Body size-dependent interspecific tolerance to cadmium and their molecular responses in the marine rotifer Brachionus spp

Although several studies have reported on different interspecific sensitivities in response to various toxicants, the response mechanisms are still poorly understood. Here, we investigate the interspecific toxicity of cadmium (Cd) and its mechanism using three marine rotifer Brachionus spp. that are distinguishable by body size, which is considered the most significant indicator of phenotypic difference. The body sizes of B. plicatilis, B. koreanus, and B. rotundiformis are significantly different throughout their life cycles (egg, neonate, and adult), with the smaller rotifer exhibiting higher sensitivity to Cd. To investigate the mechanisms that result in body size-dependent tolerance to Cd, metabolic and Cd bioaccumulation rates were investigated. Both rates have shown a significant correlation with body size, indicating that body size and its variables are important factors in determining Cd tolerance in Brachionus spp. In addition, similar patterns that further explain body size-dependent tolerance are shown in the phosphorylation status of mitogen-activated protein kinases, reactive oxygen species level, and antioxidant enzymatic activities. Our study provides valuable insight into size- and species-dependent toxicity mechanisms of species in the same genus.

Reverse taxonomy applied to the Brachionus calyciflorus cryptic species complex: Morphometric analysis confirms species delimitations revealed by molecular phylogenetic analysis and allows the (re)description of four species

The discovery and exploration of cryptic species have been profoundly expedited thanks to developments in molecular biology and phylogenetics. In this study, we apply a reverse taxonomy approach to the Brachionus calyciflorus species complex, a commonly studied freshwater monogonont rotifer. By combining phylogenetic, morphometric and morphological analyses, we confirm the existence of four cryptic species that have been recently suggested by a molecular study. Based on these results and according to an exhaustive review of the taxonomic literature, we name each of these four species and provide their taxonomic description alongside a diagnostic key.

Soft Bodies, Hard Jaws: An Introduction to the Symposium, with Rotifers as Models of Jaw Diversity

Jaws have evolved numerous times in the animal kingdom and they display a wide variety of structural, compositional, and functional characteristics that reflect their polyphyletic origins. Among soft-bodied invertebrates, jaws are known from annelids, chaetognaths, flatworms, gnathostomulids, micrognathozoans, mollusks, rotifers, and several ecdysozoans. Depending on the taxon, jaws may function in the capture of prey (e.g., chaetognaths and flatworms), processing of prey (e.g., gnathostomulids and onychophorans), or both (e.g., rotifers). Although structural diversity among invertebrates’ jaws is becoming better characterized with the use of electron microscopy, many details remain poorly described, including neuromuscular control, elemental composition, and physical characteristics, such as hardness and resistance to wear. Unfortunately, absence of relevant data has impeded understanding of their functional diversity and evolutionary origins. With this symposium, we bring together researchers of disparately jawed taxa to draw structural and mechanistic comparisons among species to determine their commonalities. Additionally, we show that rotifers’ jaws, which are perhaps the best-characterized jaws among invertebrates, are still enigmatic with regard to their origins and mechanics. Nevertheless, technologies such as energy dispersive X-ray spectroscopy (EDX) and 3D modeling are being used to characterize their chemical composition and to develop physical models that allow exploration of their mechanical properties, respectively. We predict that these methods can also be used to develop biomimetic and bioinspired constructs based on the full range of the complexity of jaws, and that such constructs also can be developed from other invertebrate taxa. These approaches may also shed light on common developmental and physiological processes that facilitate the evolution of invertebrates’ jaws.

Morphology and ultrastructure of the freshwater rotifer Brachionus bidentatus (Monogononta: Brachionidae) using scanning and transmission electron microscopy

The study of sexual reproductive behavior supported by ultrastructural evidence is important in rotifers to describe differences among potential cryptic species. In this research, the morphology of the rotifer Brachionus bidentatus is described at the ultrastructural level, using electronic microscopy, together with a brief description and discussion of its sexual reproductive behavior. The characteristics of the (a) male, (b) the female, (c) the sexual egg or cyst, (d) the partenogenic egg, (e) the no-fecundated sexual egg (male egg), and (f) the trophi, were described. Another part of this research is dedicated to the ultrastructure of the sex cells of the male rotifer B. bidentatus. Samples were obtained from La Punta pond in Cosio, Aguascalientes, Mexico (22 degrees 08' N - 102 degrees 24' W), and a culture was maintained in the laboratory. Fifty organisms, from different stages of the rotifer Brachionus bidentatus, were fixed in Formol at 4% and then prepared; besides, for the trophi, 25 female rotifer Brachionus bidentatus were prepared for observation in a JEOL 5900 LV scanning electronic microscope. In addition, for the observation of male sex cells, 500 males of Brachionus bidentatus were isolated, fixed and observed in a JEOL 1010 transmission microscope. Females of B. bidentatus in laboratory cultures had a lifespan of five days (mean+one SD = 4.69 +/- 0.48; N=13), and produced 4.5 +/- 3.67 (N=6) parthenogenetic eggs during such lifespan. In the case of non-fertilized sexual eggs, they produced up to 18 eggs (mean+one SD = 13 +/- 4.93; N=7). Sexual females produced a single cyst on average (mean +/- one SD = I +/- 0; N=20). For the sexual cycle, the time of copulation between male and female ranged from 10 to 40 seconds (mean +/- one SD = 17.33 +/- 10.55, N=7). The spermatozoa are composed of a celular body and a flagellum, the size of the body is of 300 nm while the flagellum measures 1 700nm. The rods have a double membrane. Their mean length is almost 2.45 microm +/- 0.74, N=6; and their mean wide is 0.773 microm +/- 0.241, N=11. The evidence on the specific ultrastructural characteristics of the rotifer B. bidentatus is notorious, even more in the male and in the cyst cell. Regarding the ultrastructure of the spermatozoa and the rods, compared to other species they only differ in size, despite their structural resemblance. Our study of the ultraestructure of this species adds useful information that along with molecular data will help clarify the taxonomy of brachionid rotifers.

Morphological, morphometrical and molecular (CO1 and ITS) analysis of the rotifer Asplanchna brightwellii from selected freshwater bodies in Central Mexico

We evaluated different strains of the rotifer Asplanchna brightwellii collected from central Mexico using morphology, morphometry and molecular tools (CO1 and ITS). Three distinct clonal populations from each of the 3 regions (Mexico City, State of Mexico and State of Guerrero) were established under laboratory conditions. For a given waterbody, morphometric comparisons within the populations of A. brightwellii showed almost stable measurements of trophi and with no statistically significant differences among them (p > 0.05). However, asplanchnid body length and width as well as the cyst diameter varied significantly depending on the waterbody from which A. brightwellii was collected. The smallest adults (about 700 microm) were from Valerio Trujano lake (Guerrero State) samples while the largest were from Xochimilco lake. Similar tendencies were reflected in the diameter of resting eggs. In addition, morphologically the cysts of A. brightwellii from the three waterbodies showed slightly different pattern. The number of globular structures on the surface of cysts was smaller for Valerio Trujano strain, while these were larger and less numerous for both Xochimilco and Zumpango strains. The ITS region tree displayed two groups Xochimilco and Valerio Trujano -Zumpango, this analysis did not reflect the morphological grouping; on the contrary the CO1 gene tree separated the populations according to morphological clusters and location (Xochimilco, Valerio Trujano and Zumpango lakes). When the tree was built using the combination of both ITS and CO1 sequences, the phylogenetic relationships observed on CO1 gene were consistent; but showed differences with the relationships observed on ITS region tree (only two groups).

[Effects of temperature on Keratella quadrata life table demography and morphometric characteristics]

By the method of individual culture, this paper studied the effects of temperature (10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C) on the life table demography (net reproductive rate, intrinsic rate of population increase, generation time, average lifespan, and proportion of mictic offspring) and the offspring morphometric characteristics (body length, body width, antero-median spine length, left and right antero-lateral spine lengths, left and right posterior-spine lengths, and posterior spine number) of two posterior-spined, single posterior-spined, and zero posterior-spined morphotypes of Keratella quadrata. All the test life table demographic parameters and offspring morphometric parameters differed with morphotype and temperature, and their responses to elevated temperature differed with morphotype. Temperature had significant effects on the intrinsic rate of population increase, generation time, average lifespan, and the offspring morphometric parameters (P < 0.05); morphotype had significant effects on the offspring body length, antero-median spine length, and left and right posterior-spine lengths (P < 0.05) but less effects on the life table demography (P > 0.05); and the interaction of temperature and morphotype had significant effects on the generation time and all the offspring morphometric parameters (P < 0.05). Among the three morphotypes, the two posterior-spined morphotype had shorter offspring body length (122.1+/- 0.6 microm) than the zero and single posterior-spined morphotypes (126.3 +/- 0.7 microm and 125.1 +/- 0.7 microm, respectively). The offspring antero-median spine length (32.5 +/- 0.3 microm) of the two posterior-spined morphotype was longer than that of the zero and single posterior-spined morphotypes (31.1 +/- 0.3 microm and 30.8 +/- 0.3 microm, respectively). The offspring left and right posterior-spine lengths of the two posterior-spined morphotype (31.2 +/- 1.0 microm and 32.3 +/- 0.9 microm, respectively) were similar to those of the single posterior-spined morphotype (29.5 +/-0.8 microm and 31.5 +/- 0.6 microm, respectively), but shorter than those of the zero posterior-spin ed morphotype (36.7 +/- 1.5 microm and 37.3 +/- 1.6 microm, respectively). The relationships between the offspring spine length, body width, and body length were also affected by temperature and morphotype.

[Architectonics of the central nervous system in Acoela, Plathelminthes, and Rotifera]

Based on the literature and own data, consecutive stages of development of the central nervous system (CNS) in the lower Bilateria are considered - separation of brain from parenchyma, formation of its own envelopes, and development of the stem and orthogonal nervous system. Results of histochemical (cholinergic and catecholaminergic) and immunocytochemical (5-HT- and FMRFamid immunoreactive) studies of the CNS in representatives of Acoela, free living and parasitizing Plathelminthes and Rotifera are considered. The comparative analysis makes it possible to describe development and complication of the initially primitive Bilateria plexus nervous system. A special attention will be paid to the Acoela phylogenesis, based on molecular-biology data and results of study of their nervous system.

Analysis of expressed sequence tags of the cyclically parthenogenetic rotifer Brachionus plicatilis

BACKGROUND

Rotifers are among the most common non-arthropod animals and are the most experimentally tractable members of the basal assemblage of metazoan phyla known as Gnathifera. The monogonont rotifer Brachionus plicatilis is a developing model system for ecotoxicology, aquatic ecology, cryptic speciation, and the evolution of sex, and is an important food source for finfish aquaculture. However, basic knowledge of the genome and transcriptome of any rotifer species has been lacking.

METHODOLOGY/PRINCIPAL FINDINGS

We generated and partially sequenced a cDNA library from B. plicatilis and constructed a database of over 2300 expressed sequence tags corresponding to more than 450 transcripts. About 20% of the transcripts had no significant similarity to database sequences by BLAST; most of these contained open reading frames of significant length but few had recognized Pfam motifs. Sixteen transcripts accounted for 25% of the ESTs; four of these had no significant similarity to BLAST or Pfam databases. Putative up- and downstream untranslated regions are relatively short and AT rich. In contrast to bdelloid rotifers, there was no evidence of a conserved trans-spliced leader sequence among the transcripts and most genes were single-copy.

CONCLUSIONS/SIGNIFICANCE

Despite the small size of this EST project it revealed several important features of the rotifer transcriptome and of individual monogonont genes. Because there is little genomic data for Gnathifera, the transcripts we found with no known function may represent genes that are species-, class-, phylum- or even superphylum-specific; the fact that some are among the most highly expressed indicates their importance. The absence of trans-spliced leader exons in this monogonont species contrasts with their abundance in bdelloid rotifers and indicates that the presence of this phenomenon can vary at the subphylum level. Our EST database provides a relatively large quantity of transcript-level data for B. plicatilis, and more generally of rotifers and other gnathiferan phyla, and can be browsed and searched at gmod.mbl.edu.

An analysis of species boundaries and biogeographic patterns in a cryptic species complex: The rotifer—Brachionus plicatilis

Since the advent of molecular phylogenetics, there is increasing evidence that many small aquatic and marine invertebrates--once believed to be single, cosmopolitan species--are in fact cryptic species complexes. Although the application of the biological species concept is central to the identification of species boundaries in these cryptic complexes, tests of reproductive isolation do not frequently accompany phylogenetic studies. Because different species concepts generally identify different boundaries in cryptic complexes, studies that apply multiple species concepts are needed to gain a more detailed understanding of patterns of diversification in these taxa. Here we explore different methods of empirically delimiting species boundaries in the salt water rotifer Brachionus plicatilis by comparing reproductive data (i.e., the traditional biological species concept) to phylogenetic data (the genealogical species concept). Based on a high degree of molecular sequence divergence and largely concordant genetic patterns in COI and ITS1, the genealogical species hypothesis indicates the existence of at least 14 species--the highest estimate for the group thus far. A test of the genealogical species concept with biological crosses shows a fairly high level of concordance, depending on the degree of reproductive success used to draw boundaries. The convergence of species concepts in this group suggests that many of the species within the group may be old. Although the diversity of the group is higher than previously understood, geographic distributions remain broad. Efficient passive dispersal has resulted in global distributions for many species with some evidence of isolation by distance over large geographic scales. These patterns concur with expectations that micro-meiofauna (0.1-1mm) have biogeographies intermediate to microbial organisms and large vertebrates. Sympatry of genetically distant strains is common.

A modern approach to rotiferan phylogeny: combining morphological and molecular data

The phylogeny of selected members of the phylum Rotifera is examined based on analyses under parsimony direct optimization and Bayesian inference of phylogeny. Species of the higher metazoan lineages Acanthocephala, Micrognathozoa, Cycliophora, and potential outgroups are included to test rotiferan monophyly. The data include 74 morphological characters combined with DNA sequence data from four molecular loci, including the nuclear 18S rRNA, 28S rRNA, histone H3, and the mitochondrial cytochrome c oxidase subunit I. The combined molecular and total evidence analyses support the inclusion of Acanthocephala as a rotiferan ingroup, but do not support the inclusion of Micrognathozoa and Cycliophora. Within Rotifera, the monophyletic Monogononta is sister group to a clade consisting of Acanthocephala, Seisonidea, and Bdelloidea-for which we propose the name Hemirotifera. We also formally propose the inclusion of Acanthocephala within Rotifera, but maintaining the name Rotifera for the new expanded phylum. Within Monogononta, Gnesiotrocha and Ploima are also supported by the data. The relationships within Ploima remain unstable to parameter variation or to the method of phylogeny reconstruction and poorly supported, and the analyses showed that monophyly was questionable for the families Dicranophoridae, Notommatidae, and Brachionidae, and for the genus Proales. Otherwise, monophyly was generally supported for the represented ploimid families and genera.

Postembryonic development of hard jaws (trophi) in a species belonging to theBrachionus plicatilis complex (Rotifera, Monogononta): A morphometric analysis

The presence of hard jaws (trophi), with species-specific shape and size, is a taxonomic feature of Rotifera, a group of microscopic metazoans. Since trophi are used to discriminate among species, it is important to know whether these structures change in taxonomically important ways during postembryonic development. Using both SEM and optical images, we analyzed more than 100 individuals of a single clonal lineage of a monogonont rotifer, Brachionus plicatilis, in order to describe body and trophi development after hatching. Body size, expressed as lorica width and length, was isometrically related to age of the animals only during preadult stages. Trophi size, expressed as length of the different parts, was unrelated to either age or body size. Therefore, trophi elements do not grow after hatching in B. plicatilis. Despite the dimensional invariance with age, some differences in trophi size among individuals of the same clone were recorded. No difference in left-right asymmetry of the trophi was shown; the asymmetric elements of the trophi named rami consistently had the right ramus longer than the left. This constancy is in contrast to the reported trophi asymmetries in bdelloid rotifers, in which left-right asymmetries are not constant within clonal lineages. In conclusion, we suggest that also trophi size, constant within the analyzed clone, may be used as an additional taxonomic feature to help in the discrimination of taxa within the B. plicatilis complex of cryptic species.

[Comparative studies on individual growth and development of three Brachionus angularis strains]

The embryonic developmental period (De), pre-reproductive period (Dp), the least generation time (Tg), body size of juveniles and adults, egg volume and relative egg volume of three strain Brachionus angularis from Qingdao, Guangzhou and Wuhu were studied with Scenedesmus obliquus at 2.4 x 10(6) cells.ml-1 as the rotifers' food at 25 degrees C. We found that there were significantly different in De, Dp and Tg of three strains. De of WH strain was the top, and subsequently was GZ strain and QD strain. QD strain had the longest Dp, but GZ strain had the shortest. Tg in GZ strain was the shortest, and QD strain, and WH strain were longer, respectively, but no significantly difference existed in the later two. De tended to decrease as the relative egg volume increased in the three strains. Body size at the same stage in pre-reproductive period of three strains was significantly different. WH strain had the largest body size during all of the stages. The relationships between body size and the age of the juvenile of QD, GZ and WH strain were all curvilinear. The variance of the neonates and the adults was 244.24% in WH strain, and 182.89%, 156.28% in QD and GZ strain, respectively. The adults' body size, egg size, and relative egg size was significantly different in three strains.

Dwarf male of Symbion pandora (cycliophora)

This study clarifies the identity and development of the male in the life cycle of Symbion pandora. The male is not produced directly by the feeding stage, as previously thought, but arises as a distinct individual from budding cells inside an intermediate stage named the Prometheus larva. The morphology and the development of the two distinct stages are described with light and electron microscopy. Furthermore, the following terminology is suggested to clearly distinguish between the different individuals: 1) the Prometheus larva, which is the free-swimming individual being produced inside the feeding stage; 2) the attached Prometheus larva on the feeding stage, which mostly degenerates following settlement, except for the internal budding cells; and 3) the dwarf male, which is the ciliated, sexually mature stage. The budding cells inside the attached Prometheus larva usually develop two internal dwarf males. Each dwarf male is heavily ciliated and has a well-developed nervous system with a relatively large brain, numerous gland and muscle cells, testis with bundles of sperm, and one penial structure. The male lacks a gut, as in the other free stages in the life cycle of Symbion pandora. This study also indicates that the dwarf male is freed from the attached Prometheus larva. Copulation, which has not been observed yet, probably takes place between a free-swimming male and the female, either while the female is released or afterwards.

[Phenomenon of obligate parthenogenesis in rotifer (Rotifera, Bdelloida)]

A comparative analysis of biological and morphological organization of obligate parthenogenous bdelloids and heterogonic monogononts clarifies the specificity of bdelloids' environmental adaptation and variability. It is shown that phenotypic polymorphism of bdelloids differs from that of monogononts. The heterogonic Monogononta are characterized by tremendous phenotypic diversity in body structure adapted to different biotopes in continental waters. This diversity is reflected also in structure of corona and mastax used as major criteria for definition of high range taxa (classes, orders). The polymorphism of bdelloids manifests itself in variability of tiny morphological structures connected with living in restricted volumes of water, mainly in terrestrial biotopes. Being isolated from other Rotifera at the first stages of evolution, bdelloids have been specialized for living under extremely unstable terrestrial conditions that led to the development of anhydrobiosis and loss of amphimixis. Variability of bdelloids is not connected with characters of high taxonomic ranks and has principally different nature in comparison with monogononts. Tempo of specialization seems to be slower in obligate parthenogenous rotifers than in heterogonic ones.

Micrognathozoa: a new class with complicated jaws like those of Rotifera and Gnathostomulida

A new microscopic aschelminth-like animal, Limnognathia maerski nov. gen. et sp., is described from a cold spring at Disko Island, West Greenland, and assigned to Micrognathozoa nov. class. It has a complex of jaws in its pharynx, and the ultrastructure of the main jaws is similar to that of the jaws of advanced scleroperalian gnathostomulids. However, other jaw elements appear also to have characteristics of the trophi of Rotifera. Jaw-like structures are found in other protostome taxa as well-for instance, in proboscises of kalyptorhynch platyhelminths, in dorvilleid polychaetes and aplacophoran mollusks-but studies of their ultrastructure show that none of these jaws is homologous with jaws found in Gnathostomulida, Rotifera, and Micrognathozoa. The latter three groups have recently been joined into the monophylum Gnathifera Ahlrichs, 1995, an interpretation supported by the presence of jaw elements with cuticular rods with osmiophilic cores in all three groups. Such tubular structures are found in the fulcrum of all Rotifera and in several cuticular sclerites of both Gnathostomulida and Micrognathozoa. The gross morphology of the pharyngeal apparatus is similar in the three groups. It consists of a ventral pharyngeal bulb and a dorsal pharyngeal lumen. The absence of pharyngeal ciliation cannot be used as an autapomorphy in the ground pattern of the Gnathifera because the Micrognathozoa has the plesiomorphic alternative with a ciliated pharyngeal epithelium. The body of Limnognathia maerski nov. gen. et sp. consists of a head, thorax, and abdomen. The dorsal and lateral epidermis have plates formed by an intracellular matrix, as in Rotifera and Acanthocephala; however, the epidermis is not syncytial. The ventral epidermis lacks internal plates, but has a cuticular oral plate without ciliary structures. Two ventral rows of multiciliated cells form a locomotory organ. These ciliated cells resemble the ciliophores present in some interstitial annelids. An adhesive ciliated pad is located ventrally close to a caudal plate. As in many marine interstitial animals-e.g., gnathostomulids, gastrotrichs, and polychaetes-a special form of tactile bristles or sensoria is found on the body. Two pairs of protonephridia with unicellular terminal cells are found in the trunk; this unicellular condition may be the plesiomorphic condition in Bilateria. Only specimens with the female reproductive system have been found, indicating that all adult animals are parthenogenetic females. We suggest that 1) jaws of Gnathostomulida, Rotifera, and the new taxon, Micrognathozoa, are homologous structures; 2) Rotifera (including Acanthocephala) and the new group might be sister groups, while Gnathostomulida could be the sister-group to this assemblage; and 3) the similarities to certain gastrotrichs and interstitial polychaetes are convergent.

Micrognathozoa: a new class with complicated jaws like those of Rotifera and Gnathostomulida

A new microscopic aschelminth-like animal, Limnognathia maerski nov. gen. et sp., is described from a cold spring at Disko Island, West Greenland, and assigned to Micrognathozoa nov. class. It has a complex of jaws in its pharynx, and the ultrastructure of the main jaws is similar to that of the jaws of advanced scleroperalian gnathostomulids. However, other jaw elements appear also to have characteristics of the trophi of Rotifera. Jaw-like structures are found in other protostome taxa as well-for instance, in proboscises of kalyptorhynch platyhelminths, in dorvilleid polychaetes and aplacophoran mollusks-but studies of their ultrastructure show that none of these jaws is homologous with jaws found in Gnathostomulida, Rotifera, and Micrognathozoa. The latter three groups have recently been joined into the monophylum Gnathifera Ahlrichs, 1995, an interpretation supported by the presence of jaw elements with cuticular rods with osmiophilic cores in all three groups. Such tubular structures are found in the fulcrum of all Rotifera and in several cuticular sclerites of both Gnathostomulida and Micrognathozoa. The gross morphology of the pharyngeal apparatus is similar in the three groups. It consists of a ventral pharyngeal bulb and a dorsal pharyngeal lumen. The absence of pharyngeal ciliation cannot be used as an autapomorphy in the ground pattern of the Gnathifera because the Micrognathozoa has the plesiomorphic alternative with a ciliated pharyngeal epithelium. The body of Limnognathia maerski nov. gen. et sp. consists of a head, thorax, and abdomen. The dorsal and lateral epidermis have plates formed by an intracellular matrix, as in Rotifera and Acanthocephala; however, the epidermis is not syncytial. The ventral epidermis lacks internal plates, but has a cuticular oral plate without ciliary structures. Two ventral rows of multiciliated cells form a locomotory organ. These ciliated cells resemble the ciliophores present in some interstitial annelids. An adhesive ciliated pad is located ventrally close to a caudal plate. As in many marine interstitial animals-e.g., gnathostomulids, gastrotrichs, and polychaetes-a special form of tactile bristles or sensoria is found on the body. Two pairs of protonephridia with unicellular terminal cells are found in the trunk; this unicellular condition may be the plesiomorphic condition in Bilateria. Only specimens with the female reproductive system have been found, indicating that all adult animals are parthenogenetic females. We suggest that 1) jaws of Gnathostomulida, Rotifera, and the new taxon, Micrognathozoa, are homologous structures; 2) Rotifera (including Acanthocephala) and the new group might be sister groups, while Gnathostomulida could be the sister-group to this assemblage; and 3) the similarities to certain gastrotrichs and interstitial polychaetes are convergent.

Histofluorescent labelling of catecholaminergic structures in rotifers (Aschelminthes). II. Males of Brachionus plicatilis and structures from sectioned females

1. Catecholaminergic structures in the male Brachionus plicatilis were investigated, using aqueous dansylpropranolol as fluorescent label of neurotransmitter receptors. 2. All major organs of the male are innervated by catecholaminergic systems, that may also be involved in the regulation of copulatory behavior. 3. Cryostat-sectioned preparations of the female B. plicatilis were also investigated. They provided additional information to findings on whole animals reported in our previous paper (Keshmirian and Nogrady 1987 a).

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

Cholinesterase activity has been investigated in Rotifera Bdelloidea (Philodina roseola, Philodina tubercolata, Rotaria rotatoria and other unidentified species) by histochemical methods and in vivo observations. Parallel histological studies have been carried out. The enzyme specificity was tested by employing different substrates and inhibitors. The effects in 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 effects in 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.

Correlations between ultrastructural features and contraction rates in rotiferan muscle. I. Preliminary observations on longitudinal retractor muscles in Trichocerca rattus

The Rotifer Trichocerca rattus has striated longitudinal retractor muscles. These muscles can be divided into two categories: 1. The central and ventral retractor muscles which, after fixation, are found in a supercontracted state: they probably contract very quickly. 2. The lateral retractor muscles which are in a relaxed state after fixation. However, if the animal is mechanically stimulated before fixation, these are also fixed in a contracted state: so, normally, these muscles probably contract more slowly than the first category. In the relaxed state, thin myofilaments of the lateral retractor muscles are folded at the I band level; this a consequence of their compression provoked by the contraction of central and ventral retractor muscles. In muscles of the first type, the thick myofilaments are shorter (less than 2 mu) than in the second type (2.5 mu).

Sex-specific cannibalism in the rotifer Asplanchna sieboldi

In one clone, large-morphotype females rarely exhibit tactile feeding responses to their ingestible, male clonemates but readily attack small-morphotype female clonemates and males of another, taxonomically distinct, clone. In the latter clone, cannibal females lack such selectivity, but their males are well protected from capture by very large, lateral body-wall outgrowths.