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.     

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.     

Predator–prey interactions between Dugesia gonocephala and free-living nematodes

1. Three groups of laboratory experiments clarified the role of nematodes as a potential food resource for the triclad Dugesia gonocephala. The first group measured the functional response of adult D. gonocephala feeding on juvenile or adult Caenorhabditis elegans. The feeding rates of D. gonocephala on adult and juvenile C. elegans followed a type II functional response. The maximum number of adult nematodes and juvenile nematodes eaten by a single D. gonocephala individual within 3 h was 94 and 197 nematodes, respectively. 2. A second group of microcosm experiments investigated the effect of D. gonocephala on the density and the vertical distribution of a nematode community in fine sand. The following treatments were performed: (i) microcosms with 400 nematodes and (ii) microcosms with 400 nematodes and one D. gonocephala. After 5 days, nematodes as a group, as well as the dominant species Tobrilus pellucidus and Trischistoma monohystera, showed no significant difference in vertical patterns between the treatments with and without D. gonocephala. 3. The third group of experiments determined whether grain size of the sediment (sand, fine gravel and coarse gravel) altered the ability of D. gonocephala to consume adult C. elegans. Sand and fine gravel reduced the predation effectiveness of D. gonocephala by 100%, whereas the predator consumed nematodes in coarse gravel (19 nematodes within 3 h).     

Fish predation affects the structure of a benthic community

1. We conducted an experimental study of predation by benthivorous fish on a natural community of stream invertebrates using a reach‐scale approach. Over a 2‐year period (experimental phase), the benthic invertebrate community of a stretch containing two species of benthivorous fish was compared with a fishless stretch. Thereafter, all fish were removed and benthic community structure was analysed again to account for natural differences between the two stretches (reference phase). 2. Benthivorous fish at the moderate densities investigated did not affect total benthic biomass or density, but did alter species composition. In addition, the fish effect differed between pool and riffle habitats, with larger effects in the pools indicating a habitat‐specific predation effect. In the reference phase, when all fish were removed from the stream, the difference between the two stretches was reduced. 3. The benthivorous fish reduced the densities of four taxa (Pisidium sp., Dugesia gonocephala, Gammarus pulex, Limoniidae), representing 29% of total biomass. It is possible that density reductions of other species were masked by prey migration despite the relatively large spatial scale. Indeed, higher drift activity in the upstream fishless stretch could have increased the density of Baetis rhodani in the fish stretch, as indicated by the results of a drift model. 4. Our results provide insights into stream food web ecology because fish predation showed effects even in a natural system where habitat complexity was high, environmental factors were highly variable and many predator and prey species interacted and because benthivorous fish were the focus, whereas the majority of previous predation experiments in streams have used drift‐feeding trout.     

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 review of chromosomal variation in Dugesia japonica and D. ryukyuensis in the Far East

The chromosome numbers of Dugesia japonica Ichikawa et Kawakatsu, 1964, are n = 8, 2x = 16 and 3x = 24; those of Dugesia ryukyuensis Kawakatsu, 1976, are n = 7, 2x = 14 and 3x = 21. The karyotypes of both species include diploid, triploid and mixoploid; aneuploidic and mixoaneuploidic karyotypes may occur. In 785 specimens studied of D. japonica, the occurrence rates of specimens having each karyotype are substantially the same (29–37%). Diploid sexual specimens represented nearly 10% of the total and virtually no triploid or mixoploid sexual specimens were found. The diploid karyotype can be inherited by both sexual and asexual reproduction; the triploid and mixoploid karyotypes will be inherited only by asexual reproduction. In 51 specimens studied of D. ryukyuensis, the different karyotypes are diploid (ca 39%), triploid (ca 57%) and mixoploid (ca 4%). Diploid sexual specimens represented nearly 25% of the total; sexual specimens with tripooidic karyotypes made up nearly 27%. The diploid, triploid and mixoploid karyotypes were also found in juveniles hatched from cocoons. The diploid karytyype is inherited by both sexual and asexual reproductions; the other karyotypes may be inherited by parthenogenesis or self-fertilization (including pseudogamy) and asexual reproduction.     

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.     

Chromosome bands in freshwater triclads

Four species of Triclads belonging to three families, Dugesia polychroa and Dugesia mediterranea (Dugesiidae), Planaria torva (Planariidae) and Dendrocoelum lacteum (Dendrocoelidae) were studied for chromosome banding: C-banding for all the species, ASG banding for Dugesia polychroa and G-banding for Dugesia polychroa and Dugesia mediterranea. C-banding results for Dugesia lugubris-polychroa group suggest a high level of heterochromatin evolution in the group. Small bands strictly limited to the centromeric region were seen in Dugusia lugubris and this pattern is similar to the patterns of some species belonging to other families, notably Planaria torva and Dendrocoelum lacteum. This could be considered a primitive character. In contrast numerous heterochromatin bands which are useful to characterize the different karyotypes were seen in Dugesia polychroa and Dugesia mediterranea. Our data suggest that heterochromatin is important in freshwater triclad speciation.     

Inhibitory Effect on Lipid Absorption and Variability of Chemical Constituents from Capparis sicula subsp. sicula and Capparis orientalis

In continuation of our research program on Mediterranean dietary plants, a bioassay‐guided fractionation of extracts from several accessions of Capparis sicula subsp. sicula and Capparis orientalis aerial parts was carried out. Antilipidemic activity of samples was assayed using inhibition of pancreatic lipase. To study the metabolic variability in Capparis species, HPTLC analyses were performed in order to characterize the species through the detection, isolation, and quantitative evaluation of rutin taken as significant chemical marker. The best activity was exerted by C. orientalis accession no. C10 and C. sicula subsp. sicula accession no. C6. The bioactivity evaluation of specific chemical markers, rutin and glucocapparin, led to the identification of a potent antilipidemic compound rutin. The HPTLC analysis showed large variation among the different analyzed samples with respect to rutin concentration. The chemical investigation showed a different composition between the species and between the collection zones. The variations showed by the studied accessions of caper could be attributed to exogenous factors. Capparis species contained predominantly quercetin rutinoside (rutin), accompanied by other constituents such as the glucosinolate glucocapparin. These rutin‐rich extracts exhibited pronounced dose‐dependent enzyme inhibitory activities toward pancreatic lipase.     

Reproductive biology of Dugesia sanchezi,a fresh-water planarian from Chile

Dugesia sanchezi reproduces in nature both sexually and by fission. Laboratory cultures have shown that fissioning is controlled by genetic factors. From sexual specimens randomly mated, 105 sexual and five fissiparous offspring were obtained. The former produced almost exclusively sexual descendents while the latter gave rise to fissiparous individuals, although successively many of them became sexual. These ex-fissiparous specimens show a high fertility and their offspring were almost all fissiparous, with the same characteristics displayed by the preceeding fissiparous generation. Some hypotheses are advanced in order to attempt a genetical interpretation of these results.     

THE GENETIC BASIS OF SEXUAL ISOLATION BETWEEN DROSOPHILA MELANOGASTER AND D. SIMULANS

The genetic analysis of sexual isolation between the closely-related species Drosophila melanogaster and Drosophila simulans involved two experiments with no-choice tests. The efficiency of sexual isolation was measured by the frequency of courtship initiation and interspecific mating. We first surveyed the variation in sexual isolation between D. melanogaster strains and D. simulans strains of different geographic origin. Then, to investigate variation in sexual isolation within strains, we made F₁ diallel sets of reciprocal crosses within strains of D. melanogaster and D. simulans. The F₁ diallel progeny of one sex were paired with the opposite sex of the other species. The first experiment showed significant differences in the frequency of interspecific mating between geographic strains. There were more matings between D. simulans females and D. melanogaster males than between D. melanogaster females and D. simulans males. The second experiment uncovered that the male genotypes in the D. melanogaster diallel significantly differed in interspecific mating frequency, but not in courtship initiation frequency. The female genotypes in the D. simulans diallel were not significantly different in courtship initiation and interspecific mating frequency. Genetic analysis reveals that in D. melanogaster males sexual isolation was not affected by either maternal cytoplasmic effects, sex-linked effects, or epistatic interaction. The main genetic components were directional dominance and overdominance. The F₁ males achieved more matings with D. simulans females than the inbred males. The genetic architecture of sexual isolation in D. melanogaster males argues for a history of weak or no selection for lower interspecific mating propensity. The behavioral causes of variation in sexual isolation between the two species are discussed.     

Unusual Origin of a Nuclear Pseudogene in the Italian Wall Lizard: Intergenomic and Interspecific Transfer of a Large Section of the Mitochondrial Genome in the Genus <Emphasis Type="Italic">Podarcis</Emphasis> (Lacertidae)

Two distinct cytochrome b-like sequences were discovered in the genome of Podarcis sicula. One of them represents a nuclear copy of a mitochondrial sequence (numt-sic) differing by 14.3% from the authentic mitochondrial (mt) sequence obtained from the same individual. This numt, however, differs by only 2.7% from the mt sequence found in one population of Podarcis muralis, a related species in which no corresponding numt was detected. The numt-sic sequence extends over at least 7637 bp and is homologous to a section of the mt genome spanning from the tRNA-Lys to the tRNA-Pro gene. Premature mt stop codons were detected in two of the nine protein coding genes of numt-sic. The distribution of substitutions among the three codon positions and the transition/transversion ratio of the numt-sic sequence resemble, with few exceptions, those of functional mt genes, indicating a rather recent transfer to the nucleus. Phylogenetic analyses performed on the data set including P. sicula numt-cytb sequences as well as mt-cytb sequences from the same individuals and mt sequences of various P. muralis populations suggest that numt-sic originated in P. muralis. In a geographic survey, P. sicula populations belonging to different mt lineages, covering most of the distribution area, were screened for the presence of numt-sic and for a 15-bp duplication polymorphism in the numt-nd5 sequence. Our results suggest that numt-sic has spread rapidly through the species range via sexual transmission, thereby being transferred to populations belonging to well-separated mt lineages that diverged 1–3 Mya. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Rafael Zardoya]     

The preference for movement direction in a T-maze in planarians

Characteristics of spatial orientation in T-maze were studied in 1768 Planaria of following types: Dugesia tigrina (sexless and sexual race), Dugesia lugubris, Ijmia tenuis, Bdellacephala punctata. It was shown that from one third to one half of individuals were characterized by asymmetry of movement direction preference. The preference of right turning was typical for Dugesia tigrina; Dugesia lugubris, Ijmia tenuis, Bdellacephala punctata preferred left turning. The asymmetry described is considered as a primitive form of species functional asymmetry.     

Differences in blastema-associated proteins according to position along body axis in regenerating planarians

To test the hypothesis that neoblasts in different positions in regenerating pieces of planarians may be differentially responsive to diffusible stimuli through differentially expressed membrane receptors, we compared membrane surface proteins in blastemas induced at various positions along an anterior-posterior axis in Dugesia gonocephala (Dugès). The proteins were biotinylated and identified by molecular weight in SDS-PAGE (sodium-dodecylsulfate polyacrilamide gel electrophoresis). This SDS-PAGE pattern was then compared with that of N-glycosylated proteins incorporating ³H-mannose. One 20 kDa glycoprotein present in all blastemas at 3 d was absent from more anterior blastemas at 6 d irrespective of whether those blastemas were at the cephalic or the caudal end of the regenerating piece. The expression of this protein appears to be determined by the position of the blastema along the body axis rather than by its prospective fate.     

Flatworms flatten to size up each other

When copulations are costly, fertilization is reciprocal and fecundity is positively related to size, hermaphrodites are expected to favour large partners, leading to size-assortative mating. Size-related mate choice has, however, never been observed in hermaphrodites. In the flatworm Dugesia gonocephala copulations cost time and are reciprocal, and size is a positive predictor of female fecundity. Every copulation is preceded by a phase in which one partner glides on top of the other and both spread out and flatten, suggesting that partners assess each other''s size. A total of 124 copulating pairs collected on four different dates, proved that mating is size-assorted in the field. In experiments with groups, more copulations took place between equally sized individuals than were expected when matings were random. In experiments with pairs, partners of different size exhibited twice as many mating attempts for the first copulation than did partners of the same size. We conclude that D. gonocephala employs a unique kind of pre-copulatory ''flattening'' behaviour as a mechanism to signal as well as to assess relative size. This does not only confirm that hermaphrodites can mate assortatively when certain assumptions are met, it also proves that even lower invertebrates can show active mate choice.     

Variation in morphological and behavioral traits among isofemale strains of Drosophila prolongata (Diptera: Drosophilidae)

Drosophila prolongata, a member of the rhopaloa subgroup of the melanogaster species group, occurs in Southeast Asia. Drosophila prolongata is known to have unique and prominent sexual dimorphism, with extraordinarily thick and elongated forelegs only in males. Mating behavior of D. prolongata is also characteristic: males perform “leg vibration” in their courtship toward females, in which the elongated forelegs play an important role. Comparisons with closely related species suggest that these morphological and behavioral traits have evolved rapidly after the divergence of D. prolongata. In the present study, variation in morphological and behavioral traits was examined among D. prolongata strains derived from single females collected in their natural habitats. Significant variations were detected in the size of various body parts, aggressiveness of interactions between males, and mating behavior. However, no obvious relationship was observed between morphological and behavioral traits. These results suggested that genetic factors contribute to the variation in morphological and behavioral traits in D. prolongata. The strains characterized in this study are useful for studies on the genetic mechanisms underlying the evolution of characteristic traits in D. prolongata.     

Distribution, ecology, mode of reproduction and karyology of freshwater planarians (Platyhelminthes; Turbellaria; Tricladida) in the springs of the central Pyrenees

The distribution, reproductive modality and karyology of populations of freshwater planarians were studied together with physico-chemical variables m 149 springs in the central Pyrenees Diversity was limited to four species (Dugesia (Dugesia) subtentaculata, Polycelis felina. Crenobia alpina and Phagocata vitta), already known from streams and lakes Planarians were found rarely (only a third of springs contain them), m low-moderate abundance, and any single spring did not harbour more than one species The distribution of potential predators and preys among the springs sampled was fairly uniform So. we assume that whereas predation is unlikely to influence triclad distribution, the oligotrophic character of these habitats may explain, through food shortage and ensuing interspecific competition, the presence of a single species in each spring Besides interspecific competition, the distribution of each species can also be influenced by particular abiotic parameters Temperature and current velocity appeared to be the dominant factors, the first separating C alpina from the rest of species, and the second favouring the presence of P felina in a large set of springs These factors also seem to determine planarian distribution in streams and rivers Other environmental factors such as calcium bicarbonated water (for D subtentaculata) and preference for karst systems (for Phagocata vitta) are of importance Some peculiarities of distribution, like the scarcity of C alpina in reophile habitats and the thermal tolerance of Phagocata vitta, may be due both to competition from P felina and to historical factors in the former and to morphological (presence of pigment) and ecological (epigean habits) features m the latter, respectively Karyological analyses demonstrated triploidy in all populations of D subtentaculata. a polyploid origin for C alpina and the finding in Phagocata vitta of a new polyploid series leading to the highest chromosome number in turbellarians (14n = 238) Furthermore, the basic chromosome number of C alpina (n = 21) and Phagocata vitta (n = 17) differs from those found in northern European populations (n = 7 in both, respectively) This suggests that under the specific names C alpina and Phagocata vitta more than one species actually occurs, this being a problem for further studies Whereas polyploidy has often been related to living in cold, harsh habitats, asexual reproduction has been linked to environments where biotic stress is low The preeminence of asexual reproduction (by fissiparity) and polyploid forms in freshwater planarians inhabiting the unproductive, biotically unsaturated springs of the central Pyrenees adds new evidence to strengthen such links     

Study on the phenology of Chara vulgaris in Xin’an Spring, north China

The phenology of Chara vulgaris was studied. The specimens were collected four times from April 2004 to January 2005 (one sampling per season). The water temperature, pH, dissolved oxygen, specific conductance, maximum width and maximum depth were monitored at every sampling time. Eighteen main morphological characteristics of the Chara vulgaris were also observed and measured under the microscope. The results showed that all the environmental factors had different seasonal patterns and some of the morphological characteristics had significant fluctuations, indicating differences in their seasonality. At the same time, some morphological characteristics were affected by the environmental parameters to some extent and the effect was primarily exhibited in its vegetative proportions; there was little effect on the sexual reproductive characteristics. Therefore, the relatively stable sexual reproductive characteristics can be used to identify the species.     

Investigation of extracellular phospholipase and proteinase activities of Candida species isolated from individuals denture wearers and genotypic distribution of Candida albicans strains

In order to determine the relationship between the development of denture related stomatitis (DRS) and the production of phospholipase and proteinase by Candida species, 156 Candida isolates isolated from the individuals in the control group and from the individuals different denture wearers were included in this study. According to the results of the study, C. albicans strains were determined to produce high levels of phospholipase and proteinase. It was also determined that the prevalence of phospholipase and proteinase activities in C. albicans strains isolated from individuals with DRS and from the individuals without DRS was not different. In order to determine genotypic variation of 109 C. albicans strains isolated, CA-INT-L and CA-INT-R primers specific to the site of the transposable group I intron of the 25S rRNA gene (rDNA) region were used. As a result, it was considered that, there were several other virulence factors belonging to the microorganism which played a role in the development mechanisms of the infection caused by C. albicans. In addition, according to the results of microbial genotyping, it was determined that there were no C. albicans strains specifically responsible for the development of DRS.     

The effects of group size on per capita ingestion in flatworms

1. We evaluated the effect of group size on the per capita ingestion rates of three species of flatworm, two of which actively group with conspecifics (Dugesia tigrina, D, dorotocephala) and employ mucus to capture prey, and a third species (Mesostoma ehrenbergii) that does not actively group but does use mucus to capture prey. 2. As flatworm group size increased, daily per capita ingestion first increased and then decreased for D. tigrina and D. dorotocephala. In the case of D. tigrina this pattern was observed even at low predator densities. Ingestion rates of M. ehrenbergii were largely unaffected by group size. 3. Results suggest that the observed changes in per capita ingestion rates with changes in group size previously reported for D. tigrina are related to their tendency for active grouping and are not directly a consequence of prey capture technique or experimental design. 4. We argue that freshwater triclads in general, and D. tigrina in particular, represent an ideal model system for the development and testing of group foraging theory.