Sleep is a ubiquitous biological phenomenon observed across a wide range of animal taxa, yet its structure, regulation, and evolutionary origins remain incompletely understood. In this review, we provide a comparative overview of sleep across vertebrates and invertebrates, focusing on the diversity of sleep architectures and their evolutionary implications. Mammals and most birds exhibit two distinct sleep states, rapid eye movement (REM) sleep and non-REM sleep, which are associated with functions such as memory consolidation, physiological restoration, brain development, and cognitive performance. While this biphasic sleep structure is conserved in terrestrial mammals, aquatic mammals show adaptations such as unihemispheric sleep and marked suppression of REM sleep. Monotremes exhibit sleep states in which the distinction between REM and non-REM sleep is less clear. Birds also display REM and non-REM sleep, along with unihemispheric sleep and robust homeostatic regulation. In reptiles, two alternating sleep states with distinct neural signatures have been identified, suggesting a possible ancestral form of REM sleep. In contrast, amphibians and fish also exhibit sleep or sleep-like states but the existence of canonical REM/non-REM sleep is less understood. Furthermore, sleep has been documented in jawless vertebrates and several invertebrate taxa, including cephalopods, in which active and quiet sleep states have been reported. Comparative analyses across these taxa provide important insights into how the core functions of sleep have been conserved and modified during evolution.

Sleep is a ubiquitous biological phenomenon observed across a wide range of animal taxa, yet its structure, regulation, and evolutionary origins remain incompletely understood. In this review, we provide a comparative overview of sleep across vertebrates and invertebrates, focusing on the diversity of sleep architectures and their evolutionary implications. Mammals and most birds exhibit two distinct sleep states, rapid eye movement (REM) sleep and non-REM sleep, which are associated with functions such as memory consolidation, physiological restoration, brain development, and cognitive performance. While this biphasic sleep structure is conserved in terrestrial mammals, aquatic mammals show adaptations such as unihemispheric sleep and marked suppression of REM sleep. Monotremes exhibit sleep states in which the distinction between REM and non-REM sleep is less clear. Birds also display REM and non-REM sleep, along with unihemispheric sleep and robust homeostatic regulation. In reptiles, two alternating sleep states with distinct neural signatures have been identified, suggesting a possible ancestral form of REM sleep. In contrast, amphibians and fish also exhibit sleep or sleep-like states but the existence of canonical REM/non-REM sleep is less understood. Furthermore, sleep has been documented in jawless vertebrates and several invertebrate taxa, including cephalopods, in which active and quiet sleep states have been reported. Comparative analyses across these taxa provide important insights into how the core functions of sleep have been conserved and modified during evolution.

Animals that inhabit harborages face challenges for odor localization because odorants in the stationary plume are not transferred by advection but disperse extremely slowly due to the Brownian motion of odor molecules. Domiciliary cockroaches of the genus Periplaneta, equipped with long antennae, adapt well to sheltered environments and locate odor sources without visual cues. We demonstrate that this ability is conferred by the antennotopic organization of olfactory sensory neurons, in which the more proximally located neurons send axons nearer to the axonal entries of a given glomerulus. This antennotopic organization is formed progressively by the addition of newborn olfactory sensory neurons to the proximal region of the antennal flagellum at each molting during nymphal development. This map is indeed utilized by eight distinct types of second-order neurons (projection neurons) that make synaptic connections with incoming sensory afferents at each molting and are responsive to a specific region along the flagellum. Each neuron type undergoes “surround inhibition” in which pheromonal stimulation of any areas outside the excitatory receptive field results in inhibition of firing. These features are analogous to those of visual processing. The long maneuverable antenna raises the chance to encounter odor molecules，and receptive fields tiled on the single antenna allow for the analysis of fine odor distribution (e.g., plume edge, concentration gradients) in the odorscape formed in the boundary layer.

Field metabolic rate is an index of how much energy animals expend under natural environmental conditions. Ongoing global warming raises concerns about increased energy expenditure in aquatic ectotherms, particularly fishes. Therefore, understanding the effects of global warming on fishes requires an assessment of their field metabolic rates. In this article, we focus on biologging and otolith carbon stable isotope analysis as methods for estimating field metabolic rates in fishes, and introduce their principles and applications. Because these two methods differ in the temporal resolution and accuracy of the estimates, it is important to select an appropriate method according to the research objective. Integrating eco-physiological data with environmental data will enable a better understanding of the behavioral and physiological responses of fishes to environmental change, and may further contribute to predicting their responses to climate change.

I imagine that many readers have a childhood memory of being engrossed in insect collecting with a butterfly net in hand. Now as researchers, some may be making a living by collecting insects. In the childhood, they were probably captivated by the satisfaction of catching insects, the excitement of finding insects that were camouflaged, and the thrill of encountering insects they had never seen before. Based on those experiences, many people may have learned about the fascinating and mysterious aspects of living things from insects, and perhaps even become researchers themselves. In many schools today, there are no living creatures to be seen, not even in animal enclosures, classrooms, or science labs, which makes me realize that children are becoming increasingly detached from living things. While the widespread adoption of ICT education in schools has its advantages, I feel it has also distanced us from living creatures. In times like these, I continue to advocate for the importance of learning by seeing insects alive in person in schools. I'm acutely aware that nowadays, many school teachers themselves dislike insects, and that their teaching methods are merely rushed through textbooks, failing to provide insect education that focuses on the key points to observe. As a result, insect education, which should ideally be an enjoyable gateway to science, currently fails to capture the fascinating aspects of insects in children. This article introduces the author's observations on children's understanding of insects through outreach lessons at elementary schools, and presents practical examples of insect education that have been continuously improved.