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Arthropods have small but sophisticated brains which have enabled them to adapt their behavior to a diverse range of environments. The enormous evolutionary success of arthropods in terms of species richness and diversity depends on the sophistication of their brains. Advances in neurobiology have clarified some of the sensory and motor mechanisms of the arthropod brain, but the basic rules of computation underlying the central functions of the arthropod brain remain unknown. Consequently, it is not known how the basic design of the arthropod brain differs from, or is analogous to, that of other animals, especially mammals. In this report, we argue that characteristic features of the arthropod “microbrain” can be ascribed not only to the limited number of its constituting neurons but also to the optimization to life with a small body.
The bamboo borer, Omphisa fuscidentalis, is a moth found in northern Thailand, Lao and Myanmar and its larvae feed on the inner pulp of bamboo shoots. In a tropical highland (about 500 m sea level) forest at 19°N near Chiang Mai, Thailand, the larvae feed on at least 5 bamboo species. Nucleotide sequence analysis of the region of mitochondrial cytochrome C oxidase subunit 1 gene amplified by the polymerase chain reaction (PCR) verified that larvae collected from different bamboos belong to the same species. Adults appeared in early August and laid clusters of eggs on the newly grown bamboo shoot. The newly hatched larvae bore a hole in the shoot, enter an internode of the shoot and feed on the inner pulp. After maturation in September, the larvae remain in an internodal cavity of bamboo for up to 9 months, from September to the following June. Number of larval instars was estimated by measuring the width of head capsules remained in internodes of bamboo shoots. The growth curve of the width fitted to Dyar's law and the mature larvae were estimated to be 5th instar. Mature larvae were collected in the field each month and their body weight, head capsule width, protein and fat contents and hemolymph ecdysteroid titer were measured. Body weight continuously decreased during the 9 months whereas head capsule width remained constant. Fat content fluctuated during this period while protein level remained at a similar level until March, after which it significantly increased. During this period, hemolymph ecdysteroid concentrations remained low. Current results show that the bamboo borer larvae enter diapause at the end of feeding period of the fifth (last) larval instar and the larval diapause lasts until June.
To study the causal mechanisms underlying the control of egg sex by honeybee queens (Apis mellifera), the queens were allowed to lay eggs in experimental cages without comb cells. The sex of the eggs laid were then determined by counting the number of chromosomes, and by observation of female and male pronuclei in the eggs and sperm cells on the surface of the eggs. It was found that queens laid normally fertilized diploid eggs under the experimental conditions. These results suggested that honeybee queens lay fertilized eggs when no information of comb cell size is available, thus the idea that queens would be stimulated to release sperm by small worker cells fitting queen's abdomen is not supported.
Wolbachia are a group of inherited bacteria found in a number of arthropods and cause various reproductive alterations in their hosts, including feminization, parthenogenesis and cytoplasmic incompatibility. We examined Wolbachia infection in three species of moths belonging to the sub-family Phycitinae, the Indianmeal moth Plodia interpunctella, the almond moth Ephestia cautella and the Mediterranean flour moth Ephestia kuehniella. We detected infections in E. cautella and two strains of E. kuehniella, one from Tsuchiura city and the other from Yokohama city. Wolbachia was not detected in P. interpunctella. The phylogenetic positions of Wolbachia harbored by E. cautella and E. kuehniella were estimated based on the sequences of the wsp gene which encodes a Wolbachia surface protein. We also performed crossing experiments to examine cytoplasmic incompatibility. It was shown that Wolbachia in E. cautella cause complete cytoplasmic incompatibility: no egg-hatch was observed in the cross between infected males and uninfected females. Both Tsuchiura and Yokohama strains of E. kuehniella showed partial cytoplasmic incompatibility, but the levels were significantly different between the two strains. The rates of egg hatch in the incompatible crosses within Tsuchiura and Yokohama strains were 60.8% and 16.9%, respectively.
Fluorescent chromatophores with bluish white fluorescence were detected in the guppy Poecilia reticulata. These chromatophores were observable only by means of a fluorescence microscope, and could not be observed by a standard transmission light microscope or incident light microscope. Resembling other common chromatophores, these fluorescent chromatophores were dendrictic cells and similar to other chromatophores in the size, about 50–100 μm.
Of the 17 strains examined, these fluorescent chromatophores were detected only in the R strain, and in all 12 R strain individuals examined, each presented fluorescent chromatophores.
These differences in the occurence of fluorescent chromatophores among strains suggest that the formation of these chromatophores is the result of genetic polymorphism.
Four peaks of the p-nitrophenyl phosphate (pNPP) splitting activity were obtained by QAEToyopearl chromatography in the extract of sea urchin eggs from homogenate in 0.2M KCl solution containing 0.1% Triton X100 and so on. In 2 among these 4 peaks, pNPP splitting reactions were strongly inhibited by 10nM okadaic acid (OA) and calyculin A (CLA), potent and specific inhibitors of protein phosphatase 2A (PP2A). High sensitivities of pNPP splitting reaction to OA and CLA in these 2 peaks suggest that pNPP splitting results from the reaction catalyzed by PP2A, which reaction is expected to play roles in gene expression, signal transduction and cell movement such as cell division. OA sensitive pNPP splitting activities in these 2 peaks were eluted by FPLC gel permeation chromatography (Superdex 200HR) with approximate molecular mass of 160 kDa, corresponding to that of PP2A trimeric holoenzyme in mammalian cells. By immunoblot analyses with anti-human PP2A catalytic subunit antibody, an immunoreactive 36 kDa protein was found by SDS-PAGE in a peak of OA-sensitive pNPP splitting activity, obtained by QAE-Toyopearl chromatography. Sea urchin eggs have at least 2 PP2A like enzymes with similar molecular masses to that of mammalian PP2A and one of them contains human type catalytic subunit.
Fractionation with reverse-phase HPLC and electrophoretic analyses revealed that the nuclear basic proteins in sperm of an anuran amphibian, Discoglossus pictus, consisted of weakly basic proteins without histones. Amino acid analyses indicated that none of these proteins were histones or protamines because of the low amounts of Lys and Arg. The predominant protein among those fractionated possessed an unusually high content of His and extremely low amounts of Arg and Lys, indicating that this is a unique nuclear basic protein not reported previously. The induction of a highly decondensed state of sperm nuclei upon their incubation in egg extract was accompanied by the removal of most, if not all, of this His-rich protein from the nuclei.
A series of normal stages for the embryonic development of the ice goby (shiro-uo), Leucopsarion petersii, which belongs to the Perciformes, is described. Stages are based on morphological features, by utilizing the optical transparency of live embryos from the first cleavage to the hatching stage. Fertilized eggs were obtained by artificial insemination and normal embryogenesis was accomplished in a defined medium in plastic petri dishes at 19°C. Shiro-uo eggs were surrounded by a very thin and clear chorion and could be dechorionated with forceps very easily. Developmental stages were mostly comparable to those of other fish embryos described so far, but several differences were indicated, such as the third cleavage plane being horizontal, and that the length of the cleavage cycle increased gradually from the very early stages. Also, there were differences in the relative rates of organogenesis of the brain, eyes, otic vesicles, and somites when compared to the zebrafish and medaka.
To reveal the developmental sequence of the myotomal neuromuscular system in a teleost angelfish, Pterophyllum scalare, we investigated the differentiation and axonal outgrowth of the somatic spinal motoneurons as well as the differentiation of the axial muscles by means of anatomical and histochemical methods. Acetylcholinesterase histochemistry and retrograde labeling with HRP revealed two large motoneurons in each spinal hemisegment in the late embryos. To clarify the posthatching change of the motoneuron number, the number of axons in the anal-level ventral root was counted, since ChAT-immunohistochemical labeling of cholinergic spinal neurons and electron microscopic observation in the adult showed that the ventral roots around the anal level contained only somatic motor axons. We found that 15 primary motoneurons in each spinal hemisegment participated in the muscle innervation in just-hatched larvae. The motor axons rapidly increased in number beyond the adult level within three days posthatching, and then decreased to reach the adult level within a few weeks. The result suggests that competition among the motoneurons for their target muscles takes place. To reveal the temporal sequence of differentiation of the myotomal muscle fibers, in addition to electron microscopic observation of the muscle, a fluorescent mitochondrial marker dimethylaminostyrylethylpyridiniumiodine (DASPEI) was used to detect red muscle fibers. In the late embryo, immature white muscle fibers subserving the twitching movement of the animal in the egg capsule were observed. Differentiation of the red muscle was not evident until day 10. The present results show that a complete set of the axial muscle motoneurons differentiates before the differentiation of the multiple muscle fiber types in the angelfish.
The cDNA for a protein that is related to translation elongation factor 1α (EF-1α) has been cloned from the sea urchin Anthocidaris crassispina. The sea urchin EF-1α-related protein (AcEFP) seems somewhat unique in structure compared to EF-1α of other organisms so that it is uncertain if AcEFP is a genuine EF-1α. Still, it possesses many features of typical EF-1α reported so far, suggesting that AcEFP is involved in protein synthesis or its regulation. Genomic Southern analysis indicated that the sea urchin genome contains one or at most two copies of the AcEFP gene. A single transcript of 2.2 kb is expressed ubiquitously in adult tissues examined and, during embryogenesis, zygotically after the blastula stage. Whole mount in situ hybridization showed that the AcEFP gene is also widely expressed in embryos, with relatively high expression in the gut and oral ectoderm, both of which are proliferating tissues in embryos. The expression of AcEFP was not affected in embryos by agents that destabilize the extracellular matrix (ECM), suggesting that expression of AcEFP is relatively independent of the integrity of ECM in sea urchin embryos.
The initiation of sperm motility is regulated by certain factors, including a change of osmolality or ion concentration. The cue for the initiation of sperm motility is unique to species and suits the environment in which the fertilization occurs.
In the newt, Cynops pyrrhogaster, eggs are fertilized in the cloaca of the female with sperm stored in the sperm reservoir. In this study, we investigated possible factors initiating sperm motility in this unique environment. Sperm of C. pyrrhogaster could be initiated to move by a decrease of osmolality. However, eggs were fertilized with dry sperm and developed to four-cell stage embryos without immersion in solution. They continued to develop normally to the tail-bud stage when placed in Steinberg's salt solution after fertilization. These results indicate that sperm motility was initiated without the change of osmolality around sperm. In egg-jelly extract, the activity for the initiation of sperm motility was strong and heat stable, but disappeared by proteinase treatment. ICP luminescence analysis revealed that sodium, potassium, calcium and magnesium ions were major cations in egg-jelly. The monovalent cations showed the activity for the initiation of sperm motility in high concentration at high pH, and this activity become stronger by the addition of calcium ion. However, the reconstructed ionic solution that was prepared according to the concentrations of these four ions and pH in egg-jelly did not show the activity as strong as egg-jelly extract. These results suggest that the proteinacious factor and cations in egg-jelly are significant to regulate the initiation of sperm motility in C. pyrrhogaster.
To better understand the evolution and development of the amniote cranium, it is necessary to examine non-avian, non-mammalian embryos. Herein, development of the chondrocranium in the loggerhead turtle, Caretta caretta, is described based on whole-mount and sectioned specimens. Primitive characteristics were found to be established rather early in development; at these stages, the cranium resembled not only the early amniote chondrocrania, but also those of anamniote embryos. Several characteristics were noted in the late chondrocranium that represent shared, derived characteristics of chelonians. In particular, one amniote-specific characteristic, the tropibasic trabecula, appeared at an intermediate stage of development. In addition, developmental changes in the orbital cartilage were reemphasized, and the morphological significance of the crista sellaris was discussed in terms of the basic architecture of the vertebrate neurocranium.
Reproductive patterns of female house shrew (Suncus murinus) inhabiting central Taiwan were studied from September 1990 to February 1992 with animals collected monthly. The annual average body weight was 37.4 g for adults (N=198), and 23.2 g for juveniles (N=18), respectively. The reproductive females (pregnant and lactating) were found all the year round with higher percentages (more than 80%) in spring-summer. The average litter size was 2.9 (range: 1–6). The levels of plasma estradiol-17 β in adult females were higher in March-June (140 pg/ml), and decreased gradually to 98 pg/ml in January-February. Plasma levels of estradiol-17 β in pregnant and lactating females were significantly greater than those of non-pregnant adults and of juveniles. Ovarian weights, plasma levels of estradiol-17 β, and pregnancy rate were correlated with day length. The pre-implantation mortality and post-implantation mortality of the embryos were 6.9% and 1.6%, respectively. The present study has demonstrated that the female S. murinus inhabiting central Taiwan breeds all year round with higher reproductive activity in spring and summer.
The anatomy of Littorina sitkana was examined using specimens from nine localities in northern Japan. These localities are known to be genetically clustered into two geographic groups; the first group consists of localities on the northern coast of Hokkaido along the Seas of Japan and Okhotsk and the second one comprises localities on the Pacific coasts of Hokkaido and Honshu. Anatomical surveys revealed that the mean numbers of penial glands differ significantly between the northern and Pacific sites, in correlation with the genetic variation. On the other hand, the mean relative size of the capsule gland within the pallial oviduct was positively correlated with mean sea-surface temperature, almost independently of the genetic difference. In addition, imposex was found for the first time in L. sitkana. Females frequently lacked the capsule gland in the imposex-present populations. The mean relative size of capsule gland to the whole pallial oviduct was significantly smaller there than in the imposex-free populations. The number of penial glands in males tended to be small in the imposex-present populations. The penis of imposex females was much shorter than that of males, in contrast to Nucella species occurring sympatrically on these coasts, in which the female penis is nearly as long as the male one. Although the pallial oviduct is reported to be replaced by a prostate gland in imposex females of Littorina littorea, such replacement was not found in any imposex female of L. sitkana.
A new species and genus of marine mite, Corallihalacarus chilcottensis, is described from Australia. It occurs in sandy deposits around Chilcott Island, some three hundred kilometres off the northeastern Australian coast, and can be distinguished from other marine mite species by having a flexible neck between the idiosoma and the gnathosoma. Other unusual features of this species include a large median claw on each tarsus, rigid lamellae on legs III and IV, a very long apical palp segment and closely abutting, fused or overlapping idiosomal plates. The new genus is most closely related to Mictognathus Newell and the new subfamily Mictognathinae is established to accommodate both genera.
We investigated lines of arrested growth (LAG) of long bone tissues in a total of 157 salamanders of Hynobius kimurae from Tokyo and Kyoto, Japan. The number of LAGs did not differ between femurs, humeri, and toe phalanges. We found that the first LAG is formed after the first overwintering. The number of LAGs varied from 5–14 (x¯=8.8) in reproductive males and 7–12 (x¯=9.4) in mature females in the Tokyo population, while in the Kyoto population, males and females had 6–20 (x¯=9.1) and 7–17 (x¯=9.9) LAGs, respectively. This suggests that the minimum maturation age in males is five yr in Tokyo and six yr in Kyoto, while females of both populations need at least seven yr. The female-larger sexual size dimorphism, recognized in each population of this species seems to be attributable to a greater growth rate in females after the age of male maturity. Body size growth was better in Kyoto than in Tokyo, with average adult SVL being 3.2–3.6 times and 2.2–2.3 times of SVL of metamorphs, respectively. Adults of the Kyoto population, like metamorphs, are smaller than those of the Tokyo population, and such a difference is considered to be derived not from the differential age at maturity or growth rate but from the size difference at metamorphosis. In both populations, clutch size does not correlate to female age, but older and hence larger females tended to lay larger eggs. This suggests that the female fitness increases with age, not through an increase in the number of offspring per clutch, but through an elevation of survivorship per offspring.