Hirokazu Abe

Development of a dopaminergic system in sea urchin embryos and larvae.

SUMMARY The mechanisms that regulate the organized swimming movements of sea urchin blastulae are largely unknown. Using immunohistochemistry, we found that dopamine (DA) and the Hemicentrotus pulcherrimus homolog of the dopamine receptor D1 (Hp-DRD1) were strongly co-localized in 1–2 μm diameter granules (DA/DRD1 granules). Furthermore, these granules were arranged across the entire surface of blastulae as they developed locomotory cilia before hatching, and remained evident until metamorphosis. DA/DRD1 granules were associated with the basal bodies of cilia, and were densely packed in the ciliary band by the eight-arm pluteus stage. The transcription of Hp-DRD1 was detected from the unfertilized egg stage throughout the period of larval development. Treatment with S-(–)-carbidopa, an inhibitor of aromatic-l-amino acid decarboxylase, for 20–24 h (i) from soon after insemination until the 20 h post-fertilization (20 hpf) early gastrula stage and (ii) from the 24 hpf prism larva stage until the 48 hpf pluteus stage, inhibited the formation of DA granules and decreased the swimming activity of blastulae and larvae in a dose-dependent manner. Exogenous DA rescued these deprivations. The formation of DRD1 granules was not affected. However, in 48 hpf plutei, the serotonergic nervous system (5HT-NS) developed normally. Morpholino antisense oligonucleotides directed against Hp-DRD1 inhibited the formation of DRD1 granules and the swimming of larvae, but did not disturb the formation of DA granules. Thus, the formation of DRD1 granules and DA granules occurs chronologically closely but mechanically independently and the swimming of blastulae is regulated by the dopaminergic system. In plutei, the 5HT-NS closely surrounded the ciliary bands, suggesting the functional collaboration with the dopaminergic system in larvae.

Morphology and molecular analysis of the 18S rRNA gene of oyster shell borers, Polydora species (Polychaeta: Spionidae), from Japan and Australia

Nuclear 18S rRNA gene sequences of oyster shell borers, Polydora websteri , P. calcarea and P. haswelli (Polychaeta: Spionidae), were determined for the first time. A wide range of morphological variation, particularly with regard to pigmentation, is observed among these three species. This variation was characterized at the species level. Black pigmentation pattern on the palps is suggested to be a key characteristic for species determination. Polydora websteri and P. haswelli were sister species. This is the first record of P. calcarea from Japan and Australia and P. haswelli from Japan.

Impacts of the 2011 tsunami on the subtidal polychaete assemblage and the following recolonization in Onagawa Bay, northeastern Japan.

The ecological impacts of the 2011 Great East Japan Earthquake and tsunami and the following recolonization of the subtidal benthic polychaete community were examined by monthly pre- and post-quake field surveys that were conducted in Onagawa Bay from 2007 to 2013. Before the tsunami, the species composition in this benthic community was constant and was dominated by cirratulid and magelonid polychaetes. The density and biomass of benthic polychaetes drastically decreased after the tsunami, and the polychaete community fluctuated during the 2 years after the natural disaster. Spionid and capitellid polychaetes were dominant at this period. In June 2013, the community entered a new constant stage dominated by maldanids, which is different from the pre-quake community. Ecological impacts due to chemical pollution were suggested in addition to the tsunami disturbance. These overlapping effects and physical, chemical and biological factors affected the recovery and recolonization of the polychaete community after the natural disaster.

Development of the GABA-ergic signaling system and its role in larval swimming in sea urchin

SUMMARY The present study aimed to elucidate the development and γ-amino butyric acid (GABA)-ergic regulation of larval swimming in the sea urchin Hemicentrotus pulcherrimus by cloning glutamate decarboxylase (Hp-gad), GABAA receptor (Hp-gabrA) and GABAA receptor-associated protein (Hp-gabarap), and by performing immunohistochemistry. The regulation of larval swimming was increasingly dependent on the GABAergic system, which was active from the 2 days post-fertilization (d.p.f.) pluteus stage onwards. GABA-immunoreactive cells were detected as a subpopulation of secondary mesenchyme cells during gastrulation and eventually constituted the ciliary band and a subpopulation of blastocoelar cells during the pluteus stage. Hp-gad transcription was detected by RT-PCR during the period when Hp-Gad-positive cells were seen as a subpopulation of blastocoelar cells and on the apical side of the ciliary band from the 2 d.p.f. pluteus stage. Consistent with these observations, inhibition of GAD with 3-mercaptopropioninc acid inhibited GABA immunoreactivity and larval swimming dose dependently. Hp-gabrA amplimers were detected weakly in unfertilized eggs and 4 d.p.f. plutei but strongly from fertilized eggs to 2 d.p.f. plutei, and Hp-GabrA, together with GABA, was localized at the ciliary band in association with dopamine receptor D1 from the two-arm pluteus stage. Hp-gabarap transcription and protein expression were detected from the swimming blastula stage. Inhibition of the GABAA receptor by bicuculline inhibited larval swimming dose dependently. Inhibition of larval swimming by either 3-mercaptopropionic acid or bicuculline was more severe in older larvae (17 and 34 d.p.f. plutei) than in younger ones (1 d.p.f. prism larvae).

Seasonal changes of planktonic polychaete larvae and chlorophyll a concentration in Onagawa Bay, northeastern Japan

Abstract Seasonal changes of abundance and composition of planktonic polychaete larvae were investigated monthly from January 2007 to December 2009 in Onagawa Bay, northeastern Japan. Larvae belonging to 18 families were identified: Spionidae, Serpulidae, Nephtyidae, Magelonidae, Phyllodocidae, Polynoidae, Syllidae, Capitellidae, Nereididae, Terebellidae, Arenicolidae, Chaetopteridae, Oweniidae, Pectinariidae, Glyceridae, Dorvilleidae, Sabellidae, and Lumbrineridae. The density of polychaete larvae varied from 18 to 6901 ind m−3. Spionid larvae occurred throughout the year, being the dominant family throughout the year, comprising 88.7% of the total, with those belonging to genus Polydora dominant during winter to spring and Pseudopolydora during summer to autumn. Larvae belonging to the Serpulidae, Magelonidae, Nephtyidae, Phyllodocidae, and Polynoidae tended to be frequent in summer and autumn. The close timing between phytoplankton blooms and the production of planktonic polychaete larvae is discussed, and it is noted that most planktonic polychaete larvae tended to synchronize with summer phytoplankton increases and autumn blooms in the near-surface water, but not with spring blooms. One possible explanation is the diversity of food during summer to autumn in Onagawa Bay. Only larvae belonging to the genus Polydora were synchronized with spring phytoplankton blooms, perhaps reflecting their northern biogeographic origin.

Swimming behavior of the spoon worm Urechis unicinctus (Annelida, Echiura).

Large numbers of swimming and stranding Urechis unicinctus were observed at night during low tide in Sasuhama, Miyagi Prefecture, northeastern Japan, during the periods from January to February in 2012 and 2013. Worms did not drift passively but swam actively, therefore hinting at a certain purpose for such behavior. As trochophore larvae of U. unicinctus were observed to occur simultaneously in the plankton, we infer the possibility that this is an event of reproductive swarming. Anatomical observations of both swimming and stranding U. unicinctus showed that none of the specimens had gametes, which may suggest that these were completely spent after spawning. Urechis unicinctus seemed to begin swimming after dusk and the observed swimming behavior occurred during the evening ebb tide throughout the night low tide during winter time. Stranding U. unicinctus have long been known in Japan and have been attributed to sea storms. The present study shows for the first time the possibility that U. unicinctus swims in order to reproduce at night and that this swimming behavior is closely linked to the stranding of U. unicinctus individuals.

First Report of the Morphology and rDNA Sequences of Two Pseudopolydora Species (Annelida: Spionidae) from Japan.

The morphology of two Pseudopolydora species, P. cf. reticulata Radashevsky and Hsieh, 2000 and P. achaeta Radashevsky and Hsieh, 2000 are reported from Japan for the first time. Pseudopolydora cf. reticulata was collected from Japanese tidal flats, and individuals possess the characteristic netlike pigmentation on the dorsum of anterior chaetigers and the longitudinal black band along midline of caruncle. Pseudopolydora achaeta was collected from subtidal bottom mud of Onagawa Bay, and individuals have distinctive characteristics, such as intensive black pigmentation on dorsal and ventral sides of the anterior body and nearly straight vertical rows of major spines on the fifth chaetiger. The morphology of P. cf. reticulata is very similar to that of P. cf. kempi, with which it had been confused in Japan. We analyzed the 18S and 28S rRNA gene sequences of all five Pseudopolydora species recorded from Japan and found strong evidence that they are genetically distinct. Our analysis also suggests that boring polydorids have evolved among non-boring ones; the genus Pseudopolydora, which mostly shows the non-boring form, appears to have remained in a more ancestral condition.

And then there was one: Polydora uncinata and Polydora hoplura (Annelida: Spionidae), the problematic polydorid pest species represent a single species

It is necessary to monitor shell-associated polydorid worms owing to the risk that they pose to commercially important molluscs. This requires accurate identification, but is often hampered by morphological similarities among species, insufficient type specimens, and abridged species descriptions. Thus morphological characteristics and molecular sequences of the most harmful polydorid species, Polydora uncinata from Japan and Australia and Polydora hoplura from South Africa were compared to determine whether they represent two morphologically similar, but genetically distinct species, or a single species. A wide range of morphological variation (with respect to size, length of caruncle and pigmentation patterns) was observed in each species and population, and their variations largely overlapped and revealed them to be at the intraspecific level of a single species. This was confirmed by gene sequences of nuclear 18S and 28S rRNA that were completely identical for P. uncinata and P. hoplura . The mitochondrial 16S rRNA and cyt b gene analyses also showed no genetic differences between these two species. The tree topology of the mitochondrial cyt b gene did not reflect geographic differences but instead suggests artificial transportation of the species. We recommend the synonymization of P. uncinata with P. hoplura.

Harmful Shell Borers, Polydora Species (Polychaeta: Spionidae), from Commercially Important Mollusk Shells in East Asia and Australia

Shell-boring polydorids (Polychaeta: Spionidae) are economically and ecologically important species that must be monitored owing to the risk they pose to commercially important mollusk shells. Tracking polydorid species internationally requires accurate species identification, which is based on both morphological characteristics and nuclear 18S rRNA gene sequences. Four serious shell-boring Polydora in East Asian and Australian aquaculture, i.e., Polydora brevipalpa, P. uncinata, P. haswelli, and P. aura, are described here. The shell-associated polydorids that have been reported from these areas were summarized and reviewed at the same time.

Reproduction and larval development of two sympatric Pseudopolydora species (Annelida: Spionidae) in Japan

Abstract Pseudopolydora cf. kempi and Pseudopolydora cf. reticulata, which are morphologically similar, are sympatric in Gamo Lagoon, near Sendai on the Pacific eastern coast of Honshu, Japan. Reproduction, larval development, and larval morphology of these two species were compared. The larval developmental pattern of P. cf. kempi was determined to be short-term planktonic with lecithotrophy and adelphophagy, whereas that of P. cf. reticulata was long-term planktonic with planktotrophy. The number of embryos per capsule differed between the two species: 0–16 for P. cf. kempi and 62–405 for P. cf. reticulata. Nurse eggs were only found for P. cf. kempi. The results of this study suggest that some previous studies attributed to P. kempi may have been to P. cf. reticulata or to another species in this complex.