Functional morphology of the muscles in Philodina sp. (Rotifera: Bdelloidea)

Whole-mounts of Philodina sp., a bdelloid rotifer, were stained with fluorescent-labeled phalloidin to visualize the musculature. Several different muscle types were identified including incomplete circular bands, coronal retractors and foot retractors. Based on the position of the larger muscle bands in the body wall, their function during creeping locomotion and tun formation was inferred. Bdelloid creeping begins with the contraction of incomplete circular muscle bands against the hydrostatic pseudocoel, resulting in an anterior elongation of the body. One or more sets of ventral longitudinal muscles then contract bringing the rostrum into contact with the substrate, where it presumably attaches via adhesive glands. Different sets of ventral longitudinal muscles, foot and trunk retractors, function to pull the body forward. These same longitudinal muscle sets are also used in `tun' formation, in which the head and foot are withdrawn into the body. Three sets of longitudinal muscles supply the head region (anterior head segments) and function in withdrawal of the corona and rostrum. Two additional pairs of longitudinal muscles function to retract the anterior trunk segments immediately behind the head, and approximately five sets of longitudinal retractors are involved in the withdrawal of the foot and posterior toes. To achieve a greater understanding of rotifer behavior, it is important to elucidate the structural complexity of body wall muscles in rotifers. The utility of fluorescently-labeled phalloidin for the visualization of these muscles is discussed and placed in the context of rotifer functional morphology.     

Oogenesis in Macrotrachela quadricornifera (Rotifera,Bdelloidea)

Bdelloids reproduce via obligate apomictic parthenogenesis. Oogenesis occurs through two subsequent equational divisions, with the extrusion of two polar bodies. Although the morphology of the bdelloid reproductive apparatus has been previously described, the eutely of the germarium has never been investigated. We studied oogenesis in Macrotrachela quadricornifera by assessing: (1) the constancy of oocyte number, (2) chromosome number and size, and (3) the DNA content of oocytes and blastomeres. Oocyte number at birth is constant and determines maximal fertility. We found a chromosome number of 5, in which two homologous pairs can be recognized. The genome size of the species is 0.75 picograms.     

The Philodinavidae (Rotifera Bdelloidea): a special family

Here we focus on the fine morphology and present observations on the biology of representatives of family Philodinavidae. Philodinavus paradoxus and Henoceros falcatus were collected and cultured under laboratory conditions. Rotifers of both species are tiny, about 200 μm long, have protrudable trophi and creep with leech-like movements. A very specific feature of these rotifers is their corona; a V-shaped lower lip contours the mouth opening, bilaterally bordered by two arched cuticular structures (‘cheeks’). The presence of the cheeks is a feature shared by the third genus, Abrochtha. On the basis of the morphology and biology of the three genera, we advance the hypothesis that Philodinavus is a primitive bdelloid, and that it can have originated Henoceros and Abrochtha, from which the other bdelloids could have stemmed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Comparison of five strains of a parthenogenetic species,Macrotrachela quadricornifera (Rotifera,Bdelloidea)

Five clonal populations belonging to the parthenogenetic species Macrotrachela quadricornifera were analyzed electrophoretically. The populations stemmed from samples collected from different environments paired geographically: water bodies (C, P, F) and terrestrial mosses (Ml, M2). The six enzymes considered were: leucine amino peptidase (LAP), arginine phosphokinase (APK), glucose phosphate isomerase (PGI), and esterases (EST) and malic enzyme (ME). The results are interpreted under the assumption that bdelloid rotifers have a diploid chromosome set. A genetic interpretation of the banding patterns was attempted. A relatively high degree of enzymatic polymorphism among the strains was found. Only 27% of alleles are shared by all strains. The relationship among the strains was examined by single-link cluster analysis: we can distinguish moss and water populations, regardless of their geographic origins, and in accord with the results of a life-history traits study on the same strains. The differences in life-history parameters among the five strains may be due not only to phenotypic plasticity induced by the environment, but to real genetic divergence.     

Rotifer neuropharmacology--I. Cholinergic drug effects on oviposition of Philodina acuticornis (Rotifera, Aschelminthes)

The presence of acetylcholine in the culture medium was found to result in egg retention in the bdelloid rotifer Philodina acuticornis in a dose-dependent fashion, with no other discernible physiological effect. When six to eight eggs accumulate, the animals distend, burst and die. No other cholinergic agonist has been shown to produce a similar effect. The antagonistic effect of six anticholinergic drugs and five acetylcholinesterase-inhibitor insecticides was investigated on egg retention. All compounds were found to inhibit this phenomenon to varying degrees, but on the basis of their EC50 neuromuscular blockers appear to be most active in inhibiting egg retention. We suggest, therefore, that egg retention is caused by a spasm or increased tone of the cloacal sphincter rather than a paralysis of muscles needed in the peristaltic expulsion of the egg. Five acetylcholine-esterase inhibitory insecticides also inhibit egg retention.     

Bdelloid Rotifers (Rotifera, Bdelloidea) as a Component of Soil and Land Biocenoses

Morphological, physiological, and ecological adaptations of bdelloid rotifers (phylum Rotifera, class Bdelloidea) to the conditions of soil and land biocenoses are described. The morphological structures, obligate parthenogenesis, and anhydrobiosis allowed these rotifers to colonize various semiaquatic areas with sharp fluctuations of environmental conditions: the edaphon, coniferous and deciduous litters, mosses, and lichens. The role of bdelloid rotifers in the food web and environmental indication is noted. Controversial problems concerning the origin of this group of worms are considered.     

Fine structure of the accessory glands of the female genital tract of the ichneumonid Pimpla turionellae (Insecta,Hymenoptera)

Summary The female accessory glands include the tubular poison gland, the paired, lemon-shaped uterus glands, and Dufour's gland, an unbranched tubular organ. They consist essentially of a single layer of epithelium cells surrounded by a basement membrane. The lumen is lined by cuticle. The proteinaceous secretion of the poison gland is released into intracellular ducts provided with microvilli, each connected to a channel lined with cuticle which leads to the central lumen of the gland. The channel is formed by special canal cells. Nerve endings are interspersed among the gland cells. The uterus gland consists of four cell types derived from a single type of precursor cell found in newly hatched wasps. Type I cells are covered by type II cells and are thus without contact to the luminal surface of the gland. They contain stacks or whorls of mitochondria and smooth cisternae in an alternating arrangement. Vesicles with a secretory product are found in cells of types II and III. Deep anastomosing infoldings of the plasmalemma, stabilized by microtubules and dense material at the branchings, are characteristic for type II cells. Most secretory vesicles are found in type III cells, the prevalent cell type which is thought to be the source of the lipoprotein secretion. Coated vesicles are present at deep infoldings of the plasmalemma. The greatly enlarged apical surface area of type IV cells and the presence of mitochondria in slender outgrowths is suggestive of an osmoregulatory function. In Dufour's gland, two cell types appear in succession, the first with a very dense cytoplasm, the second with dense inclusions and many seemingly empty vesicles of smooth endoplasmic reticulum. The secretion products, lecithin and a cholesterol ester, are thought to be formed by the second cell type. The dense inclusion might be lecithin, which reacts with osmium tetroxide. The cholesterol ester could have been washed out of the empty vesicles by the embedding procedure.     

Life histories of some species of Rotifera Bdelloidea

Nine species of Rotifera Bdelloidea have been cultured under laboratory conditions. The species were collected from two different environments: one group from water courses, the other from terrestrial mosses. Life tables have been determined and population dynamics parameters have been calculated. The characteristics of the life history seem to be related to the natural environmental conditions of the species. The patterns of reproductive output may develop as adaptations to different selective pressures: species from unpredictable environments face the probability of leaving no young at all, while species from stable environments are less conservative in their energy budget. Life characteristics are discussed from the point of view of adaptive strategies.     

Macrotrachela quadricornifera (Rotifera, Bdelloidea); a SEM Study on Active and Cryptobiotic Animals

The general morphology of Macrotrachela quadricornifera Milne, 1886 in the active and cryptobiotic states is analyzed under the scanning electron microscope. Some foot peculiarities not previously observed are reported, in particular the canaliculated spurs and presence of a sort of groove on the toes. The integument of active animals is perforated with pores and is micro-sculptured in the trunk region. During cryptobiosis, the animal is contracted, its toot and head being retracted into the trunk: the same microsculpture of the trunk integument is observed.     

Spatial distribution and population dynamics of a benthic rotifer, Embata laticeps (Murray) (Rotifera, Bdelloidea) in the bed sediments of a gravel brook

• 1 The spatial and temporal distributions of the most abundant bdelloid rotifer, Embata laticeps (Murray), inhabiting the sediment surface and the hyporheic interstitial of a gravel stream were investigated between October 1991 and October 1992. Three temporal peaks of population density occurred during the year at the sediment surface differing in their riming from the density peaks detected within the bed sediments.
• 2 The depth distributions of E. laticeps in pool and riffle areas differed significantly. Higher abundances were found between 10 and 20 cm depth in the pool and between 20 and 30 cm in the riffle area. In these two sites a significant effect of surface discharge (estimated 1 week before sampling) on rotifer densities was found. Discharge greater than 0.424 m³s^?1 significantly reduced the densities in the riffle, while only at values greater than 1.660m³s^?1 were abundances influenced in the pool area.
• 3 The percentages of egg-bearing females were higher within the bed sediment than in the surface layer, and in the pool area than in the riffle. Thus, overall mean values of population increase were higher in the pool habitat (x?= 0.015 ± SE 0.029 day^?1) than in the riffle and at the sediment surface (x?= 0.004 ± 0.025 and 0.005 ± 0.026 day^?1, respectively). In addition, population growth fluctuated more strongly at the sediment surface than within the hyporheic intersiritial. Comparison of the observed values of population increase with a randomization test, where observed densities were randomly permuted, revealed no significant differences between those observed and values from a random model. Thus, a clear trend in population growth of E. laticeps over time could not be demonstrated in this gravel stream.

     

Histochemical investigations of Rotifera Bdelloidea. I. Localization of cholinesterase activity

Summary Cholinesterase activity has been investigated in Rotifera Bdelloidea (Philodina roseola, Philodina tubercolata, Rotaria rotatoria and other unidentified species) by histochemical methods andin vivo observations. Parallel histological studies have been carried out. The enzyme specificity was tested by employing different substrates and inhibitors. The effectsin vivo of tubocurarin, bungarotoxin and acetylcholine were also observed. Acetylcholinesterase activity is localized in the nervous and muscular tissues, in sensory organs and in all the ciliated cells. Secretory cells (subcerebral, salivary and pedal glands) and gonad cells (nuclei of the syncytial vitellarium and follicular layer, oocytes and eggs) show both acetyl-and butyrylcholinesterase activities. The effectsin vivo of cholinesterase inhibitors, as well as those of tubocurarin, bungarotoxin and acetylcholine, are consistent with the histochemical results, indicating a cholinergic system of transmission and acetylcholinesterase, as well as butyrylcholinesterase, activity.This paper is dedicated to my master, the late Professor António Minganti.     

Fine structure of the Nassonow's gland in the neotenic endoparasitic of female Xenos vesparum (Rossi) (Strepsiptera, Insecta)

Nassonow's gland consists of a number of cells with ducts that open on to the ventral surface of the brood canal in the cephalothoracic region of a neotenic female strepsipteran. The structural organization of the gland is reminiscent of the class 3 of the epidermal gland cells as defined by Noirot and Quennedey [Ann. Rev. Entomol. 19 (1974) 61], which consists of secretory and duct forming cells. The ultrastructure of the Nassonow's gland is described in female Xenos vesparum (Rossi) parasitic in the social wasp Polistes dominulus Christ. The large secretory cells are clustered in groups of three to four, rich in smooth endoplasmic reticulum and produce a secretion made up of lipids. In young females, just before mating, the ultrastructure of the cells and their inclusions indicate that they are active. In old-mated females the Nassonow's gland degenerates. Microvilli line an extracellular cavity and there are pores present in the irregularly thick cuticle of the efferent duct. The small duct forming cells, intermingle with epidermal cells, overlap secretory cells and produce a long efferent duct, the cuticle of which becomes thick close to its opening in the brood canal. Nassonow's gland could be the source of a sex pheromone, which might be capable of attracting the free-living male to a permanently endoparasitic female.     

Motricity of the female genital apparatus in mammals. Hormonal correlations]

The motility and the pharmacological reactivity of the uterine tract of mammals are linked with the ovarian cycle and the gestation. In the birds, the study of general scheme of the hormonal mechanism and the uterine motility involued in the ovulation, the egg formation and the uterine dilatation can be used as an experimental model of the mammalian gestation.     

A novel adhering junction in the apical ciliary apparatus of the rotifer Brachionus plicatilis (Rotifera, Monogononta)

Cultures of the rotifer Brachionus plicatilis were examined with regard to their interepithelial junctions after infiltration with the extracellular tracer lanthanum, freeze-fracturing or quick-freeze deepetching. The lateral borders between ciliated cells have an unusual apical adhering junction. This apical part of their intercellular cleft looks desmosome-like, but it is characterized by unusual intramembranous E-face clusters of particles. Deep-etching reveals that these are packed together in short rows which lie parallel to one another in orderly arrays. The true membrane surface in these areas features filaments in the form of short ribbons; these are produced by projections, possibly part of the glycocalyx, emerging from the membranes, between which the electron-dense tracer lanthanum permeates. These projections appear to overlap with each other in the centre of the intercellular cleft; this would provide a particularly flexible adaptation to maintain cell-cell contact and coordination as a consequence. The filamentous ribbons may be held in position by the intramembranous particle arrays since both have a similar size and distribution. These contacts are quite different from desmosomes and appear to represent a distinct new category of adhesive cell-cell junction. Beneath these novel structures, conventional pleated septate junctions are found, exhibiting the undulating intercellular ribbons typical of this junctional type, as well as the usual parallel alignments of intramembranous rows of EF grooves and PF particles. Below these are found gap junctions as close-packed plaques of intramembranous particles on either the P-face or E-face. After freeze-fracturing, the complementary fracture face to the particles shows pits, usually on the P-face, arrayed with a very precise hexagonal pattern.     

Fine structure of the fat body in the female tickOrnithodoros (Pavlovskyella) erraticus (Ixodoidea: Argasidae)

The fat body in femalOrnithodoros (Pavlovskyella) erraticus Lucas consists of cell strands slung in the haemolymph but abundant around the tracheal trunks, midgut and reproductive system. The narrow cisternae of rough endoplasmic reticulum (RER) occupying most of the cell cytoplasm develop rapidly after feeding and become responsible for the formation of lipid droplets associated with glycogen particles. During oogenesis, RER and Golgi bodies are involved in protein synthesis which could be related to vitellogenesis. No ultrastructural investigations appear to have been made on the fat body in argasid ticks.     

Fine structure of the female reproductive system in a viviparous insect, Glossina morsitans morsitans (Diptera, Glossinidae)

The female reproductive system of the tsetse fly Glossina morsitans morsitans is analysed by scanning electron microscopy (SEM). The study focuses in particular on the choriothete, a peculiar uterine structure involved in the viviparous mode of reproduction of Glossina morsitans morsitans.Under light microscopy, the choriothete appears formed by numerous tongue-like folds projecting towards the uterine lumen and lined by a thin cuticle. SEM analysis highlights for the first time a distinctive new feature that is not visible by traditional histological methods. That is a cuticular covering of the choriothete, which shows numerous thorns in the form of crest-like structures arranged in nearly parallel lines. The role of the choriothete in pregnancy and in larval nourishment is discussed.