implying high fecundity and an ecological role of the hatchlings as micro- and mesoplankton. The Chicxulub impact at the Cretaceous/Paleogene (K/Pg) boundary 66 million years ago is the likely trigger for the extinction of ammonoids. Ammonoids likely persisted after this event for 40-500 thousand years and are exclusively represented by heteromorphs. The ammonoid extinction is linked to their small hatchling sizes, planktotrophic diets, and higher metabolic rates than in nautilids, which survived the K/Pg mass extinction event.

Cephalopods: Ambassadors for rethinking cognition

Traditional approaches in comparative cognition have a long history of focusing on a narrow range of vertebrate species. However, in recent years the range of model species has expanded. Despite this development, invertebrate taxa are still largely neglected in comparative cognition, which limits our ability to locate the origins of cognitive traits. The time has come to rethink cognition and develop a more comprehensive understanding of cognitive evolution by expanding comparative analyses to include a diverse range of invertebrate taxa. In this review, we contend that cephalopods are suitable ambassadors for rethinking cognition. Cephalopods have large complex brains, exhibit sophisticated behavioral traits, and increasing evidence suggests that they possess complex cognitive abilities once thought to be unique to large-brained vertebrates. Comparing cephalopods with vertebrates, whose cognition has evolved independently, provides prominent opportunities to circumvent current limitations in comparative cognition that have arisen from traditional vertebrate comparisons. Increased efforts in investigating the cognitive abilities of cephalopods have also led to important welfare-related improvements. These large-brained molluscs are paving the way for a more inclusive approach to investigating cognitive evolution that we hope will extend to other invertebrate taxa.

A phylogenetic approach to understand the evolution of reproduction in coleoid cephalopods

A central question in the evolution of life-histories is whether organisms reproduce once or repeatedly. For cephalopods, the main differences between semelparous and iteroparous are based on ovulation pattern and spawning type. The different reproductive strategies in coleoid cephalopods could be related to the habitat in which the species dwell (coastal vs. oceanic) and/or to environmental forces, thus, both aspects should be quantitatively evaluated under an evolutionary perspective to reconstruct: (a) the ancestral ovulation type of coleoid cephalopods, and (b) the potential of correlated evolution between ovulation type versus habitat and environment. Ancestral states of ovulation type were estimated using stochastic mapping based on literature data (i.e. synchronous or asynchronous), and this information was combined with a new molecular phylogeny including 165 species. The evolutionary correlation between ovulation type, habitat, and environment was estimated by means of the Markov model comparing the rates of gain and loss. The estimates of ancestral states of ovulation type for coleoid cephalopods resulted in a high probability that Octopodiformes evolved from synchronous ovulation type, and Decapodiformes from asynchronous ovulation type. The three traits evaluated presented phylogenetic signal, although no correlation was found between habitat and ovulation type. Overall, species in stable environments showed a tendency towards synchronous ovulation type, while the asynchronous ovulation pattern was found more frequently in species that live in unstable environments, being this last trait also responsible for triggering the change of ovulation type in some species throughout evolution.

Biochemical Composition and Energy Strategy Along the Reproductive Cycle of Female Octopus vulgaris in Galician Waters (NW Spain)

The common octopus, Octopus vulgaris, has a short life cycle, growing rapidly to maturity, spawning once, and characterized by an asynchronic oocyte development and a synchronic ovulation dying after breeding. This species has a protein and amino acid metabolism and it is usually defined as an income breeder. However, most biochemical studies lack an examination of the whole reproductive cycle, in particular the spawning process. We here studied the biochemical changes and determined the energy strategy along reproduction in female O. vulgaris, and found that proteins were the main energy reserve, primarily located in the body muscle when sexually maturing and decreasing during breeding. Lipids were also an important source of energy in the ovary and digestive gland and decreased during breeding too. By contrast, glycogen had a minor contribution to the energy content and was the unique compound that increased in spawning and post-spawning females. Additionally, the most abundant fatty acids (FA) in all tissues were 16:0, 18:0, 20:1n9, 20:4n6 (ARA), 20:5n3 (EPA) and 22:6n3 (DHA), with a clear predominance of long-chain polyunsaturated FA. The FA profile of mature ovaries was compared with other life stages finding similitudes with eggs, hatchlings and juveniles but considerable differences with paralarvae which showed higher DHA/ARA and EPA/ARA ratios. Therefore, we found important biochemical changes along the reproductive cycle that determined the energetic signature in each tissue, though no significant energy trade-offs between tissues were found, suggesting that, on the one hand, female O. vulgaris obtained energy directly from food accumulated simultaneously in the somatic and reproductive tissues during sexual maturation. However, an energy reallocation from somatic to reproductive growth would occur once vitellogenesis has started, so that the rate at which body growths would decrease in favor of ovary growth. On the other hand, during breeding, a general decrease in the energy content occurred in all tissues, so that the ovary would be responsible for the spawning success, whereas muscle tissues and digestive gland would independently supply the energy needed for the body maintenance safeguarding the female survival needed for the maternal care.

The Nidobiome: A Framework for Understanding Microbiome Assembly in Neonates

The importance of microbial associations to animals' development, physiology, and fitness is widely recognized. In most animals, these microbial associations must be developed anew with every generation, making microbiome assembly a critical ecological and evolutionary process. To fully understand neonate microbial colonization, we need to study the interacting effects of neonate, parents, nest, and external environment. We propose an integrative approach based on the concept of the 'nidobiome', a new unit of microbiome-host interactions, which brings together these key elements. We discuss the contribution of each element on microbial colonization at different stages of host development, and we provide a framework based on key developmental events to compare microbiome assembly across animal species.

The breeding strategy of female jumbo squid Dosidicus gigas: energy acquisition and allocation

Reproductive investment generally involves a trade-off between somatic growth and energy allocation for reproduction. Previous studies have inferred that jumbo squid Dosidicus gigas support growth during maturation through continuous feeding (an “income” source). However, our recent work suggests possible remobilization of soma during maturation (a “capital” source). We used fatty acids as biochemical indicators to investigate energy acquisition and allocation to reproduction for female D. gigas. We compared the fatty acid profiles of the ovary to those of the mantle muscle (slow turnover rate tissue, representing an energy reserve) and the digestive gland (fast turnover rate organ, reflecting recent consumption). For each tissue, the overall fatty acids among maturity stages overlapped and were similar. The changes with maturation in fatty acid composition in the ovary consistently resembled those of the digestive gland, with the similarity of fatty acids in the mantle muscle and the ovary increasing during maturation, indicating some energy reserves were utilized. Additionally, squid maintained body condition during maturation regardless of increasing investment in reproduction and a decline in feeding intensity. Cumulatively, D. gigas adopt a mixed income-capital breeding strategy in that energy for reproduction is mainly derived from direct food intake, but there is limited somatic reserve remobilization.

Spatial distribution of oncocerid cephalopods on a Middle Devonian bedding plane suggests semelparous life cycle

Reproductive strategies of extinct organisms can only be recognised indirectly and hence, they are exceedingly rarely reported and tend to be speculative. Here, we present a mass-occurrence with common preservation of pairs of late Givetian (Middle Devonian) oncocerid cephalopods from Hamar Laghdad in the Tafilalt (eastern Anti-Atlas, Morocco). We analysed their spatial occurrences with spatial point pattern analysis techniques and Monte Carlo simulations; our results shows that the pairwise clustering is significant, while ammonoids on the same bedding plane reveal a more random distribution. It is possible that processes such as catastrophic mass mortality or post-mortem transport could have produced the pattern. However, we suggest that it is more likely that the oncocerids were semelparous and died shortly after mating. These findings shed new light on the variation and evolution of reproductive strategies in fossil cephalopods and emphasise that they cannot be based on comparisons with extant taxa without question.

Changes in Biochemical Composition and Energy Reserves Associated With Sexual Maturation of Octopus maya

Climate conditions are related to changes in the biochemical composition of several tissues and associated to the processes of growth and sexual development in cephalopods. The biochemical composition (protein, glucose, cholesterol, acylglycerides) and hemocytes of the hemolymph, the hepatosomatic and gonadosomatic indices, and the reserves of the gonad, hepatopancreas and muscle (lipids, glycogen, and caloric value of muscle) of Octopus maya were determined and related to sex and season. A total of 154 wild animals were used (≈50 caught per season) and the multivariate analysis of the biochemical indicators of the tissues allowed following the variations during winter, dry and rainy season. The permutational MANOVA showed that both sex and season contributed significantly to variations in metabolites and energy reserves. However, the non-significant interaction term indicated that the biochemical composition changed with the seasons in a similar way and regardless of sex. The pattern observed in metabolites and reserves indicates a variation associated with growth and the reproductive peak, but may also reflect a physiological response to seawater temperature. The present study provides reference values for several physiological indicators in O. maya that may be useful for programs monitoring wild populations, as well as to design diets and management protocols to produce octopus under controlled conditions.

Elevated seawater pCO2 affects reproduction and embryonic development in the pygmy squid, Idiosepius pygmaeus

The oceans are absorbing additional carbon dioxide (CO2) from the atmosphere and projected future CO2 levels and ocean acidification could have negative implications for many marine organisms, especially during early life stages. Cephalopods are ecologically important in marine ecosystems, yet the potential effects of increased partial pressure of CO2 (pCO2) in seawater on cephalopod reproduction and embryonic development are little studied. We allowed adult two-toned pygmy squid (Idiosepius pygmaeus) to breed in ambient control (~445 μatm; ~8.05 pHT) or elevated pCO2 conditions (~940 μatm; ~7.78 pHT) and compared reproductive traits in adults and developmental characteristics of their eggs, which remained in control or elevated pCO2 treatments until hatching. Breeding pairs at elevated pCO2 produced clutches with 40% fewer eggs, vitelli that were 14% smaller directly after spawning, embryos that were 5% smaller upon hatching, and eggs with an 8% increase in late-stage egg swelling compared with pairs at control conditions. Elevated pCO2 did not affect fertility, time to hatch, or hatching success. Eggs were laid 40% closer together in elevated pCO2 compared with control conditions, indicating a possible effect of elevated pCO2 on reproductive behaviour. These results show that elevated pCO2 can adversely affect reproduction and embryonic development of the two-toned pygmy squid. As the potential for adaptation is influenced by reproductive success, testing the capacity for squid to adapt to future ocean conditions should be a priority for future research.

Sexual Selection and the Evolution of Male Reproductive Traits in Benthic Octopuses

Competition between same-sex organisms, or intra-sexual selection, can occur before and after mating, and include processes such as sperm competition and cryptic female choice. One of the consequences of intra-sexual selection is that male reproductive traits tend to evolve and diverge at high rates. In benthic octopuses, females often mate with more than one male in a single reproductive event, opening the venue for intra-sexual selection at multiple levels. For instance, males transfer spermatophores through hectocotylus, and can remove the spermatophores left by other males. Considering the limited evidence on post-copula competition in benthic octopuses, and the potential to affect the evolution of reproductive traits within octopodids, we put this hypothesis to a test employing a phylogenetic comparative approach. We combined data on hectocotylized arm length (HAL), ligula length (LL), spermatophore length (SL) with a Bayesian molecular phylogeny of 87 species, to analyze how reproductive traits have diverged across lineages and covary with body size (mantle length; ML). First, additionally to ML, we estimated the phylogenetic signal (λ) and mode of evolution (κ) in each reproductive trait. Second, we performed phylogenetic regressions to quantify the association among reproductive traits and their co-variation with ML. This analysis allowed us to estimate the phenotypic change along a branch into the phylogeny, and whether selection may have played a role in the evolution and diversification of specific clades. Estimations of λ were always high (>0.75), indicating concordance between the traits and the topology of the phylogenetic tree. Low values of κ (<1.0) suggested that evolution depends on branch lengths. All reproductive traits exhibiting a positive relation with ML (β > 0.5 in all cases). Overall, evolutionary rate models applied to the SL-ML regression suggested that octopuses of the family Megaleledonidae have evolved larger spermatophores than expected for their size. The regression HAL-ML indicated that HAL was more variable in Megaleledonidae than in the remaining clades, suggesting that the high divergence across species within this group might partially reflect intra-sexual selection. These results support the hypothesis that, at least in some lineages, sexual selection may account for the divergence in reproductive traits of male octopuses.

Tactical Tentacles: New Insights on the Processes of Sexual Selection Among the Cephalopoda

The cephalopods (Mollusca: Cephalopoda) are an exceptional class among the invertebrates, characterised by the advanced development of their conditional learning abilities, long-term memories, capacity for rapid colour change and extremely adaptable hydrostatic skeletons. These traits enable cephalopods to occupy diverse marine ecological niches, become successful predators, employ sophisticated predator avoidance behaviours and have complex intraspecific interactions. Where studied, observations of cephalopod mating systems have revealed detailed insights to the life histories and behavioural ecologies of these animals. The reproductive biology of cephalopods is typified by high levels of both male and female promiscuity, alternative mating tactics, long-term sperm storage prior to spawning, and the capacity for intricate visual displays and/or use of a distinct sensory ecology. This review summarises the current understanding of cephalopod reproductive biology, and where investigated, how both pre-copulatory behaviours and post-copulatory fertilisation patterns can influence the processes of sexual selection. Overall, it is concluded that sperm competition and possibly cryptic female choice are likely to be critical determinants of which individuals' alleles get transferred to subsequent generations in cephalopod mating systems. Additionally, it is emphasised that the optimisation of offspring quality and/or fertilisation bias to genetically compatible males are necessary drivers for the proliferation of polyandry observed among cephalopods, and potential methods for testing these hypotheses are proposed within the conclusion of this review. Further gaps within the current knowledge of how sexual selection operates in this group are also highlighted, in the hopes of prompting new directions for research of the distinctive mating systems in this unique lineage.

Gonadal sex differentiation and development during early ontogenesis in the breeding kisslip cuttlefish (Sepia lycidas)

To understand and obtain basic information on sex differentiation in the kisslip cuttlefish (Sepia lycidas), the gonadal sex differentiation process was investigated histologically. An undifferentiated gonad consisting of germ cells and somatic cells was found to form at a caudal site in the space between the internal yolk sacks of cuttlefish embryos at 14 and 21 days after spawning (DAS). Sexual dimorphism in the gonad was first detected at around 28 DAS. Meiotic oocytes were observed as the first visible morphological characteristic of ovaries in the gonads of some cuttlefish embryos at 28 DAS. In other individuals, neither meiotic germ cells, nor the appearance of a testicular structure, were observed in the gonad even after 10 days post hatching (DPH). Seminiferous tubules, consisting of a small number of spermatogonia and a surrounding basement membrane, were the first visible morphological characteristic of the testis in the male gonad, detected at around 20 DPH. This is the third report on the gonadal sex differentiation process in cephalopods.

Transcriptome analysis for identifying possible causes of post-reproductive death of Sepia esculenta based on brain tissue

BACKGROUND

The subpeduncle lobe/olfactory lobe-optic gland axis is called the endocrine regulation center of cephalopods. However, little is known about the mechanism of the subpeduncle lobe/olfactory lobe-optic gland axis regulate the sexual maturation and post-reproductive death of Sepia esculenta Hoyle.

OBJECTIVES

The primary objective of this study was to provide basic information for revealing the mechanism of the subpeduncle lobe/olfactory lobe-optic axis regulating the rapid post-reproductive death of S. esculenta.

METHODS

In this paper, Illumina sequencing based transcriptome analysis was performed on the brain tissue of female S. esculenta in the three key developmental stages: growth stage (BG), spawning stage (BS), and post-reproductive death stage (BA).

RESULTS

A total of 66.19 Gb Illumina sequencing data were obtained. A comparative analysis of the three stages showed 2609, 3333, and 170 differentially expressed genes (DEGs) in BG-vs-BA, BG-vs-BA, and BS-vs-BA, respectively. The Gene Ontology (GO) enrichment analysis of DEGs revealed that the regulation of cyclin-dependent protein serine/threonine kinase activity, oxidative phosphorylation, and respiratory chain were significantly enriched. The significant enrichment analysis of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway identified pathways associated with the regulation of death, such as the mammalian target of rapamycin (mTOR) signaling pathway, AMPK signaling pathway, oxidative phosphorylation, and cell cycle.

CONCLUSION

The post-reproductive death of S. esculenta was found to be a complex energy steady-state regulation network system. The mTOR acted as an energy receptor and had a key role in regulating energy homeostasis.

Grow Smart and Die Young: Why Did Cephalopods Evolve Intelligence?

Intelligence in large-brained vertebrates might have evolved through independent, yet similar processes based on comparable socioecological pressures and slow life histories. This convergent evolutionary route, however, cannot explain why cephalopods developed large brains and flexible behavioural repertoires: cephalopods have fast life histories and live in simple social environments. Here, we suggest that the loss of the external shell in cephalopods (i) caused a dramatic increase in predatory pressure, which in turn prevented the emergence of slow life histories, and (ii) allowed the exploitation of novel challenging niches, thus favouring the emergence of intelligence. By highlighting convergent and divergent aspects between cephalopods and large-brained vertebrates we illustrate how the evolution of intelligence might not be constrained to a single evolutionary route.

Multiple optic gland signaling pathways implicated in octopus maternal behaviors and death

Post-reproductive life in the female octopus is characterized by an extreme pattern of maternal care: the mother cares for her clutch of eggs without feeding until her death. These maternal behaviors are eradicated if the optic glands, the octopus analog of the vertebrate pituitary gland, are removed from brooding females. Despite the optic gland's importance in regulating maternal behavior, the molecular features underlying optic gland function are unknown. Here, we identify major signaling systems of the Octopus bimaculoides optic gland. Through behavioral analyses and transcriptome sequencing, we report that the optic gland undergoes remarkable molecular changes that coincide with transitions between behavioral stages. These include the dramatic upregulation and downregulation of catecholamine, steroid, insulin and feeding peptide pathways. Transcriptome analyses in other tissues demonstrate that these molecular changes are not generalized markers of senescence, but instead, specific features of the optic glands. Our study expands the classic optic gland-pituitary gland analogy and more specifically, it indicates that, rather than a single 'self-destruct' hormone, the maternal optic glands employ multiple pathways as systemic hormonal signals of behavioral regulation.

A mating plug in a squid? Sneaker spermatophores can block the female sperm-storage organ in Doryteuthis plei

Males from numerous animal taxa have evolved strategies for obstructing the female genitalia with copulatory plugs, reducing the risk of sperm competition and thus resulting in an advantage in sexual selection. Several lines of evidence suggest that sperm competition is a common feature in the complex squid mating systems, which include the evolution of alternative mating tactics (consort vs. sneaker). However, mating plugs have hitherto not been reported for the group. Investigating the female sperm-storage organ (i.e., seminal receptacle, SR) of the squid Doryteuthis plei, we found cases in which everted spermatophores (i.e., spermatangia) were implanted into the SR and blocking its opening. Here, we describe this finding of "plugged spermatangia" based on microscopy analyses (histology and microCT) of SRs of females from three experimental groups (before and after recent mating and after egg release). We show that sneaker male spermatophores may block the opening of the SR, possibly functioning as temporary copulatory plugs that physically obstruct the SR. Together with previous experimental data on spermatophore functioning, our results suggest that plug efficiency is high until at least 5 h after mating, when spermatangia are turgid and full of sperm, clogging the organ's opening. After that time, plugs gradually decrease their efficiency as they lose turgidity by releasing part of their sperm content. However, one experimental female still had a plugged spermatangium blocking a major portion of the opening even after 48 h without mating. Within the context of squid mating systems and sexual selection, we hypothesize that plugged spermatangia are a sneaker strategy associated with minimizing sperm competition between sneaker males.

Between semelparity and iteroparity: Empirical evidence for a continuum of modes of parity

The number of times an organism reproduces (i.e., its mode of parity) is a fundamental life-history character, and evolutionary and ecological models that compare the relative fitnesses of different modes of parity are common in life-history theory and theoretical biology. Despite the success of mathematical models designed to compare intrinsic rates of increase (i.e., density-independent growth rates) between annual-semelparous and perennial-iteroparous reproductive schedules, there is widespread evidence that variation in reproductive allocation among semelparous and iteroparous organisms alike is continuous. This study reviews the ecological and molecular evidence for the continuity and plasticity of modes of parity-that is, the idea that annual-semelparous and perennial-iteroparous life histories are better understood as endpoints along a continuum of possible strategies. I conclude that parity should be understood as a continuum of different modes of parity, which differ by the degree to which they disperse or concentrate reproductive effort in time. I further argue that there are three main implications of this conclusion: (1) that seasonality should not be conflated with parity; (2) that mathematical models purporting to explain the general evolution of semelparous life histories from iteroparous ones (or vice versa) should not assume that organisms can only display either an annual-semelparous life history or a perennial-iteroparous one; and (3) that evolutionary ecologists should base explanations of how different life-history strategies evolve on the physiological or molecular basis of traits underlying different modes of parity.

The Digestive Tract of Cephalopods: a Neglected Topic of Relevance to Animal Welfare in the Laboratory and Aquaculture

Maintenance of health and welfare of a cephalopod is essential whether it is in a research, aquaculture or public display. The inclusion of cephalopods in the European Union legislation (Directive 2010/63/EU) regulating the use of animals for scientific purposes has prompted detailed consideration and review of all aspects of the care and welfare of cephalopods in the laboratory but the information generated will be of utility in other settings. We overview a wide range of topics of relevance to cephalopod digestive tract physiology and their relationship to the health and welfare of these animals. Major topics reviewed include: (i) Feeding cephalopods in captivity which deals with live food and prepared diets, feeding frequency (ad libitum vs. intermittent) and the amount of food provided; (ii) The particular challenges in feeding hatchlings and paralarvae, as feeding and survival of paralarvae remain major bottlenecks for aquaculture e.g., Octopus vulgaris; (iii) Digestive tract parasites and ingested toxins are discussed not only from the perspective of the impact on digestive function and welfare but also as potential confounding factors in research studies; (iv) Food deprivation is sometimes necessary (e.g., prior to anesthesia and surgery, to investigate metabolic control) but what is the impact on a cephalopod, how can it be assessed and how does the duration relate to regulatory threshold and severity assessment? Reduced food intake is also reviewed in the context of setting humane end-points in experimental procedures; (v) A range of experimental procedures are reviewed for their potential impact on digestive tract function and welfare including anesthesia and surgery, pain and stress, drug administration and induced developmental abnormalities. The review concludes by making some specific recommendations regarding reporting of feeding data and identifies a number of areas for further investigation. The answer to many of the questions raised here will rely on studies of the physiology of the digestive tract.

Guidelines for the Care and Welfare of Cephalopods in Research -A consensus based on an initiative by CephRes, FELASA and the Boyd Group

This paper is the result of an international initiative and is a first attempt to develop guidelines for the care and welfare of cephalopods (i.e. nautilus, cuttlefish, squid and octopus) following the inclusion of this Class of ∼700 known living invertebrate species in Directive 2010/63/EU. It aims to provide information for investigators, animal care committees, facility managers and animal care staff which will assist in improving both the care given to cephalopods, and the manner in which experimental procedures are carried out. Topics covered include: implications of the Directive for cephalopod research; project application requirements and the authorisation process; the application of the 3Rs principles; the need for harm-benefit assessment and severity classification. Guidelines and species-specific requirements are provided on: i. supply, capture and transport; ii. environmental characteristics and design of facilities (e.g. water quality control, lighting requirements, vibration/noise sensitivity); iii. accommodation and care (including tank design), animal handling, feeding and environmental enrichment; iv. assessment of health and welfare (e.g. monitoring biomarkers, physical and behavioural signs); v. approaches to severity assessment; vi. disease (causes, prevention and treatment); vii. scientific procedures, general anaesthesia and analgesia, methods of humane killing and confirmation of death. Sections covering risk assessment for operators and education and training requirements for carers, researchers and veterinarians are also included. Detailed aspects of care and welfare requirements for the main laboratory species currently used are summarised in Appendices. Knowledge gaps are highlighted to prompt research to enhance the evidence base for future revision of these guidelines.