Ultrastructural observations on gastrodermal regeneration in the planarian Dugesia japonica (Turbellaria)

The earliest detectable change during regeneration of the gastrodermis in Dugesia japonica was an aggregation of regenerative cells underneath the gastrodermis remaining at the wound margin. The gastrodermal cells in experimental regenerates retained some of their original characters and presented no indication of cell dedifferentiation. The regenerative cells came into contact with the basal surface of gastrodermal cells, forming stratified cell layers. Differentiation of these cells into gastrodermal cells was initiated by the development of synthetic organelles within their cytoplasm. These differentiating cells gave rise to two different types of gastrodermal cells, namely phagocytic cells and sphere cells. In later stages, there was an apparent movement of differentiated gastrodermal cells towards the parenchyma.     

On the taxonomic status of a Dugesia species from Buenos Aires (Platyhelminthes: Turbellaria: Tricladida)

The taxonomic and distributional statuses of the freshwater planarians of South America are imperfectly understood, and a comprehensive review is sorely needed. The species known from the vicinity of Buenos Aires, Argentina, was first described by Böhmig (1902) under the name Planaria dubia Borelli, 1895. Subsequent authors (Kenk, 1930, 1974; Cazzaniga & Curino, 1987) have cast doubt on this assignation. Some have assigned it to Dugesia anceps Kenk; Hyman (1959) was inclined to regard the Buenos Aires planarian as a geographical variant of Dugesia sanchezi Hyman. A comparison of D. sanchezi from the mountainous region of central Chile with specimens from Buenos Aires confirms that the Argentinian material is a distinct species.The differences between the two species are subtle. The Argentinian specimens are distinctive in their possession of infranucleate epithelia of the atria, penis, and bursal canal, as well as in their penial structure. In both species, the epithelia of the atria and bursal canal are glandular. Those of D. sanchezi are nucleate and their secretions are cyanophilous. In the Argentinian specimens, these same epithelia are infranucleate; but while the secretion of the bursal canal is indeed cyanophilous, that of the atrium is erythrophilous. The presence, in these same specimens, of cyanophilous glands opening into the penial vesicles, and of erythrophilous glands whose secretions contribute to a viscous plug in the ejaculatory duct, suggests a difference in the physiology of copulation.It is apparent that the Argentinian specimens are distinct from D. sanchezi Hyman, and probably they represent a new species, one to be described in detail elsewhere. In any case, Hyman's (1959) suggestion that D. sanchezi occurs near Buenos Aires is mistaken; so also is Cazzaniga's & Curino's (1987) identification of specimens from Buenos Aires as D. anceps.     

Karyology and karyotype analysis of diploid freshwater planarian populations of the Dugesia gonocephala group (Platyhelminthes,Tricladida) found in Sardinia

Karyology and karyotype analysis were carried out on freshwater planarian populations of the Dugesia gonocephala group. The strains studied were all diploid with chromosomic number 2n = 16; n = 8. They came from 12 sites mainly localized on the west of the island of Sardinia. Three karyotypes indicated with the letters A, B and C were found in which eight homomorphic pairs of chromosomes were easily identified. In karyotype A all chromosomes are metacentric. Ten populations of the twelve examined showed this karyotype which appears to be the most common. In karyotype B the seventh pair of chromosomes is submetacentric. This karyotype is quite common having been previously found in another eight Sardinian localities. Karyotype C differs from the others in having submetacentric third and seventh pairs of the chromosome complement. It was found in only one locality. The differences observed between these three karyotypes could be interpreted either as sign of differentiation at species level, or as an intraspecific variation due to chromosome mutations (pericentric inversions). This revised version was published online in July 2006 with corrections to the Cover Date.     

The karyotypes of Dugesia species from Spain (Turbellaria,Tricladida)

Some species of Planarians, new to Spain, are recorded. Dugesia polychroa, D. sicula, D. iberica and D. gonocephala s. 1. have been investigated karyologically. The former possesses a diploid complement characteristic of the biotype A (2n = 8); the second is diploid with 2n = 18; diploidy and triploidy were found in sexual populations of D. iberica with n = 8. Triploidy occurred in all the asexual strains of the D. gonocephala group with a basic number of either 8 or 9. In this latter case B-chromosomes were occasionally found.     

On the karyology of Dugesia gonocephala s.l. (Turbellaria,Tricladida) from Montpellier,France

Two species belonging to the Dugesia gonocephala group are found in the area of Montpellier, France. The karyology of these two species, D. gonocephala s. str. and S. subtentaculata, and of fissiparous Dugesia races has been studied.Two populations belonging to D. gonocephala s. str. are diploids with a chromosome number of 16, whereas the specimens of a third population are sexual aneuploids; the majority of cells possess 24 chromosomes, but some cells contain 23 or 25. The specimens attributable to D. subtentaculata are triploids, the most notable karyological feature being the presence of a single unmatched acrocentric chromosome. The fissiparous Dugesia strains are all aneuploids, the most common chromosome number being 27 with up to three small B-chromosomes.     

Genetic divergence in Northamerican freshwater planarians of the Dugesia dorotocephala group (Turbellaria, Tricladida, Paludicola)

The genetic differentiation between the members of the Dugesia (Girardia) dorotocephala group was analyzed by means of multilocus electrophoresis, and comared to that of another planarian secies, D. tahitiensis, also belonging to the subgenus Girardia. The species examined were: D. dorotocephala s.s (2n = 16), D. arizonensis (2n = 8), D. jenkinsae (2n = 8), and the above mentioned D. tahitiensis (2n = 16). The former three species inhabit North America, and show different proportion of fissiparous and sexual individuals; the latter species inhabits Polynesia and is fully asexual. A total of 11 enzyme loci were genetically analyzed: Mdh-1, Mdh-2, Zdh-1, Idh-2, G3pdh, Got-1, Ck, Pgm-2, Ada, Mpi, and Gpi. Low values of observed mean heterozygosity per locus (Ho) were found in the populations studied, ranging from 0 to 0.18 (average 0.08. In asexual populations (except that of D. tahitiensis) fixed heterozygosity was observered in all the individuals for 1 or 2 loci. The genetic divergence between the species examined is very high, with many loci showing discriminating alleles in different taxa (Nei's genetic distance varies from 0.871 to 1.759). The populations of D. dorotocehala s.s., on the contrary, appear to be genetically quite homogenous average D= 0.019), and the genetic distance values are apparently unrelated to their geographic location and to their way of reproduction. The genetic distance between D. tahitiensis, a species not included in the D. dorotocephala group and D. dorotocephala s.s. is 1.314 and hence similar to the D value between two members of;he dorotocephala group: D. dorotocephala and D. jenkinsae (D = 1.303). The genetic relationships among the populations studied were established by UPGMA cluster analysis and multidimensional scaling. The descendence of the North American species with 2n = 8 from a dorotocephala-like ancestor with 2n = 16 is considered. It is suggested that the latter, as well as a tahitiensis-like line, also having 2n = 16, have originated from a common ancestor by geographic isolation.     

Distribution,abundance, and size of rhabdoids in Dugesia polychroa. (Turbellaria: Tricladida)

The ontogenetic changes in the distribution, abundance, and size of rhabdoids were examined in an undisturbed laboratory population of Dugesia polychroa. Irrespective of triclad age, rhabdoids in the epidermis and parenchyma were more abundant on the dorsal than the ventral side of the body. No significant differences were found in the abundance of epidermal or parenchymal rhabdoids among the anterior, medial, and posterior regions of the body. Rhabdoid number and size changed significantly with triclad age, with a marked depression coinciding with the onset of cocoon production. Rhabdoid discharge was correlated with physical and/or physiological disturbance and occurred in the absence of any overt environmental disturbance. Simple allometric relationships were observed between rhabdoid size and number on one hand and body plan area on the other. Different allometric trends were observed from field-collected individuals compared to the undisturbed laboratory population. The potential function of rhabdoids in the Tricladida is discussed in light of these findings.     

Positional information and gonadal differentiation in the planarian Dugesia lugubris (Turbellaria)

The planarian Dugesia lugubris is a balanced hermaphrodite, meaning that male genetic factors are in equilibrium with female factors. Differentiation of the gonads is controlled by the region in which they develop. According to the classical theory of germ cell formation, these cells stem from neoblasts that are induced to differentiate by factors specific to the gonadal regions, factors presumably due to gradients formed by neurosecretory activity of the cephalic ganglia and longitudinal nerve cords. A more recently proposed theory holds that germ cells in regenerates originate not from neoblasts but from dedifferentiated cells and that characteristics of the gonadal regions are determined by direct interactions of cells here. Results of our experiments with homo- and autoplastic grafst support the classical theory. Prepharyngeal portions grafted onto posterior body portions retained their ability to maintain or induce development of ovaries. Postpharyngeal portions grafted onto anterior portions produced only testes even though the brain developed normally in these regenerates. Under these experimental conditions, gonad regeneration took longer than it does in normal regeneration (i.e., that in which body regions are not displaced).Translated, from the French, by Marianne Klauser and Seth Tyler.     

Monoclonal antibodies as markers of specific cell types and regional antigens in the freshwater planarian Dugesia (G.) tigrina

We have produced monoclonal antibodies (mAb's) against antigens of the fresh-water planarian Dugesia (G.) tigrina (Girard) using standard protocols. Labeling these mAb's with PAP (peroxidase-antiperoxidase) and indirect-immunofluorescence methods, we then determined the distribution of their antigens in the planarian. Out of 112 mAb's that showed some specificity for restricted parts of the planarian, 71 were found to be cell- or tissue-specific — among them 36 for parenchymal cells, 7 for muscle cells, 11 for epidermal cells, 8 for gastrodermis, and 7 to basement membrane. Another 41 showed different, but overlapping, regional specificities, namely to pharynx and parenchyma. So far, we have been unable to isolate specific mAb's against undifferentiated cells (neoblasts). These mAb's should be important tools in study of tissue and cell morphology, regeneration, and growth and degrowth.     

Repeated DNA elements in planarians of the Dugesia gonocephala group (Platyhelminthes,Tricladida)

The results of the isolation of repetitive DNA elements in the genome of Dugesia etrusca, a species of the Dugesia gonocephala group, are reported. These sequences, about 1.4 kb long, represent only a part of longer interspersed genomic units (De1 family) and appear to be limited to the genome of some planarians of this group, as indicated by a Southern blot analysis performed in different species and populations. The genomic relationships among different species and populations of the D. gonocephala group are discussed in relation to the results obtained in the present work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Notes on the biology of some psammophile Turbellaria of the Black Sea

The biology of two marine turbellarians, Cercyra hastata (Tricladida) and Pseudomonocelis ophiocephala (Proseriata) has been studied over a period of five years. They are the main components of the biocoenosis of the saccocirrus sand of Sevastopol Bay. These species have a significant role in the processes of secondary production and transformation of the organic matter in the coastal zone.     

Adenylate cyclase in regenerating tissues of the planarian Dugesia lugubris (O. Schmidt)

Adenylate cyclase (AC) was localized ultracytochemically in certain tissues of the regenerating planarian Dugesia lugubris. Studies were carried out from one hour after injury up to the 5th day of regeneration. It was found that the greatest amount of active AC appears during the initial hours of regeneration in the membranes of the muscle cells near the wound, in the epithelial cells surrounding the wound, and in rhabdite-forming cells and neoblasts.     

Predation potential of three flatworm species (Platyhelminthes: Turbellaria) on mosquitoes (Diptera: Culicidae)

We conducted a field survey for flatworms to select species as potential biological control agents against Aedes aegypti and Culex pipiens (Diptera, Culicidae) breeding in artificial containers. Laboratory experiments were performed to determine the daily predation rate, differential predation on each mosquito larval instar, selective predation on either A. aegypti or C. pipiens, and predator tolerance to water from artificial containers. Girardia anceps (Tricladida, Paludicola, Dugesiidae), Mesostoma ehrenbergii and Bothromesostoma cf. evelinae (Rhabdocoela, Typhloplanoida, Typhloplanidae) were found in temporary puddles and permanent pools. In the laboratory, they killed between 52% and 100% of immature mosquitoes coexisting in the same habitat. No preference of flatworms for mosquito preys was detected. Predation rate was related to predator size and instar of preys. Girardia anceps and B. evelinae survived after a dry period and when re-flooding occurred, they laid eggs. Tolerance to water from artificial containers was highest in G. anceps and this species could be a suitable predator to reduce mosquito populations from artificial containers using an inoculative approach.     

The influence of body size on immediate reproductive success in Dugesia gonocephala (Tricladida,Paludicola)

The individual reproductive output of the stream-dwelling flatworm Dugesia gonocephala was investigated. Various measures of reproductive success were related to body size. (I) For the first 30 days in the laboratory small individuals produced no cocoons, individuals of intermediate size produced unfertilized cocoons and large individuals usually produced fertilized cocoons. (II) In individuals that produced a cocoon, no correlation was found between the number of cocoons produced in one month and body size. (III) Large individuals, however, produced larger cocoons. This was not due to the fact that unfertilized cocoons were smaller. (IV) Large cocoons tended to contain more young. (V) The average size of young hatching from large cocoons was larger. (VI) Large individuals produced their first cocoon soon after their arrival in the laboratory and seemed to have a higher chance of producing a fertilized first cocoon. (VII) A trade-off existed between producing many small versus few large young.     

A new and aberrant species of Dugesia (Platyhelminthes,Tricladida, Dugesiidae) from Madagascar

In this paper we report a new species of Dugesia of the family Dugesiidae from Madagascar, representing the fourth species of freshwater planarian known from this global biodiversity hotspot. In some respects the new species is aberrant, when compared with its congeners, being characterized by a head with smoothly rounded auricles, a peculiar course of the oviducts, including the presence of a common posterior extension, and by the asymmetrical openings of the vasa deferentia at about halfway along the seminal vesicle. Further, it is characterized by a ventral course of the ejaculatory duct with a terminal opening, very long spermiducal vesicles and unstalked cocoons. Its diploid chromosome complement with 18 chromosomes represents an uncommon feature among fissiparous species of Dugesia.     

Regenerative and reproductive capacities of the fissiparous planarian Dugesia tahitiensis

A pilot study was performed to assess the regenerative capacities of Dugesia tahitiensis Gourbault, 1977, an exclusively fissiparous planarian species. Animals measuring 9.5–12.5 mm in length were used. Head regeneration rate determined by the appearance of eye spots (Brødsted, 1969: 29–46) was extremely high: at 23 °C, it took 43–59 h to regenerate clearly discernible eye spots in 28 specimens. For comparison, 3.8 days were reported for the regeneration of eye spots in 11.9–12.7 mm long D. tigrina (Girard) at 24 °C (Mead, 1985). As all posterior fragments regenerated a head, irrespective of the cutting level, D. tahitiensis seems to match the Phagocata velata (Stinger) type with a head frequency of 100% at every level (Teshirogi et al., 1977; cf. also Brøndsted, 1969:30).     

Occurrence and abundance of a mariner-like element in freshwater and terrestrial planarians (Platyhelminthes, Tricladida) from southern Brazil

Transposable elements are DNA sequences present in all the large phylogenetic groups, both capable of changing position within the genome and constituting a significant part of eukaryotic genomes. The mariner family of transposons is one of the few which occurs in a wide variety of taxonomic groups, including freshwater planarians. Nevertheless, so far only five planarian species have been reported to carry mariner-like elements (MLEs), although several different species have been investigated. Regarding the number of copies of MLEs, Girardia tigrina is the only planarian species in which this has been evaluated, with an estimation of 8,000 copies of the element per haploid genome. Preliminary results obtained in our laboratory demonstrated that MLE is found in a large number of different species of planarians, including terrestrial. With this in mind, the aim was to evaluate the occurrence and estimate the number of MLE copies in different planarian species collected in south Brazil. Twenty-eight individuals from 15 planarian species were analyzed. By using PCR and the hybridization of nucleic acids, it was found that MLE was present in all the analyzed species, the number of copies being high, probably over 10(3) per haploid genome.     

Planarian mitochondria I. Heterogeneity of cytochrome c oxidase subunit I gene sequences in the freshwater planarian,Dugesia japonica

Summary We have detected sequence heterogeneity in the cytochrome c oxidase subunit I (COI) gene of a freshwater planarian, Dugesia japonica, collected in one locality. A part of the COI gene was amplified via the polymerase chain reaction (PCR) using template DNA prepared from a mixture of 500 individuals or from each of 18 individuals. Analyses of DNA sequences by standard strategies for cloning and sequencing or by direct sequencing clearly show that (1) considerable sequence heterogeneity exists in DNA prepared from the mixed individuals, (2) 11 individuals have almost identical sequences (type A), and (3) 7 individuals have sequences different from one another (Seq-D 1 to SeqD7; collectively called type D). Each of the Seq-D1-D7 sequences except for Seq-D5 shows some heterogeneity even in a single individual (heteroplasmy). A possible cause of the sequence heterogeneities is discussed.Offprint requests to: Y. Bessho     

A new species of land planarian from Madeira (Platyhelminthes, Turbellaria, Tricladida)

A new species of terrestrial planarian from Madeira, Kontikia bulbosa sp. nov. , is described. The genus Kontikia is redefined and its scope and status reviewed.     

The preferential accumulation of cadmium in the head portion of the freshwater planarian, Dugesia japonica (Platyhelminthes: Turbellaria)

Free-living freshwater planarians are considered to have the potential for development as an experimental model for toxicological studies on xenobiotics, including metals. However, little was known about the distribution patterns of metals in the body of treated planarians. This study was conducted to determine the tissue distribution patterns of cadmium (Cd) in different body portions of the treated planarian, Dugesia japonica. Results showed that Cd accumulated in the head of planarians at a significantly higher concentration than in the tail. After examining the level of metallothionein (MT), we suggested that the tissue distribution pattern of Cd might be related to MT induction patterns. In contrast, in planarians treated with copper (Cu), neither the tissue accumulation of Cu nor the multiples of induction of MTs significantly differed between different portions. Furthermore, a higher Cd accumulation rate in the head of planarians caused more-severe oxidative stress to appear in this portion and also a higher susceptibility to a lethal concentration of Cd. Finally, both in vitro and in vivo acetylcholinesterase activities in both body portions of planarians were inhibited by Cd. The present study provides the first report that different metals are distributed in various body portions with different patterns in the planarian.