Many attempts have been made to identify natal stream odors for salmon olfactory homing. It has recently been hypothesized that odors are dissolved free amino acids; however, it is unknown whether these odors change on a seasonal or annual basis. We analyzed dissolved free amino acid (DFAA) concentration and composition of water from the Teshio River in Hokkaido, Japan, where chum salmon (Oncorhynchus keta) returned for spawning, during juvenile downstream migration in spring and adult upstream migration in autumn with a 4-year difference. Among the 19 amino acids found in the Teshio River water, DFAA concentrations fluctuated largely, but 5–7 stable DFAA compositions (mole %) were found between the spring and autumn samples over a 4-year span. Two kinds of artificial stream water (ASW) were prepared using the same DFAA concentration in the Teshio River during the time of juvenile imprinting in spring (jASW) and adult homing in autumn (aASW), after a 4-year period. In behavioral experiments of upstream selective movement in a 2choice test tank, 4-year-old mature male chum salmon captured in the Teshio River showed significant preference for either jASW or aASW when compared to control water, but did not show any preference with respect to jASW or aASW. In electro-olfactogram experiments, adults were able to discriminate between jASW and aASW. Our findings demonstrate that the long-term stability of the DFAA compositions in natal streams may be crucial for olfactory homing in chum salmon.

Many animals show lateral bias in various behaviors. In fish, behavioral laterality has been studied from the perspective of its relation with brain lateralization. On the other hands, in some fishes, head dimorphism (righty or lefty) corresponds to behavioral laterality, such as foraging behavior. To examine the correlation between morphological asymmetry and behavioral laterality associated with brain lateralization, we conducted two behavioral tests (the detour test and fast-start test) using a poeciliid fish, Girardinus metallicus. In both behavioral tests, some individuals tended to move rightward, while others tended to move leftward, in a manner associated with head incline. In the detour-test, righty individuals primarily detoured leftward, whereas lefty individuals primarily detoured rightward. In the fast-start tests, the reverse tendency was seen; righty individuals tended to escape rightward, whereas lefty individuals tended to escape leftward. Such results indicate that brain lateralization may be also associated with morphological asymmetry.

Many organisms have the ability to alter their development in the presence of predators, leading to predator-induced defenses that reduce vulnerability to predation. In the water flea Daphnia pulex, small protuberances called ‘neckteeth’ form in the dorsal neck region in response to kairomone(s) released by predatory phantom midges (Chaoborus larvae). Although previous studies suggested that kairomone sensitivity begins when chemoreceptors begin to function during embryogenesis, the exact critical period was unknown to date. In this study, we investigated the period of kairomone sensitivity and the process of necktooth formation in D. pulex through extensive treatments with pulses of kairomone(s). First, we described the time course of embryogenesis, which we suggest should be used as the standard in future studies. We found the kairomone-sensitive period to be relatively short, extending from embryonic stage 4 to postembryonic first instar. We observed cell proliferation and changes in cell structure in response to the kairomone treatment, and propose a model for necktooth formation. Preliminary LiCl treatment suggests the Wnt signaling pathway involved in crest formation as a candidate for the molecular mechanism underlying this process. Our study provides basic insight toward understanding the mechanisms underlying adaptive polyphenism in D. pulex.

The genus Astreopora is a small but ancestral group in Acroporidae, which is one of the most diverse and dominant families of scleractinian coral in Indo-Pacific reefs. We estimated the species boundaries of Astreopora corals using two molecular markers: a mitochondrial non-coding region and a nuclear ribosomal 5.8S region. Seven species (59 specimens) commonly observed around Japan (Astreopora expansa, A. gracilis, A. incrustans, A. listeri, A. myriophthalma, A. cf. suggesta, and Astreopora sp.1) were investigated, and we observed no genetic divergence in the mitochondrial marker, suggesting that these species are closely related, consistent with a species complex or recent divergence, although genotyping by the marker is not so sensitive. In the nuclear 5.8S region, 121 clones consisted of six species were divided into the four major genetic groups. Although there were no monophyletic clades, the two dominant species A. myriophthalma and A. gracilis rarely shared the same haplotypes, suggesting that gene flow is limited between them. However, A. incrustans frequently shared the same haplotypes with A. gracilis although the distributions do not overlap. We found that the ancestral genus Astreopora in Acroporidae shows less genetic variation than traditionally identified morphospecies. Although further research on fertilization rate among these species is required to determine if there are reproductive barriers, the low level of genetic diversification in this genus hints that some ecological differences among acroporid corals play a role in the evolution of scleractinian corals, considering that the other members of this family, Acropora and Montipora, are highly diversified.

The Ryukyu-Taiwan region is an island arch with intervening waters of varying distances and depths. This study examines the geographic genetic structure of two sympatric sea kraits, Laticauda laticaudata and L. semifasciata, in the region, to infer factors affecting the extent of dispersal and other biogeographical traits of these amphibious reptiles. Sequence analyses of the mitochondrial cytochrome b gene revealed four and 16 haplotypes for L. laticaudata (136 individuals) and L. semifasciata (177 individuals), respectively. For both species, population pairwise F_ST analyses revealed significant genetic differentiations among islands and island groups, which are separated by deep straits, suggesting that deep waters serve as obstacles for dispersal in both species. Significant genetic differentiation was detected even among islands of the same basin in L. laticaudata, but not in L. semifasciata, and the isolation by distance analyses revealed no significant correlation between geographic and genetic distances in the former species. These results further suggest that L. laticaudata has stronger site fidelity or degree of philopatry than L. semifasciata. Based on the geographic genetic patterns, the historical biogeography of the two species in the Ryukyu-Taiwan region is also discussed.

The terrestrial mammalian fauna of the North Japanese island, Hokkaido, is more similar to that of Southern Siberia than to the main island of Japan, Honshu. Three species of the genus Myodes (Muridae, Rodentia) are found on Hokkaido, but not on Honshu. While Myodes rufocanus and M. rutilus are widely distributed across Hokkaido as well as the Eurasian continent, M. rex, which is endemic to Hokkaido and its adjacent islands, shows a discontinuous distribution pattern. We analyzed the phylogeographic history of M. rex using the mitochondrial DNA control region in order to interpret their discontinuous distribution pattern. Phylogenetic relationships among 54 distinct haplotypes showed that M. rex can be divided into four clades that occur on the northern, central, and southern regions of the Hokkaido mainland and on Rishiri Island, respectively. The phylogroups in the northern and central regions were largely separated in space, although several areas of sympatry were found. The phylogroup in the southern region, which was clearly separated from other phylogroups, showed markedly low genetic variability. All analyzed individuals from the population on Rishiri belonged to a separate lineage. Across a range of divergence rate estimates, we dated the basal divergence of all phylogroups to the mid to late Pleistocene, with subsequent signals of population expansion within lineages. We conclude that current phylogeographic structure in M. rex likely reflects Pleistocene survival in several separate refugia in situ. Past glacial ages have thus played an important role in shaping the current distribution patterns of mammalian species on Hokkaido.

The function of allogeneic recognition in a marine sponge, Halichondria japonica, was examined by use of cut pieces contact assay. Individuals of this species were able to distinguish an allogeneic individual from an autogeneic one, and showed rejection reactions against allogeneic individuals. There were two types of allogeneic rejection reaction: barrier formation at the contact area to separate from allogeneic individuals and necrosis with cytotoxic reactions at the contact area. In both types of rejection reactions, mesohyl cells accumluate at the contact area at the early stages of the rejection reaction. Fusion between two pieces of allogeneic individuals was very rare, and in most of combinations of allogeneic individuals rejection reactions appeared at the contact area. Xenogeneic rejections were also observed. Halichondria japonica showed rejection reaction against individuals of Halichondria okadai, but the intensity of rejection was less than that of allogeneic rejection.

Antifreeze proteins (AFPs) refer to a class of polypeptides that are produced by certain vertebrates, plants, fungi, and bacteria and which permit their survival in subzero environments. In this study, we report the molecular cloning, sequence analysis and three-dimensional structure of the axolotl antifreeze-like protein (AFLP) by homology modeling of the first caudate amphibian AFLP. We constructed a full-length spleen cDNA library of axolotl (Ambystoma mexicanum). An EST having highest similarity (∼42%) with freeze-responsive liver protein Li16 from Rana sylvatica was identified, and the full-length cDNA was subsequently obtained by RACE-PCR. The axolotl antifreeze-like protein sequence represents an open reading frame for a putative signal peptide and the mature protein composed of 93 amino acids. The calculated molecular mass and the theoretical isoelectric point (pl) of this mature protein were 10128.6 Da and 8.97, respectively. The molecular characterization of this gene and its deduced protein were further performed by detailed bioinformatics analysis. The three-dimensional structure of current AFLP was predicted by homology modeling, and the conserved residues required for functionality were identified. The homology model constructed could be of use for effective drug design. This is the first report of an antifreeze-like protein identified from a caudate amphibian.

We analyzed the ultrastructural features of the claw closer muscles in two estuarine crabs, Cyrtograpsus angulatus and Neohelice granulata, by transmission electron microscopy. Adult male crabs at intermolt stage were collected in the Mar Chiquita Coastal Lagoon (Buenos Aires, Argentina). The muscle fibers of both species showed evident striations, peripheral and intermyofibrillar nuclei, clefts in continuity with T and Z tubules, sarcoplasmic reticulum and T tubules forming dyads and triads usually located between the A and I bands, and mitochondria located mainly beneath the sarcolemma. Glycogen was observed as diffuse, small particles among myofilaments. The claw closer muscle of C. angulatus exhibited two fiber types: one with relatively fast-contracting fibers (shorter sarcomeres, myofilaments with an ordered arrangement, lineal Z discs, a well-developed sarcotubular system) and fatigue-resistant (numerous large mitochondria); and the other type, with slower-contracting fibers (longer sarcomeres, less orderly arranged myofilaments, wavy Z discs, a less developed sarcotubular system) and less resistant to fatigue (lower mitochondrial density). N. granulata showed only the slow, less resistant to fatigue type. The fibers less resistant to fatigue and more slowly contracting would presumably be used primarily for displays and agonistic interactions, whereas fast fibers with abundant mitochondria would be associated with continuous movements during feeding and grooming.

The blood supply in the large intestine of seven specimens of the lesser anteater, Tamandua tetradactyla, studied. The method included preparation of the macroscopic collection report, perfusion of the arterial network with water, injection of colored latex, fixation in formaldehyde, and preservation in ethanol. For our description and analyses, we performed dissections under mesoscopic light and made photo documentation of our observations. The large intestine of T. tetradactyla is irrigated by the caudal mesenteric artery (rectum, left colic fold, descending colon and transverse colon) and cranial mesenteric artery (right colic fold, cecal pouch). We observed that the large intestine in these animals is implied in the abdominal wall without becoming affixed to the wall, or developing adhesions on individual segments. The caudal mesenteric artery feeds the straight collateral branches (primary, secondary, and tertiary) and a few juxtacolic arched branches (first and second order). The straight branches emerge from the arched branches, bifurcate, and embrace the intestinal loop to irrigate it. The presence of anastomoses between the CaMA and the CrMA apparently ensures a relatively stable flow in the event of failure of either. This is very important, as the peritoneum in this species is completely dependent on blood from these two arteries. The model of vascularization and fixation of the large intestine into the abdominal wall of T. tetradactyla is different from that in other vertebrates.

In some species of bivalve, there are two highly diverged mitochondrial genomes, one found in all individuals (F type) and the other normally in males only (M type). In Mytilus, a maternally-dependent sex ratio of the progeny has been reported. Some females almost exclusively produce daughters, while others produce a high proportion of sons. We previously reported that in M. galloprovincialis, M type mtDNA copy number may be maintained during spermatogenesis and the development of larvae of male-biased mothers to sustain the doubly uniparental inheritance system. In this study, we investigated transcription levels of M type mtDNA before and after fertilization to understand its function in the germ line. First, we quantified transcription levels of M type mtDNA in testicular cells dissected using laser-capture micro-dissection. The transcription levels of M type mtDNA were not significantly different between spermatogonia and spermatocytes versus spermatids and spermatozoa. Next, we examined differences in transcription levels of M type mtDNA between larvae from male-biased and female-biased mothers. The transcription levels of M type mtDNA significantly increased 24 and 48 h after fertilization in male-biased crosses. By contrast, transcription levels significantly decreased in female-biased crosses. These results suggest M type mtDNA may play a role in early germ line formation.

Pristionchus pacificus Sommer, Carta, Kim, and Sternberg, 1996 is an important model organism in evolutionary biology that integrates developmental biology with ecology and population genetics. This species is part of a sub-complex of the genus Pristionchus that is considered to have originated in East Asia. Here, we describe two new species of Pristionchus, P. maxplancki and P. quartusdecimus, which were isolated from beetles in Japan, supporting the hypothesis that a region including Japan is the origin of diversification of the P. pacificus species complex. Phytogeny inferred from a partial small subunit rRNA gene and 25 ribosomal protein genes shows P. maxplancki to be the closest known outgroup to a triad of sibling species, including P. pacificus. Pristionchus quartusdecimus is a putative outgroup to the P. pacificus species complex, supporting a more ancient origin of Pristionchus species in the region. Species diagnoses are based on morphological and molecular characters, in addition to reproductive isolation for P. maxplancki. Members of the P. pacificus species complex as well as P. quartusdecimus are distinguished by stegostomatal structures, male genital papilla arrangement, and gubernaculum shape. The discovery of a new member of the P. pacificus species complex allows greater precision in polarizing and reconstructing ancestral states in the comparative model system centering on P. pacificus. Together with previous reports, these findings support an important biogeographic role of Japan in the evolution of the genus Pristionchus and the P. pacificus species complex, especially the associated phenotypic evolution of mouth morphology.