Biogeochemical influence on carbon isotope signature in boreal lake sediments

The functional morphology of the feeding palps and prostomium of the spionid polychaetes Streblospio benedicti and S. shrubsolii was studied. Three functional groups of cilia of the feeding palps were found on both species – frontal cilia, latero-frontal cirri and lateral cilia. Frontal cilia line the food groove and transport food particles to the pharynx, and have been reported for all spionid polychaetes except species of the genus Scolelepis. Latero-frontal cirri deflect particles onto the frontal surface and have been observed in several spionid genera including Paraprionospio, Streblospio, Polydora and Dipolydora. Lateral cilia beat in continuous metachronal waves creating lateral vortices that potentially entrain suspended particles, and are known in Paraprionospio and Streblospio. The two species of Streblospio did differ in the distribution of prostomial papillae. These papillae are eversible and thought to function in particle selection as particles on the pharynx come in contact with the papillae. Prostomial papillae were restricted to the peripheral surface of S. benedicti and were widely scattered on all surfaces of the prostomium of S. shrubsolii. A conical tentaculate structure occurs between the branchiae of the first setiger of S. benedicti, but only a low raised elevation is present on S. shrubsolii.     

Morphogenesis and phenotypic divergence in two developmental morphs of Streblospio benedicti (Annelida,Spionidae)

Abstract. The morphology of marine invertebrate larvae is strongly correlated with egg size and larval feeding mode. Planktotrophic larvae typically have suites of morphological traits that support a planktonic, feeding life style, while lecithotrophic larvae often have larger, yolkier bodies, and in some cases, a reduced expression of larval traits. Poecilogonous species provide interesting cases for the analysis of early morphogenesis, as two morphs of larvae are produced by a single species. We compared morphogenesis in planktotrophic and lecithotrophic morphs of the poecilogonous annelid Streblospio benedicti from the trochophore stage through metamorphosis, using observations of individuals that were observed alive, with scanning electron microscopy, or in serial sections. Offspring of alternate developmental morphs of this species are well known to have divergent morphologies in terms of size, yolk content, and the presence of larval bristles. We found that some phenotypic differences between morphs occur as traits that are present in only one morph (e.g., larval bristles, bacillary cells on the prostomium and pygidium), but that much of the phenotypic divergence is based on heterochronic changes in the differentiation of shared traits (e.g., gut and coelom). Tissue and organ development are compared in both morphs in terms of their structure and ontogenetic change throughout early development and metamorphosis.     

Consequences of a poecilogonous life history for genetic structure in coastal populations of the polychaete Streblospio benedicti

In many species, alternative developmental pathways lead to the production of two distinct phenotypes, promoting the evolution of morphological novelty and diversification. Offspring type in marine invertebrates influences transport time by ocean currents, which dictate dispersal potential and gene flow, and thus has sweeping evolutionary effects on the potential for local adaptation and on rates of speciation, extinction and molecular evolution. Here, we use the polychaete Streblospio benedicti to investigate the effects of dimorphic offspring type on gene flow and genetic structure in coastal populations. We use 84 single nucleotide polymorphism (SNP) markers for this species to assay populations on the East and West Coasts of the United States. Using these markers, we found that in their native East Coast distribution, populations of S. benedicti have high‐population genetic structure, but this structure is associated primarily with geographic separation rather than developmental differences. Interestingly, very little genetic differentiation is recovered between individuals of different development types when they occur in the same or nearby populations, further supporting that this is a true case of poecilogony. In addition, we were able to demonstrate that the recently introduced (~100 ya) West Coast populations probably originated from a lecithotrophic population near Delaware.     

Spermatogenesis and sperm ultrastructure in three species of polydora and in streblospio benedicti (Polychaeta: Spionidae)

Summary Spermatogenesis was studied at the ultrastructural level in Polydora ligni, P. websteri, P. socialis and Streblospio benedicti. Spermatogonia, spermatocytes, spermatids and mature sperm are described. In all four species, meiosis occurs in the coelom following release of spermatogonia from the gonad. In Polydora spp., chromatin condensation is lamellar with no microtubules present during nuclear elongation. In S. benedicti, chromatin condensation is fibrous with a manchette of microtubules present around the nucleus. In all four species, the acrosome forms from a Golgi-derived vesicle situated at the base of spermatids. The acrosome in Polydora spp. is conical with a distinctive substructure whereas the S. benedicti acrosome is long and spiral. The implantation fossa is short in all species except P. ligni. All four species have elongated sperm heads. The middlepiece as well as the nucleus is elongated in Polydora spp. whereas S. benedicti has a long nucleus but a short middlepiece. Platelet-shaped electron-dense bodies are present throughout the nuclear region and middlepiece of Polydora spp. and the nuclear region of S. benedicti. These membrane-bounded bodies may be energy storage organelles. The use of ultrastructural data in analysis of sibling species complexes is discussed.Contribution Number 203 from Harbor Branch Foundation, Inc.     

Ultrastructural Observations on the Larva of Loxosoma pectinaricola Franzén (Entoprocta,Loxosomatidae)

The larva of Loxosoma pectinaricola Franzén has been studied using scanning and transmission electron microscopy. The embryo develops surrounded by an egg envelope attached to the brood chamber. The newly released larva measures about 100 μm in length and is characterized by a prominent apical organ, stalked vesicles, paired lateral sense organs and a prototroch. The apical organ consists of at least four cell types: (1, 2) two types of ciliated cells, (3) vacuolated cells and (4) myoepithelial cells. The apical organ and frontal ganglion are tightly juxtaposed in the upper tier of the episphere. The stalked vesicles each consisting of two cells are unique evaginations of the epidermis. There are about twenty stalked vesicles with a maximum diameter of about 20.0 μm. The ciliated, knob-shaped, paired lateral sense organs are situated fronto-laterally on the episphere. The prototroch is comprised of a row of contiguous prototroch cells each containing about eighteen long cilia. The apical organ, frontal ganglion and paired lateral sense organs are suggested to be sensory structures that play an important role in active locomotion, settlement site selection and metamorphosis.     

Olfactory metamorphosis in the Coastal Giant Salamander (Dicamptodon tenebrosus)

This study examined the gross morphology and ultrastructure of the olfactory organ of larvae, neotenic adults, and terrestrial adults of the Coastal Giant Salamander (Dicamptodon tenebrosus). The olfactory organ of all aquatic animals (larvae and neotenes) is similar in structure, forming a tube extending from the external naris to the choana. A nonsensory vestibule leads into the main olfactory cavity. The epithelium of the main olfactory cavity is thrown into a series of transverse valleys and ridges, with at least six dorsal and nine ventral valleys lined with olfactory epithelium, and separated by ridges of respiratory epithelium. The ridges enlarge with growth, forming large flaps extending into the lumen in neotenes. The vomeronasal organ is a diverticulum off the ventrolateral side of the main olfactory cavity. In terrestrial animals, by contrast, the vestibule has been lost. The main olfactory cavity has become much broader and dorsoventrally compressed. The prominent transverse ridges are lost, although small diagonal ridges of respiratory epithelium are found in the lateral region of the ventral olfactory epithelium. The posterior and posteromedial wall of the main olfactory cavity is composed of respiratory epithelium, in contrast to the olfactory epithelium found here in aquatic forms. The vomeronasal organ remains similar to that in large larvae, but is now connected to the mouth by a groove that extends back through the choana onto the palate. Bowman's glands are present in the main olfactory cavity at all stages, but are most abundant and best developed in terrestrial adults. They are lacking in the lateral olfactory epithelium of the main olfactory cavity. At the ultrastructural level, in aquatic animals receptor cells of the main olfactory cavity can have cilia, short microvilli, a mix of the two, or long microvilli. Supporting cells are of two types: secretory supporting cells with small, electron-dense secretory granules, and ciliated supporting cells. Receptor cells of the vomeronasal organ are exclusively microvillar, but supporting cells are secretory or ciliated, as in the main olfactory cavity. After metamorphosis two distinct types of sensory epithelium occur in the main olfactory cavity. The predominant epithelium, covering most of the roof and the medial part of the floor, is characterized by supporting cells with large, electron-lucent vesicles. The epithelium on the lateral floor of the main olfactory cavity, by contrast, resembles that of aquatic animals. Both types have both microvillar and ciliated receptor cells. No important changes are noted in cell types of the vomeronasal organ after metamorphosis. A literature survey suggests that some features of the metamorphic changes described here are characteristic of all salamanders, while others appear unique to D. tenebrosus.     

Pineal regeneration in the frog, Rana pipiens, following embryonic extirpation

This report describes the capacity of larvae of the Leopard frog, Rana pipiens, to regenerate pineal tissue after embryonic pinealectomy, and presents experimental evidence for frontal organ dependence on the epiphysis. In addition, it was found that the “brow spot,” a pigment-free region located in the epidermis betweeen the eyes, is dependent on the frontal organ for its formation. This report also substantiates that the absence of the pineal organ in larval animals does not affect growth or development through metamorphosis.     

Ultrastructure of the sexually dimorphic tarsal glands and tegumental glands in gonyleptoid harvestmen (Opiliones,Laniatores)

In at least four closely related families of the diverse harvestmen lineage Gonyleptoidea, males may possess sexually dimorphic tarsal glands in the swollen tarsomeres of the basitarsus and/or metatarsus of leg I. The first histological and ultrastructural examination of the sexually dimorphic tarsal glands in leg I focused only on Manaosbiidae. In this study, we examine the morphology and ultrastructure of the sexually dimorphic glands, and their associated glandular openings, found in the basitarsus and/or metatarsus of leg I of males representing Cosmetidae, Gonyleptidae, and Cranaidae (glandular openings only). In cosmetids and gonyleptids, the tarsal glands are made up of 20–60 glandular units that form distinct groups within the prolateral and retrolateral half of the tarsomere. Each glandular unit consists of a pair of terminal secretory cells, an intercalary cell wrapped around the receiving canal, and a canal cell tightly wrapped around the length of the conducting canal. Cosmetidae, Gonyleptidae, and Cranaidae exhibit remarkably similar tarsal glands and gland openings although the location of the glands in the leg differs slightly among them. Males of these three families exhibit markedly different glands and glandular openings compared to males of the family Manaosbiidae. The sexually dimorphic tarsal glands may provide an important morphological character for determining phylogenetic relationships among gonyleptoid families. Finally, we provide morphological and ultrastructural data for the common tegumental glands. These data indicate that the sexually dimorphic tarsal glands are strikingly similar to, and may possibly be derived from, the tegumental glands. J. Morphol. 274:1203–1215, 2013. © 2013 Wiley Periodicals, Inc.     

Structure and function of the head in flabelligerid polychaetes

The functional anatomy of the head of Flabelliderma commensalis is described and compared to other flabelligerid polychaetes. Prostomial parts include the dorsal lip, the palps, two pairs of nuchal organs, four eyes and the prostomial lobe and ridge. The eyes are inverse pigment cup types with the medial portions of the sensory cells expanded to form a clear lens-like body. Peristomial parts include the median and ventral lips, the branchial membrane and the branchiae. The derivation of the nephridiopore is unknown. The spiraled branchiae of Coppingeria and the gill books of Diplocirrus are newly described variations in branchial structure. The head is retractable in some species and the anterior setigers are modified to form a protective setal cage. Two methods are employed for feeding: one for host fecal pellets and the other for detrital materials. Chemoreception, respiration, feeding and cleaning rely on a complex pattern of ciliary currents.     

The tympanal hearing organ of the parasitoid fly Ormia ochracea (Diptera, Tachinidae, Ormiini)

Tympanate hearing has evolved in at least 6 different orders of insects, but had not been reported until recently in the Diptera. This study presents a newly discovered tympanal hearing organ, in the parasitoid tachinid fly, Ormia ochracea. The hearing organ is described in terms of external and internal morphology, cellular organization of the sensory organ and preliminary neuroanatomy of the primary auditory afferents. The ear is located on the frontal face of the prothorax, directly behind the head capsule. Conspicuously visible are a pair of thin cuticular membranes specialized for audition, the prosternal tympanal membranes. Directly attached to these membranes, within the enlarged prosternal chamber, are a pair of auditory sensory organs, the bulbae acusticae. These sensory organs are unique among all auditory organs known so far because both are contained within an unpartitioned acoustic chamber. The prosternal chamber is connected to the outside by a pair of tracheae. The cellular anatomy of the fly's scolopophorous organ was investigated by light and electron microscopy. The bulba acustica is a typical chordotonal organ and it contains approximately 70 receptor cells. It is similar to other insect sensory organs associated with tympanal ears. The similarity of the cellular organization and tympanal morphology of the ormiine ear to the ears of other tympanate insects suggests that there are potent constraints in the design features of tympanal hearing organs, which must function to detect high frequency auditory signals over long distances. Each sensory organ is innervated by a branch of the frontal nerve of the fused thoracic ganglia. The primary auditory afferents project to each of the pro-, meso-, and metathoracic neuropils. The fly's hearing organ is sexually dimorphic, whereby the tympanal membranes are larger in females and the spiracles larger in males. The dimorphism presumably reflects differences in the acoustic behavior in the two sexes.     

Development of oral and branchial muscles in lancelet larvae of Branchiostoma japonicum

The perforated pharynx has generally been regarded as a shared characteristic of chordates. However, there still remains phylogenetic ambiguity between the cilia‐driven system in invertebrate chordates and the muscle‐driven system in vertebrates. Giant larvae of the genus Asymmetron were reported to develop an orobranchial musculature similar to that of vertebrates more than 100 years ago. This discovery might represent an evolutionary link for the chordate branchial system, but few investigations of the lancelet orobranchial musculature have been completed since. We studied staged larvae of a Japanese population of Branchiostoma japonicum to characterize the developmental property of the orobranchial musculature. The larval mouth and the unpaired primary gills develop well‐organized muscles. These muscles function only as obturators of the openings without antagonistic system. As the larval mouth enlarged posteriorly to the level of the ninth myomere, the oral musculature was fortified accordingly without segmental patterning. In contrast, the iterated branchial muscles coincided with the dorsal myomeric pattern before metamorphosis, but the pharynx was remodeled dynamically irrespective of the myomeric pattern during metamorphosis. The orobranchial musculature disappeared completely during metamorphosis, and adult muscles in the oral hood and velum, as well as on the pterygial coeloms developed independently. The lancelet orobranchial musculature is apparently a larval adaptation to prevent harmful intake. However, vestigial muscles appeared transiently with the secondary gill formation suggest a bilateral ancestral state of muscular gills, and a segmental pattern of developing branchial muscles without neural crest and placodal contributions is suggestive of a precursor of vertebrate branchiomeric pattern. J. Morphol. 275:465–477, 2014. © 2013 Wiley Periodicals, Inc.     

The fine structure of a cephalic sensory receptor in the copepod Doropygus seclusus Illg (Crustacea: Copepoda: Notodelphyidae)

A cephalic organ of presumed sensory function is described in nauplii and copepodids of the ascidicolous copepod Doropygus seclusus Illg. The receptor, located bilaterally in the anterodorsal head region, is composed of dendrites of extra optic protocerebral origin which have ciliary protrusions with basal bodies, no rootlets, and a basal infrastructure of the 9 + 0 type. The cilia do not branch and their distal terminations contain only one to four microtubules. In nauplii and free-living copepodids, a large epidermal supporting cell encapsulates the end of one dendrite and its cilia in a sac. Other dendrites and their cilia pass through the supporting cell and, terminally, the cilia escape to form a whorled fascicle which contacts the anterolateral cephalic cuticle. The latter end organ reaches its greatest development in the second copepodid stage — the stage which infects the ascidian. All of the symbiotic stages of the copepod have only a proportionately smaller end organ of the saccular type and apparently lack the end organ consisting of whorls of ciliary ends. The function of the receptor is unknown, but it is suggested that the end organ which disappears in the symbiotic stages functions in second copepodids in host recognition.     

Evolution and diversification of a sexually dimorphic luminescent system in ponyfishes (Teleostei: Leiognathidae), including diagnoses for two new genera

A phylogeny was generated for Leiognathidae, an assemblage of bioluminescent, Indo‐Pacific schooling fishes, using 6175 characters derived from seven mitochondrial genes (16S, COI, ND4, ND5, tRNA‐His, tRNA‐Ser, tRNA‐Leu), two nuclear genes (28S, histone H3), and 15 morphological transformations corresponding to features of the fishes' sexually dimorphic light‐organ system (LOS; e.g., circumesophageal light organ, lateral lining of the gas bladder, transparent flank and opercular patches). Leiognathidae comprises three genera, Gazza, Leiognathus, and Secutor. Our results demonstrate that Leiognathidae, Gazza, and Secutor are monophyletic, whereas Leiognathus is not. The recovered pattern of relationships reveals that a structurally complex, strongly sexually dimorphic and highly variable species‐specific light organ is derived from a comparatively simple non‐dimorphic structure, and that evolution of other sexually dimorphic internal and external features of the male LOS are closely linked with these light‐organ modifications. Our results demonstrate the utility of LOS features, both for recovering phylogeny and resolving taxonomic issues in a clade whose members otherwise exhibit little morphological variation. We diagnose two new leiognathid genera, Photopectoralis and Photoplagios, on the basis of these apomorphic LOS features and also present derived features of the LOS to diagnose several additional leiognathid clades, including Gazza and Secutor. Furthermore, we show that five distinct and highly specialized morphologies for male‐specific lateral luminescence signaling, which exhibit species‐specific variation in structure, have evolved in these otherwise outwardly conservative fishes. Leiognathids inhabit turbid coastal waters with poor visibility and are often captured in mixed assemblages of several species. We hypothesize that the species‐specific, sexually dimorphic internal and external modifications of the leiognathid LOS provide compelling evidence for an assortative mating scheme in which males use species‐specific patterns of lateral luminescence signaling to attract mates, and that this system functions to maintain reproductive isolation in these turbid coastal environments. © The Willi Hennig Society 2005.     

Control and Consequences of Alternative Developmental Modes in a Poecilogonous Polychaete

SYNOPSIS. The poecilogonous polychaete Streblospio benedicti(Webster) exhibits both planktotrophic and lecithotrophic modesof larval development. The alternative trophic modes are associatedwith differences in age and size at maturation, offspring number,size and energetic investment, larval planktonic period, morphologyand survivorship. This paper reviews a decade of research intothe control and consequences of the traits associated with planktotrophyand lecithotrophy in S. benedicti. The dominant control on reproductiveand developmental characters is genetic. Significant additivegenetic variance has been detected for egg diameter, fecundity,larval planktonic period and aspects of larval morphology. However,environmental factors such as temperature, food quality andphotoperiod, and intrinsic factors such as maternal age, exertconsiderable influence on non-trophic developmental traits (e.g.,offspring number, size and energy content). Demographic consequencesof development mode are reviewed for field and laboratory demesof S. benedicti dominated by individuals exhibiting either planktotrophyor lecithotrophy. Similar population size structure, fluctuationsin abundance, P: B ratios, and estimated population growth ratesare achieved through trade-offs between survivorship and fecundity. Development mode may best be viewed as a complex set of traitsthat are intimately linked developmentally and evolutionarilyto other aspects of an organism's life history. Greater insightinto the control and consequences of development mode shouldresult from further investigation of these linkages     

Junctional complexes of the branchia and gut of the tunicate,Pyrosoma atlanticum (Pyrosomatida,Thaliacea)

Summary The branchia of pyrosomes has been found to be like that of ascidians in that it shares with the latter, besides the presence of peribranchial chambers, stigmata bordered by clusters of seven rows of flattened cells, each bearing a single row of long cilia. The intercellular junctions between ciliated cells of the branchial basket and between the cells lining the gut, in pyrosomes, have been studied in thin sections and by freeze-fracture. In both tissues tight and gap junctions are present, but the former are much more extensive in the gut. The gap junctions in the branchial basket exhibit some atypical features. Moreover, although there are extensive zonulae adhaerentes between the ciliated cells of the branchial basket, there are none between the epithelial cells of the intestinal tract. This feature of the branchiae, together with the alignment of their cells into highly ordered rows of seven cells, are similar to those found in some groups of ascidians. The evolutionary relationships between pyrosomes and the aplousobranch ascidians are considered in the light of these results.     

Leagues of their own: sexually dimorphic features of meiotic prophase I

Meiosis is a conserved cell division process that is used by sexually reproducing organisms to generate haploid gametes. Males and females produce different end products of meiosis: eggs (females) and sperm (males). In addition, these unique end products demonstrate sex-specific differences that occur throughout meiosis to produce the final genetic material that is packaged into distinct gametes with unique extracellular morphologies and nuclear sizes. These sexually dimorphic features of meiosis include the meiotic chromosome architecture, in which both the lengths of the chromosomes and the requirement for specific meiotic axis proteins being different between the sexes. Moreover, these changes likely cause sex-specific changes in the recombination landscape with the sex that has the longer chromosomes usually obtaining more crossovers. Additionally, epigenetic regulation of meiosis may contribute to sexually dimorphic recombination landscapes. Here we explore the sexually dimorphic features of both the chromosome axis and crossing over for each stage of meiotic prophase I in Mus musculus, Caenorhabditis elegans, and Arabidopsis thaliana. Furthermore, we consider how sex-specific changes in the meiotic chromosome axes and the epigenetic landscape may function together to regulate crossing over in each sex, indicating that the mechanisms controlling crossing over may be different in oogenesis and spermatogenesis.

     

Distribution of Streblospio benedicti (Webster, 1879) and Manayunkia aestuarina (Bourne, 1883) (Annelida: Polychaeta) in the Vistula Lagoon of the Baltic Sea

The polychaetes Streblospio benedicti (Webster, 1879) and Manayunkia aestuarina (Bourne, 1883) have been recorded in the Vistula Lagoon of the Baltic Sea since the mid 1990s. The impact that salinity and the necrozooplankton (dead plankton) concentration in the near-bottom layer have on their distributional patterns was studied. The spatial distribution of these polychaetes depends on the water salinity; however, no correlation was found between their abundance and the necrozooplankton concentration. An area of high necrozooplankton concentration was defined for the near-bottom water layer in the central part of the lagoon; its position is mostly determined by the currents. We assume that the sustainable presence of S. benedicti and M. aestuarina is supported by their opportunistic species biology patterns and the lagoon hydrology, even in the last decade of unfavorable water mineralization conditions.     

Biological activity in the antarctic zooplankton community

Summary Zooplankton biomass and respiratory ETS activity were studied along a transect at 49°W, running from open Scotia Sea water (57°S) into the Weddell Sea pack ice (62°S) in November–December 1988. Zooplankton biomass and respiratory activity were relatively high in the ice edge region and in the frontal zone separating the Scotia Sea from waters in the south; low biomasses and activities were encountered under the pack ice. The higher activities in the frontal zone were mainly attributed to locally higher water temperatures, while in the ice edge region they were probably related to changes of the Zooplankton population into more active developmental stages. This development in life stages is possibly a response to ice edge generated phytoplankton blooms. A comparison of the most abundant Zooplankton taxa indicated that amphipods and euphausiids had relatively the highest weight specific ETS activities. The developmental stages of Euphausia superba, from juvenile to sexually mature adults, showed a large variability in ETS activity; only the most inactive stages were found under the pack ice. The difference in respiration between the most active and inactive stages was at least a factor of 6 and is of importance to the overwintering of the species in the under ice habitat.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation