Most animals exhibit circadian rhythms in various physiological and behavioral functions regulated by circadian clock that resides in brain and in many peripheral tissues. Temperature cycle is an important time cue for entrainment, even in mammals, since the daily change in body temperature is thought to be used for phase regulation of clocks in peripheral tissues. However, little is known about the mechanisms by which temperature resets the clock. In the present study, we investigated the effect of temperature on circadian activity rhythm and clock gene transcription by using the cricket, Gryllus bimaculatus. We show that temperature cycle can entrain both behavioral and transcriptional rhythms of clock genes, such as period, timeless, cryptochrome2 and cycle in the circadian pacemaker tissue, optic lobe. Under temperature cycle, phase of evening peak of locomotor activity occurred 1 h before the warm-to-cold phase transition, which is associated with earlier peaks of mRNA expression rhythm of the clock genes than that under light/dark cycles. When the temperature cycle was advanced by 6 h, behavioral rhythms re-entrained to newly phased temperature cycle after ∼16 transient cycles. The mRNA oscillation of period and timeless gained stable rhythm under phase advanced temperature cycles with a lesser number of transient cycles than cryptochrome2 and cycle. These results suggest that temperature cycle can entrain behavioral and molecular rhythms in cricket and clock genes vary in sensitivity to temperature. It is thus likely that clock genes play differential roles in resetting the clock with environmental temperature changes.

Mammalian T cell death-associated gene 8 (TDAG8)s are activated by extracellular protons. In the present study, we examined whether the TDAG8 homologs of other species are activated by protons as they are in mammals. We found that Xenopus TDAG8 also stimulated cAMP response element (CRE)-driven promoter activities reflecting the activation of Gs/cAMP signaling pathways when they are stimulated by protons. On the other hand, the activities of chicken and zebrafish TDAG8s are hardly affected by protons. Results using chimeric receptors of human and zebrafish TDAG8s indicate that the specificity of the proton-induced activation lies in the extracellular region. These results suggest that protons are not an evolutionarily conserved agonist of TDAG8.

Cofilin, a member of the ADF/cofilin family, is an actin-binding protein which is widely distributed among eukaryotic organisms and involved in actin filament dynamics in a variety of cell types. In mammalian striated muscles, muscle-type cofilin (MCF or cofilin-2) is predominantly expressed. Previous investigations have shown that MCF plays an essential role in the regulation of assembly of contractile apparatus in skeletal muscle, but its role in cardiac muscle has remained unclear. In the present study, in order to further clarify the role of MCF in organization of myofibrillar structure in vivo, we generated chimeric mice with a combination of MCF-deficient cells that were generated by Cfl2-knockout (Cfl2^-/-) and wild type cells containing MCF, and examined the effect of MCF deficiency on striated muscles, especially on the fine structures of contractile apparatus in cardiac muscle. We found that mice chimeric for MCF deficient cells exhibited structural defects in their skeletal muscles as previously reported. Histological analysis showed that MCF deficiency leads to degradation of myofibers and promotion of muscle regeneration. Electron microscopic observation of cardiac muscle of the chimeric mice showed coexistence of the cells with normal sarcomeres and those with disorganized myofibrils in a chimeric pattern. In these cofilin-deficient cells, myofilaments were scattered in the cytoplasm and myofibrillar structures were severely disrupted. These results provide strong evidence for that MCF plays a critical role in the formation and the maintenance of myofibril structure not only in skeletal muscle but also in cardiac muscle.

Reproductive strategy is an important aspect of biological diversity. In tardigrades, several reproductive modes, including sexual reproduction, are known. However, tardigrade mating behavior has been observed only rarely in most species, and in some cases, especially in the freely ovipositing eutardigrades, remains entirely unknown. In the present study, we cultured two sexually reproducing tardigrade species that lay eggs freely, Paramacrobiotus sp. TYO strain and Macrobiotus shonaicus, to investigate and compare their courtship, mating, and chromosome morphology. Mating behavior was observed and recorded in both species. The entire mating sequence, including courtship, was categorized into five discrete steps common to two species, as follows: [1] Tracking: the male tracks and orientates toward the female; [2] Touching: the male makes contact with the cloaca of the female; [3] Standstill: the female ceases movement until male ejaculation is complete; [4] Ejaculation: the male curls its caudal end and ejaculates into the cloaca from close range; [5] Contraction: the female contracts its ventral side after ejaculation to capture spermatozoa deposited in the external environment in close proximity to the cloaca. Some notable differences between the two species were observed in the steps 3–4. First, oviposition was observed at 40 min in Paramacrobiotus sp. TYO strain, and a few days after mating in M. shonaicus, respectively. Comparisons of chromosome morphology before and after mating indicated that oocytes are arrested at metaphase I in both species. Spermatozoa attach to the interior of the chorion of laid eggs.

Rapid expansion of sika deer, in both number and distribution, in the Japanese Archipelago has resulted in serious ecological disturbance. In the present study, the population structure and migration patterns of sika deer (Cervus nippon) among Toyama and adjacent Prefectures were investigated using 11 polymorphic microsatellite loci. Deviation from Hardy–Weinberg equilibrium was detected in both total and individual regional sika deer samples from Toyama Prefecture. Results of pairwise F_ST results, factorial correspondence analysis, and STRUCTURE analysis indicated that sika deer in Toyama are not genetically distinct from those in adjacent Prefectures. Bayesian STRUCTURE results suggested the existence of two distinct clusters. However, multiple lines of genetic structure and high admixture were detected across the populations located in the central region of Toyama Prefecture. Both contemporary and historical migration analyses showed that dispersal into Toyama Prefecture from neighboring prefectures was high, especially migration from the prefecture on the east into Toyama Prefecture, and bidirectional dispersion between Toyama Prefecture and the prefecture to the south. Knowledge of such genetic structures and population dynamics is required for appropriate management and conservation of sika deer populations in the Japanese Archipelago.

Insects are the most diverse organisms in the world and have been in existence since ca. 480 Ma; given this, they can provide profound insights into evolution. Among them, the order Ephemeroptera is one of the most basal clades of winged insects. This makes Ephemeroptera a significant key taxon in understanding the macro-evolution or the insect groundplan. In the development of biological evolutionary studies of this taxon, it is important to establish a technique for cross-breeding. Furthermore, the establishment of these techniques also makes a great contribution in the fields of micro-evolution. In a non-model taxon, the mayfly, subcultivation in the laboratory has been thus far considered impossible. With the exception of some parthenogenetic strains, it is extremely difficult to mate these insects in artificial environments. In this study, we established a successful artificial mating technique, i.e., a “hand-pairing” based cross-breeding method for mayflies. Furthermore, we also succeeded in clearly verifying by a genotyping method that the offspring reproduced by hand-pairing were in fact derived from the actual male and female which were used for hand-pairing. We established a reproductive experimental technique for hand-pairing of Dipteromimus tipuliformis and verified this technique by means genotyping. This technique could allow the artificial control of fertilization timing, and result in offspring which can be verified as to their status by means of genotyping. This achievement will be extremely important in the future for both the macro- and micro-evolutionary studies of insects.

In some species, male traits are more exaggerated than female traits. To understand the evolution and maintenance of such male traits, it is important to clarify their function in contexts of both intra- and intersexual selection. However, information about the function of specific male traits in both male–male competition and female mate choice remains limited. Male Puntius titteya assume a bright red, carotenoid-based coloration over the whole body. A previous study revealed that females in this species prefer to mate with redder males. In the present study, we examined the function of male coloration in male–male competition under both white and green light conditions. Under white light, in which males could perceive red coloration, males with higher color saturation compared to their opponents became dominant. On the other hand, under green light, in which males could not accurately perceive red coloration, the effect of male coloration on male–male competition disappeared, and only male body size significantly influenced intermale competition, i.e., larger males were dominant. These results indicate that, under environments in which red coloration can be assessed by males, body coloration affects male–male competition. These findings suggest that carotenoid-based coloration in P. titteya males plays a key role in both intra- and intersexual selection.

Many cichlid species in the shallow-shore of Lake Tanganyika suffer damage from attacks by the scale-eater Perissodus microlepis. Many prey fish engage in warning behaviors to this predator. It has been hypothesized that, if prey fish have difficulty employing such behavioral tactics, morphological defenses against scale-eating, such as hard scales, will evolve. The shrimp-eating cichlids, Altolamprologus compressiceps (Ac) and Neolamprologus fasciatus (Nf), exhibit hunting behaviors in which they remain motionless for up to 10 seconds while aiming at prey, when they are vulnerable to scale-eating predators; thus, these fish have likely evolved morphological defenses against “scale-attacks”. We tested this hypothesis in Ac and Nf, as well as three other predatory fish, Lamprologus callipterus, Lepidiolamprologus elongatus and Lep. attenuatus, that are not motionless for such a long time. Under natural conditions, Ac and Nf were rarely attacked, while the other three species were attacked frequently. When freshly killed specimens of these five species were displayed underwater in the presence of P. microlepis, Ac was rarely attacked, while Nf and the three other species were attacked frequently. Among the five fish species, the force required to tear off scales was highest for Ac, and this force was negatively correlated with the frequency of attacks on the displayed fish. These results support the hypothesis that the hard scales of Ac function as an anti-scale-attack measure, although it remains unclear why free-swimming Nf were rarely attacked while aiming at prey, despite the fact that the force required to tear off its scales was not large.

Sperm competition can theoretically affect sperm morphology; however, it remains unclear whether and how sperm morphology tracks the intensity of sperm competition in each population. The barn swallow Hirundo rustica is a model species used in the study of sexual selection, and exhibits considerable variation in extra-pair paternity (percentage extra-pair young, ca. 3–30%) among populations. In the Joetsu population of the barn swallow, extra-pair paternity is virtually absent (< 3%), providing a rare opportunity to study sperm morphology under limited sperm competition, and to compare it with those reported in populations with frequent extra-pair paternity (>15%). We found that head, midpiece, and total sperm length were significantly shorter in the Joetsu population than in populations with frequent extra-pair paternity. Moreover, the variability in total sperm length, measured as the coefficient of variation in the Joetsu population, was twice as high as that of populations with frequent extra-pair paternity. These results are consistent with a positive, directional, and stabilizing effect of sperm competition on sperm morphology. Together with previous studies in populations with frequent extra-pair paternity, the current study provides one of few sets of evidence to show a link between the intensity of sperm competition and the mean and variance of sperm morphology within a wild bird species.

Bioconvection is a form of collective pattern formation driven by negative gravitaxis of swimming microorganisms. In bioconvection, the interaction between individual swimmers results in self-organization leading to the development of a macroscopic structure typically 100–1000 times greater than an individual microorganism. To gain insight into the role of gravity in this self-organization phenomenon, we investigated the bioconvective behavior of the ciliate Tetrahymena thermophila under short-term partial gravity, i.e., gravitational acceleration < 1 g, achieved by quasiparabolic flight maneuvers of an aircraft. The bioconvective responses of T. thermophila were assessed by observing the collective motion simultaneously in two separate scales, which we call macroscale and microscale, using a newly designed “dual-objective” device with two different magnifications. Microscale analysis revealed that the magnitude of gravikinesis, i.e., active regulation of the propulsive thrust, decreased almost linearly with changes in gravitational acceleration, while gravitactic characteristics, assessed by the distribution of the swimming direction, did not change significantly during partial gravity. Macroscale analysis demonstrated that downward plumes of convection pattern gradually shortened from the lower end, and disappeared under partial gravity. The sustained time of the plumes decreased almost linearly with changes in gravitational acceleration. The response of downward plumes to partial gravity may be attributable to the accumulation of cells into blobs in downward migration, which increases the rate of downward migration enough to exceed the rate of upward movement, which is enhanced due to gravikinesis. This suggests that gravity may act on cells involved in collective pattern formation differently than on free-swimming cells.

The two-pore domain potassium ion (K ⁺ ) channel-related K ⁺ (TREK) channel and melatonin receptors play roles in the regulation of reproduction in zebrafish. Since reproduction is regulated by diurnal rhythms, the TREK family and melatonin receptors may exhibit diurnal rhythms in expression. In this study, we aimed to investigate diurnal variations of the gene expressions of TREK family and melatonin receptors and their associations with kisspeptin and gonadotrophin-releasing hormone (GnRH). Diurnal variations of trek1b, trek2a, trek2b, mt1, mt2, mel1a, kiss2 and gnrh3 expressions were examined by real-time PCR. For reproduction-related genes, kiss2 and gnrh3 exhibited diurnal rhythms. trek2a revealed a diurnal rhythm in the TREK family. mt2 and mel1c exhibited diurnal rhythms in the melatonin receptors. Since Trek2a regulates gnrh3 expression, the diurnal rhythm of gnrh3 expression suggests to be regulated by the diurnal rhythm of trek2a expression.