In diurnal and nocturnal organisms, daily activity is regulated by the perception of environmental stimuli and circadian rhythms, which enable organisms to maintain their essential behaviors. The Japanese sand lances genus Ammodytes are coastal marine fish that exhibit unique nocturnal sand burrowing behavior. To elucidate the extrinsic and intrinsic regulation of this behavior and its endocrinological basis, we conducted a series of rearing experiments under various light conditions and hormone administrations. Under a light-dark photoperiod, the fish showed three types of behavior: sand buried, head-exposed from sand, and swimming/feeding. During the transition from dark to light periods, the fish first showed head exposure, followed by swimming and foraging, and buried themselves in the sand immediately after shifting to the dark period. Under constant light conditions, fish exhibited swimming behavior during the period corresponding to the acclimated light period. In addition, swimming did not occur under constant dark conditions but head exposure was observed at the time of the dark-light transition during acclimation. These observations indicate that the essential behavior of sand lances is regulated by both light and circadian rhythms. Subsequently, a melatonin-containing diet promoted the onset of burrowing in 10 to 120 min in a dose-dependent manner at 0.3–128 µg/g-diet, suggesting the direct behavioral regulation by this hormone. These findings suggest that the behavior of sand lances is strictly regulated by an intrinsic mechanism and that melatonin is a regulatory endocrine factor that induces burrowing behavior.

To explore the physiological role and/or pharmacological effects of ommochrome, which is a natural organic pigment widely distributed in Protostomia, we attempted to investigate the influence of ommochrome on RT-PCR and activities of restriction enzymes. It was found that ommin, an ommochrome purified from the diapause eggs of Bombyx mori, inhibited the RT-PCR and restriction enzyme activities. The mechanism of these inhibitory reactions is assumed to be the direct binding of ommochrome to DNA rather than acting against the enzymes because, similarly to actinomycin D, there is a phenoxazine ring in the structure of ommin that is known to be intercalated to DNA. To reveal the ommin/DNA interaction, it was investigated by computational approaches such as molecular docking, molecular dynamics simulation, and free energy calculation. From the computational analyses, it was expected that ommin would bind to DNA with almost the same strength as actinomycin D and intercalate into DNA. This is the first report on the pharmacological effect of ommochrome and its inhibitory mechanism obtained from biochemical and computational analyses.

Vestimentiferan tube worms (Annelida: Siboglinidae) were discovered in a hydrothermal field at a depth of 195 m in the crater of the submarine volcano Omuro Dashi in the Izu-Ogasawara Arc. Based on the nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene in individuals sampled in 2022, they were identified as Lamellibrachia satsuma Miura, Tsukahara & Hashimoto, 1997. STRUCTURE analysis and discriminant analysis of principal components (DAPC) based on 14 microsatellite markers showed a large genetic deviation of the population of Omuro Dashi from those of Kagoshima Bay and the north Mariana Arc (the Nikko and Daikoku Seamounts), whereas the population of Omuro Dashi did not show significant genetic deviation from that of the Nikko Seamount based on the COI gene. All analyses showed that individuals of a methane seep area on the Kanasu-No-Se Bank, the Nankai Trough, which were collected only in 1994, were more closely related to those of Omuro Dashi than to those of other habitats. These results suggest that the ancestors of the Omuro Dashi and Nankai Trough populations originated from migrants from the north Mariana Arc and that there might be undiscovered source population(s) of L. satsuma around the Nankai Trough.

Coral-dinoflagellate symbiosis is a unique biological phenomenon, in which animal cells engulf single-celled photosynthetic algae and maintain them in their cytoplasm mutualistically. Studies are needed to reveal the complex mechanisms involved in symbiotic processes, but it is difficult to answer these questions using intact corals. To tackle these issues, our previous studies established an in vitro system of symbiosis between cells of the scleractinian coral Acropora tenuis and the dinoflagellate Breviolum minutum, and showed that corals direct phagocytosis, while algae are likely engulfed by coral cells passively. Several genera of the family Symbiodiniaceae can establish symbioses with corals, but the symbiotic ratio differs depending on the dinoflagellate clades involved. To understand possible causes of these differences, this study examined whether cultured coral cells show phagocytotic activity with various dinoflagellate strains similar to those shown by intact A. tenuis. We found that (a) A. tenuis larvae incorporate Symbiodinium and Breviolum, but not Cladocopium, and very few Effrenium, (b) cultured coral cells engulfed all four species but the ratio of engulfment was significantly higher with Symbiodinium and Breviolum than Cladocopium and Effrenium, (c) cultured coral cells also phagocytosed inorganic latex beads differently than they do dinoflagellates. It is likely that cultured coral cells preferentially phagocytose Symbiodinium and Breviolum, suggesting that specific molecular mechanisms involved in initiation of symbiosis should be investigated in the future.

Aquaporin (AQP) 7 and AQP9 are membrane channel proteins called aquaglyceroporins and are related to glucose and lipid metabolism. AQP7 is mainly expressed in white adipose tissue (WAT) and is involved in releasing glycerol into the bloodstream. AQP9 is the glycerol channel in the liver that supplies glycerol to the hepatic cells. In this study, we investigated the relationship between the expression of aquaglyceroporins and lifestyle-related diseases, such as obesity and fatty liver, using 22-week-old db/db mice. Body weight, WAT, and liver weight showed increases in db/db mice. The levels of liver lipids, plasma lipids, insulin, and leptin were also increased in db/db mice. Gene expression related to fatty acid and triglyceride synthesis in the liver was enhanced in db/db mice. In addition, gene and protein expression of gluconeogenesis-related enzymes was increased. Conversely, lipolysis-related gene expression in WAT was reduced. In the db/db mice, AQP9 expression in the liver was raised; however, AQP7 expression in WAT was reduced. These results suggest that in db/db mice, enhanced hepatic AQP9 expression increased the supply of glycerol to the liver and induced fatty liver and hyperglycemia. Additionally, reduced AQP7 expression in WAT is associated with excessive lipid accumulation in adipocytes. Aquaglyceroporins are essential molecules for glucose and lipid metabolism, and may be potential target molecules for the treatment of obesity and lifestyle-related diseases.

The turtle olfactory organ consists of the upper (UCE) and lower (LCE) chamber epithelium, projecting to the ventral and dorsal parts of the olfactory bulbs, respectively. The UCE is associated with glands, contains ciliated olfactory receptor neurons, and is assumed to detect odorants primarily in air, while the LCE is devoid of glands, contains microvillous olfactory receptor neurons, and is assumed to detect odorants primarily in water. Examining the olfactory system of the pig-nosed turtle, Carettochelys insculpta, this study found that both the upper and lower chambers of the nasal cavity were lined with sensory epithelium devoid of associated glands and contained ciliated olfactory receptor neurons. Moreover, the olfactory bulbs were not divided into dorsal and ventral parts. These results suggest that the olfactory system of the pig-nosed turtle is a single system specialized for detecting odorants in water.

Variation in morphological traits of anurans has evolved due to the pressures imposed by inhabiting different environments. The Japanese stream toad, Bufo torrenticola, breeds in running water, such as mountain streams, where the larvae grow. This lotic-breeding habit of B. torrenticola was suggested to have evolved from a lentic-breeding ancestor. Evolutionary shift of breeding habit from lentic- to lotic-breeding caused larval morphological changes to adapt to the stream habitat. However, morphological adaptation associated with the larval habitat of these three types of Japanese toads has not been explored well. In this study, we applied geometric morphometrics and distance measurements to compare body and eye characters among the tadpoles of three Japanese toads. The results showed that B. torrenticola has more dorsally and posteriorly positioned eyes, and a longer and wider rostrum because of having a larger mouth and more-developed oral muscles than its close relatives. These characters might be related to lotic lifestyle. Meanwhile, tadpoles of B. torrenticola and its sister taxon B. japonicus japonicus showed similar eye growth pattern, supporting their close phylogenetic relationship. Some of the lotic-adapted characters have also been reported in other lotic tadpoles, which is indicative of convergent evolution among stream-adapted tadpoles.

The nematode Cruzia tentaculata is reported here for the first time in the land snail Megalobulimus abbreviatus in southern Brazil. The snails were infected with a high prevalence of larvae up to the L3 stage (68.6%). Cysts were located mainly in the mantle (pulmonary cavity) and the nerve ring. No other helminths were identified in the collected snails. Some physiological aspects were compared between snails infected with L3 larvae and non-infected snails and among infected animals with different parasite loads. No differences were found in hemolymph protein, glucose, or urea content between L3-infected and non-infected snails, nor among animals with different parasite loads. Discontinuous lesions in the rectum associated with the presence of encapsulated larvae were visible in animals with high parasite loads and were more frequent in adult animals. All analyses were carried out during the breeding season; however, the albumen glands of mature snails had a smaller volume in those with higher parasite loads. Ovotestis weight was also significantly negatively correlated with parasite load. Snail reproductive capacity could, therefore, be partially impaired but only for individuals with higher parasite loads. Considering only the measured parameters, natural infection by C. tentaculata does not appear to affect intermediary metabolism of M. abbreviatus. A greater number of larvae and greater severity of tissue injuries are more frequently observed in older snails.

The deep-sea buccinid snail genus Bathyancistrolepis is redefined based on the reconstruction of a molecular phylogeny and morphological examination of shell and radular characters. This genus is distinguished from other genera of the subfamily Parancistrolepidinae with a combination of shell traits, including (1) a low spire, (2) sharp, carinate spiral cords or keels and (3) a long, curved siphonal canal, but not with a difference in radular morphology as suggested by previous authors. Three allopatric or parapatric species are recognized in the upper bathyal (447–2057 m) waters around Japan and Taiwan: B. tokoyodaensis from off Hokkaido to Sagami Bay in the Northwest Pacific, B. trochoidea off Kumano-nada to Miyazaki in the Northwest Pacific and along Nansei Islands in the East China Sea, and B. taiwanensis sp. nov. in the South China Sea. These species bear large paucispiral protoconchs that are indicative of benthic early development without a pelagic larval period, and hence low dispersal capability. Seafloor topography seems to have acted as a barrier for their dispersal; the range of B. tokoyodaensis supports the previous finding that Izu Peninsula delimits westward distribution of bathyal gastropod species of boreal origins.