Ultrastructure of the nuchal organs in the polychaete Platynereis dumerilii (Annelida,Nereididae)

Abstract. We examined the nuchal organs of adults of the nereidid polychaete Platynereis dumerilii by means of scanning and transmission electron microscopy. The most prominent features of the nuchal organs are paired ciliary bands located dorsolaterally at the posterior margin of the prostomium. They are composed of primary sensory cells and multiciliated supporting cells, both covered by a thin cuticle. The supporting cells have motile cilia that penetrate the cuticle and are responsible for the movement of water. Subapically, they have a narrowed neck region; the spaces between the neck regions of these supporting cells comprise the olfactory chamber. The dendrites of the sensory cells give rise to a single modified cilium that crosses the olfactory chamber; numerous thin microvillus-like processes, presumably extending from the sensory cells, also traverse the olfactory chamber. At the periphery of the ciliated epithelium runs a large nervous process between the ciliated supporting cells. It consists of smaller bundles of sensory dendrites that unite to form the nuchal nerve, which leaves the ciliated epithelium basally and runs toward the posterior part of the brain, where the perikarya of the sensory cells are located in clusters. The ciliated epithelium of the nuchal organs is surrounded by non-ciliated, peripheral epidermal cells. Those immediately adjacent to the ciliated supporting cells have a granular cuticle; those further away have a smooth cuticle. The nuchal organs of epitokous individuals of P. dumerilii are similar to those described previously in other species of polychaetes and are a useful model for understanding the development of nuchal organs in polychaetes.     

Expression of dachshund in wild-type and Distal-less mutant Tribolium corroborates serial homologies in insect appendages

We isolated the homologue of the Drosophila gene dachshund (dac) from the beetle Tribolium castaneum. Tc'dac is expressed in all appendages except urogomphi and pleuropodia. Tc'dac is also active in the head lobes, in the ventral nervous system, in the primordia of the Malpighian tubules and in bilateral stripes corresponding to the presumptive dorsal midline. Expression of Tc'dac in the labrum lends support to the interpretation that the insect labrum is derived from a metameric appendage. The legs of Tribolium accommodate two Tc'dac domains, of which the more distal one corresponds to the single dac domain described for Drosophila leg discs. In contrast to Drosophila, where this domain is thought to intercalate between the homothorax (hth) and the Distal-less (Dll) domains, in Tribolium it arises from within the Dll domain. In embryos mutant for the Tc'Dll gene we find that the distal Tc'dac domain in the legs, as well as the expression in the labrum, are deleted while the proximal leg domain and the mandibular expression are unaffected. Based on Tc'dac expression in wild-type and mutant embryos, we demonstrate serial homology of the complete mandible with the coxa of the thoracic legs, which affirms the gnathobasic nature of the insect mandible.     

Taxonomy of reproductive Nereididae (Annelida) in multispecies swarms at Ambon Island,Indonesia

Multispecies, or mass, spawning of different invertebrate species is well known for coral reef systems; however, incidences involving polychaetes are poorly documented. In this study we report on mass swarming, prior to spawning, of Nereididae at Ambon Island, Maluku, on three occasions: in 1866, inferred from an historical sample deposited in Naturalis, Leiden, and in March, 2009 and 2014, based on newly collected samples. The 2009 and 2014 events co-occurred with spawning of other polychaetes, known locally as wawo and including the widespread Indo-Pacific eunicid, Palola viridis (Gray in Stair). Ten species of reproductive Nereididae are described, including Composetia marmorata (Horst) new combination, formerly Ceratonereis marmorata; epitokous modifications are described for both sexes of each species including taxonomically important features such as body colour and number of pre-natatory chaetigers. Three distinct types of natatory region morphologies are recognized, which appear to characterise groups of genera. The ten new records brings to 13 the total number of nereidid species known to undergo mass swarming at Ambon Island; a key to the 13 species is provided. Species composition varies slightly between the three time periods: four species were common between all three periods, five species were in common between 1866 and 2014, and four species were in common between 1995 and 2009/14. Two species of Neanthes and one of Nereis are identified as potentially new and will be described in subsequent papers.     

Phylogeography and cryptic introduction of the ragworm Hediste diversicolor (Annelida,Nereididae) in the Northwest Atlantic

Many benthic marine invertebrates show striking range disjunctions across broad spatial scales. Without direct evidence for endemism or introduction, these species remain cryptogenic. The common ragworm Hediste diversicolor plays a pivotal role in sedimentary littoral ecosystems of the North Atlantic as an abundant prey item and ecosystem engineer, but exhibits a restricted dispersal capacity that may limit connectivity at both evolutionary and ecological time scales. In Europe, H. diversicolor is subdivided into cryptic taxa and genetic lineages whose distributions have been modified by recent invasions. Its origin in the northwest Atlantic has not been adequately addressed. To trace the age and origin of North American ragworm populations, we analyzed mtDNA sequence data (COI) from the Gulf of Maine and Bay of Fundy (n=73 individuals) and compared our findings with published data from the northeast Atlantic. Our results together with previous data indicate that two species of the H. diversicolor complex have independently colonized the northwest Atlantic at least three different times, resulting in two distinct conspecific assemblages in the Bay of Fundy and Gulf of Maine (respectively) that are different from the species found in the Gulf of St. Lawrence. North American populations had significantly lower genetic diversity compared with populations in the northeast Atlantic, and based on patterns of shared identity, populations in the Bay of Fundy originated from the Baltic Sea and North Sea. Populations from the Gulf of Maine were phylogenetically distinct and most likely originated from unsampled European populations. Analyses of the North American populations revealed patterns of post‐colonization gene flow among populations within the Gulf of Maine and Bay of Fundy. However, we failed to detect shared haplotypes between the two regions, and this pattern of complete isolation corroborates a strong phylogeographic break observed in other species.     

苯丙氨酸羟化酶在日本刺沙蚕脑内的表达分析

苯丙氨酸羟化酶(PAH)是芳香族氨基酸羟化酶家族(AAAHs)的一员,催化苯丙氨酸(Phe)转化为酪氨酸(Tyr)。运用Western blotting技术检测沙蚕PAH免疫原性。制作沙蚕头部石蜡切片,运用免疫组织化学技术,检测PAH蛋白表达定位情况。解剖剥离沙蚕脑组织,提取总RNA,运用RT-PCR技术克隆pah基因片段,构建质粒并转化入大肠杆菌中扩增,挑单一均匀菌落培养,双酶切鉴定后测序并比对同源性。Western blotting结果表明pah表达的蛋白存在于沙蚕脑内,免疫组化标记技术结果表明苯丙氨酸羟化酶主要分布在日本刺沙蚕前脑中腹侧、中脑背侧和两侧。RT-PCR结果表明沙蚕脑内存在苯丙氨酸羟化酶基因,且与多种动物pah具有同源性。在蛋白质和核酸水平鉴定了低等环节动物日本刺沙蚕脑组织内苯丙氨酸羟化酶的存在,为进一步研究无脊椎动物中枢神经系统内芳香族氨基酸羟化酶的基因分化奠定基础。     

Epitoky in Nereis (Neanthes) virens (Polychaeta: Nereididae): a story about sex and death

The nereidid Nereis (Neanthes) virens undergoes drastic behavioural, morphological and physiological changes during its sexual maturation (epitoky). This metamorphosis prepares benthic worms for a brief pelagic existence devoted to mating although in N. virens only mature males leave their burrows to swarm. After spawning, individuals of both sexes die. Specific adjustments of energy metabolism pathway allowing higher muscular activity and swimming capacity remain to be eluded. This study compared atokous worms (immature) and epitokous (mature) swimming males and benthic females of N. virens to detect metabolic changes that could occur during epitoky. Epitokous males showed significantly higher electron transport system, citrate synthase and aspartate aminotransferase activities (p<0.01) and significantly lower lactate dehydrogenase activity (p<0.01) compared to atokous worms and epitokous females. There was no difference in antioxidant enzyme capacities between epitokes and atokes. Lipase and trypsin activities were significantly lower (p<0.01) in epitokous males. The enzymatic changes observed are likely related to the metabolic adjustments required to support higher swimming abilities. Maintenance of antioxidant capacities could be related to protection of germinal tissues more than long term survival, since N. virens die after spawning.     

The distribution of an immunoreactive endothelin-like substance in the nervous system of the nereid,Neanthes diversicolor (Annelida)

Summary The distribution of an immunoreactive endothelin-1-like peptide was investigated in the nereid, Neanthes diversicolor, using an antiserum raised against synthetic endothelin-1. Immunoreactive perikarya were localized in the brain, and nerve fibers containing endothelin-1-like material were found in the neuropil occupying the central portion of the brain. No immunostained fiber elements were traced in the circumesophageal connectives. Immunoreactive perikarya occurred in the subesophageal ganglion. From this ganglion, specifically stained fibers run posteriorly toward the ventral nerve cord. In each segmental ganglion, immunoreactive neurons were observed in medio-ventral and latero-ventral regions, and one or two marked fibers extended to the parapodium. In the parapodium, small immunoreactive perikarya and fiber elements were visible. Immunolabeled fibers occurred in the stomatogastric nerves, in the wall of the buccal cavity, and in the pharynx, esophagus, intestine and its anal region. Immunoreactive perikarya and nerve fibers were visualized between the circular muscle layer and epithelial cell layer in the esophagus and intestine. The endothelin-1-like substance shown to occur in N. diversicolor appears to function as a neurotransmitter or neuromodulator.     

Particle size selection in individuals from epifaunal versus infaunal populations of the nereidid polychaete Neanthes succinea(Polychaeta: Nereididae)

Neanthes succinea (Frey & Leuckart, 1847) is a common nereidid polychaete of both epifaunal and infaunal estuarine habitats. The gut contents of individuals collected from two epifaunal and two infaunal habitats are compared. Our a priori expectation was that individuals from epifaunal habitats would be classified as macrophagous with guts indicating carnivory and/or macroalgal herbivory, while individuals from infaunal habitats would be classified as microphagous with guts indicating deposit feeding. At all four locations gut contents indicated deposit feeding with little indication of macrophagous feeding. Average particle sizes for mineral grains did not differ between the four collection sites. For the two infaunal locations mean size of the mineral grains in gut contents was significantly smaller than ambient sediments. In addition to mineral grains, guts contained diatoms, dinoflagellates, macrophytic detritus, protozoan tests, and a variety of metazoans. Our study demonstrates that caution is necessary when inferring feeding type from morphology and that population and habitat specific differences in diet can occur within the same species.     

Correlation of expression patterns of homothorax, dachshund, and Distal-less with the proximodistal segmentation of the cricket leg bud

We describe the expression pattern of Gryllus homothorax (Gbhth) and dachshund (Gbdac), a cricket homologue of Drosophila homothorax and dachshund, together with localization of Distal-less or Extradenticle protein during leg development. We correlated their expression patterns with the morphological segmentation of the leg bud. The boundary of Gbhth/GbDll subdivision is correlated with the segment boundary of the future trochanter/femur at early stages. Gbdac expression subdivides the leg bud into the presumptive femur and more distal region. During the leg proximodistal formation, although the early expression patterns of GbDll, Gbdac, and Gbhth significantly differ from those of Drosophila imaginal disc, their expression patterns in the fully segmented Gryllus leg were similar to those in the Drosophila late third instar disc.     

Heterochromatic self-association, a determinant of nuclear organization, does not require sequence homology in Drosophila

Chromosomes of higher eukaryotes contain blocks of heterochromatin that can associate with each other in the interphase nucleus. A well-studied example of heterochromatic interaction is the brown(Dominant) (bwD) chromosome of D. melanogaster, which contains an approximately 1.6-Mbp insertion of AAGAG repeats near the distal tip of chromosome 2. This insertion causes association of the tip with the centric heterochromatin of chromosome 2 (2h), which contains megabases of AAGAG repeats. Here we describe an example, other than bwD, in which distally translocated heterochromatin associates with centric heterochromatin. Additionally, we show that when a translocation places bwD on a different chromosome, bwD tends to associate with the centric heterochromatin of this chromosome, even when the chromosome contains a small fraction of the sequence homology present elsewhere. To further test the importance of sequence homology in these interactions, we used interspecific mating to introgress the bwD allele from D. melanogaster into D. simulans, which lacks the AAGAG on the autosomes. We find that D. simulans bwD associates with 2h, which lacks the AAGAG sequence, while it does not associate with the AAGAG containing X chromosome heterochromatin. Our results show that intranuclear association of separate heterochromatic blocks does not require that they contain the same sequence.     

Integrative taxonomy does not support the occurrence of two species of the Squalius squalus complex (Actinopterygii,Cypriniformes, Cyprinidae) in Italy

The systematic is still unresolved for the genus Squalius (Cyprinidae, Leuciscinae), a rich group of small to large fishes widely distributed throughout Europe. The distinction of one of the Italian narrowly endemic species, Squalius albus (Bonaparte, 1838), described for the area surrounding lake Trasimeno, from the more common and widespread Squalius squalus (Bonaparte, 1837) is doubtful. The application of integrative taxonomy, with DNA taxonomy and quantitative morphometric, using both living and preserved individuals collected from lake Trasimeno before Squalius sp. restocking, allowed us to explicitly test for the identity of the two species in the complex. COI barcoding data, used for phylogenetic reconstructions, underlined that two clades may exist in the complex; nevertheless, DNA taxonomy (ABGD and GMYC) and morphometrics show no statistical support for their identity as separate species. Moreover, during our survey of the genetic diversity of the Italian Squalius, we provided further support for the species status of Squalius lucumonis, and found evidence of the occurrence in Southern Italy of another chub species, Squalius vardarensis (Karaman, 1928), previously known only from the Southern part of the Balkan Peninsula.     

Expression patterns of fork head and goosecoid homologues in the mollusc Patella vulgata supports the ancestry of the anterior mesendoderm across Bilateria

We have characterised orthologues of the genes fork head and goosecoid in the gastropod Patella vulgata. In this species, the anterior-posterior (AP) axis is determined just before gastrulation, and leads to the specification of two mesodermal components on each side of the presumptive endoderm, one anterior (ectomesoderm), and one posterior (endomesoderm). Both fork head and goosecoid are expressed from the time the AP axis is specified, up to the end of gastrulation. fork head mRNA is detected in the whole endoderm, as well as in the anterior mesoderm, whereas goosecoid is only expressed anteriorly, in the three germ layers. The two genes are thus coexpressed in the anterior mesoderm, suggesting the latter's homology with vertebrate prechordal mesoderm. In addition, since prechordal plate is known to belong to an anterior, so called "head organiser", and since its inductive role is dependent on the function of the vertebrate fork head and goosecoid orthologues, we further suggest that the anterior mesoderm may also have a role in anterior inductive patterning in Spiralia. Finally, we propose that a mode of axial development involving two organisers, one anterior and one posterior, is ancestral to the Bilateria, and that both organisers evolved from the single head organiser of a putative hydra-like ancestor.