Creation of an albino squid line by CRISPR-Cas9 and its application for in vivo functional imaging of neural activity

Genetic mechanisms of animal camouflage: an interdisciplinary perspective

Camouflage is a classic example of a trait wherein animals respond to natural selection to avoid predation or attract prey. This unique phenomenon has attracted significant recent attention and the rapid development of integrative research methods is facilitating advances in our understanding of the in-depth genetic mechanisms of camouflage. In this review article, we revisit camouflage definitions and strategies and then we examine the underlying mechanisms of the two most common forms of camouflage, crypsis and masquerade, that have recently been elucidated using multiple approaches. We also discuss unresolved questions related to camouflage. Ultimately, we highlight the implications of camouflage for informing various key issues in ecology and evolution.

Embryonic development of a centralised brain in coleoid cephalopods

The last common ancestor of cephalopods and vertebrates lived about 580 million years ago, yet coleoid cephalopods, comprising squid, cuttlefish and octopus, have evolved an extraordinary behavioural repertoire that includes learned behaviour and tool utilization. These animals also developed innovative advanced defence mechanisms such as camouflage and ink release. They have evolved unique life cycles and possess the largest invertebrate nervous systems. Thus, studying coleoid cephalopods provides a unique opportunity to gain insights into the evolution and development of large centralised nervous systems. As non-model species, molecular and genetic tools are still limited. However, significant insights have already been gained to deconvolve embryonic brain development. Even though coleoid cephalopods possess a typical molluscan circumesophageal bauplan for their central nervous system, aspects of its development are reminiscent of processes observed in vertebrates as well, such as long-distance neuronal migration. This review provides an overview of embryonic coleoid cephalopod research focusing on the cellular and molecular aspects of neurogenesis, migration and patterning. Additionally, we summarize recent work on neural cell type diversity in embryonic and hatchling cephalopod brains. We conclude by highlighting gaps in our knowledge and routes for future research.

Dynamic skin behaviors in cephalopods

The coleoid cephalopods (cuttlefish, octopus, and squid) are a group of soft-bodied mollusks that exhibit a wealth of complex behaviors, including dynamic camouflage, object mimicry, skin-based visual communication, and dynamic body patterns during sleep. Many of these behaviors are visually driven and engage the animals' color changing skin, a pixelated display that is directly controlled by neurons projecting from the brain. Thus, cephalopod skin provides a direct readout of neural activity in the brain. During camouflage, cephalopods recreate on their skin an approximation of what they see, providing a window into perceptual processes in the brain. Additionally, cephalopods communicate their internal state during social encounters using innate skin patterns, and create waves of pigmentation on their skin during periods of arousal. Thus, by leveraging the visual displays of cephalopods, we can gain insight into how the external world is represented in the brain and how this representation is transformed into a recapitulation of the world on the skin. Here, we describe the rich skin behaviors of the coleoid cephalopods, what is known about cephalopod neuroanatomy, and how advancements in gene editing, machine learning, optical imaging, and electrophysiological tools may provide an opportunity to explore the neural bases of these fascinating behaviors.

A perspective on neuroethology: what the past teaches us about the future of neuroethology

For 100 years, the Journal of Comparative Physiology-A has significantly supported research in the field of neuroethology. The celebration of the journal's centennial is a great time point to appreciate the recent progress in neuroethology and to discuss possible avenues of the field. Animal behavior is the main source of inspiration for neuroethologists. This is illustrated by the huge diversity of investigated behaviors and species. To explain behavior at a mechanistic level, neuroethologists combine neuroscientific approaches with sophisticated behavioral analysis. The rapid technological progress in neuroscience makes neuroethology a highly dynamic and exciting field of research. To summarize the recent scientific progress in neuroethology, I went through all abstracts of the last six International Congresses for Neuroethology (ICNs 2010-2022) and categorized them based on the sensory modalities, experimental model species, and research topics. This highlights the diversity of neuroethology and gives us a perspective on the field's scientific future. At the end, I highlight three research topics that may, among others, influence the future of neuroethology. I hope that sharing my roots may inspire other scientists to follow neuroethological approaches.

Molluscan Genomes Reveal Extensive Differences in Photopigment Evolution Across the Phylum

In animals, opsins and cryptochromes are major protein families that transduce light signals when bound to light-absorbing chromophores. Opsins are involved in various light-dependent processes, like vision, and have been co-opted for light-independent sensory modalities. Cryptochromes are important photoreceptors in animals, generally regulating circadian rhythm, they belong to a larger protein family with photolyases, which repair UV-induced DNA damage. Mollusks are great animals to explore questions about light sensing as eyes have evolved multiple times across, and within, taxonomic classes. We used molluscan genome assemblies from 80 species to predict protein sequences and examine gene family evolution using phylogenetic approaches. We found extensive opsin family expansion and contraction, particularly in bivalve xenopsins and gastropod Go-opsins, while other opsins, like retinochrome, rarely duplicate. Bivalve and gastropod lineages exhibit fluctuations in opsin repertoire, with cephalopods having the fewest number of opsins and loss of at least 2 major opsin types. Interestingly, opsin expansions are not limited to eyed species, and the highest opsin content was seen in eyeless bivalves. The dynamic nature of opsin evolution is quite contrary to the general lack of diversification in mollusk cryptochromes, though some taxa, including cephalopods and terrestrial gastropods, have reduced repertoires of both protein families. We also found complete loss of opsins and cryptochromes in multiple, but not all, deep-sea species. These results help set the stage for connecting genomic changes, including opsin family expansion and contraction, with differences in environmental, and biological features across Mollusca.

High-level RNA editing diversifies the coleoid cephalopod brain proteome

Coleoid cephalopods (octopus, squid and cuttlefish) have unusually complex nervous systems. The coleoid nervous system is also the only one currently known to recode the majority of expressed proteins through A-to-I RNA editing. The deamination of adenosine by adenosine deaminase acting on RNA (ADAR) enzymes produces inosine, which is interpreted as guanosine during translation. If this occurs in an open reading frame, which is the case for tens of thousands of editing sites in coleoids, it can recode the encoded protein. Here, we describe recent findings aimed at deciphering the mechanisms underlying high-level recoding and its adaptive potential. We describe the complement of ADAR enzymes in cephalopods, including a recently discovered novel domain in sqADAR1. We further summarize current evidence supporting an adaptive role of high-level RNA recoding in coleoids, and review recent studies showing that a large proportion of recoding sites is temperature-sensitive. Despite these new findings, the mechanisms governing the high level of RNA recoding in coleoid cephalopods remain poorly understood. Recent advances using genome editing in squid may provide useful tools to further study A-to-I RNA editing in these animals.

Neural control of cephalopod camouflage

In Die Another Day, James Bond receives an Aston Martin that can render itself invisible by dynamically reproducing the surroundings on the car's "polymer skin". In what is widely regarded as the worst Bond movie ever, the invisible car scene is cited as the moment the plot plunges into the truly absurd. But what if nature had actually invented such a technology, and did so hundreds of millions of years ago? The coleoid cephalopods - octopus, cuttlefish and squid - are living examples of dynamic camouflage. Their skin is covered with a high-resolution array of 'cellular pixels' (chromatophores) that are controlled by the brain. To disappear into their surroundings, cephalopods recreate an approximation of their environment on their skin by activating different combinations of colored chromatophores. However, unlike the fictional Bond car, whose surface is coated in tiny cameras to detect the environment, cephalopods don't see the world with their skin. Instead, the visual world is detected by the eyes, processed in the brain, and then used to activate motor commands that direct the skin's camouflage pattern. Thus, cephalopod skin patterns are an external manifestation of their internal perception of the world. How do cephalopods approximate the world with their skin? What can this teach us about how brains work? And which neurobiological tools will be needed to uncover the neural basis of camouflage?

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.

Stranger than fiction

Martin introduces a special issue on cephalopods, showcasing their fascinating biology and highlighting recent developments in the field.

Cephalopod behaviour

Underlying all animal behaviors, from the simplest reflexive reactions to the more complex cognitive reasoning and social interaction, are nervous systems uniquely adapted to bodies, environments, and challenges of different animal species. Coleoid cephalopods - octopuses, squid, and cuttlefish - are widely recognized as the most behaviorally complex invertebrates and provide exciting opportunities for studying the neural control of behaviour. These unusual molluscs evolved over 400 million years ago from slow-moving armored forms to active predators of coastal and open ocean ecosystems. In this primer we will discuss how, during cephalopod evolution, the relatively simple ganglion-based molluscan nervous system has been extensively transformed to control the complex bodies and process extensive visual, tactile, and chemical sensory inputs, and summarize some recent findings about their fascinating behaviors.

Comparison of Blastema Formation after Injury in Two Cephalopod Species

Regeneration is the ability to functionally replace significant amounts of lost tissue or whole appendages like arms, limbs or tentacles. The amount of tissue that can be regenerated varies among species, but regeneration is found in both invertebrate and vertebrate animals. Cephalopods have been broadly reported in the literature to regenerate their arms. There are over 800 species of Cephalopod; however, regeneration has only been documented in the literature in a few species (1). Here we compare arm regeneration in two species of cephalopod, the Octopus bimaculoides and the hummingbird bobtail squid Euprymna berryi.